bluuebunny/crossref_metadata_2025 huggingface dataset:
Pathway mediating hypotension elicited by stimulation of the amygdala in the rat
Authors: Faiers AA , Calaresu FR , Mogenson GJ
Published: December 2017

Cardiovascular responses were elicited from 372 histologically verified sites in the amygdala and closely adjacent structures in 82 rats under urethan or chloralose anesthesia. Arterial hypotension was elicited at low current intensities from the medial, central, lateral, and basal nuclei of rats under either anesthetic; the hypotension was still elicited in artificially respired paralyzed rats. Stimulation of the cortical nucleus produced variable changes in arterial pressure. The hypotension elicited under urethan was not found to be correlated with changes in the frequency of electrical activity of hippocampus, amygdala, or septum or to be associated with electrical seizures. Hypertension was usually elicited from the medial nucleus at high current intensities and was attributed to current spread to the cortex ventral to the medial nucleus from which hypertension was elicited at low current intensities. Stimulation of the central, basal, and lateral nuclei under chloralose elicited bradycardia. Lesions of the stria terminalis had no effect on the hypotension, whereas lesions of the ipsilateral medial forebrain bundle abolished this response.
Reversible hemodynamic defect in glomerular filtration rate after ischemic injury
Authors: Daugharty TM , Brenner BM
Published: December 2017

In Wistar rats with surface glomeruli 3 h of nearly complete occlusion of the left renal artery resulted in uniform falls (similar to50%) in ipsilateral whole-kidney glomerular filtration rate (GFR) and single-nephron GFR (SNGFR) and in urinary findings consistent with impaired water reabsorption. Since the fall in SNGFR was accompanied by a proportional fall in glomerular plasma flow rate (GPF), and since net ultrafiltration pressure at afferent and efferent ends of the glomerular capillary was unchanged from preischemic levels, these findings suggest that the fall in SNGFR was a hemodynamic consequence of the fall in GPF. To test this hypothesis, GPF was restored to preischemic levels by means of acute infusion of homologous, isoncotic plasma. GPF and SNGFR uniformly increased, on average to preischemic levels, whereas net ultrafiltration pressure at afferent and efferent ends of the glomerular capillary again remained essentially unchanged. These studies demonstrate that the fall in SNGFR in this model of ischemic injury is causally related to the accompanying fall in GPF. Of interest, despite this reversal of the defect in GFR, fractional water reabsorption remained impaired. This restoration of GFR but not reabsorption by plasma infusion abruptly converts this ischemic lesion from nondiuretic to diuretic.
Transport of Na, Cl, and water by the rabbit corneal epithelium at resting potential
Authors: Klyce SD
Published: December 2017

Theophylline (1 mM) produced a net transport of Na and Cl from aqueous humor to tears (.02-.04 mumol/cm2 h) in the isolated rabbit cornea denuded of endothlium and in the presence of normal resting potential (25-35 mV). The active transport of Na (tears to aqueous) and of Cl (aqueous to tears), estimated with the Goldman constant-field equations, was confirmed. A 10 degrees C rise in temperature produced changes close to those predicted for passive processes in both unidirectional fluxes of Na and in the tears-to-aqueous flux of Cl, but not for the aqueous-to-tears flux of Cl. Theophylline treatment doubled Cl permeability but did not significantly affect Na or urea permeability, suggestingspecificity of affect. In separate experiments it was shown that stromal thinning occurred in previously swollen corneas when the endothelium was blocked by silicone oil and the epithelium was treated with theophylline. These findings provide further support for the argument that the mammalian epithelium could have an active role in the regulation of corneal thickness in situ.
Mechanism of cholecystokinin inhibition of lower esophageal sphincter pressure
Authors: Fisher RS , DiMarino AJ , Cohen S
Published: December 2017

The purpose of this study were 1) to quantify the lower esophageal sphincter (LES) response to intravenous cholecystokinin (CCK) in both man and the opossum in vivo, 2) to characterize the interaction of CCK and gastrin on circular muscle of the LES, and 3) to determine the site of action of CCK on LES muscle. In both man and the opossum LES pressure was decreased significantly by either constant intravenous infusion or bolus injection of CCK. In vitro dose-response curves to gastrin I, CCK, and the octapeptide of CCK (OP) demonstrated that both CCK and OP were partial agonists on the LES muscle. Both CCK and OP contract LES muscle at lower threshold doses, but give smaller maximum responses than gastrin I. The maximum response of LES muscle to CCK was antagonized only by atropine and tetrodotoxin, but not by other antagonists, suggesting that CCK contracts LES muscle by acetylcholine release. In vitro studies on LES muscle showed that CCK selectively antagonized the effect of gastrin I, but not other agonists. These studied suggest that CCK reduces LES pressure in vivo by inhibition of the endogenous gastrin effect.
Adenosine metabolism in cultured chick-embryo heart cells
Authors: Mustafa SJ , Berne RM , Rubio R
Published: December 2017

Adenosine, a coronary vasodilator, in involved in the regulation of coronary blood flow, but the mechanism (s) of vasodilation especially with respect to the influence of dipyridamole and aminophylline are not clearly understood. Cultured cardiac cells of 16-day-old chick embryos were used as a model for the mammalian heart. Hypoxia produced a twofold increase in the production of adenosine and its metabolic products in this preparation, indicating that the source of adenosine in the hypoxic heart is the myocardial cell. Neither dipyridamole (1 times 10-minus 6M) nor aminophylline (1 times 10-minus 5M) blocked the release of adenosine from the myocardial cells, but dipyridamole aminophylline was without effect. These data suggest that dipyridamole exerts its vasodilator effect by blocking the uptake of adenosine into the cells, thereby increasing its extracellular levels and the concentration of adenosine in the vicinity of coronary resistance vessels. The mechanism whereby aminophylline attenuates the vasodilation produced by adenosine is not known. However, aminophylline does not interfere with the release or uptake of adenosine.
Effects of acid-base changes, hypoxia, and catecholamines on ventricular performance
Authors: Beierholm EA , Grantham RN , O'Keefe DD , Laver MB , Daggett WM
Published: December 2017

Extracellular pH changes were produced in dogs with tris (hydroxy-methyl)-aminomethane (Tris) or NaHCO3 in the presence or absence of hypoxemia and before and after beta-adrenergic blockade with propranolol. Ventricular performance (VP) was evaluated by measurement of maximum rate of rise of left ventricular pressure (dp/dt max) and left ventricular end-diastolic pressure in the canine right heart bypass preparation with aortic pressure, heart rate, and cardiac output held constant. Low pH diminished VP. Hypoxemia did not alter VP within the pH, suggesting that decreased V observed with acidosis before propranolol was due primarily to decreased myocardial response to catecholamines. Increase of pH with Tris increased VP significantly more than with NaHCO3. Beta blockade diminished the response of VP to Tris at a high pH;prior administration of reserpine abolished the inotropic effect of Tris. The data suggest that Tris can influence VP independent of its effect on pH. This effect is probably mediated by the interaction between endogenous catecholamines and myocardial beta receptors.
Fibrinogen levels after inflammation or endotoxin in normal and hypophysectomized rats
Authors: Goodnight SH , Rapaport SI , Zivelin A
Published: December 2017

The hypothesis that pituitary hormones are required for increased fibrinogen synthesis after inflammation or endotoxin was tested by measuring plasma fibrinogen concentrations after inflammation or endotoxin in normal and hypophysectomized rats. Animals were divide into groups receiving no exogenous adrenal steroids, low-dose adrenal steroids, or high-dose adrenal steroids. Hypophysectomy failed to prevent fibrinogen levels from rising after intramuscular turpentine (mean 240 mg/100 ml prior to and 556 mg/100 ml 24 h after turpentine). Steroids did not suppress this rise. Endotoxin, 5 mug/100 g, caused a marked rise in fibrinogen in normal rats at 24 h (mean 296 mg/100 ml before endotoxin and 554 mg/100 ml after endotoxin). This dose of endotoxin killed hypophysectomized rats within 12 h. Hoevr, if hypophysectomized rats were protected with high-dose adrenal steroids, then 5 mug of endotoxin per 100 g caused the same fibrinogen rise as in normal rats (mean 299 mg/100 ml before endotoxin and 587 mg/100 ml after endotoxin). Aparently, pituitary hormones are not necessay for increased fibrinogen synthesis after either inflammation or endotoxin in the rat.
Z protein in hepatic uptake and esterification of long-chain fatty acids
Authors: Mishkin S , Stein L , Fleischner G , Gatmaitan Z , Arias IM
Published: December 2017

Fatty acids radioactivity was bound to Z protein in liver after administration of['3H]oleate to rats or to a perfused rat liver preparation. Pretreatment withflavaspidic acid (340 mumol/kg), a potent inhibitor of fatty acid binding to hepatic Zprotein in vitri, effectively reduced oleate radioactivity bound to Z by 90.2 plusor minus 4.3% and 85.0 plus or minus 6.2% in the intact rat and perfused liver, respectively. In spite of this effect, pretreatment of rats with flavaspidic acid did notalter plasma clearance, hepatic uptake, and esterification of ['3H]oleate. In contrast, in the perfused liver preparation, infusion of flavaspidic acid (340 mumol/kg)or bromosulphalein (360 mumol/kg) increased uptake of ['3H]oleate at least twofold,and oleate esterification was decreased by 15-30%. These results suggest that the binding of long-chain fatty acids to Z protein is not an obligatory step in their uptakeby the liver and that Z protein may be involved in fatty acid esterification.
Myocardial substrate utilization in perfused hearts isolated from adrenalectomizedcats
Authors: Beardsley AC , Lefer AM
Published: December 2017

Isolated hearts form chronically adrenalectomized cats were perfused with Krebs-Henseleit buffer plus either glucose (10mM) or palmitate (0.4 mM) under various conditions of constant pressure and constant flow. Glucose uptake in adrenalectomizedhearts was not diminished from control values under conditions of constant pressure, constant flow, anoxia, or insulin stimulation. Palmatic acid uptake and oxygen consumption were significantly reduced (P less than 0.02) in adrenalectomized hearts. This diminished fatty acid utilization was also reflected in a significantly lower CO'2 production and incorporation of the palmitate into myocardial triglycerides. The decreased fatty acid uptake by adrenalectomized cat hearts may represent aserious defect in myocardial metabolism since lipids are the major energy substrate forthe heart. Whether the defect occurs in fatty acid transport or activation cannot beelucidated by this study. However, it is unlikely that this defect has a major contributory effect on the dysfunction of adrenalectomized hearts since the myocardium iscabable of using other energy substrates readily.
Mechanism of methylxanthine sensitization of norepinephrine responses in a coronaryartery
Authors: Kalsner S , Frew RD , Smith GM
Published: December 2017

Beta-adrenergic receptor-mediated relazation to norepinephrine was enhanced by caffeine amd aminophylline in a coronary artery preparation of the beef in vitro.Augmented responses were not obtainable in the presence of known inhibitors of the extraneuronal uptake and metabolism of norepinephrine, estradiol-17beta, and the haloalkylamine GD-131, which themselves potentiate responses. In addition, the effect on the norepinephrine dose-response curve of the combination of a methyixanthine and U-0521,the latter a potent inhibitor of catechol O-methyltransferase, the major enzyme of catecholamine inactivation in vascular tissue, did not differ from that of U-0521 alone.Studies of the extraneuronal accumulation of '3H-labeled norepinephrine revealed that caffeine and aminophylline, along with the known inhibitors, materially reduced theaccumulation of label in coronary tissue. It is concluded that the methylxanthinesenhance beta-adrenergic receptor-mediated responses via a blockade of catecholamine uptake, giving rise to an increased concentration of agonist at receptors, and not by an action linked to cyclic AMP accumulation, consequent to receptor activation.
Effects of a diphophonate on calcium metabolism in calcium-deprived rats
Authors: Morgan DB , Gasser A , Largiader U , Jung A , Fleisch H
Published: December 2017

Calcium metabolism was studied in growing rats, submitted to calcium deprivation ofvarious intensity. A decreased intake resulted in decreased net absorption of calcium(V'na), no change in bone formation (V'o+), and an increase in bone resorption (V'o -). In animals given dichloromethylene disphosphate (Cl'2MDP), a compoundknown to inhibit bone resorption, V'o+ was less than in the controls but again the same at all calcium intakes; V'na was below V'o+, V'o- still increased as the calcium intake was reduced. The various kinetic parameters in rats receiving Cl'2MDPwere indistinguishable from published data in parathyroidectomized (PTX) animals, yetblood calcium was low in PTX rats but normal in Cl'2MDP-atreated rats. It appears that the rat has an efficient mechanism for increasing bone resorption which is not inhibited by Cl'2MDP and does not require parathyroid hormone.
Peritubular pH and PCO'2 in renal tubular acidification
Authors: Mello Aires M , Malnic G
Published: December 2017

The influence of peritubular capillary pH and PCO'2 on renal tubular acidification was studied in rats by luminal and peritubular perfusion techniques. Luminal stopped-flow microperfusions were carried out with bicarbonate or alkaline phosphate solutions and luminal pH continuously measured by antimony micorelectrodes. Peritubular calpillary microperfusions were carried out with mammalian Ringer solution kept at different pH and PCO'2. The acidification process was assessed in terms of 1)maximal pH differences, 2)rates of pH change, and 3)rates of bicarbinate reabsorption or H'+ ion secretion. During peritubular perfusions at physiological pH and PCO'2 tubular acidifying capacity was maintained at near-normal levels. Perfusingcapillaries at high pH and low PCO'2, especially with bicarbonate Ringer, acidification was markedly depressed; it was moderately reduced at a peritubular pH of 5.6. At a capillary pH of 7.4, acidification was similiar at low and physiological PCO'2and enhanced at elevated PCO'2. Systemic respiratory acidosis enhanced acidification in the proximal tubule, but reduced it in distal segments.
Determinants of peritubular capillary fluid uptake in hydropenia and saline and plasma expansion
Authors: Blantz RC , Tucker BJ
Published: December 2017

Hydrostatic (HPc) and oncotic (phic) pressures within the peritubular capillary, tubular pressure (Pt), nephron filtration rate, and plasma flow, and proximal fractional and absolute reabsorption (APR) were measured in anesthetized rats during hydropenia and plasma and saline expansion. Net interstitial pressure (phii-HPi) was estimated from subcapsular hydrostatic and oncotic pressures during saline expansion and these data were applied to a mathematical model of peritubular capillary fluid uptake to determine the profile of effective reabsorption pressure (ERP) with distance (x*) alongthe capillary and calculate the peritubular capillary permeability coefficient (LpAr). ERPX* = (PHIC MINUS HPC)X* MINUS (PHII MINUS HPi) and APR = ERPX*LpAr.During saline expansion phii minus HPi was -12.1 plus or minus 0.8 mmHg and ERP,3.8 mm. The LpAr was 0.07 nl/s per g KW per mmHg, and this value was applied to hypropenia and plasma expansion to determine ERP and phii minus HPi. The phiiminus HPi was +6.0 and +5.0 mmHg, respectively, and ERP was 4.1 and 3.5 mmHg.Efective reabsorptive pressure remained positive along x* in all states, and phii minus HPi correlated best changes in phic and poorly with changes in efferent plasma flow. The APR did not correlate with either calculated phii minus HPi or the transepithelial driving pressure, Pt + phii minus HPi.
Uptake of lactate by dog skeletal muscle in vivo and the effect of free fatty acids
Authors: Dunn RB , Critz JB
Published: December 2017

These experiments were designed to determine: 1) if lactate can be extracted from the arterial blood and utilized by resting skeletal muscle of the dog, and 2) if lactate uptake or production by skeletal muscle is influenced by the level of circulating free fatty acids. Skeletal muscle arteriovenous differences in lactate were measured at several arterial lactate and free fatty acid concentrations. With sodium pentobarbital anesthesia and a low concentration of free fatty acids, arterial lactate concentrations of 1-2 mM were associated with extraction of lactate; however, when circulating free fatty acids were elevated (greater than 1 mM), no extraction of lactate occurred at these lactate concentrations. The relationship between arterial free fatty acids and uptake or release of lactate demonstrated in these in vivo studies suggest that the inhibition of free fatty acid release from adipose tissue that occurs when the arterial lactate concentration increases may function facilitate the metabolism of lactate by skeletal muscle.
Cardiac and respiratory effects of digitalis during chronic hypoxia in intact conscious dogs
Authors: Beller GA , Giamber SR , Saltz SB , Smith TW
Published: December 2017

The arrhythmogenic and respiratory effects of ouabain during chronic hypoxia were studied in 10 unanesthetized dogs in a hypobaric chamber (446 mmHg) following 7-19 (mean 14.7) days of continuous exposure at this altitude. Another 15 dogs studied at sea level comprised the normoxic control group. In both groups, a 7.5-mug/kg loading dose of ouabain was followed by infusion of ouabain at 3.0 mug/kg per min to ECG evidence of toxicity. Mean arterial Po2 was 46 +/- 5 mmHg in chronically hypoxic dogs as compared to 86 +/- 7 mmHg in normoxic animals (P less than 0.001). Mean hematocrit was 54 +/- 1% in hypoxic and 43 +/- 2% in normoxic groups (P less than 0.001). In five dogs studied first at sea level and subsequently under conditions of chronic hypoxia, mean maximum left ventricular dP/dt and peak (dP/dt)P-1 were unchanged. Marked hyperventilation during ouabain infusion was observed. In normoxic dogs mean arterial pH rose from 7.43 +/- 0.05 to 7.70 +/- 0.02 U, and Pco2 fell from 41 +/- 4 to 15 +/- 1 mmHg during ouabain administration (P less than 0.001). Similar changes were observed in hypoxic dogs. There was no significant difference in the mean toxic dose of ouabain in chronically hypoxic (71 +/- 11 mug/kg) versus normoxic (78 +/- 12 mug/kg) animals. Thus, in contrast to acute hypoxia, chronic hypoxia in unanesthetized dogs was not associated with a significant reduction in the dose of ouabain required to produce toxic arrhythmias. Chronic hypoxia was also not associated with alterations in left ventricular performance.
Major and collateral components of blood flow to pregnant sheep uterus
Authors: Fuller EO , Galletti PM , Takeuchi T
Published: December 2017

In vivo measurements of vessel diameter, latex injections, and acrylic-cast studies indentified the middle uterine arteries as the main source of blood supply to the pregnant sheep uterus. Collateral circulation stemmed from the dorsal uterine arteries, and the ovarian arteries, and small cervical branches derived from the external iliac arteries (in decreasing order of importance). These morphological observations were related to estimates of collateral flow obtained during isolated, in situ perfusion of the pregnant sheep uterus carried out through the cannulated middle uterine arteries. Collateral blood flow was estimated from the shift of the flow-pressure curve produced by inflation of a balloon catheter advanced into the aorta below the renal arteries. Middle uterine artery flow to one horn increased from 162 +/- 23 ml/min in midgestation to 323 +/- 44 ml/min near term. Collateral uterine blood flow did not change significantly: 82 +/- 15 ml/min in midterm, 74 +/- 9 ml/min near term. Collateral flow consituted a larger fraction of inflow to the horn containing the fetus in 9 of 10 single pregnancies.
Reflex sympathetic changes in aortic diastolic pressure-diameter relationship
Authors: Pagani M , Schwartz PJ , Bishop VS , Malliani A
Published: December 2017

In anesthetized vagotomized cats with the chest opened and artificially ventilated, aortic blood pressure (AP) and external diameter (AD; ultrasound technique) were measured in the proximal third of the descending thoracic aorta. Slow sinusoidal oscillations (0.2-0.3 Hz in aortic volume were produced by a piston pump connected to a femoral artery. Diastolic pressure-diameter relationship (PDR) curves were obtained during control conditions and during stimulation of either the cut central end of the left inferior cardiac nerve (ICN) or the decentralized thoracic sympathetic chain (SC). In six cats with both carotid arteries occluded ICN stimulation reflexly shifted the PDR curves to lower diameters for any given pressure (mean deltaAD 3.2% at control AP). A smaller response to ICN stimulation was obtained in five cats with one patent carotid artery (mean deltaAD 2.3% at control AP). Stimulation of sympathetic efferents to the aorta (SC) caused similar responses in five animals (mean deltaAD 3.4% at control AP). This reflex control of the thoracic aorta may be involved in cardioaortic coupling and may influence the sensitivity of aortic mechanoreceptors.
Spinal autonomic afferents in elicitation of tachycardia in volume infusion in the dog
Authors: Gupta PD
Published: December 2017

Intravenous infusion of blood (36 ml/kg body wt) elicited tachycardia in artificially ventilated anesthetized dogs with intact autonomic innervation and in dogs with cardiac beta-receptor blockade. In contrast, infusion elicited bradycardia in dogs with section of the spinal cord at C6-C7, and in dogs with combined spinal section and cardiac beta-receptor blockade. The control heart rate was less than or equal to 110 beats/min in all the animals. The presence of infusion-induced tachycardia in dogs with beta-receptor blockade, i.e., dogs in which cardiac sympathetic efferents were blocked, and its absence in dogs with combined spinal section and beta-receptor blockade, i.e., dogs in which spinal autonomic afferents plus cardiac sympathetic efferents were blocked, may be the result of an additional interruption of spinal autonomic afferents by spinal section. It is concluded that tachycardia elicited by infusion may be partly due to a reflex with its afferent pathway in the spinal cord and its efferent pathway in the vagus nerves.
Inotropic responses to digoxin during hypoxia and autonomic blockade
Authors: Halloran KH , Downing SE
Published: December 2017

Inotropic responses to digoxin (0.08 mg/kg) were studied in dogs and compared with responses during hypoxemia and autonomic blockade. Changes in left ventricular contractility (VC) were assessed by constructing function curves relating left ventricular (dP/dt)max and stroke volume to end-diastolic pressure. Augmentation of VC was observed 20 min after digoxin infusion and continued to increase until termination of the experiment after 60 min. In animals subjected to autonomic blockade with practolol, TEAC, and atropine, the increases in VC after digoxin were substantially greater. Equally large increases occurred in blocked dogs during sustained hypoxia (Pao2 = 28 mmHg). However, in animals without blockade there was a progressive fall in VC during hypoxia despite digoxin infusion, although less than in those not given digoxin. Serum digoxin levels were measured by radioimmunoassay and did not differ significantly in blocked compared to unblocked dogs or in hypoxic compared to nonhypoxic animals. These findings indicate that digoxin protects the heart from the decrease in myocardial contractility which occurs during extended hypoxia. This protective effect is more pronounced in animals deprived of autonomic function, possibly reflecting the elimination of reflex sympathetic withdrawal ordinarily induced by digitalis.
Mechanics of guinea pig taenia coli smooth muscle during anoxia and rigor
Authors: Bose D , Bose R
Published: December 2017

Potassium-contracted guinea pig taenia coli relaxed when exposed to hypoxic glucose-free conditions, and this was followed by a second contraction. During this second contraction, which was not inhibited by ethylene glycol-his-(beta-aminoethylether)-N,N'-tetracetic acid (EGTA) the muscle was in rigor. After development of this contraction the muscle did not have an active state and was less extensible than a muscle normally contracted with KCl. Tension during rigor in an isometrically contracting muscle was short-lived in contrast to shortening during rigor development in a lightly loaded isotonically contracting muscle. These findings, together with the observation of irreversible lengthening of a muscle in rigor on stretching, suggest that rigor linkages can be broken. Glucose removal under aerobic conditions did not produce rigor, but oxygen removal in the presence of glucose resulted in relaxation followed by secondary contraction. This later contraction, unlike that accompanying rigor, was reversed by removal of calcium with EGTA. These data imply that in the absence of oxygen the removal of cytoplasmic free-Ca2+ is inhibited.
Effect of norepinephrine on myocardial intracellular hydrogen ion concentration
Authors: Riegle KM , Clancy RL
Published: December 2017

The effect of norepinephrine (NE) on the intracellular hydrogen ion concentration [H+]i of isolated rat hearts perfused with a modified Krebs-Henseleit solution (SHS) was determined. The [H+]i was calculated with the [14C]-dimethyloxazolidinedione method. Respiratory or metabolic acidosis was produced by equilibrating the KHS with 20% C02 or decreasing the [HC03-] of the KHS, respectively. Three types of experiments were carried out: 1) beta blockade--MJ 1999 (Sotalol) was added to the KHS; 2) control--no pharmacological treatment; and 3) NE-norepinephrine was added to the KHS. The effective CO2 buffer values (delta[HC03-]i/deltapHi) during respiratory acidosis were: beta blockade, 11; control, 35; and NE, 84. The production of metabolic acidosis resulted in the following [H+]i changes: beta blockade, 52 mM; control, 60 nM; and NE 7 nM. These results suggest that NE markedly attenuates the changes in [H+]i accompanying respiratory and metabolic acidosis and may account in part for previous observations that the effective C02 buffer value of cardiac muscle in vivo is greater than that in vitro.
Catecholamines and exercise-induced glucagon and fatty acid mobilization in the rat
Authors: Luyckx AS , Dresse A , Cession-Fossion A , Lefebvre PJ
Published: December 2017

Physical exercise in rats provokes an increase in plasma glucagon and free fatty acid concentrations. The persistence of exercise-induced glucagon stimulation in adrenodemedullated animals and conversely, its inhibition by immunosympathectomy, (-)-ropranolol, and pindolol substantiate the conclusion that stimulation of the alpha2 cells in exercise involves sympathetic stimulation of the beta-adrenergic receptors. The reduction of free fatty acid mobilization by immunosympathectomy and (-)-propranolol and its persistence after adrenodemedullation suggest that it is similarly mediated, at least in part, by adipose cell beta-sympathetic receptors.
Kidney and urinary bladder functions of the rainbow trout in Mg and Na excretion
Authors: Beyenbach KW , Kirschner LB
Published: December 2017

Magnesium concentration in the urinary bladder of marine teleosts is high and [Na] is low. The inverse relationship may be due to the coupling of Mg secretion to Na reabsorption through a common tubular transport system or coupling may be indirect. Unanesthetized sea-water-adapted Salmo gairdneri were infused with saline or MgCl2, and ureteral urine was collected. Over a wide range of Mg excretion rates, tubular Mg secretion and Na reabsorption show no clear correlation as might be expected from an obligatory tubular Mg/Na exchange. Instead ureteral Mg and Na concentrations and excretion rates are positively correlated. These data are not consistent with the presence of a tubular exchange system. When ureteral urine was allowed to remain in the urinary bladder before being analyzed the inverse relationship between [Mg] and [Na] developed because the bladder reabsorbed Na and H2O, thereby concentrating Mg. Hence, tubular Mg/Na exchanges do not produce the inverse Mg/Na relationship in bladder urine. Instead, Mg is secreted in the nephron, while Na and H2O are reabsorbed from the bladder.
Phosphatemic action of 1,25-dihydroxyvitamin D3
Authors: Steele TH , Engle JE , Tanaka Y , Lorenc RS , Dudgeon KL , DeLuca HF
Published: December 2017

The action of a single intraperitoneal injection of 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) was investigated in thyroparathyroidectomized (TPTX) vitamin D-deficient phosphate-depleted rats. After 14 h, plasma inorganic phosphorus (Pi) was significantly greater in animals receiving 1,25(OH)2D3 than in D-deficient controls, but urinary Pi excretion was very low in both groups and not significantly different in the rats given 1,25(OH)2D3. Clearance studies indicated that the D-deficient controls reabsorbed more than 99% of their filtered Pi. Avid Pi reabsorption continued even after the infusion of sufficient phosphate to raise the plasma and filtered Pi to approximately 3 times normal. Fractional calcium excretion (FECa) exceeded fractional sodium excretion (FENa) by severalfold, but FECa decreased strikingly during phosphate infusion. In animals that manifested a substantial elevation of plasma Pi after 1,25(OH)2D3, FECa was significantly less than in D-deficient controls. Therefore, the increase in plasma Pi following 1,25(OH)2D3 administration occurs independently of any effect on renal Pi reabsorption and may be responsible, at least in part, for the amelioration of hypercalciuria after 1,25(OH)2D3 treatment.
Metabolism and temperature regulation in young harbor seals Phoca vitulina richardi
Authors: Miller K , Irving L
Published: December 2017

Metabolism and the ability to regulate core and peripheral temperatures under a variety of ambient conditions were studied in five unrestrained pups (less than 5 wk old) and four 3- to 5-mo-old harbor seals. Pups born with nonlanugo (adultlike) hair and little fat were able to swim in 5 degrees C water for several hours without becoming hypothermic. They were also found to tolerate 5 degrees C air temperature with the fur wet and exposed to a 35-knot wind. Basal metabolism in pups averaged 0.8 ml O2 g-1 h-1, which is 2.6 times the predicted value for an adult mammal of the same weight. Lower critical temperature in air was about 3 degrees C. Oxygen uptake in 3- to 5-mo-old seals under basal conditions was 0.5 ml g-1 h-1. Minimal thermal conductance values were .02 and .015 ml O2 g-1 h-1 degrees C-1 in pumps and 3- to 5-month-old seals, respectively. Appendages, and to a lesser extent the skin on the torso, cooled appreciably at lower air temperatures, and the flippers were kept just above freezing in subzero air. Tissue insulation provided by low peripheral temperatures and a high resting metabolic rate enable newborn and developing harbor seals to tolerate the low temperatures encountered in their natural environment.
Capillary and cell wall permeability to potassium in isolated dog hearts
Authors: Tancredi RG , Yipintsoi T , Bassingthwaighte JB
Published: December 2017

From venous tracer-dilution curves recorded after 36 pulse injections of 42KCl and 131I-labeled albumin into the coronary artery inflow of 15 isolated canine heart preparations, we calculated maximal fractional extractions (Emax) and capillary permeability-surface area products (PScap) for 42K+ over a range of plasma flows (FP) from 0.3 to 1.7 ml min-1 g-u. At low FP (less than 1.0), Emax was 0.60 +/- 0.0l (mean +/- SD) and PScap was 0.72 +/- 0.20 ml min-1 g-1; at high FP (greater than 1.0), Emax decreased to 0.49 +/- 0.05 and PScap increased to 1.06 +/- 0.18. Continuous recording (gamma detector) of residual myocardial 42K+ in seven hearts showed that the mean fractional escape rate of tracer between 30 and 60 min after injection was 0.011-0.023 min-1; higher rates were observed at high FP, when the residue of 42K+ decreased to less than 10% of the injected dose by 60 min. Using PScap measured at high FP and considering the virtual intracellular volume of distribution for K+ to be 20 ml/g, we calculated the permeability-surface area product for sarcolemma (PScw) as 0.54-0.73 ml min-1 g-1, or about 50% of PScap. Considering sarcolemmal surface area (Scw) as 4,200 cm2/g and capillary surface area (Scap) as 500 cm2/g, cell permeability is low, with Pcw:Pcap being less than 0.08.
Effect of pH on ionic exchange and function in rat and rabbit myocardium
Authors: Poole-Wilson PA , Langer GA
Published: December 2017

The effects of pH variation on ionic exchange and mechanical function were studied in the arterially perfused rat and rabbit septa. The pH and PCO2 of the control perfusate were 7.40 and 39 mmHg, respectively. In the rabbit septum a metabolic acidosis (pH equals 6.82, PCO2 equals 39 mmHg) caused a loss of 16% of control tension in 12 min. Na+ and K+ exchange were unaltered. A comparable respiratory acidosis (pH equals 6.81, PCO2 equals 159 mmHg) caused a 51% loss of tension in 2 min. Na+ exchange was unaltered but K+ efflux fell from 8.9 +/- 0.6 (mean +/- SE) to 4.9 +/- 0.3 mmol/kg dry wt per min (P less than 0.001, n equals 10). A net gain of K+ of 16.9 +/- 1.7 (n equals 14) mmol/kg dry wt occurred and was attributable to a delayed fall in K+ influx relative to efflux over 15 min. The net gain could not be mimicked by epinephrine administration or blocked by propranolol and was absent in the beating rat septum and the quiescent rabbit septum. These results suggest that the net uptake of K+, which appears to be dependent on a period of depolarization, and the changes of contractility are controlled by the H+ ion concentration at a cellular site whose exchange with the extracellular space is characterized by a considerable restriction of diffusion. Changes of contractility are not related to the net uptake of K+.
Positive inotropic effects of methoxamine: evidence for alpha-adrenergic receptors in ventricular myocardium
Authors: Rabinowitz B , Chuck L , Kligerman M , Parmley WW
Published: December 2017

The present study was undertaken to evaluate the effects of methoxamine on force development and adenyl cyclase activity in cat ventricular myocardium. Methoxamine produced a dose-related increase in force development of isometrically contracting cat papillary muscles. The positive inotropic effects of methoxamine were not altered by beta-adrenergic blockade (propranolol), or catecholamine depletion by prior reserpinization, but were completely prevented by alpha-adrenergic blockade (phentolamine or ergotamine). Neither ergotamine, phentolamine, nor methoxamine had any direct effects on adenyl cyclase activity. Phentolamine did not attenuate the increase in force development produced by paired electrical stimulation, suggesting that it does not block the entry of calcium into the muscle. In summary, methoxamine produced a dose-related increase in force development of the cat papillary muscle that was selectively blocked by alpha-adrenergic receptors in ventricular myocardium.
Effect of renal decapsulation on renal function
Authors: Hebert LA , Stuart KA , Stemper JA
Published: December 2017

Marked increases in renal volume commonly occur in acute tubular necrosis and acute transplant rejection. Based on studies in the dog, we have previously suggested that the renal swelling observed in states of acute renal injury may be due principally to an increase in compliance of the kidney. The present study was undertaken in an effort to assess whether compliance-mediated increases in renal volume might affect renal function. In 15 dogs we compared the function of a decapsulated kidney (DK) to that of the contralateral intact kidney (IK); in 12 dogs we compared the function of a partially decapsulated kidney (PDK) to that of the contralateral IK. We compared the function of DK or PDK to IK, first under control conditions (ureteral pressure (UP) equals 0 mmHg), then at increased intrarenal pressure (UP equals 30 mmHg for both kidneys plus iv saline loading), and then during a recovery period (UP of both kidneys restored to 0 mmHg). The rationale is that probably DK is more compliant than IK; thus at increased intrarenal pressure DK volume should increase more than IK volume. Under control conditions DK and IK function were normal and equal; however, during increased intrarenal pressure, glomerular filtration rate (GFR) was about 20% less and Na and H20 excretion were about 30% less in DK than in IK. When intrarenal pressure was restored toward control by lowering UP to 0 mmHg, DK and IK function were once again equal. Similar but less marked changes occurred in the experiments comparing PDK and IK function. The impairment of renal function in DK vs. IK at increased intrarenal pressure was not explained by renal blood flow distribution, backdiffusion of glomerular filtrate, or by surface losses of fluid from DK. We suggest that impairment of renal function in DK vs. IK during increased intrarenal pressure is in some way related to the greater expansion of DK (21.0 +/- 0.02%) vs. IK (9.7 +/- 0.03%) at increased intrarenal pressure.
Effect of [Sar1, Ala8]angiotensin II on renal vascular resistance
Authors: Satoh S , Zimmerman BG
Published: December 2017

Partial occlusion of the renal artery (RAO) was induced in dogs anesthetized with pentobarbital or morphine chloralose-urethan. The effect of [Sar1, Ala8]angiotensin II (P-113) was compared before and during RAO on blood flow and vascular resistance of the contralateral kidney. An increase in renin secretion rate was obtained in the ischemic kidney, which was accompanied by an increase in renal vascular resistance (RVR) in the contralateral kidney and a rise in systemic blood pressure. P-113 given intra-arterially to the contralateral kidney consistently increased renal blood flow and decreased RVR during RAO, but did not alter RVR significantly before RAO. The elevation in renin secretion rate decreased between 30 and 122 min after the initiation of RAO in the pentobarbital-anesthetized dogs but not in the chloralose-urethan-anesthetized dogs. These experiments indicate that during RAO release of renin causes, through formation of angiotensin, an increase in RVR in the contralateral kidney and intra-arterial administration of P-113 restores the vascular resistance to a near-normal level.
Sex differences in reflex tachycardia induced by hypotensive drugs in unanesthetized rats
Authors: Bunag RD , Walaszek EJ , Mueting N
Published: December 2017

Possible sex differences in autonomic regulation of the heart were studied by injecting standard hypotensive doses of histamine or bradykinin to induce reflex tachycardia in awake rats. Although depressor responses to both drugs were unaltered, the tachycardia was greatly reduced by beta-adrenergic blockade with propranolol and abolished almost completely after combined blockade with propranolol and atropine. These findings indicate that the tachycardia was mostly due to increased sympathetic stimulation wiht a minor contribution from parasympathetic withdrawal. With large doses of bradykinin, direct myocardial stimulation also seemed likely, since some residual tachycardia remained even after combined blockade. Reflex tachycardia was generally more pronounced in male than in female rats. Because males had lower base-line heart rates and more tachycardia that was resistant to beta-adrenergic blockade than females, autonomic regulation was concluded to be predominantly parasympathetic in males and sympathetic in females. Whereas the exact cause of these variations in chronotropic regulation is unknown, it was considered possible that differences in sex hormones may have affected sensitivity of some component of the reflex arc.
Active transport of iron to mucosal surface of rat jejunum
Authors: Guy MJ , Schachter D
Published: December 2017

Estimations of steady-state fluxes of divalent Fe across rat intestinal segments in vitro provide evidence for two active transport mechanisms. Segments of the distal small intestine transport the mineral against electrochemical potential gradients from the serosal to the mucosal surface. Active transport in the reverse direction was confirmed with segments of proximal duodenum. The distal mechanism is dependent on cellular metabolism and is markedly decreased by metabolic inhibitors or in the absence of a metabolizable hexose. Cycloheximide, which inhibits protein biosynthesis, also blocks the active transport. Perfusion of jejunal and duodenal intestinal loops in situ in anesthetized rats provides evidence that endogenous Fe can be transferred to the lumen by a process otherthan shedding of mucosal cells. It is suggested that such transfer may occur via the active transport mechanism.
Relationship of mammary blood flow to parturition in the ewe
Authors: Burd LI , Lemons JA , Makowski EL , Battaglia FC , Meschia G
Published: December 2017

Mammary blood flow was measured in conscious, unanesthetized ewes with electromagnetic flow probes prior to spontaneous labor (four animals) or during the induction of premature labor (four animals) by administration of dexamethasone, 1 mg/24 h, to the fetus. In all animals an increase in mammary blood flow was noted prior to delivery. Dexamethasone administered to one mother in the same dose did not induce labor or produce an increase in mammary blood flow. These results suggest that the fetal adrenal gland influences maternal mammary blood flow prior to delivery.
Localization of renal tubular uric acid transport defect in gouty chickens
Authors: Zmuda MJ , Quebbemann AJ
Published: December 2017

Chickens genetically selected for high incidence of articular gout and hyperuricemia were used to determine the site of defective uric acid (UA) transport in gout. The Sperber technique was used to compare the tubular secretion of preformed UA with the tubular secretion of UA formed within the tubular cells in gouty and nongouty chickens of the same strain. In gouty chickens, the tubular excretion ratio of preformed [14C]UA was 36% of the value obtained in nongouty chickens of the same strain, whereas the tubular excretion ratios of [14C]UA formed within the tubular cells from [14C]guanine were equal in the two types of chickens. This suggests that a UA transport is located at the peritubular membrane and that this mechanism is defective in gouty chickens. In addition, the transport of p-aminohippurate (PAH) was normal in gouty chickens, which suggests that the transport mechanism for UA is distinct from that for PAH.
Effects of mannitol on cardiac ultrastructure and microcirculation following anoxia
Authors: Christodoulou J , Erlandson R , Smithen C , Killip T , Brachfeld N
Published: December 2017

Electron microscopic and microcirculatory effects of hyperosmolal mannitol were evaluated in the isolated perfused isovolumic rat heart. Specimens for ultrastructural examination were obtained in 26 experiemnts after 15 min of sequential aerobic, anoxic, and reoxygenated perfusion using an isosmolal perfusate of Krebs-Ringer-Henseleit bicarbonate buffer (KRB) (osmolality equals 290 mosmol/kg) vs. a hyperosmolal solution of KRB + mannitol (equals 350 mosmol/kg). No significant changes were noted during aerobic perfusion. Anoxic hearts perfused with isosmolal KRB demonstrated the most severe ultrastructural alterations including: mitochondrial swelling with disruption of cristae, myofibrillar fusion and contraction bands, and subsarcolemmal edema and vacuolization. These subcellular changes were not only partially reversed by oxygenated isosmolal perfusion but were significantly reversed during both the anoxic and reoxygenation perfusion periods with mannitol added. Following silicone rubber injection of the microcirculation, only focal capillary endothelial cell swelling was noted, and no difference in arteriolar or capillary filling was observed with either perfusate. Thus, mannitol significantly reversed the postanoxic ultrastructural changes consistently observed in the absence of increased osmolality. No gross effect on vascular patency could be demonstrated.
Chloride balance in Rana pipiens
Authors: Alvarado RH , Poole AM , Mullen TL
Published: December 2017

Frogs kept in dilute solutions of Cl- maintain a steady state with respect to this ion. Chloride is exchanged at a rate of about 15 mumol 100 g-1 h-1 (47 nmol cm-2 h-1). Over 90% of the efflux is integumentary of which about 50% is diffusion of the total influx. The rest is carrier mediated, half of which is exchange diffusion and half active transport. The chloride transport system displays saturation kinetics and is inhibited by acetazolamide. Uptake of Cl- is not dependent on concomitant uptake of cations. Salt-depleted frogs accumulate Cl- from dilute KCl or choline chloride in exchange for an endogenous base, probably HCO-3. High bath concentrations of NaCl (greater than 5 mM) abolish the active uptake of Cl- and increase the passive permeability of the skin to Cl-.
Localization of contractile-dependent Ca: comparison of Mn and verapamil in cardiac and skeletal muslce
Authors: Langer GA , Serena SD , Nudd LM
Published: December 2017

The effects of two excitation-contraction uncoupling agents, manganese (Mn) and verapamil, are compared in heart and fast-twitch skeletal muscle. Particular attention is given to the effect of the agents on the first contraction following a period of quiescence when the agents are administered during the quiescent period. Mn significantly diminishes dP/dt of the first beat in heart muscle, whereas verapamil has no significant effect. Neither Mn nor verapamil has a significant effect on the first postquiescent contraction in skeletal muscle, though verapamil produces a diminution of dP/dt in subsequent contractions in both tissues. A comparison of the effect of the agents on 45Ca exchange in heart cells in tissue culture indicates that Mn induces a rapid displacement of a rapidly exchangeable component of heart-cell calcium with subsequent inhibiton of influx. Verapamil, by contrast, produces no rapid displacement but only an inhibiton of influx. The functional and Ca-exchange effect of the two agents are compatible with a model which places most of the contractile-dependent Ca at the cellular surface in heart muscle and at deeper, intracellular sites in fast-twitch skeletal muscle.
Nitrogen utilization within equine large intestine
Authors: Wootton JF , Argenzio RA
Published: December 2017

The distribution of nitrogen in ligated segments of the stomach and intestine of two groups of ponies has been examined at sacrifice 2, 4, 8, and 12 h following the final 12-h scheduled feeding of diets designed to provide either 1) ample protein, or 2) limited protein plus supplemental urea as the major nitrogen source. Concentrations and total quantities of total N, NH3, urea plus NH3, and alpha-amino N were determined, and protein N was calculated by difference. Liquid marker (PEG) distribution rate constants and N concentrations were used to calculate rates of entry and exit by digesta flow for the large intestinal compartments. These values, together with measured accumulations of each constituent, allowed assessment of transitory net appearance and net disappearance within each compartment due to processes other than flow along the tract. The data suggested cyclic fluctuations of microbial populations within the large intestine, particularly the dorsal and ventral colon. These segments also were implicated as major sites of microbial protein synthesis and degradation. the former process appeared more evident in animals consuming the urea-supplemented diet.