bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of age and hypertension on utilization of glucose by rat aorta
Authors: Daly MM
Published: December 2017

Aortic intima-media was isolated from three groups of rats varying in age from 6.5 to 72 wk and from 16-wk-old rats with renal hypertension and sham-operated controls. Tissues were incubated with [U-14C]glucose for 3 h, and the incorporation of glucose into lactate, carbon dioxide, and total lipids was measured. The amounts of glucose converted to each product, per microgram of aortic DNA, increased with advancing age of donor rats over the entire range of age studied. Effects of hypertension on aortic glucose utilization were in the same direction as the effects of age, but more pronounced. Effects of age and hypertension were greatest on the conversion of glucose to carbon dioxide and least on its conversion to lipids. Significant although less marked increases in aortic glucose utilization with age and hypertension were also revealed when results were calculated on the basis of tissue weight.
Oxygen consumption by human and rodent striated muscle in vitro
Authors: Hofmann WW
Published: December 2017

Oxygen consumption has been measured in human and rodent striated muscle in vitro with a platinum-silver electrode system. The effects of excess potassium, caffeine, insulin, osmotic shock, halothane, and Na-pump blockade have been investigated and the differences from amphibian muscle responses are outlined. It has been found that normal human muscle, like that of rodents, is relatively indifferent to major surface depolarization and osmotic shock, as far as oxygen requirements are concerned. Surgical damage to muscle fibers causes them to react unpredictably to pharmacological tests. The results in normal muscles may be of use in the further study of certain muscular diseases.
Intramyocardial distribution of blood flow in hemorrhagic shock in anesthetized dogs
Authors: Carlson EL , Selinger SL , Utley J , Hoffman JI
Published: December 2017

In 34 anesthetized, open-chest dogs aortic blood pressure was kept at 35-40 mmHg for 3 h to determine if maldistribution of coronary blood flow (CBF) could contribute to the irreversibility of hemorrhagic shock. Six dogs were pretreated with phenoxybenzamine (PBZ) and 11 dogs (3 with PBZ) received hypertonic mannitol infusions in late hemorrhage. Changes of heart rate, cardiac output, and peripheral resistance were similar to those described by others. In untreated dogs total and left ventricular CBF fell, as did coronary vascular resistance. However, minimal coronary resistance after transient ischemia rose progressively and the ratio of subendocardial:subepicardial flow fell, as did the percentage of diastolic coronary flow. Mannitol infusion returned CBF and steady-state and minimal postischemic coronary resistance to control values and also returned to normal the increased myocardial water content found in late hemorrhage. Phenoxybenzamine delayed but did not prevent the rise of coronary vascular resistance or decreased subendocardial flow. These studies suggest that there may be subendocardial ischemia, possibly due to myocardial edema, in hemorrhagic shock.
Sudden potential drop in bullfrog gastric mucosa
Authors: Kidder GW  , Montgomery CW
Published: December 2017

The previously reported sudden potential drop (SPD), which occurs under anoxia in 10% CO2, has been further explored. We find several conditions necessary for this effect: 1) anoxia; 2) serosal pH less than 7.1;3) presence of chloride; and 4) a PD, either spontaneous or voltage clamped, which changes across the region of 10 mV, serosal positive. With the first three conditions satisfied, a reversible decrease in measured resistance can be produced at will by changing the clamp voltage. In the anoxic, low-resistance state, changes in K+ or C1- concentration give little change in voltage, showing that the increased conductivity is not selective for either ion. A model is proposed containing a shunt-resistance element whose resistance is a step function of PD. This model can mimic the responses of the tissue and provides a working model for the SPD.
Low Na+ effects on PAH transport and permeabilities in isolated snake renal tubules
Authors: Dantzler WH , Bentley SK
Published: December 2017

Effects of low sodium concentrations on p-aminohippurate (PAH) transport by isolated, perfused snake (Thamnophis spp.) distal-proximal renal tubules were studied. Replacement of sodium in bath with choline led to significant depression of net PAH transport from bath to lumen in less than 10 min and to maximum depression (to 25-30% of control) in about 30 min, but transport still occurred against concentration gradient. In absence of sodium, PAH concentration in cell water was markedly depressed, but was still slightly greater than that in bath or lumen. Apparent permeability of peritubular membrane, determined from PAH efflux from tubules with oil-filled lumens, averaged about 0.5 X 10(-5) cm s-1 in 150 mM sodium and about 1.1 X 10(-5) cm s-1 in sodium-free medium. Data suggest that both decreased rate of active transport and increased apparent permeability of peritubular membrane contribute to depression of net transepithelial PAH transport and cell water PAH concentration in sodium-free medium. When sodium was restored to bath, net PAH transport nearly tripled in 15 min. Reduction of bath sodium concentration to one-half control or perfusion with sodium-free medium in lumen and control medium in bath had no effect on net PAH transport.
Effects of time on volume and distribution of coronary collateral flow
Authors: Marcus ML , Kerber RE , Ehrhardt J , Abboud FM
Published: December 2017

Changes in the volume and distribution of collateral blood flow were studied during the 1st h after coronary occlusion in nine open-chest dogs. Labeled microspheres (7-10 mum) were injected into the left atrium prior to and 20 s, 5 min, and 60 min after acute occlusion of the midcircumflex coronary artery so that myocardial perfusion to small segments of the entire left ventricle could be measured. The segmental perfusions were classified as normally perfused, severely hypoperfused, moderately hypoperfused, and borderline hypoperfused. Standard hemodynamic measurements were obtained and relative coronary vascular resistance to the normally perfused and hypoperfused zones was calculated. The principal conclusions of the study are as follows: 1) during the 1st h after coronary occlusion the collateral flow to the hypoperfused myocardium increases substantially; 2) the increase in collateral flow is distributed fairly evenly to various hypoperfused zones and is associated with a marked decrease in coronary vascular resistance; and 3) as a result of this influx in collateral flow the size of the hypoperfused area decreases and the relative proportion of severely hypoperfused segments within the hypoperfused area decreases.
Influence of thyroxine on adult rat lung oxygen consumption and ultrastructure
Authors: Joyner LR , Massaro GD , Massaro D
Published: December 2017

We studied the oxygen consumption (QO2) of lung slices and the ultrastructure of the pulmonary granular pneumocyte in rats whose level of circulating thyroxine was altered. Rats given thyroxine for 6 days (1.0 mg-kg-1-day-1) and sacrificed on the 7th day had a serum thyroxine level of 18.9 +/- 2.7 mug/100 ml (mean +/- SD); rats given diluent alone for 6 days had a serum thyroxine level of 4.67 +/- 0.53 mug/100 ml. Rats subjected to a sham thyroidectomy has a serum thyroxine level of 7.27 +/- 1.47 mug/100 ml, whereas rats subjected to thyroidectomy had a serum thyroxine level of 1.13 +/- 0.55 mug/100 ml when sacrificed. The QO2 of lung slices from rats with high levels of circulating thyroxine was significantly greater than that of rats that received diluent alone. The QO2 of slices from rats whose thyroid glands were excised was significantly lower than the QO2 of slices from sham-operated rats. We did not find quantitative ultrastructural differences in granular pneumocyte mitochondria and lamellar bodies of rats given thyroxine compared to rats given diluent or between rats subjected to sham thyroidectomy compared to rats whose thyroid glands were removed.
Effects of salicylate and bile salt on ion transport by isolated gastric mucosa of the rabbit
Authors: Fromm D , Schwartz JH , Quijano R
Published: December 2017

The effects of luminal addition of salicylate and taurocholate on ion transport by fundic mucosa were examined in vitro using isotopic and pH stat techniques. Salicylate, 3 mM, did not alter, but 20 mM caused a 40% decrease in, the acid secretory rate. Taurocholate, 20 mM, caused a transient, apparent cessation of acid secretion followed by stimulation. Salicylate, 3 or 20 mM, increased Na+ but not Cl- permeability at luminal pH 7. At luminal pH 4, however, salicylate increased Cl- in addition to Na+ and H+ permeability. Taurocholate, 10 or 20 mM, increased both cation and anion permeability at pH 7 and 4. Addition of salicylate or taurocholate results in stimulation of net Na+ transport. While salicylate and taurocholate increase cation permeability at pH 7, they have differing effects on acid secretion and anion permeability. The data suggest that salicylate and taurocholate alter cation permeability by different mechanisms and are consistent with the concept that enhanced diffusion of H+ into the tissue causes a nonspecific alteration in the permeability pathway.
Effects of altering O2 delivery on VO2 of isolated, working muscle
Authors: Horstman DH , Gleser M , Delehunt J
Published: December 2017

Maximal oxygen consumption (VO2 max) and muscle blood flow (Q max) were measured in an isolated gracilis muscle preparation before and after alteration in perfusion pressure (BP), arterial oxygen saturation (SaO2), and hemoglobin concentration (Hb). Q varied directly with BP and inversely with Hb (viscosity) but was unaffected by changes in arterial SaO2. VO2 max varied directly with oxygen delivery under all conditions. These results indicate that VO2 max is normally limited by oxygen delivery rather than any intrinsic limiting of oxygen consumption of the muscle.
Sympathetic control of Na, K transport in perfused submaxillary main duct of rat
Authors: Schneyer LH
Published: December 2017

The effect of stimulating the sympathetic innervation to rat submaxillary gland on ductal transport of Na, K, and water and on transepithelial PD was tested in the main excretory duct during perfusion through its lumen. Stimulation of the sympathetic nerve, supramaximally, caused a decrease of 30-40% in net flux of Na from, and of K to, the lumen in ducts perfused with medium containing Na and K in isotonic concentrations. Net flux of water was unaffected. Transductal PD decreased by about 30% during supramaximal stimulation. Changes in PD and net cation fluxes were reversible. These effects of supramaximal stimulation of the sympathetics on ductal transport resemble those reported to occur after large doses of isoproterenol and suggest an adrenergic secretomotor innervation to the ducts. However, changes in PD evoked by supramaximal stimulation of the sympathetic nerve could not be suppressed with propranolol, but were with phenoxybenzamine, indicating that alpha-adrenergic receptors are primarily involved in mediating at least the electrical responses of duct cells to sympathetic nerve stimulation.
Protein composition of lung fluids in acute alloxan edema in dogs
Authors: Vreim CE , Staub NC
Published: December 2017

In 11 anesthetized dogs with acute alloxan-induced pulmonary edema, we measured the protein composition of 1-mul samples of plasma, free interstitial fluid, alveolar fluid, and airway fluid. We obtained plasma and airway fluid at regular intervals as edema developed. We sampled alveolar fluid by pleural micropuncture in the unfrozen, excised lung and free interstitial fluid from perivascular cuffs in the frozen, excised lung. The average (+/- 1 SD) total protein concentration of plasma was 4.9 +/- 0.6, airway fluid 4.4 +/- 0.7, free interstitial fluid 4.9 +/- 0.7, and alveolar fluid 5.2 +/- 0.8 g/100 ml. The average fractions of albumin were 0.42 +/- 0.05, 0.50 +/- 0.05, 0.49 +/- 0.06, and 0.49 +/- 0.07, respectively. By paired analysis, the protein concentration of interstitial fluid was not significantly different from alveolar fluid. The protein concentration of airway fluid was significantly less than that in interstitial and alveolar fluid. The albumin fraction of the three lung fluids was identical but significantly different from plasma. We conclude that in alloxan-induced pulmonary edema the lung fluids contain high concentrations of protein and the alveolar epithelial membrane becomes freely permeable to protein molecules.
Modification of in vivo lacrimal gland secretion by 2,4-dinitrophenol
Authors: Pholpramool C , Botelho SY
Published: December 2017

Mecholyl-stimulated flow from the excretory duct of the rabbit lacrimal gland in vivo was recorded continuously and samples of Mecholyl-stimulated fluid were collected before, during, and after 30 min of local intra-arterial infusion of 2,4-dinitrophenol (DNP). Compared with the control period, Mecholyl-stimulated flow during the DNP infusion was 60-70% less; [K+] was the same and [Na+] and [Cl-] were higher in the Mecholyl-stimulated fluid. The changes that occurred during the DNP infusion were not produced by infusion of the solvent (NaHCO3) or an acid with similar pK (para-aminohippuric acid) nor were the changes related to any effect of DNP on the general circulation. The magnitude of the changes during the DNP infusion increased as the dose of DNP increased and the inhibition of flow changes in [Na+] and [Cl-] during the DNP infusion were reversible. The results are compatible with the hypothesis that stimulation by Mecholyl involves oxidative metabolsim at the duct level but they do not exclude the possibility that oxidative metabolism may also be involved in formation of the primary fluid at the acinar level.
Effect of magnesium on rat nephron sodium reabsorption: a segmental analysis
Authors: Ploth DW , Sawin LL , DiBona GF
Published: December 2017

To evaluate the effect of hypermagnesemia on distal nephron sodium reabsorption, renal clearance, micropuncture, microinjection, and electrophysiological studies were performed in the anesthetized rat before and after intravenous administration of MgCl2, MgSO4, and Na2SO4. Along the proximal tubule, MgCl2 caused a 21% decrease and MgSO4 a 17% decrease in fractional sodium reabsorption, while only a 4% decrease was observed with Na2SO4. In the loop segment, the decrease in fractional sodium reabsorption was 7% with MgCl2, 15% with MgSO4, and 12% with Na2SO4. In the distal tubule and collecting duct, MgCl2 and MgSO4 had no effect on fractional sodium reabsorption, whereas Na2SO4 significntaly depressed sodium reabsorption to a greater extent in the collecting duct than in the distal tubule. Microinjection studies, however, showed that both MgSO4 and Na2SO4 depressed lumen-to-plasma sodium movement across the collecting duct. Early and late distal tubular transepithelial potential difference was unaffected by MgCl2, whereas it was increased by both MgSO4 and Na2SO4. The decrease in sodium reabsorption along the distal tubule and collecting duct produced by Na2SO4 and probably MgSO4 may relate to the increased transepithelial electrochemical gradient for sodium transport produced by the poorly reabsorbable sulfate anion.
Evidence for an intrarenal beta receptor in control of renin release
Authors: Johnson JA , Davis JO , Gotshall RW , Lohmeier TE , Davis JL , Braverman B , Tempel GE
Published: December 2017

Infusion of isoproterenol intravenously in normal dogs at rates of 0.10 or 0.018 mug/min per kg body wt increased renin secretion; at the lower infusion rate arterial pressure (AP) and renal blood flow (RBF) were unchanged. Isoproterenol was also infused into the renal artery in normal dogs at 0.10 mug/min per kg; renin secretion increased in association with an increase in RBF but AP was unchanged. Plasma K concentration was consistently decreased in all three of the above experiments and because hypokalemia is known to increase renin release isoproterenol was not infused intrarenally at the lower rate; the decrease in plasma K level precluded relating the entire response in renin release to isoproterenol. Intrarenal infusion of propranolol at 0.05 mg/kg per h in Na-depleted dogs decreased renin secretion whereas intravenous infusion at the same dose failed to alter renin release. Intrarenal infusion of propranolol at this rate in Na-depleted dogs with a denervated, nonfiltering kidney also decreased renin release. In contrast, intrarenal infusion of phentolamine or phenoxybenzamine in normal dogs failed to alter renin secretion in doses that blocked alpha-adrenergic receptors. These experiments provide strong evidence for an intrarenal beta-adrenergic receptor that mediates renin release, and it seems likely from the experiment in the denervated, nonfiltering kidney that the receptor is located in the juxtaglomerular cells.
Factors influencing left ventricular shortening in isolated canine heart
Authors: Weber KT , Janicki JS , Reeves RC , Hefner LL
Published: December 2017

To assess in the intact ventricle the steady-state influence of several mechanical variables on the extent of left ventricular midwall circumferential shortening, a pressure servo system was utilized in isolated canine hearts. The system permits continuous monitoring of ventricular volume and control of diastolic and systolic pressures. After determination of the diastolic volume at zero filling pressure (V0), a series of variably preloaded or afterloaded contractions were generated including the isovolumic state. Contractile state was manipulated in a positive (calcium, 12-18 mg/100 ml; norepinephrine, 0.4-1.4 mug/min) or negative (propranolol, 0.12-0.50 mg/min) direction. Force and length terms derived for a thick-walled sphere were expressed per cross-sectional area of muscle and length, respectively, calculated at V0. For any preload, an inverse linear (r greater than 0.96) force-shortening relation was obtained, and each line was identified by its slope and isovolumic load (sigma0). Both slope and sigma0 increased with positive inotropic agents (vis-a-vis propranolol) or increments in preload. Thus, in the intact ventricle an inverse linear relation characterizes the force-shortening relation with the amount of shortening determined by initial fiber length, afterload, and the contractile state of the myocardium.
Origin of great cardiac vein and coronary sinus drainage within the left ventricle
Authors: Roberts DL , Nakazawa HK , Klocke FJ
Published: December 2017

The relative contributions of left anterior descending (LAD) and left circumflex (LC) arterial inflow to blood sampled at various points within the great cardiac vein (GCV) and coronary sinus (CS) have been investigated in open-chest dogs. Dissolved helium (He) and hydrogen (H2) were infused into external circuits perfusing the LAD and LC, respectively, and their steady-state concentrations were measured chromatographically at various points within the GCV and CS. Under basal conditions GCV H2 averaged only 5% of mid-CS H2 and did not change greatly during alterations of preload and afterload or during selective LAD or LC obstruction and vasodilation. The relationship of mid-CS He to GCV. He was more variable under basal conditions and changed noticeably during selective changes in LAD or LC inflow. Appreciable amounts of He were present consistently in left marginal vein drainage. We conclude that: 1) GCV blood is remarkably free of LC inflow in both normal and abnormal physiological states; 2) the origin of mid-CS blood is more variable, both from animal to animal and in individual animals before and after interventions; 3) a portion of LAD drainage normally reaches the CS through circumflex venous branches rather than the GCV.
Erythropoietin production after renal denervation or beta-adrenergic blockade
Authors: Fink GD , Fisher JW
Published: December 2017

The ability of either beta-adrenergic blockade or bilateral renal denervation to alter erythropoietin (ESF) production in rabbits exposed to hypobaric hypoxia was studied. ESF elaboration during 5 h of exposure to hypoxia was not affected by beta-blockade, but was markedly reduced by prior surgical denervation of both kidneys. After 18 h of hypoxia plasma ESF levels in renal denervated rabbits did not differ significantly from those of sham-operated controls. Previous studies have shown that ESF production during this more prolonged exposure to hypoxia was significantly inhibited by some beta-adrenergic blocking agents. Combined renal denervation and beta-blockade were more effective than renal denervation alone in attenuating ESF production during 5 h of exposure to hypoxia. However, ESF elaboration during 18 h of hypoxia was significantly greater in animals with combined denervation and beta-blockade than in control rabbits. These results suggest the existence of two distinct mechanisms for ESF production in rabbits exposed to hypobaric hypoxia.
Site of kininogenase secretion in the dog nephron
Authors: Scicli AG , Carretero OA , Hampton A , Cortes P , Oza NB
Published: December 2017

We determined the site of kininogenase secretion in the nephron by performing stop-flow studies in dogs. Kininogenase activity, inulin, sodium, and potassium were measured in the same fractions. The highest kininogenase concentration was found in the fractions with the lowest sodium concentration corresponding to urine samples that must have been trapped in the distal nephron. Kininogenases in these urine fractions were 5-17 times higher than in fractions from the proximal nephron or from the free-flow sample. The ratio of kininogenase increase to inulin increase was always higher than 3.0, thus indicating that the increase in kininogenase concentration was mainly due to secretion and not to water reabsorption. When a peak of potassium was present, it occurred 1-2 ml before the peak of kininogenases. We concluded that kininogenases are secreted into the urine at the level of the distal nephron by either the tubule itself or by a specialized structure located at this part of the nephron, such as the macula densa.
Reflex limb dilatation following norepinephrine and angiotensin II in conscious dogs
Authors: Vatner SF , McRitchie RJ
Published: December 2017

Effects of intravenous and intra-arterial norepinephrine (NE) and angiotensin II (AN) were compared in 18 conscious dogs instrumented with Doppler or electromagnetic flow probes on the iliac, mesenteric, and renal arteries, and catheters in the aorta and iliac arteries. NE and AN administered intravenously constricted the mesenteric and renal beds, and constricted the iliac bed when administered directly into the iliac artery. In contrast, intravenous NE and AN caused striking reflex increases in iliac flow and reductions in iliac resistance, respectively, in 12 of 18 dogs studied. The reflex iliac dilatation was not prevented by beta blockade with propranolol, cholinergic blockade with atropine, or prostaglandin synthetase inhibition with indomethacin. However, the responses were abolished by either phentolamine, 1 mg/kv iv, or after local blockade of the limb with either phentolamine, 0.5 mg/kg, or with tripelennamine, 2 mg/kg. The dilatation was not prevented by either bilateral carotid sinus and aortic nerve section or by bilateral vagotomy alone, but was prevented by a combination of these procedures. Thus, intravenous NE and AN cause striking reflex iliac dilatation in the limb in the conscious dog; the afferent arc of this reflex involves both arterial baroreceptor and vagal pathways, while the efferent mechanism involves an interaction of alpha-adrenergic and histaminergic receptors.
Frequency-force relationships of mammalian ventricular muscle in vivo and in vitro
Authors: Kahn ML , Kavaler F , Fisher VJ
Published: December 2017

The change in contractility with increasing heart rate was studied in the left ventricle of dogs and in isolated trabeculae carneae of cats. For some of the studies in situ a transient isovolumic state was created by aortic occlusion. At physiological temperatures the frequency-force relationship is flatter than at room temperature and at the same temperature it is flatter in vivo than in vitro. The frequency-(dF/dt)max relationship is steeper than the frequency-force relationship at both temperatures in vivo and in vitro. The frequency-(dF/dt)max relationship is steeper in vitro than it is in situ, although the discrepancy is less marked than in the case of the frequency-force relationship. It is concluded that "staircase" plays less of a physiological role in adjustment of contractile state in situ than might be inferred from studies of isolated tissue.
Electromyographic response of respiratory muscles during elastic loading
Authors: Kelsen SG , Altose MD , Stanley NN , Levinson RS , Cherniack NS , Fishman AP
Published: December 2017

The response of respiratory motor neurons to graded elastic loading was assessed in anesthetized dogs by recording the electromyogram (EMG) from the diaphragm (ED) and the intercostal muscle (EIC). Elastic loads were applied for 1-20 breaths. The effects of changes in PCO2 on respiratory motor neuron output was assessed by applying loads during the course of CO2 rebreathing. On the first loaded breath, ED and EIC increased reflexly due chiefly to prolongation of inspiration. Vagotomy or vagal cooling to block the Hering-Breuer reflex eliminated the increase in ED and diminished the increase in EIC. During the second to fifth breath, the level of EMG activity was disproportionately high for the level of PCO2, suggesting an additional reflex component over and above the reflex activity present on the first loaded breath.
Renal effect of meclofenamate in presence and absence of superfusion bioassay
Authors: Satoh S , Zimmerman BG
Published: December 2017

Systemic blood pressure (SBP), renal blood flow (RBF), renal vascular resistance (RVR), and arterial and renal venous prostaglandin E (PGE) concentrations were determined in pentobarbital-anesthetized dogs.The effect of sodium meclofenamate infused into the renal artery was compared under two sets of conditions. In experiments carried out under control conditions, SBP, RBF, and RVR were stable and meclofenamate caused only a slight decrease in RBF (5.4%) and increase in RVR.
Effect of occlusion duration on reactive hyperemia in sartorius muscle capillaries
Authors: Johnson PC , Burton KS , Henrich H , Henrich U
Published: December 2017

Reactive hyperemia was studied in cat sartorius muscle by measurement of venous outflow and capillary red cell velocity following occlusions of 5-120 s. The peak value for volume flow rose in a graded manner as occlusion duration increased, reaching a level of 280% above control following 120 s of occlusion. By contrast, peak values for capillary flow were 200% above control even after short (10-15 s) occlusions and increased moderately thereafter to 280% above control following 120-s occlusions.
Effect of graded bilirubin loads on bilirubin transport by perfused rat liver
Authors: Bloomer  , Zaccaria J
Published: December 2017

Features of hepatic bilirubin transport were studied with the isolated perfused rat liver. Male Wistar rats weighing 350-400 g were used as liver donors. When bilirubin was constantly infused into the perfusion medium, which contained sheep erythrocytes and 3.0 g/100 ml bovine serum albumin, the maximal excretion rate for bilirubin was 14.4 +/- 1.2 mug/min per g liver. Over a wide range of constant bilirubin infusion rates which went as high as 25.9 mug/min per g liver, there was no effect on bile flow, bile acid excretion, or the pattern of bilirubin conjugates in bile. The hepatic extraction efficiency for unconjugated bilirubin from the perfusate also remained constant averaging 26%. However, when bolus injections of bilirubin were used to produce higher levels of unconjugated bilirubin in the perfusate than could be attained during constant infusion, the disappearance rate of [14C]bilirubin from the perfusate decreased with increasing bilirubin concentrations. This was consistent with saturation of the hepatic removal of unconjugated bilirubin.
Disposition of plasma cholesterol in the pregnant hypocholesterolemic rabbit
Authors: Ross AC , Zilversmit DB
Published: December 2017

Processes that might explain the hypocholesterolemia observed in pregnant rabbits were studied in animals fed a cholesterol-free chow diet. Excretion of endogenous steroids, measured after administration of a single intravenous dose of radioactive cholesterol, averaged 75 mg/day in controls and 96 mg/day in pregnant hypocholesterolemic rabbits. The mass of maternal plasma cholesterol transferred to the fetuses was measured in animals in which a constant plasma cholesterol specific activity was maintained. Placental transfer during the first 28 days of gestation ranged from 2 to 12 mg/day for mothers carrying litters of one to eight fetuses. It is concluded that loss of maternal plasma cholesterol due to placental transfer is small compared to loss by fecal steroid excretion. Because large decreases in plasma cholesterol concentration during pregnancy and increases at parturition were not accompanied by changes in the slopes of the specific activity-time curves, it appears most likely that cholesterol in isotopic equilibrium with plasma cholesterol is temporarily and reversibly sequestered in maternal tissues of the pregnant rabbit.
Effect of initial length on relations between oxygen uptake and load in dog muscle
Authors: Stainsby WN , Barclay JK
Published: December 2017

Oxygen uptake for brief tetanic contractions was calculated from measurements of blood flow and blood arteriovenous oxygen content differences. Each muscle preparation was pretested under isometric conditions to establish optimal length, Lo. After this one group of preparations performed afterload isotonic contractions at several loads with initial length, Li, less than Lo. The other groups of preparations performed similar contractions with Li greater than Lo. When Li was less than Lo, oxygen uptake for the highest load was always greater than oxygen uptake at the lowest load whereas intermediate loads were usually higher than both extremes. However, when Li was greater than Lo, oxygen uptake at the highest load was always less than oxygen uptake at the lowest load; again the intermediate loads were usually higher than both extremes. The data confirm and extend similar effects of initial length on heat production for contractions by amphibian muscles (7). It seems likely that the differences in initial lengths may account for the fact that the Fenn effect has not previously been observed in studies of mammalian skeletal muscle energetics.
Effect of cervical sympathetic nerve stimulation on canine carotid sinus reflex
Authors: Bolter CP , Ledsome
Published: December 2017

In the chloralose-anesthetized dog the carotid sinus on one side of the neck was isolated vascularly. Pressure in the isolated sinus [carotid sinus pressure (CSP)], electrocardiogram, and systemic arterial pressure were recorded. Both vagosympathetic trunks were cut and the contralateral common carotid artery was occluded or the contralateral sinus nerve was cut to reduce reflex buffering of arterial pressure changes. By varying CSP from 50 to 250 mmHg the full range of the reflex response was examined. Electrical stimulation of the peripheral end of the cut ipsilateral cervical sympathetic nerve brought about a rapid decrease in mean arterial pressure (MAP) and heart rate (HR) at lower CSPs, no change in these variables at midrange CSPs, and a gradual increase at higher CSPs, such that the gain of the reflex was reduced (1.89 +/- 0.19 to 1.33 +/- 0.15 mmHg/mmHg). The decrease in MAP and HR at lower CSPs implies an increase in baroreceptor activity whereas the converse would appear to occur at higher CSPs. These responses attained a maximum value at low stimulus frequencies (less than 10 Hz).
Hemodynamic mechanisms influencing sodium excretion during angiotensin infusion
Authors: Johannesen J , Omvik P , Kiil F
Published: December 2017

To examine mechanisms of transition between antinatriuresis and natriuresis, angiotensin II was first infused intrarenally (0.001-0.07 mug/kg-min) in anesthetized dogs; glomerular filtration rate (GFR), sodium excretion, and intrarenal pressure (IRP), indicating tubular pressure, fell as during mechanical aortic constriction. During supplementary intravenous infusion (0.10-0.30 mug/kg-min), renal blood flow (RBF) rose toward control (tachyphylaxis). Tubular reabsorption increased but was still 17.1% below control. Filtration fraction averaging 0.31 remained constant. Sodium excretion and IRP exceeded control but were normalized by restoring renal arterial pressure mechanically. During intrarenal angiotensin infusion, carotid constriction increased blood pressure more, but RBF, IRP, and sodium excretion less than intravenous angiotensin. Intrarenal infusion of angiotensin at 0.10-0.20 mug/kg-min increased RBF and sodium excretion more in infused than in contralateral kidneys. Thus, angiotensin natriuresis depends on increased perfusion pressure and is augmented as tachyphylaxis develops. High correlation between sodium excretion and IRP at unchanged filtration fraction suggests a regulation of sodium excretion by hydrostatic rather than oncotic pressures in glomerular and peritubular capillaries.
Regulatory and secondary water intake in rats with lesions of the zona incerta
Authors: Evered MD , Mogenson GJ
Published: December 2017

Bilateral electrolytic lesions of the zona incerta (ZI) permanently reduced daily water intake of rats by 20-30%. Lesioned rats did not differ from controls in daily food intake, body weight, hematocrit, or serum osmolality, Na+ or K+ levels. The hypodipsia was not caused by changes in water requirements or excretory function or by a nonspecific depression of behavior. Compensatory reductions in water losses maintained fluid balance. Lesioned rats drank as much water as controls in response to intracellular and extracellular dehydration, but unlike controls, appeared to restrict their daily water intake to these regulatory responses. Lesions of the ZI attenuated the ingestion of extra water observed when rats were maintained on a liquid diet adequate to meet fluid requirements, and daily water intake of lesioned but not control rats closely followed changes in water needs. It was concluded that lesions of the ZI reduce daily water intake towards minimal requirements for fluid balance by attenuating secondary drinking (drinking independent of water needs for fluid homeostasis.
Elastic behavior of brain tissue in vivo
Authors: Walsh EK , Schettini A
Published: December 2017

A measurement system and a test sequence have been developed to determine the in vivo elastic response of brain tissue in terms of a pressure-depth ratio. This parameter appears sensitive to changes in the tissue environment that may occur due to the influence of, e.g., anesthetic agents, hyperventilation, etc., and thus may be useful in evaluating such influences. The measurements are made with the dura-arachnoid membranes intact, thus maintaining the influence of the cerebrospinal fluid compartment on the response behavior of the brain tissue that comprises the subpial region. As an integral part of the test, the procedure also serves to determine the depth or position of the subpial region and thus assures that the subsequent pressure-depth measurements invole brain tissue response. Finally, some discussion is given to relating the measured pressure-depth ratio to the classical elastic modulus. Values of the pressure-depth ratio and the corresponding elastic modulus for seven dogs are given.
Effect of prolonged angiotensin II infusion on thirst
Authors: Trippodo NC , McCaa RE , Guyton AC
Published: December 2017

To determine the effect of prolonged angiotensin II (A-II) infusion on thirst, daily water intake by drinking was measured in dogs during a 4-day control period, a 4-day period of vehicle infusion without A-II, a 10-day period of A-II infusion, and a 4-day recovery period of vehicle infusion without A-II. During the control period and the periods of vehicle infusion in the absence of A-II, daily water intake by drinking in four dogs averaged 118 +/- 20 ml/day (mean +/- SE). During the 10-day period of A-II infusion at the rate of 13.0 ng/kg per min drinking increased to 269 +/- 49 ml/day (paired t; P less than 0.05). Angiotensin II infusion at the rate of 26.0 ng/kg per min produced a sustained increase in water intake in two dogs during an 8-day period of infusion. These results demonstrate that in dogs, prolonged infusion of angiotensin II stimulates the thirst mechanism and that the effect lasts for more than a few days.
Direct neural inhibition of insulin secretion in response to systemic hypoglycemia
Authors: Miller RE , Waid TH , Joyce MP
Published: December 2017

The innervated pancreas of an anesthetized small "pancreas" dog was cross-perfused with blood from a large "support" dog in order to separate neural from blood-borne influences on the immunoreactive insulin secretion rate (ISR). The arterial plasma reducing sugar (sugar) concentration could be varied independently in the pancreas dog systemic circulation and in its pancreas. After tying of the hepatic arteries and portal vein in the pancreas dog, its systemic arterial plasma sugar concentration was allowed to fall in 10 experiments. This was prevented in five control experiments by intravenous glucose infusion (7 mg/kg-min). In all experiments, pancreatic arterial plasma sugar concentration was sustained, and at 40 min it was elevated 50 mg/100 ml by glucose infusion into the pancreatic blood supply. Bilateral splanchnic nerve section at 120 min caused an increase of the ISR in all experiments, but a greater rise occurred from the pancreases of the 10 dogs allowed to become hypoglycemic (P less than .02). In two further experiments, the splanchnic nerves were not cut, and no rise in ISR occurred. In conclusion, systemic hypoglycemia can inhibit insulin secretion by means of the splanchnic nerves.
Dopamine-induced dissociation between renal metabolic rate and sodium reabsorption
Authors: Johannesen J , Lie M , Mathisen O , Kiil F
Published: December 2017

The stimulatory effect of dopamine on renal energy metabolism and its relationship to changes in tubular sodium reabsorption and plasma concentration of free fatty acids (FFA) were examined in anesthetized dogs. Dopamine infused intravenously at 25 mug/kg body wt-min for 30-60 min increased renal oxygen consumption (Rvo2) by 28 +/- 3%; glomerular filtration rate rose from 37 +/- 3 to 40 +/- 2 ml/min without significant changes in sodium excretion. Plasma FFA increased about 6 times. Total-body metabolic rate increased to 152 +/- 7% and fell to 119 +/- 5% of control after normalizing plasma FFA by beta-pyridylcarbinol; Rvo2 remained unchanged. Cortical and outer medullary heat accumulation rated increased to 137 +/- 6 and 133 +/- 10% after 1 h and to 163 +/- 18 and 179 +/- 26% of control after 2 h of dopamine infusion without further changes in sodium reabsorption. Furosemide reduced cortical and outer medullary metabolic rates as much as in control experiments (14 +/- 8 and 69 +/- 7%, respectively). Hence, dopamine exerts a renal calorigenic effect which cannot be accounted for by increased sodium reabsorption or attributed to increased supply of FFA.
Estimation of glucose turnover and recycling in rabbits using various [3H, 14C]glucose labels
Authors: Dunn A , Katz J , Golden S , Chenoweth M
Published: December 2017

The glucose replacement rate, percent carbon recycling, mean glucose transit time, and the glucose mass were determined in fasted unanesthetized rabbits after administration of [2-3H,U-14C]-, [3-3H,U-14C]-, [5-3H,U-14C]- or [6-3H,U-14C]glucose using the procedures of Katz et al. (10). The glucose replacement rates and carbon recycling determined with [2-3H,U-14C] and [5-3H,U-14C]glucose are equivalent and greater than those obtained with [3-3H,U-14C]- and [6-3H,U-14C]glucose. Although the means of the glucose replacement rates and percent carbon recycling obtained using [3-3H,U-14C]- and [6-3H,U-14C]glucose are similar, greater variation resulted using the former tracer. Comparisons of detritiation rates and percent carbon recycling using [2-3H,U-14C]- and [6-3H,U-14C]glucose suggest that about 10% of tritium is lost from carbon 2 via futile cycling at the glucose 6-phosphate level. Similarly, comparisons of [5-3H,U-14C]- and [6-3H,U-14C]glucose metabolism suggest that about 10% of tritium lost from carbon 5 occurs via futile cycling at the fructose diphosphate level and/or via the transaldolase reaction. Our results indicate that [6-3H,U-14C]glucose is the more suitable tracer for determining the glucose replacement rate and carbon recycling in vivo.
Absence of fetal placental waterfall phenomenon in chronically prepared fetal lambs
Authors: Thornburg KL , Bissonnette JM , Faber JJ
Published: December 2017

An electromagnetic flow sensor was placed on the distal fetal aorta (umbilical flow fraction 78.1 +/- 1.6 SEM, %), an inflatable occluder was tied around the umbilical cord, and catheters were placed in distal branches of an umbilical artery and vein, a uterine vein, and in the amniotic cavity. An inflatalbe occluder was tied around the vagina of some of the ewes. Control values 3 days after surgery were (mean +/- SE): fetal femoral artery pH, 7.37 +/- 0.01; umbilical blood flow, 186 +/- 14 ml-min-1 .kg fetus-1; fetal arterial blood pressure, 39 +/- 3 mmHg; and umbilical venous pressure, 7.4 +/- 1.0 mmHg (above intrauterine pressure). Fetal weight at autopsy was 3.1 +/- 0.3 kg, n = 11. Small increases in umbilical vein pressure caused immediate decreases in placental blood flow without decreases in fetal arterial blood pressure. The relation between venous pressure and umbilical blood flow at constant arterial pressure was that of an inert system, i.e., no evidence of a surrounding pressure (Starling resistor effect or waterfall phenomenon) could be found with increases in venous pressures of 2-40 mmHg. The results were not affected by increases in uterine vein pressure between 2 and 30 mmHg, nor by anesthesia and supine position of the ewe, nor by ganglionic blockade of the fetal ANS. It was concluded that surrounding pressures in the fetal placental circulation could not be demonstrated.
Neurally mediated increase in mitosis and DNA of rat parotid with increase in bulk of diet
Authors: Schneyer CA , Hall HD
Published: December 2017

A transient burst of mitosis was induced in rat parotid gland 2 days after change from a diet of solid chow only to one consisting of 50% inert cellulose and 50% solid chow (bulk diet). Mitosis was thus induced when glandular activity was changed from normal levels (solid chow) to levels greater than normal (bulk diet). Elimination of either autonomic pathway inhibited the mitotic response, but elimination of the parasympathetic had the greater inhibitory influence. The burst of mitosis induced by bulk diet was followed by increases in total DNA (16%), RNA (24%) and weight (27%) of the gland 2 wk after the dietary change. These changes did not occur when both autonomic pathways were, or only the parasympathetic was, removed immediately prior to the dietary change. Effects of sympathectomy were less pronounced. The parasympathetic innervation has the principal role in regulation of mitosis, cell number and size, and nucleic acid content when glandular activity is increased above normal by physiological means.
Intestinal villus blood flow measured with carbon monoxide and microspheres
Authors: Micflikier AB , Bond JH , Sircar B , Levitt MD
Published: December 2017

The purpose of the present study was to compare the small intestinal blood flow that equilibrates with luminal CO (FLco) with simultaneous determinations of villus blood flow measured by a recent modification of the microsphere technique. These studies, carried out in rabbits, showed that FLco closely correlated (r = 0.83) with villus flow measured with microspheres over a three-fold range of flows, and the mean rate of flow to the villi by both techniques was about 0.08 ml/min X g of intestine. Thus, FLco appears to be a measure of villus blood flow. Based on previous studies of inert gas uptake from the rabbit small intestine, it appears that absorption of readily diffusible substances in the rabbit can be represented by a simple two-component model: a flow-limited component in which substances equilibrate with villus blood flow and are carried away without subsequent countercurrent exchange, and a diffusion-limited component which presumably represents uptake by the blood flow of the crypt region or submucosa.
Heat loss from feet of herring gulls at rest and during flight
Authors: Baudinette RV , Loveridge JP , Wilson KJ , Mills CD , Schmidt-Nielsen K
Published: December 2017

The role of the feet of herring gulls (Larus argentatus) in heat dissipation was estimated during rest and wind-tunnel flight. We determined the blood flow to the feet and the arteriovenous temperature difference and thus estimated heat loss from the feet. Determinations of oxygen consumption and respiratory water loss at rest gave a heat production of about 8 W; 37-56% of this heat was lost from the feet (air temp = 10-35 degrees C). During flight heat production was estimated to be about 57 W and heat loss from the feet was 46 W, about 80% of the heat production in flight. Thus the webbed feet are an important avenue of heat loss in the herring gull.
Alteration of canine renal vascular response to hemorrhage by inhibitors of prostaglandin synthesis
Authors: Data JL , Chang LC , Nies AS
Published: December 2017

The involvement of prostaglandins in the redistribution of renal cortical blood flow to inner cortical nephrons during hemorrhagic hypotension was studied in the pentobarbital-anesthetized dog. Total renal blood flow and distribution of renal cortical flow were determined with the radioactive microsphere technique by dividing the cortex into four zones of equal thickness, zone 1 being outermost and zone 4 being juxtamedullary. Two inhibitors of prostaglandin synthesis were used: indomethacin 8 mg/kg and aspirin 100 mg/kg. The inhibitor or the vehicle was given intravenously prior to a control period which was followed by a hemorrhage sufficient to decrease arterial pressure by about one-third. The distribution of cortical flow was determined before hemorrhage, during hemorrhagic hypotension, and after transfusion. In the vehicle-treated dogs, total renal blood flow was well maintained, but flow redistributed to favor the inner cortical nephrons. This vasodilation in the inner cortex was blocked by both inhibitors of prostaglandin synthesis resulting in a decrease in total renal blood flow and relative ischemia of the juxtamedullary nephrons. Salicylate levels required to accomplish blockage of inner cortical vasodilaton were less than 7 mg/100 ml. These studies indicate that prostaglandins are responsible for the decreased vascular resistance of the inner cortical nephrons which results in the redistribution of blood flow during hemorrhage, and when prostaglandin synthesis is blocked, the kidney vasculature constricts during hemorrhage.