bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of diuretic response associated with atrial tachycardia
Authors: Boykin J , Cadnapaphornchai P , McDonald KM , Schrier RW
Published: December 2017

Left atrial pacing was performed in three groups of anesthetized dogs. In the first group of eight intact dogs a mean increase in atrial rate (AR) from 140 +/- 7 to 244 +/- 6 was associated with a decrease in urinary osmolality (U osmol) from 631 +/- 72 to 264 +/- 43 mosmol/kg (P less than .001), and free-water clearance (CH20) increased from -.325 +/- .06 to +.355 +/- .15 ml/min (P less than .001). At the same time left atrial pressure (LAP) increased from 6 +/- 1 to 15 +/- 1 mmHg (P less than .001). A second group of studies was performed in six hypophysectomized, steroid-replaced animals receiving 40-50 muU/kg per min of antidiuretic hormone (ADH). In these animals AR was increased from 148 +/- 17 to 250 +/- 17 but diuresis did not occur. In these studies Uosmol was 690 +/- 55 before and 704 +/- 49 mosmol/kg after atrial pacing and CH20 also did not change. Left atrial pressure increased from 10 +/- 2 to 19 +/- 2 mmHg during atrial pacing. A third group of studies was performed in five animals with bilateral cervical vagotomy. In these animals AR was increased from 159 +/- 6 to 258 +/- 17 and LAP increased from 7 +/- 1 to 16 +/- 2 mmHg. Osmolality increased from 808 +/- 72 to 1,049 +/- 65 musmol/kg (P less than .005) and CH20 was unchanged. These results, therefore, indicate that atrial tachycardia primarily increases renal water excretion by suppressing ADH release. This reflex is dependent on the integrity of cervical vagal pathways.
Distal site of action of parathyroid hormone on phosphate reabsorption
Authors: Knox FG , Lechene C
Published: December 2017

The sites of inhibited phosphate transport following administration of bovine parathyroid hormone (bPTH) to thyroparathyroidectomized (TPTX) dogs were investigated. Phosphate reabsorption by the proximal and distal nephron was studied using recollection micropuncture, stop-flow methodology, and electron-probe microanalysis. Following bPTH, delivery of phosphate from the proximal tubule increased from 26 to 37% of the filtered load, P less than .01. Fractional phosphate excretion increased from 2.3 +/- 1.5 to 21.4 +/- 2.3%, P less than .001. The increased delivery of phosphate at the point of micropuncture in the proximal tubule accounted for approximately half of the phosphaturia. In six TPTX dogs, which were saline loaded, similiar increases in phosphate delivery from the proximal tubule from 27 +/- 1 to 36 +/- 2% of the filtered load resulted in a strikingly smaller phosphaturia, 5.1 +/- 1 to 9.8 +/- 2.4%, NS. In stop-flow experiments, phosphate concentratin ratios were slightly increased in the proximal nephron and markedly increased in the distal nephron following bPTH. It is concluded that parathyroid hormone markedly decreases phosphate transport in the distal nephron.
Effect of calcium on magnesium absorption
Authors: Behar J
Published: December 2017

The effect of calcium on magnesium absorption was studied in the rat ileum in vivo. The increase in the luminal concentration of calcium led to a progressive decrease in magnesium absorption, which was accompanied by a parallel decrease in net sodium absorption. This calcium effect was also observed when sodium chloride was replaced by urea. However, a consistent correlation was observed between the magnitude of net magnesium absorption and the rates of net water absorption of all calcium concentrations. These findings suggest that calcium decreases magnesium absorption by a nonspecific reduction in membrane permeability to solutes that induce net water flow and are consistent with the concept that magnesium is transported by solvent "drag". The increase in the luminal concentration of calcium resulted in an increase in tissue accumulation of magnesium. This increase in tissue accumulation of magnesium was associated with a decrease in net sodium absorption and in the negativity of the transmural PD. These findings suggest an additional mechanism of magnesium transport operating independently of net water flow.
Inhibition of urate excretion by pyrazinoate: a micropuncture study
Authors: Roch-Ramel F , Weiner IM
Published: December 2017

Anesthetized monkeys (Cebus albifrons) undergoing moderate mannitol diuresis were treated with infusions containing lithium urate to elevate the urate concentration in plasma to 45-68 mug/ml and containing the uricosuric drug, 2-nitroprobenecid, to enhance the renal clearance or urate. The urate/inulin clearance ratio was 0.55 +/- 0.03. When pyrazinoate was added to the infusion the clearance ratio fell to 0.26 +/- 0.02. Analysis of free-flow micropuncture samples revealed a major effect of pyrazinoate in the proximal tubule, although an additional, smaller action in the distal tubule could not be definitely excluded. When droplets containing [14C]urate and [3H]inulin were streaked on the surface of the left kidney more urate than inulin appeared in the urine from that kidney (but not the other) within the first 3 min after application. This "excess" excretion of urate could be largely eliminated by pretreatment with pyrazinoate. The results suggest that pyrazinoate inhibits secretion of urate in the proximal tubule.
Release of adenosine by hypoxic canine lung tissue and its possible role in pulmonary circulation
Authors: Mentzer RM  , Rubio R , Berne RM
Published: December 2017

Adenosine is a possible mediator of myocardial and skeletal muscle blood flow regulation. Whether adenosine plays a similar role in modulating the pulmonary pressor response to acute alveolar hypoxia is not known. Adenosine levels (nmol/g tissue) in lung in six dogs ventilated with 95% N2, and 5% CO2 for a period of 3 min increased nearly 10-fold. Inosine and hypoxanthine, adenosine enzymatic degradation products, sustained a 10- and 7-fold increase, respectively. These degradative products are mainly formed in the capillary endothelial cells that contain the degradative enzyme nucleoside phosphorylase as demonstrated by histochemical techniques. To determine the effect of ATP, ADP, AMP, and adenosine on the pulmonary circulation, the in situ left lower lobe of 10 dogs was perfused at either free flow or constant flow via its pulmonary artery. ATP and ADP increased lobar vascular resistance; AMP and adenosine decreased the resistance. During hypoxic ventilation, adenosine infusions (100 nmol/ml blood) entirely abolished the increase in vascular resistance that was due solely to hypoxia. Dipyridamole produced similar responses. These data indicate that adenosine is a pulmonary vasodilator and that it may modulate the pulmonary pressor response to acute alveolar hypoxia. The findings suggest that the use of adenosine or dipyridamole may be beneficial in patients with pathologic elevations of the pulmonary vascular resistance which are a result of an exaggerated pulmonary pressor response to hypoxia, as seen in high-altitude pulmonary edema or that following cerebral injury.
Mechanisms of disposal of acid and alkali in rabbit duodenum
Authors: Fiddian-Green RG , Silen W
Published: December 2017

Stripped duodenal mucosa of rabbits was mounted in Ussing chambers containing a Ringer solution gassed with 100% O2. The disappearance of acid or alkali from the mucosal solution of short-circuited tissue was measured with a pH stat while the serosal pH was kept at 7.4. The duodenum rapidly disposed of both acid and alkali; neither property was altered by gassing with N2 while iodoacetate was in the perfusing solutions. Prevention of release of CO2 from the mucosal chamber obliterated the early rapid phase of acid disposal by the mucosa while a similar maneuver in the serosal chamber increased the appearance of serosal acid without altering the rate of acid disposal. Gut sacs of rabbit duodenum in vitro and in vivo showed a positive correlation between acid disposal and the rate of luminal CO2 production. While acid disposal progressively decreased with time for the in vitro gut sacs, the in vivo gut sac showed no fatigue in this respect. Luminal acidification in the Ussing chamber was associated with a profound reduction in short-circuit current (Isc), partially reversible by elevation of the mucosal pH but not by luminal glucose. Our data suggest that acid disposal occurs in part by intraluminal neutralization and in part by diffusion into the mucosa.
Renovascular resistance and noradrenaline
Authors: Bomzon L , Rosendorff C
Published: December 2017

Stimulation of the renal nerves can cause cortical vasoconstriction either by direct activation of vascular smooth muscle or by the generation of angiotensin II following renin release from the juxtaglomerular cells. High doses ( greater than 5 mug/min) of the renal neurotransmitter noradrenaline (NA) infused into the renal artery of the baboon causes cortical vasoconstriction. This NA-induced vasoconstriction is significantly reduced (P less than 0.001) by SQ20881, an inhibitor of converting enzyme, and by saralasin, a competitive inhibitor of angiotensin II. These results suggest that NA stimulates the renin-angiotensin mechanism. The further addition of the alpha-adrenergic blocking agent, phenoxybenzamine, to the NA-SQ20881 or NA-saralasin infusate completely abolishes NA-induced cortical vasoconstriction. These results suggest that NA-induced cortical vasoconstriction in the kidney is mediated by activation of both the renin-angiotensin system and alpha-adrenergic receptors.
Glucose turnover values in the dog obtained with various species of labeled glucose
Authors: Altszuler N , Barkai A , Bjerknes C , Gottlieb B , Steele R
Published: December 2017

Recent studies proposed that [2T]glucose is preferable to [14C]-glucose as a tracer for the measurement of glucose turnover. However, higher values for glucose turnover were obtained using [2T]glucose than with [14C]glucose. The present study explores the merit of another species of tritiated glucose, [3T]glucose. Utilizing isotope-dilution principles, comparison is made of glucose turnover values determined by use of [2T]glucose, [3T]glucose, and [6-14C]glucose. Glucose turnover using [2T]glucose was 1.51 +/- 0.07 times greater than that using [6-14C]glucose, after correction for recycling of 14C. However, glucose turnover values obtained with [3T]glucose were similar to those obtained with [6-14C]glucose. There were no temporal or quantitative differences in appearance of tritium (T) in plasma water after injection of [2T]- and [3T]glucose. A methylprednisolone regimen in the normal dog increased glucose turnover as determined by all three tracers, but the increase observed using [2T]glusoce was significantly greater than that using that two other tracers. Thiement for [6-14C]glucose for measurement of glucose turnover in the dog.
Rattlesnake venom shock in the rat: development of a method
Authors: Carlson RW , Schaeffer RC  , Whigham H , Michaels S , Russell FE , Weil MH
Published: December 2017

A model in Wistar rats (n = 30, 279-345 g) was developed to study circulatory, respiratory, metabolic, and lethal effects of an intravenous infusion (30 min; 1.25, 1.5, 1.75, and 2.0 mg/kg) of rattlesnake (Crotalus viridis helleri) venom. Venom produced perfusion failure with lactacidemia, hemoconcentration, hypoproteinemia, and death. The severity of poisoning was proportional to the quantity of venom given and to the elevation in lactic acid and hematocrit. Hemorrhages in the diaphragm, intercostal muscles, and intestine were observed at necropsy. In a separate test, rats (n = 12, 311-355 g) received an infusion of 1.5 mg/kg of venom or physiological salt solution. Blood volume was measured 30 min after the end of infusion in both groups with radioiodinated (125I) human serum albumin (RIHSA) and 51Cr-labeled rat red cells. Venom produced a significant reduction in total blood volume index (35%, P less than 0.001), plasma volume index (46%, P less than 0.001), and red cell mass indec (22% P less than 0.005). The slope of the RIHSA-disappearance curve of animals that received venom was more than twice that of the control group. We conclude that perfusion failure following rattlesnake envenomation is associated with hypovolemia due to increases in vascular permeabiltiy and hemorrhage.
Chymodenin, a duodenal peptide: specific stimulation of chymotrypsinogen secretion
Authors: Adelson JW , Rothman SS
Published: December 2017

Chymodenin, a basic porcine duodenal peptide, was administered to anesthetized rabbits intravenously or added to the medium bathing the isolated pancreas. In the 10(-8)M range, chymodenin rapidly increased chymotrypsinogen (ChTg) secretion, did not increase lipase secretion, and modestly enhanced protein secretion (which could be attributed primarily to augmented ChTg secretion). The increased ChTg output was too rapid to be the result of increased rates of protein synthesis and could not be attributed to the exocytosis os zymogen granule contents because of the enzyme-;pecific nature of the response. In contrast to shymodenin, cholinergic stimulation in vitro produced a relatively lipase-rich, chymotrypsinogen-poor secretion. Lipase and ChTg outputs, which varied relatively independently under unstimulated conditions, covaried in the presence of chymodenin. The existence of a duodenal peptide that produces an enzyme-specific response supports the hypothesis that the secretion of digestive enzymes during digestion is a highly regulated process in which the enzyme content of pancreatic secretion varies with differences in the composition of intestinal substrates.
Micropuncture study of renal magnesium transport in magnesium-loaded rats
Authors: Brunette MG , Vigneault N , Carriere S
Published: December 2017

Mg transport in the deep loop of Henle was studied in 15 young rats (50-60 g) after acute systemic Mg loading (UFMg (ultrafilterable Mg) 4.77 meq/liter). Intratubular Mg was measured with a recently described fluorometric microtechnique. The mean values of the TF/P inulin and TF/UF Mg ratios were 3.32 +/- 0.13 and 4.25 +/- 0.17, respectively. The proportion of filtered Mg recovered in this part of the nephron was therefore 131.2 +/- 5.0%, indicating that an appreciable amount of Mg entered the lumen prior to the sites of puncture. A significant correlation between the TF/P inulin and TF/UF Mg ratios suggests that water reabsorption also contributes to the high concentration of Mg in the loop of Henle during systemic Mg loading. In another series of young rats (90-160 g), similarly loaded with MgCl2 (UFMg 5.81 meq/liter), Mg and inulin were measured in superficial proximal (PT) and distal tubules (DT). Punctures were paired at two sites of the same PT and DT. The Mg concentration increased progressively along the PT in such a way that 90.5% of the filtered load still remained in the late proximal loops. If superficial and deep proximal tubules behave in a similar manner, it may be concluded that the site of entry of Mg is located between the late accessible part of the PT and the bend of the loop of Henle. Only 58.0 +/- 3.0% of the filtered Mg was delivered to the DT, indicating that Mg is extensively reabsorbed in the ascending limb, despite systemic loading. The proportion of filtered Mg did not vary along the DT, indicating no net reabsorption.
Effects of an angiotensin inhibitor on adrenocortical response to angiotensin II, ACTH, and K
Authors: Forman BH , Fernandez-Cruz A , Kuczala ZJ , Mulrow PJ
Published: December 2017

A competitive inhibitor of angiotensin II has been studied in nephrectomized dogs treated with dexamethasone to suppress ACTH secretion. The inhibitor, [1-sarcosine, 8-alanine]angiotensin II (P113), has been shown by previous investigators to inhibit the pressor action of angiotensin II but not the pressor effect of other pressor agents. The present experiments demonstrate that P113 inhibits the stimulation of aldosterone secretion by angiotensin II but not by ACTH or potassium infusions. Therefore, P113 appears to be a specific inhibitor of angiotensin's action on both vascular and adrenocortical tissue. In this dog preparation, P113 has a mild nondose-related agonistic action on the blood pressure and a nonsignificant action on aldosterone secretion, although in some dogs P113 appears to have a definite agonist effect.
Brain indole and catecholamines of turkeys during exposure to temperature stress
Authors: El Halawani ME , Waibel PE
Published: December 2017

Turnovers of dopamine (DA), norepinephrine (NE), epinephrine (E), and 5-hydroxytryptamine (5-HT) were determined in the brains of male turkeys during acute, chronic, and posttemperature stress. Changes induced in the depletion of endogenous monoamine levels 6 h after tyrosine hydroxylase or tryptophan hydroxylase inhibitions were regarded as changes in turnovers. High or low ambient temperature had no effect on brain DA turnover, whether the temperature stress was acute (6 h) or chronic (5 wk). Brain NE turnover increased upon acute exposure to either a cold (5 degrees C) or warm (32 degrees C) environment. Chronic exposure (5 wk) to such temperatures reduced significantly (P less than 0.001) the elevated NE turnover. The central E and 5-HT turnovers of birds kept at 32 degrees C for 6 h decreased and increased, respectively, whereas determination of E and 5-HT of birds kept at 5 degrees C showed an opposite pattern. Five weeks of continuous exposure to high and low environmental temperatures did not alter the changes in E and 5-HT turnovers from those observed during acute stress. Exposure of heat- or cold-reared turkeys to 24 degrees C reversed the changes in E and 5-HT turnovers. Thus the results indicated an increase in NE turnover only during acute exposure to thermal stress. However, the changes in E and 5-HT turnovers persisted during chronic exposure.
Mechanism of the inhibition of myocardial protein synthesis during oxygen deprivation
Authors: Lesch M , Taegtmeyer H , Peterson MB , Vernick R
Published: December 2017

Inhibition of protein synthesis during anoxia in the isolated rabbit right ventricular papillary muscle preparation is totally reversible for up to 2 h if glucose concentration is increased during anoxia. The degree of inhibition of protein synthesis during anoxia is, however, not altered by the presence of increased glucose. Thus inhibition of myocardial protein synthesis induced by anoxia need not be related to irreversible disruption of cellular integrity but may represent metabolic regulation of the synthesis. Tissue content of ATP, ADP, AMP, CP, and lactate and phenylalanine incorporation into protein were measured in individual papillary muscles incubated with varying degrees of O2 deprivation and varying substrates and metabolic inhibitors to determine if the inhibition during anoxia could be ascribed to alterations in tissue high-energy phosphate, adenine nucleotide levels, or rate of metabolic flux through the glycolytic and/or Krebs cycle. Protein synthesis was inhibited in muscles incubated in 15 mM glucose during anoxia despite the fact that in the presence of increased glucose, tissue levels of ATP, ADP, and AMP were equal to that of controls. Protein synthesis was normal in muscles made sufficiently hypoxic so that ATP and CP were significantly decreased and lactate increased. Inhibition of Krebs cycle activity with pentenoate failed to effect the rate of protein synthesis. We conclude that anoxic inhibition of myocardial protein synthesis is due neither to high-energy phosphate depletion nor inhibition of Krebs cycle acitivity. The possibility remains that the inhibition may be related to accumulation of glycolytic intermediates or by-products other than lactate.
Cholecystokinin-decreased food intake in rhesus monkeys
Authors: Gibbs J , Falasco JD , McHugh PR
Published: December 2017

Five rhesus monkeys were infused intravenously with partially purified cholecystokinin (CCK) Just prior to a test meal of solid food after overnight food deprivation; CCK produced large, rapid, dose related suppressions of feeding. The lowest dose tested (5 Ivy U/kg body wt) produced a significant inhibition of food intake (26% suppression, P less than 0.05). Equivalent infusions of partially purified CCK or the synthetic COOH-terminal octapeptide of CCK (a pure fragment with all the biological activity of the full molecule) produced equivalent suppressions. In a second experiment, gastric preloads of a potent releaser of endogenous CCK, L-phenylalanine (L-Phe), and a weak releaser, D-phenylalanine (D-Phe) were compared for their relative abilities to suppress food intake at a test meal in nine rhesus monkeys after overnight deprivation. L-Phenylalanine produced large, rapid, dose-related suppressions of feeding, but D-Phe did not. The threshold dose of L-Phe was 0.5 g/kg (32% suppression, P less than 0.01). Neither CCK nor L-Phe caused signs of illness in these experiments. The results demonstrate that intravenous exogenous CCK suppresses feeding in rhesus monkeys and suggest that endogenous CCK has the same effect; they are consistent with the hypothesis that CCK is a satiety signal.
Interplay among carotid sinus, cardiopulmonary, and carotid body reflexes in dogs
Authors: Mancia G , Shepherd JT , Donald DE
Published: December 2017

Interactions among vascular reflexes evoked from carotid sinuses, carotid bodies, and cardiopulmonary region were examined in anesthetized, atropinized, and respired dogs with aortic nerves cut. The carotid sinuses were perfused at 220, 150, and 40-50 mmHg; the chemoreceptors were stimulated by perfusion with hypoxic hypercapnic blood. Cardiopulmonary vasomotor inhibition was interrupted by vagal cold block. Measurements were made of arterial blood pressure and of kidney and hindlimb vascular resistance. At sinus pressures less than 170-160 mmHg, cardiopulmonary vasomotor inhibition increased with increase in blood volume. At high sinus pressure, interruption of this augmented cardiopulmonary inhibition was as ineffective in changing vascular resistance as interruption of the lesser inhibition present during normovolemia. Chemoreceptor stimulation increased the response to vagal block at intermediate but not at high or low sinus pressure. The studies demonstrate the dominant role of the carotid sinus reflex when the three systems interact and the ineffectiveness of chemoreceptor stimulation when carotid or cardiopulmonary inhibition is maximal.
Comparison of arterial hemodynamics in the mongrel dog and the racing greyhound
Authors: Cox RH , Peterson LH , Detweiler DK
Published: December 2017

This study was undertaken to define certain differences in cardiovascular function between mongrel (M) and greyhound (GH) dogs. In unanesthetized, trained, chronically instrumented animals mean arterial pressure was significantly higher in the GH (118 vs. 98 mmHg). This was associated with a significantly higher cardiac index in the GH (4.3 vs 3.1 liters/min per m2) and a lower calculated peripheral resistance. Central venous renin activity was significantly lower in the GH when unanesthetized (1.51 vs. 2.88 ng/ml per h). Values of vascular impedance at several selected arterial sites were lower in the GH compared to the M, suggesting differences in arterial wall mechanical properties. The hydraulic power delivered to the aorta by the left ventricle in the GH was twice that of the M (1,166 vs. 564 mol wt). Oscillatory power represented a greater fraction of total aortic power in the GH (15.7 vs. 10.8%). Differences were also observed in the hemodynamic response to acute pentobarbital anesthesia. Thus the young adult GH is hemodynamically different from its mongrel counterpart. These differences bear some resemblance to hemodynamic changes seen in various types of experimental hypertension in animals and to those observed in the early phase of essential hypertension in man.
Relationship between clearances of Ca and Na: effect of distal diuretics and PTH
Authors: Costanzo LS , Weiner IM
Published: December 2017

One of the objectives of this study was to determine whether or not the absence of parathyroid hormone (PTH) modifies quantitatively the acute action of chlorothiazide (CTZ) to lower the clearance ratio, CCa/CNa. The same group of dogs was studied with standard clearance techniques before and after thyroparathyroidectomy (T-PTX), and after T-PTX during the infusion of PTH. There was no significant difference in the response to CTZ before or after T-PTX, or during the infusion of PTH. The effects of PTH and a maximally effective dose of CTZ were additive. A second objective of this work was to ascertain whether or not two other diuretics which act on the distal tubule, amiloride and triamterene, had actions on CCa/CNa similar to that of CTZ. Amiloride caused a reduction in CCa/CNa which, even at maximally effective doses, was much smaller than the effect of CTZ. Maximally effective doses of amiloride and CTZ had additive actions. Triamterene was evaluated at only one dose; it also lowered the ratio CCa/CNa.
Ion-osmotic hyperthermia during exercise in dogs
Authors: Greenleaf JE , Kolzowski S , Nazar K , Kaciuba-Uscilko H , Brzezinska Z , Ziemba A
Published: December 2017

The influence of intravenous infusions of various concentrations of NaCl solutions on temperature regulation was investigated in dogs at rest and during moderate exercise for 1 h on a treadmill. Infusion of hypertonic solutions either before and during exercise resulted in elevated (P less than 0.05) plasma Na+ and osmotic concentrations and produced higher equilibrium levels (P less than 0.05) of rectal temperature (Tre) during exercise (prehypertonic 40.9 degrees C vs. no infusion 40.4 degrees C; hypertonic 40.8 degrees C vs. isotonic infusion 40.4 degrees C), but not at rest. Increasing the [Na+] and osmotic concentrations above 170 meq/liter and 325 mosmol/kg, respectively, resulted in no additional increase in exercise Tre. Water consumption during exercise decreased (P less than 0.05) plasma [Na+], osmolality, and the equilibrium level of Tre to control levels. There was no effect of changes in plasma volume (PV) of +/- 8% on the time course, equilibrium level, or change in Tre during exercise. At the end of exercise, there were moderate correlations (P less than 0.01) between Tre and [Na+] (r = 0.51) and Tre and osmoti (r = 0.52) concentrations. It was concluded that a) the exercise Tre responses of the dog respond quantitatively like man to elevated plasma [Na+] and osmolality, b) the Tre levels are not influenced by changes in PV, and c) water intake significantly reduces the ion-osmotic hyperthermia.
Modification of stimulated lacrimal gland flow by sympathetic nerve impulses in rabbit
Authors: Botelho SY , Martinez EV , Pholpramool C , Prooyen HC , Janssen JT , De Palau A
Published: December 2017

This study was undertaken to determine if sympathetic nerve impulses modify lacrimal gland fluid (LGF) flow, which was continuously recorded from a cannula in the excretory duct of the lacrimal gland in rabbits anesthetized with pentobarbital sodium. The preganglionic trunk of the superior cervical ganglion was stimulated with electrical stimuli during pilocarpine-induced and reflexly induced secretion. Stimuli equal to or 6-8 times stronger than the intensity that produced maximal pupil dilation caused inhibition followed by poststimulus enhancement of LGF flow when the prestimulus LGF flow was greater than 3.0 mul/min. When the prestimulus LGF flow was less than 0.8 mul/min, the stronger stimulation enhanced LGF flow but the weaker stimulation produced inhibition followed by poststimulus enhancement of LGF flow. Although no measurements of lacrimal gland blood flow were made, the alterations in these responses, which occurred during alpha- and beta-adrenergic blockade, were consistent with the changes in sympathetically induced blood flow that occur during alpha- and beta-blockade in other organs.
Basis for phase relations between baroreceptor and sympathetic nervous discharge
Authors: Gebber GL
Published: December 2017

The phase relations between the cardiac cycle and sympathetic nervous discharge (SND) were studied with an average-response computer in the anesthetized cat. Maximum SND occurred during early diastole at heart rates between 3 and 4 beats/s. Dramatic shifts in the phase relations between SND and the cardiac cycle accompanied the decrease in heart rate produced by stimulation of the distal end of the cut right vagus nerve. The point of maximum SND was shifted from early diastole to near peak systole and then into the late diastolic phase of the preceding cardiac cycle as heart rate was progressively lowered to 2 beats/s. These observations indicate that synchronization of SND during each cardiac cycle is not the simple consequence of the waxing and waning of baroreceptor nerve activity. Rather, 1:1 locking of bursts of SND to the cardiac cycle is explained on the basis of entrainment by the baroreceptor reflexes of a sympathetic rhythm of central origin. An inhibitory-phasing hypothesis is proposed to account for entrainment. In addition, two components (spinal and brainstem) of sympathoinhibition associated with the pulse-synchronous discharge of the carotid sinus nerve were revealed when the 1:1 relationship between bursts of SND and the cardiac cycle was disrupted at heart rates below 2 beats/s.
Acetate as a metabolic substrate in the fetal lamb
Authors: Char VC , Creasy RK
Published: December 2017

Fetal acetate metabolsim was studied in chronically catheterized fetal lambs of 110-141 days' gestation. Acetate concentration was measured enzymatically in whole blood drawn simultaneously from maternal and fetal pre- and postplacental vessels. The oxygen content of the fetal blood samples was also measured. Fetal umbilical venous acetate concentration was found to be proportional to the maternal arterial acetate concentration and had a mean value of 0.366 mM. Fetal blood acetate increased significantly, by a mean of 0.081 mM, during circulation through the placenta. This increase was proportional to both the maternal acetate concentration and the concentration gradient of acetate across the placenta. The mean maternal arterial acetate concentration was 1.153 mM. Maternal blood lost significant amounts of acetate, 0.112 mM, during circulation through the uterus and appeared to be the source of the acetate being gained by the fetus. It is estimated that a total of 23 mmol of acetate/kg of fetal weight is being taken up by the fetus each day, providing it with 0.560 g of carbon/kg. Comparisons of acetate uptake with fetal oxygen uptake indicate 10% of the daily fetal oxygen consumption would be required to completely oxidize the acetate being gained by the fetus.
Characterization of midbrain component of the trigger for arousal from hibernation
Authors: Beckman AL , Satinoff E , Stanton TL
Published: December 2017

The ability of the midbrain reticular formation (MRF) to trigger arousal from hibernation and to change body temperature (Tb) during euthermia was tested in golden-mantled ground squirrels (Citellus lateralis). During hibernation (ambient temperature 5-6 degrees C) microinjections of cholinomimetic compounds (acetylcholine and carbachol) triggered full arousal or produced transient increases in Tb in 15 out of 19 tests; MRF microinjections of norepinephrine (NE) and 5-hydroxytryptamine (5-HT), at the same concentrations that produced full arousal when microinjected into the preoptic/anterior hypothalamus (PO/AH) area in previous experiments, has no effect on Tb in 13 out of 16 tests. In experiments on euthermic ground squirrels tested at an ambient temperature of 25 degrees C, MRF microinjections of acetylcholine raised Tb, whereas the monoamines had no significant effects. These results show that cholinoceptive neurons in the MRF can trigger arousal from hibernation and increase Tb during euthermia. The failure of NE and 5-HT to produce any significant effects at the same doses that were reported to be effective in the PO/AH indicates that the functional organization of the MRF portion of the arousal mechanism is different from that reported for the PO/AH.
Effect of exercise on hormone-sensitive lipase activity in rat adipocytes
Authors: McGarr JA , Oscai LB , Borensztajn J
Published: December 2017

Hormone-sensitive lipase activity was measured in adipocytes of rats subjected to a 12-wk program of treadmill running. Enzyme activity in the runners sacrificed immediately after exercise increased 2.5-fold (P less than 0.001) in tissue exposed to epinephrine and threefold (P less than 0.001) in tissue not exposed to epinephrine, when the results were expressed per gram of adipose tissue. Increases of almost the same magnitude were observed in runners sacrificed 24 h after their last bout of work. These significant increases in enzyme activity, however, were the result of a significant reduction in the size of cells in the epididymal fat pads of the exercisers compared with those of the freely eating sedentary animals (68.7 +/- 2.7 mum vs. 82.0 +/- 2.7 mum; P less than 0.01). When the results were expressed on a per-cell basis, therefore, hormone-sensitive lipase activity, assayed in the presence or absence of epinephrine, was unaffected by the exercise program. These results provide evidence that the lipolytic capacity of adipocytes of normal, untrained rats is sufficiently large to meet the increased demand for free fatty acids imposed by the exercise program without the need for an adaptive increase in enzyme activity.
Ca-activated ATPase activity in subcellular fractions of mouse pancreatic islets
Authors: Formby B , Capito K , Egeberg J , Hedeskov CJ
Published: December 2017

Ca-stimulated ATPase activity has been demonstrated in homogenates of mouse pancreatic islets. On subcellular fractionation Ca-ATPase activity was found in secretory granules, mitochondria, and microsomes, but not in the postmicrosomal fractions. Highest specific activity was found in the granules. In all active subcellular fractions two Km(Ca) values for Ca-ATPase around 7.0 X 10(-6) and 1.8 X 10(-7) M were estimated. Assuming an ATP hydrolysis:Ca pumping ratio of 1:2, the highest capacity for active Ca transport was found in secretory granules and mitochondria. Concentrations of 40 mM or higher of Na and 10(-5) M cyclic AMP inhibited Ca-ATPase in all subfractions. Caffeine at a concentration of 10 mM inhibited Ca-ATPase significantly in secretory granules and microsomes. Also MG-ATPase activity was demonstrated in the various subfractions. This activity was compared with that of Ca-ATPase at identical concentrations of free metal ions and in the absence or presence of various inhibitors. It was concluded that high-affinity Ca-ATPase and Mg-ATPase are two different enzymic entities. Ca-ATPase may tentatively be assumed to participate in active transport of Ca between intracellular compartments and to constitute a Ca-accumulating system which returns the cytosolic free Ca concentration to the resting state after stimulation of the beta-cells by secretagogues. This enzyme may therefore play a significant role in regulation of insulin release.
Tracer experiment design for unique identification of nonlinear physiological systems
Authors: DiStefano JJ
Published: December 2017

The design of tracer kinetic experiments, the purpose of which is to elucidate uniquely the internal couplings of a nonlinear dynamic system, is considered for a practical class of models of physiological systems. The extent of information about the real system contained in tracer kinetic data is a central issue. Criteria for determining whether nonlinear model parameters can be estimated from small-signal, "linearizing" tracer experiments are developed and illustrated by examples. The concept of "structural identifiability" is employed in this analysis to determine which model parameters can be and which cannot be determined "uniquely" from given input-output data; a step-by-step procedure based on an extension of this concept is presented for adapting the overall approach to the experimental design problem. Estimation of unmeasurable endogenous inputs and system state variables, problems that are intimately related to parameter estimation for physiological systems, are also considered.
Neurons intrinsic to arterioles initiate postcontraction vasodilation
Authors: Honig CR , Frierson JL
Published: December 2017

Ganglion cells exist in muscle arterioles. To determine the role of these intrinsic neurons in postcontraction vasodilation, isolated dog gracilis muscles were studied. A single twitch elicited vasodilation, but no vasodilator metabolites appeared in the venous effluent. Contraction at 2/s lowered resistance within 1 s whereas dilator metabolites were not demonstrable in the effluent until 15-20 s. During contraction the magnitude and time course of vasodilation were the same during constant and variable flow, and at various values of PaO2 and PVO2. In contrast, resistance was strongly correlated with flow and PO2 during recovery. Some resting muscles were perfused with venous blood from contracting donors. The rate of metabolic vasodilation in recipient muscles was about 10 times less than the rate of vasodilation in the donors. Lidocaine and procaine blocked postcontraction vasodilation but did not influence postocclusion vasodilation, metabolic vasodialtion, or autoregulation. The degree of block was the same in acutely and chronically denervated muscles. The effect of local anesthetics could not be accounted for by properties of skeletal or vascular smooth muscles. Conclusions: 1) intrinsic neurons initiate postcontraction vasodilation; 2) metabolites account for sustained vasodilation during recovery.
Norepinephrine turnover in heart and spleen of 7-, 22-, and 34 degree C-acclimated hamsters
Authors: Jones SB , Musacchia XJ
Published: December 2017

Norepinephrine (NE) turnover rates were measured in hamster (Mesocricetus auratus) heart and spleen tissues after 7-10 wk exposure to 7, 22, and 34 degrees C. The competitive inhibitor of NE synthesis, alpha-methyl-p-tyrosine methyl ester, was injected (200 mg/kg, ip) into acclimated animals. At sequential periods after drug treatment, hamsters were sacrificied by cervical transection, and tissues were removed and frozen. Rate constants, turnover time, and turnover rates were determined from regression analysis of NE tissue decay. Heart NE turnover was highest in cold-acclimated and lowest in heat-exposed animals (.111 and .047 mug/g per h, respectively), control values being intermediate (.081 mug/g per h). NE turnover is inversely related to tissue levels in the myocardium of temperature-acclimated hamsters. Spleen NE turnover was lowest with heat exposure, but spleen tissue levels of NE with heat or cold exposure were not different from control (22 degrees C) measurements. Heat-acclimated hamsters are slightly hyperthermic (Tre, 37.24 +/- .18 C; P, .032) compared to 22 degrees C-maintained controls (Tre, 36.85 +/- .07), but body temperature were unchanged with 7 degrees C exposure. The implication of altered NE synthesis is that sympathetic nerve activity is decreased with heat acclimation and increased with cold acclimation.
Importance of pulmonary ventilation in respiratory control in the bullfrog
Authors: Gottlieb G , Jackson DC
Published: December 2017

Pulmonary and cutaneous O2 consumption (Vo2) and CO2 production (Vco2) were measured simultaneously in bullfrogs Rana catesbeiana at 20 degrees C. The lungs were responsible for 77.3-91.0% of the total Vo2 and 28.5-74.9% of the total VCO2. The distribution of the total exchange between the lungs and skin depended on metabolic rate; frogs with higher rates relied more heavily on the pulmonary mode for both Vo2 and Vco2. When prevented from ventilating their lungs in an O2-rich environment, bullfrogs developed severe respiratory acidosis, demonstrating the importance of lung exchange in normal acid-base balance. When frogs were totally submerged in an O2-saturated medium, skin Vco2 increased linearly to a steady-state value which approximated the preapneic total Vco2. In these same animals, arterial Pco2 increased proportionately to the increase in skin Vco2, indicating that skin diffusion capacity for CO2 was unaffected. We conclude that the control of breathing in the bullfrog in response to changes in metabolic rate relies predominantly on changes in lung ventilation while the skin plays a more passive role.
Spinal subarachnoid perfusion of rhesus monkeys
Authors: Kessler JA , Fenstermacher JD , Owens ES
Published: December 2017

A technique of spinal subarachnoid perfusion is descirbed which effectively isolates the spinal cord from the remainder of the central nervous system. A method of obtaining and analyzing spinal cord tissue after subarachnoid perfusion is presented. The spinal subarachnoid space of 12 rhesus monkeys was perfused with [14C]sucrose, [14C]ethylenediaminetetraacetic acid-calcium complex (EDTA), and dextran blue as test substances. The sucrose and EDTA spinal cord distribution spaces are 13.6 +/- 0.9% in white matter and 18.1 +/- 1.4% in gray matter. The diffusion coefficient in tissue of sucrose is 1.7 x 10(-6) cm2/s and of EDTA is 1.55 x 10(-6) cm2/s. The spinal cord tortuosity factor is 2.0-2.1. Six rhesus monkeys were infused intravenously with [3H]sucrose and [14C]EDTA; the spinal capillary exchange half-time from blood to extracellular fluid was greater than 6 h for both sucrose and EDTA.
Effects of anesthetic agents on autoregulation of renal hemodynamics in the rat and dog
Authors: Conger JD , Burke TJ
Published: December 2017

Controversy has existed over apparent dissimilarities in the autoregulatory capacities of the rat and dog. A protocol was designed to evaluate both the effects of the anesthetic agents. Nembutal (used most commonly in dogs) and Inactin (most frequently employed in rats) and the species peculiarities of these two mammals on autoregulation of renal blood flow (RBF) and glomerular filtration rate (GFR). With Nembutal autoregulation of RBF was present in both experimental animals. Inactin impaired RBF autoregulation similarly in both species. With impaired RBF autoregulation similarly in both species. With either anesthetic GFR was autoregulated well in both rat and dog. Comparison of the two species revealed a greater RBF per gram kidney weight and a higher renal perfusion pressure (RPP) at which autoregulation of both hemodynamic parameters was lost in the rat. It is concluded from these studies that 1) the frequent use of Inactin in the rat in large part accounts for the observed lack of autoregulation of RBF in this animal and 2) renal hemodynamic responses are qualitatively similar in rat and dog when the same anesthetic agents are used.
Metabolic response to carbon monoxide by isolated rat lungs
Authors: Bassett DJ , Fisher AB
Published: December 2017

Glucose metabolism was studied in isolated rat lungs ventilated with 95% O2.5% CO2 (control), 95% N2: 5% CO2 (hypoxia), and 95% CO:5% CO2 (carbon monoxide) and perfused for 100-120 min with Krebs-Ringer-bicarbonate buffer, pH 7.4, containing [U-14C] and [3-3H]glucose. The production of 14C-labeled lactate plus pyruvate (L + P) and of 14CO2 represented 48% and 22% respectively, of the total [14C]glucose utilization. The lactate-to-pyruvate ratio (L/P) was 8.7. Tritium was recovered predominantly as 3H2O in the perfusate. Wth carbon monoxide ventilation, L + P production was increased by 357% with an L/P of 52.9, and 14CO2 production was markedly decreased. A 56% decrease in lung ATP content was associated with decreased incorporation of 14C into fatty acids. Compared with CO, changes with N2 ventilation were less marked, indicating that ventilation with CO is a more effective method with which to study inhibtion of oxidative metabolism. The lung exhibits a Pasteur effectbintain ATP content or its supply for synthetic activity.
Modification of aortic barorecptor resetting in the spontaneously hypertensive rat
Authors: Sapru HN , Wang SC
Published: December 2017

Aortic barorecptor function was studied in spontaneously hypertensive rats (SHR) of various ages and normotensive Wistar rats. The aortic arch was isolated and perfused, and the activity of the left aortic nerve was recorded. The threshold pressure to elicit barerecptor firing was 80-120 mmHg in normotensive Wistar rats. Resetting of barorecptors (threshold pressure 160-180 mmHg) was found in all untreated SHR of 35-70 wk of age. Resetting of barorecptors was prevented in SHR by starting treatment with antihypertensive agents at the age of 11 wk. Treatment of 32-wk old SHR with antihypertensive agents for 4-6 wk resulted in reversal of barorecptor resetting in 50% animals. The percentage of SHR showing complete reversal of resetting did not increase even when the duration of treatment was tripled. In 52- to 64-wk old SHR, treated with antihypertensive agents, reversal of baroceptor resetting was seen in only 30% animals. It was concluded that baroceptor resetting in SHR was secondary to hypertension. Hypertension, in turn, induced hypertrophy of the tunica media of the aorta. Histological studies showed a close correlation between aortic hypertrophy resetting. Aortic hypertrophy may, therefore, be one of the important factors involved in baroceptor resetting.
Release of prostaglandin F2alpha during splanchnic artery occlusion shock
Authors: Flynn JT , Bridenbaugh GA , Lefer AM
Published: December 2017

Prostaglandin F2alpha concentrations were determined in hepatic portal venous plasma of dogs during splanchnic artery occlusion (SAO) shock and in nonshock control dogs. Dogs subjected to SAO shock exhibited a dramatic decrease in mean arterial blood pressure and significant increases in portal venous PGF2alpha and amino-nitrogen concentrations, as well as in cathepsin D and MDF activities. Dogs treated with indomethacin prior to SAO shock did not exhibit a significant increase in portal venous PGF2alpha. Indomethacin had no effect on the increase of plasma amino-nitrogen and only slightly reduced portal venous cathepsin D activity during SAO shock. Nevertheless, indomethacin significantly attenuated the severity of the postrelease hypotension observed in SAO shock and diminished the plasma accumulation of MDF. These studies indicate that prostaglandins are released from the splanchnic region during SAO shock and that this release can be prevented by pretreatment with indomethacin. The role of endogenously released prostaglandins in SAO shock is not clear, but the magnitude of the increase warrants further study.
Nonshivering thermogenesis induced by repetitive cooling of spinal cord in the rat
Authors: Banet M , Hensel H
Published: December 2017

The effect of prolonged and repetitive cooling of the spinal cord on the sensitivity to the metabolic effect of exogenous noradrenaline and on the resistance to cold exposure was studied in the white male rat. The spinal cord of 10 animals was cooled for an average of 90 h-9 h/day 5 days/wk - to a level that induced an increase in oxygen uptake of almost 70%. Oxygen consumption was then measured at 30 degrees C before and 1 h after a subcutaneous injection of noradrenaline (0.4 mg/kg). Following the noradrenaline injection, the experimental animals increased oxygen uptake by 71%, while the control ones increased it by only 33% (P less than 0.01). During exposure to -20 degrees C, the experimental animals, despite their increased capacity for nonshivering thermogenesis, did not maintain rectal temperature longer than the control ones, thus showing that other factors also play a significant role in cold adaptation in the rat.