bluuebunny/crossref_metadata_2025 huggingface dataset:
Right atrial appendectomy reduces the renal response to acute hypervolemia in the rat
Authors: Veress A. T. , Sonnenberg H.
Published: December 2017

We have shown previously that an extract of atrial tissue from rat heart contains a potent natriuretic factor. In this study anesthetized rats were connected to a respirator and the right atrial appendage was either excised, using a loop ligature (experimental group), or the loop was placed around the appendage and then removed (sham-operated group). After equilibration and control urine collection periods an isooncotic Ringers-albumin solution was infused intravenously (25% of estimated blood volume), and renal function was monitored over the next hour. There were no differences between groups in control period arterial or central venous pressures, heart rates, cardiac outputs, renal blood flows, or filtration rates. However, the diuretic and natriuretic responses to infusion in the experimental group were only one half of those in the sham-operated series (vol = 23.4 +/- 6.2 vs. 68.2 +/- 11.0 microliter X min-1 X g kidney wt-1, UNa V = 2,731 +/- 856 vs. 6,504 +/- 962 nmol X min-1 X g kidney wt-1). These differences were not affected by prior bilateral vagotomy. Administration of homologous atrial natriuretic factor or furosemide resulted in identical renal responses in both groups. We conclude therefore that acute hypervolemia is associated with release of atrial natriuretic factor into the bloodstream and that removal of the atrial appendage reduces the amount available for such release.
Release of natriuretic factor from rat heart-lung preparation by atrial distension
Authors: Dietz J. R.
Published: December 2017

The hypothesis that an increase in blood volume results in the release of an atrial natriuretic factor (ANF) via atrial stretch was examined using an isolated rat heart-lung preparation. The heart lung preparation was perfused with a fluorocarbon emulsion for two periods of 20 min. During the first period the venous return reservoir was placed at a level of 1–2 cm above the right atrium [low central venous pressure (low CVP)] and at a level 7–12 cm above the heart (high CVP) for the second period. The perfusate used for each period was collected and saved for later analysis of natriuretic activity using anesthetized rats as a bioassay. Samples of either low or high CVP perfusate were infused into the abdominal aorta of the assay rats while urine was collected from a bladder catheter. A 3-min infusion of the high CVP perfusate at a rate of 0.5 ml/min resulted in an increase in urine flow from 10 to 28 microliter/min (P less than 0.01), sodium excretion from 0.14 to 1.34 mueq/min (P less than 0.01), and potassium excretion from 0.17 to 0.81 mueq/min (P less than 0.01). Infusion of the low CVP perfusate failed to produce a significant diuresis, natriuresis, or kaliuresis. These results are consistent with the hypothesis that ANF may be a hormone involved in the control of blood volume.
Splenic red cell sequestration and blood volume measurements in conscious pigs
Authors: Hannon J. P. , Bossone C. A. , Rodkey W. G.
Published: December 2017

When estimated by the dilution of 51Cr-labeled red blood cells under nearly basal conditions, immature splenectomized pigs (n = 20) had a circulating red cell volume of 17.8 +/- 1.64 (SD) ml/kg. At an assumed body-to-large vessel hematocrit (BH:LH) ratio of 0.9, plasma volume was 49.6 +/- 3.12 ml/kg and blood volume 67.3 +/- 3.67 ml/kg. Sham-operated pigs (n = 20) had a circulating red cell volume of 16.2 +/- 1.39 ml/kg, a plasma volume of 51.1 +/- 3.42 ml/kg, and blood volume of 67.2 +/- 4.12 ml/kg. Kinetic analysis of early 51Cr loss from the circulating blood of the sham-operated pigs indicated a splenic red cell sequestration of 4.5 +/- 0.89 ml/kg and a t1/2 of 9.76 +/- 1.93 min for splenic red cell turnover. Epinephrine injection (n = 6) and physical restraint (n = 8) caused rapid mobilization of splenic red blood cells in sham-operated pigs. Volume estimates in splenectomized pigs (n = 7) based on simultaneous dilutions of 51Cr-labeled red blood cells and 125I-labeled bovine albumin gave circulating red cell, plasma, and blood volumes of 18.4 +/- 2.46, 60.7 +/- 4.01, and 79.0 +/- 3.51 ml/kg, respectively, and a BH:LH ratio of 0.756 +/- 0.029. The latter value may have reflected an overestimation of plasma volume by the 125I-labeled albumin procedure.
Thermal responses to central angiotensin II, SQ 20881, and dopamine infusions in sheep
Authors: Huang B. S. , Kluger M. J. , Malvin R. L.
Published: December 2017

The thermoregulatory role of brain angiotensin II (ANG II) was tested by intracerebroventricular (IVT) infusion of ANG II or the converting enzyme inhibitor SQ 20881 (SQ) in 15 conscious sheep. Deep body temperature decreased 0.30 +/- 0.07 degree C (SE) during the 3-h period of IVT ANG II (25 ng/min) infusion (P less than 0.05) and increased 0.50 +/- 0.13 degree C during IVT SQ (1 microgram/min) infusion (P less than 0.01). To determine whether the rise in body temperature after IVT SQ infusion might be the result of a central renin-angiotensin system (RAS), SQ was infused IVT in five conscious sheep 20 h after bilateral nephrectomy. This resulted in a significant rise in body temperature of 0.28 +/- 0.05 degree C (P less than 0.05). When vasopressin antidiuretic hormone (ADH) was infused intravenously at the same time of IVT SQ infusion, the rise in temperature was depressed, but ADH did not lower the temperature below basal. IVT dopamine (20 micrograms/min) increased body temperature by 0.40 +/- 0.04 degree C (P less than 0.01), which was qualitatively similar to the result with IVT SQ. These data support the hypothesis that endogenous brain ANG II may play a role in thermoregulation. Furthermore, plasma ADH level, regulated in part by brain ANG II, is probably not the mediator of that thermoregulation. The similar effects of IVT dopamine and SQ on body temperature strengthen the hypothesis that dopamine may be involved in the central action of brain ANG II.
Blood pressure and norepinephrine spillover during propranolol infusion in humans
Authors: Best J. D. , Halter J. B.
Published: December 2017

To determine whether a reflex increase of sympathetic nervous system activity contributes to maintenance of blood pressure during acute beta-adrenergic blockade, we measured plasma norepinephrine levels and norepinephrine kinetics during propranolol administration. During a 90-min infusion of propranolol (10 mg iv + 80 micrograms/min) in 12 normal subjects, heart rate fell from 56 +/- 2 to 49 +/- 2 (SE) beats/min (P less than 0.001), but there was no fall in mean arterial blood pressure (84 +/- 3 mmHg before and 86 +/- 3 mmHg after propranolol). Arterial plasma norepinephrine levels rose from 183 +/- 20 to 250 +/- 29 pg/ml during propranolol (P less than 0.001), suggesting increased sympathetic vasoconstrictor tone. However, isotope dilution studies using tritiated norepinephrine infusion showed that arterial plasma levels of tritiated norepinephrine rose from 743 +/- 78 to 1,002 +/- 101 dpm/ml during propranolol (P less than 0.001), indicating a reduction in the rate of norepinephrine clearance from plasma. The calculated fall in clearance from 1.90 +/- 0.13 to 1.42 +/- 0.11 1/min (P less than 0.001) entirely accounted for the rise in plasma norepinephrine, since the calculated rate of norepinephrine spillover into plasma remained at the base-line level of 340 +/- 40 ng/min during propranolol. In control studies on four subjects, arterial plasma norepinephrine levels and norepinephrine kinetics did not change from base line during the control period. We conclude that maintenance of blood pressure during propranolol infusion is not due to a reflex generalized increase of sympathetic vasoconstrictor tone.
Corticosterone: narrow range required for normal body and thymus weight and ACTH
Authors: Akana S. F. , Cascio C. S. , Shinsako J. , Dallman M. F.
Published: December 2017

ACTH secretion appears to be under fairly tight negative feedback control by corticosteroids secreted from the adrenal cortex. In these studies we determined the circulating levels of a constant corticosterone signal that best restored body weight gain, thymus weight and ACTH levels to normal in bilaterally adrenalectomized rats given saline to drink. Young male rats were treated at the time of adrenalectomy with subcutaneously implanted pellets of wax or various ratios of corticosterone-cholesterol. Sham-adrenalectomized rats and adrenalectomized rats given corticosterone in the drinking fluid served as comparison groups. Rats were killed 3, 7, or 14 days after adrenalectomy. There was no difference in levels of plasma corticosterone in the morning and in the evening in pellet-implanted rats in contrast to the diurnal variation in the reference groups. Circulating corticosterone levels that best restored body weight, thymus weight, and resting and stress-induced ACTH levels to normal ranged between 4.5 and 7.4 micrograms/dl. Plasma corticosterone levels of 8-11 micrograms/dl were excessive and levels of 2-4 micrograms/dl were not adequate. We conclude that there is a very narrow range of plasma corticosterone compatible with normal growth rate, thymus mass and ACTH secretion. These results reveal the necessity for strict negative feedback regulation of ACTH secretion by corticosteroids.
Afferent axons in abdominal vagus mediate satiety effect of cholecystokinin in rats
Authors: Smith G. P. , Jerome C. , Norgren R.
Published: December 2017

Selective section of afferent vagal axons that reach below the diaphragm blocks the satiating effect of peripherally administered cholecystokinin in the rat. Section of the analogous efferent axons has no effect. After the behavioral tests, the selective axonal sections were confirmed with horseradish peroxidase histochemistry.
Atriopeptin II lowers cardiac output in conscious sheep
Authors: Breuhaus B. A. , Saneii H. H. , Brandt M. A. , Chimoskey J. E.
Published: December 2017

Atrial natriuretic peptides cause natriuresis, kaliuresis, diuresis, and hypotension. They relax vascular smooth muscle in vitro, and they dilate renal vessels in vivo. Hence, we tested the hypothesis that they produce hypotension by lowering total peripheral resistance. The studies were performed in conscious chronically instrumented sheep standing quietly in their cages. Atriopeptin II (AP II) was infused into the right atrium for 30 min at 0.1 nmol X kg-1 X min-1. Atriopeptin II lowers arterial pressure (9%, P less than 0.05) by lowering cardiac output (18%, P less than 0.05), stroke volume (28%, P less than 0.05), and right atrial pressure (2.3 mmHg, P less than 0.05). Heart rate and total peripheral resistance increase (16 and 13%, respectively, P less than 0.05). Partial ganglionic blockade with trimethaphan camsylate during AP II infusion prevents the increases in heart rate and total peripheral resistance. The changes in right atrial pressure, stroke volume, and cardiac output persist, and arterial pressure falls further (27%, P less than 0.05). These hemodynamic data are consistent with direct AP II-induced relaxation of venous smooth muscle with reduction of venous return, right atrial pressure, stroke volume, cardiac output, and arterial pressure, followed by reflex activation of the sympathetic nervous system to increase heart rate and total peripheral resistance. Because partial ganglionic blockade alone and AP II alone cause similar reductions in right atrial pressure (2.1 and 2.3 mmHg, respectively) but AP II causes a greater fall in stroke volume (28 vs. 13%), it is possible that AP II also causes coronary vasoconstriction.
Effect of deep hypoxia on acid-base balance in trout: role of ion transfer processes
Authors: Thomas S. , Fievet B. , Motais R.
Published: December 2017

Continuous recordings were made of pH, Po2, and Pco2 of arterial blood in an extracorporeal circulation during a 20-min period of deep hypoxia (inspired Po2 = 40 Torr) and subsequent normoxia in rainbow trout. Blood concentrations of lactate, Na+, K+, and Cl- and net fluxes of electrolytes across gills and kidney were also continuously monitored. Deep hypoxia induced a short respiratory alkalosis followed by a marked metabolic acidosis. The acidification is biphasic in nature. The first rapid phase of acidification is not related to lactic acid production. On the other hand, the second phase of acidification is associated with lactic acid diffusion into the blood. However, a considerable proportion of the lactate ions is balanced by Na+ ions coming from a shift in the distribution of this cation between intra- and extracellular compartments. Most of the H+ ions formed from the dissociation of lactic acid are buffered in the intracellular space. The acidification period is also characterized by a very small increase in plasma Cl- content, much less than that of Na+, and by the apparent accumulation of an unknown anion in the blood. Recovery from hypoxia is associated with a pH readjustment, a large and identical decline of blood Na+ and Cl- contents without modification of the concentrations of K+, lactate, and the unknown anion. During this period the branchial ionic exchanges are slightly stimulated, but in the acid-base regulation as a whole, the branchial regulatory processes only play a minor part, the ionic movements being mainly performed by transfer between intra- and extracellular spaces.(ABSTRACT TRUNCATED AT 250 WORDS)
Mammalian metabolite flux rates in a teleost: lactate and glucose turnover in tuna
Authors: Weber J. M. , Brill R. W. , Hochachka P. W.
Published: December 2017

Lactate and glucose turnover rates were measured by bolus injection of [U-14C]lactate and [6-3H]glucose in cannulated lightly anesthetized skipjack tuna, Katsuwonus pelamis. Our goals were to find out whether the high rates of lactate clearance reported during recovery from burst swimming in tuna could be accounted for by high blood lactate fluxes; to extend the observed correlation between lactate turnover and lactate concentration in mammals to a nonmammalian system, and to assess the importance of lactate and glucose as metabolic fuels in tuna and to compare their flux rates with values reported for mammals. Measured lactate turnover rates ranged from 112 to 431 mumol X min-1 X kg-1 and were correlated with blood lactate concentration. Glucose turnover rate averaged 15.3 mumol X min-1 X kg-1. When correcting for body mass and temperature, skipjack tuna has at least as high or even higher lactate turnover rates than those recorded for mammals. Tuna glucose turnover rate is similar to that of mammals but much higher than levels found in other teleosts. Even the highest lactate turnover rate measured in tuna cannot fully account for the rate of blood lactate clearance observed during recovery, suggesting that some of the lactate produced in skeletal muscle must be metabolized in situ. After injection of [U-14C]lactate, less than 5% of the total blood activity was recovered in glucose, suggesting that the Cori cycle is not an important pathway of lactate metabolism in tuna.
Response of hamster circadian system to transitions between light and darkness
Authors: Albers H. E.
Published: December 2017

The effects of exposure to sudden transitions from dark to light (DL) and light to dark (LD) were determined on the free-running circadian activity rhythm of Syrian hamsters. The activity rhythm was phase delayed by 1-2 h by DL transitions provided during the 12-h interval before activity onset (subjective day). In contrast, DL transitions produced phase advances of approximately 1 h 2-12 h after activity onset. LD transitions tended to produce phase advances throughout the circadian cycle. During the subjective day, LD transitions resulted in phase advances of up to 4 h. After the onset of activity, LD transitions produced phase advances of a lesser magnitude than during the subjective day. In addition, some phase delays were also observed. When the phase shifts produced by DL and LD transitions were combined additively these transitions could account for the phase shifts previously reported for brief pulses of light.
Maintenance of carotid baroreflex function in advanced age in the rat
Authors: Wei J. Y. , Mendelowitz D. , Anastasi N. , Rowe J. W.
Published: December 2017

To evaluate the influence of age per se on the carotid sinus baroreceptors in the absence of hypertension and atherosclerosis, we employed the Fischer 344 rat model. In 14 adult (A, 6-9 mo) and 9 senescent (S, 24-26 mo) normotensive male Fischer 344 rats the left carotid sinus region was vascularly isolated with sinus nerve intact and perfused with oxygenated modified Kreb's solution. Simultaneous measurements of intrasinus pressure and femoral arterial pressure response were obtained during linear pressure increases (20-200 mmHg) in the vascularly isolated sinus. There was no age difference in base-line arterial pressure or heart rate. Both age groups demonstrated similar positive relations between basal femoral arterial pressure and the magnitude of the femoral pressure response to equivalent carotid sinus pressures. There were similar estimated sinus volumes at onset of systemic response (39 +/- 1, A; 39 +/- 1 microliter, S), time to initial systemic pressure response (9 +/- 1, A; 7 +/- 1 s, S), mean rates of femoral pressure decline (1.8 +/- 0.3, A; 2.1 +/- 0.3 mmHg/s, S), and return to base line (1.5 +/- 0.3, A; 1.4 +/- 0.3 mmHg/s, S) as well as magnitudes of systolic (25 +/- 3, A; 26 +/- 4 mmHg, S) and diastolic (21 +/- 2 A; 22 +/- 4 mmHg, S) pressure drops. Thus, in the Fischer 344 rat model of aging, which differs from the human in that it is not complicated by hypertension or atherosclerosis, carotid sinus baroreflex function appears to be well maintained in senescence.
Hepatic portal glucose infusions decrease food intake and increase food preference
Authors: Tordoff M. G. , Friedman M. I.
Published: December 2017

We examined the contribution of experimental factors to the hepatic control of food intake. Rats with either hepatic portal or jugular catheters were infused four times with glucose (4.5 mg/min) and equitonic saline (2 ml/2 h). During the infusions their food contained nonnutritive chocolate or chicken flavor, depending on the infusate received. Hepatic portal glucose decreased food intake relative to saline and no infusion conditions, but jugular glucose did not. When allowed to choose between the flavors associated with each infusate, rats with hepatic portal catheters preferred the flavor eaten during glucose infusion, and rats with jugular catheters showed no preference. These results suggest that a mechanism located in the liver can reduce food intake without producing malaise and that portal glucose can act as an unconditioned stimulus for the acquisition of a learned food preference. Several reports that hepatic portal infusions do not alter feeding behavior may be explained by a failure to control for previous experience in the test situation.
Changes in cardiac output and vascular resistance during behavioral stress in the rat
Authors: Hubbard J. W. , Cox R. H. , Sanders B. J. , Lawler J. E.
Published: December 2017

Normotensive Wistar-Kyoto (WKY) rats and borderline hypertensive rats (BHR) were exposed to aversive classical conditioning procedures and chronically instrumented with arterial catheters and electromagnetic flow probes around the ascending aorta. After postoperative recovery, hemodynamic measurements and blood samples were obtained from conscious animals at rest and during aversive conditioning. The cardiovascular response to the behavioral stress consisted of a significant increase in mean arterial blood pressure, total peripheral resistance index, cardiac index, heart rate, and aortic dP/dt for both strains. However, the elevated vascular resistance seen in the BHR resulted in a significantly greater increase in mean arterial blood pressure (21 mmHg) compared with the WKY rats (14 mmHg). In addition, the BHR showed a significantly (P less than 0.05) greater plasma norepinephrine concentration (760 +/- 99 pg/ml) in response to the stress than did the WKY rats (559 +/- 53 pg/ml). These data suggest that an increase in cardiac output, elevated vascular resistance, and increased sympathetic drive may contribute to the development of stress-induced hypertension in this animal model.
Analysis of factors involved in determining urinary bladder voiding cycle in urethan-anesthetized rats
Authors: Maggi C. A. , Giuliani S. , Santicioli P. , Meli A.
Published: December 2017

The mechanism(s) involved in determining the voiding cycle of the rat urinary bladder have been investigated in urethan-anesthetized animals. Fluid emission is almost confined to that phase of the voiding cycle which is characterized by the presence of a series of high-frequency oscillations in intraluminal pressure (IPHFO). During this phase the mean urethral flow rate reached a maximum and fluid was expelled in a stream-like fashion. The index obtained by multiplying the amplitude of IPHFO by their duration was significantly related to the maximal value of urethral flow rate. The IPHFO were selectively abolished by administration of d-tubocurarine at a dose that barely affects detrusor contractility. Moreover, d-tubocurarine reduced mean urethral flow rate and increased residual volume. The reflex (hexamethonium sensitive) mechanism(s) responsible for the generation of IPHFO is more developed in male than female rats. This mechanism, which involves activation of skeletal muscle, plays a significant role in determining bladder voiding in this species.
Lung mechanics and connective tissue levels in starvation-induced emphysema in hamsters
Authors: Karlinsky J. B. , Goldstein R. H. , Ojserkis B. , Snider G. L.
Published: December 2017

The effect of starvation on lung mechanics, morphometry, and levels of connective tissue components was determined in young adult golden Syrian hamsters. A base-line control, fed control, and starved group were studied. Fed group animals increased body weight by 13%, but dry lung weight did not increase above that of the base-line controls. The total lung capacity when transpulmonary pressure was at 25 cmH2O (TLC25) also increased by 20% above base-line controls. The mean TLC25 of the starved group was greater than that of the base-line control group but less than that of the fed control group (P less than 0.05). Volume-corrected air-filled volume pressure (VP) curves of the three groups were similar. Volume-corrected saline-filled VP curves were identical in the three groups. Total lung collagen, elastin, glycosaminoglycan, and protein were similar in the three groups. Air space size was significantly increased and mean internal surface area was significantly decreased in the starved group compared with the base-line and fed controls. No evidence of alveolar wall destruction was evident by light or electron microscopy. We conclude that severe starvation of young adult hamsters produces air space enlargement without changes in lung elastic recoil. The mechanism of alveolar wall remodeling is not yet understood in this model of emphysema.
Circadian urinary excretion rhythms in adrenalectomized rats
Authors: Poulis J. A. , Roelfsema F. , van der Heide D.
Published: December 2017

The impact of the adrenal system on urinary rhythms was investigated in adrenalectomized (ADX) rats under various experimental conditions. During a 12:12 light-dark cycle the acrophases were shifted in ADX rats with respect to control rats. Under constant light conditions ADX rats displayed free-running rhythms, similar to those of control rats. The periods were stable in blind rats but not in rats maintained on a constant light cycle. The abrupt change in period, which occurred after approximately 8 days, suggests a stage of internal desynchronization. A 6-h delay in the administration of corticosterone to ADX rats caused a delay shift of the acrophases. A single intraperitoneal injection of corticosterone in blind free-running ADX rats caused delay or advance shifts so that we could construct phase-response curves for the various excretory rhythms. These observations indicate that the adrenals are not essential for the establishment of the urinary rhythms; however, corticosterone influences the phase setting of these rhythms. The site of action is probably the X pacemaker (controlling the body temperature rhythm), although we cannot totally exclude an additional effect on secondary (renal) oscillators.
Metabolic sources of energy for hummingbird flight
Authors: Suarez R. K. , Brown G. S. , Hochachka P. W.
Published: December 2017

It has been known for some two decades that hovering flight in hummingbirds is the most energetically expensive muscle work known among vertebrates, but the metabolic support for such work has never been clarified. Measurement of the maximum activities of key enzymes of carbohydrate, fat, and amino acid catabolism in flight muscle and heart of rufous hummingbirds (Selasphorus rufus) reveals that the high ATP requirements of short-term hovering flight can only be supported by the oxidation of carbohydrate. Fat oxidation can support a substantially lower maximum rate of ATP turnover, indicating that this process can power only the lower +.++energetic requirements of long-term forward or migratory flight. Mitochondria isolated from flight muscle oxidize pyruvate and palmitoyl-CoA equally well. The inhibition of pyruvate oxidation by palmitoyl-CoA oxidation provides a mechanism by which fat oxidation inhibits carbohydrate oxidation in the transition from short- to long-term flight.
Alpha 1-adrenergic receptor activation depolarizes rat supraoptic neurosecretory neurons in vitro
Authors: Randle J. C. , Bourque C. W. , Renaud L. P.
Published: December 2017

Intracellular data were obtained from 35 supraoptic nucleus neurosecretory neurons maintained in vitro in intra-arterially perfused explants of rat hypothalamus. Addition of norepinephrine, phenylephrine, or methoxamine, but not isoproterenol (30-200 microM), consistently induced membrane depolarization, bursting activity, and an associated prolongation in action potential duration, effects that were reversibly antagonized by the alpha 1-antagonist prazosin. Norepinephrine-evoked depolarizations demonstrated no consistent change in membrane resistance and were reduced both by membrane hyperpolarization and by raising extracellular K+. Norepinephrine shortened the time course of spike hyperpolarizing afterpotentials and increased the magnitude of late depolarizing afterpotentials. It is proposed that one of norepinephrine's actions on supraoptic neurons involves K+ channels, perhaps by modulation of a transient K+ current known as A current.
Doubly labeled water method: in vivo oxygen and hydrogen isotope fractionation
Authors: Schoeller D. A. , Leitch C. A. , Brown C.
Published: December 2017

The accuracy and precision of the doubly labeled water method for measuring energy expenditure are influenced by isotope fractionation during evaporative water loss and CO2 excretion. To characterize in vivo isotope fractionation, we collected and isotopically analyzed physiological fluids and gases. Breath and transcutaneous water vapor were isotopically fractionated. The degree of fractionation indicated that the former was fractionated under equilibrium control at 37 degrees C, and the latter was kinetically fractionated. Sweat and urine were unfractionated. By use of isotopic balance models, the fraction of water lost via fractionating routes was estimated from the isotopic abundances of body water, local drinking water, and dietary solids. Fractionated water loss averaged 23% (SD = 10%) of water turnover, which agreed with our previous estimates based on metabolic rate, but there was a systematic difference between the results based on O2 and hydrogen. Corrections for isotopic fractionation of water lost in breath and (nonsweat) transcutaneous loss should be made when using labeled water to measure water turnover or CO2 production.
Increased permeability of a glial blood-brain barrier during acute hyperosmotic stress
Authors: Mackie K. , DePasquale M. , Cserr H. F.
Published: December 2017

Brain volume is regulated during acute hypernatremia in the little skate, Raja erinacea, based on the gain of osmolytes, including sodium, chloride, and potassium [Cserr et al., Am. J. Physiol. 245 (Regulatory Integrative Comp. Physiol. 14): R853-R859, 1983]. In this study we show that this volume regulatory response is complete in 35 min and examine the mechanism of sodium influx across the blood-brain barrier over this period. Skates have a glial blood-brain barrier. Blood-to-brain transfer constants (K1) for 22Na and [14C]mannitol were measured using the integral technique of [Ohno et al.Am. J. Physiol. 235 (Heart Circ. Physiol. 4): H299-H307, 1978]. In skates injected intramuscularly with isotonic saline (controls) or with hypertonic NaCl or fructose, K1 for sodium increased linearly with osmolality. This increase was the same for hypernatremia and fructose-induced hypertonicity, and it was not affected by the “loop” diuretic bumetanide. K1 for mannitol also increased with osmolality. These results suggest that hypertonicity increases barrier permeability by a nonselective mechanism. The contribution of influx across the blood-brain barrier to tissue sodium gain during acute hypernatremia is assessed using a diffusional model of plasma-brain exchange.
Atrial stretch-induced diuresis in Brattleboro rats
Authors: Kaufman S. , Stelfox J.
Published: December 2017

Inflation of a balloon at the superior vena caval/right atrial junction of the conscious Brattleboro rat initiated a rapid and significant diuresis, natriuresis, and kaliuresis (urine volume increased from 20.8 +/- 0.8 to 28.5 +/- 1.3 ml/h, P less than 0.005; urine sodium increased from 2,417 +/- 115 to 3,510 +/- 230 mu eq/h, P less than 0.005; urine potassium increased from 351 +/- 52 to 478 +/- 58 mu eq/h, P less than 0.05; n = 6). Bilateral renal denervation did not significantly alter this response. Since the Brattleboro rat is totally deficient in antidiuretic hormone (ADH) and since inflation of the balloon causes no change in blood pressure, the reflex increase in urinary salt and water output must be mediated, at least in part by a blood-borne factor other than ADH.
Cardioinhibitory effect of atrial peptide in conscious rats
Authors: Allen D. E. , Gellai M.
Published: December 2017

The hemodynamic and renal excretory responses to 150-min atriopeptin II (AP II) infusion (330 ng X kg-1 X min-1) were assessed in five chronically instrumented rats with (FR protocol) and without (NR protocol) replaced urinary fluid losses. The observed changes were compared with those obtained by vehicle in the same rats. The hypotension seen with AP II infusion (120-min value: -27 +/- 2%, FR and NR responses combined) was due solely to a decreased cardiac output (CO; 120-min combined value: -34 +/- 3%). Total peripheral resistance remained unchanged or slightly elevated. A drop in stroke volume plus a later-developing (by 75-90 min) decrease in heart rate contributed to the CO decline. This latter bradycardic component, the opposite response to that typically produced reflexly by hypotension, was reversed by atropine sulfate treatment at 120 min and may thus be neural in origin. The finding of similar hemodynamic changes in the FR and NR rats and the lack of a significant effect of AP II on hematocrit suggest that volume depletion or a plasma extravasation were not contributors to the cardioinhibitory effect of the peptide.
Chemical microstimulation of the septal area lowers arterial pressure in the rat
Authors: Gelsema A. J. , Calaresu F. R.
Published: December 2017

Electrical stimulation of the septal area has been previously reported to result in either an increase or a decrease in arterial pressure (AP) and heart rate (HR) depending on the site of stimulation within the septum or on the anesthetic. These conflicting results could be due to the different proportions of cell bodies and fibers activated by electrical stimulation at different sites and to the different anesthetics acting differently on cell bodies and fibers. To study the cardiovascular responses to activation of cell bodies, DL-homocysteate (20-50 nl) was injected into histologically verified sites in the lateral septum (LS), the medial septum (MS), the nucleus of the vertical limb of the diagonal band of Broca (NDBB), and in the bed nucleus of the stria terminalis (BST) in urethananesthetized, paralyzed, and artificially ventilated rats. Injections in the LS, MS, and NDBB elicited a decrease in AP [-12.6 +/- 0.9 (SE) mmHg, n = 111] accompanied by variable changes in HR. In a group of spontaneously breathing rats anesthetized with urethan, AP responses were not significantly different from those obtained in paralyzed animals. Finally, in a group of animals under alpha-chloralose, AP responses were not significantly different from those observed in animals under urethan. Homocysteate application in the BST resulted in either depressor [-10.8 +/- 0.9 (SE) mmHg, n = 20] or pressor responses [13.7 +/- 1.9 (SE) mmHg, n = 9].(ABSTRACT TRUNCATED AT 250 WORDS)
Role of atrial natriuretic factor in the natriuresis of acute volume expansion
Authors: Khraibi A. A. , Granger J. P. , Burnett J. C. , Walker K. R. , Knox F. G.
Published: December 2017

The quantitative role of atrial natriuretic factor (ANF) in mediating the natriuresis induced by acute volume loading was determined in these studies. Plasma level of ANF (PANF), glomerular filtration rate (GFR), and renal excretory responses were measured in three groups of anesthetized Sprague-Dawley rats. In one group of rats (n = 8), acute volume expansion was established by intravenous infusion of saline (5% body wt) over a period of 30 min. A second group of rats (n = 13) was infused with synthetic ANF (2 micrograms X kg-1 X h-1 iv) to mimic the high PANF observed during acute volume loading. A third group (n = 13) served as control. PANF was similar and significantly elevated (P less than 0.05) in volume-expanded and ANF-infused groups compared with control. In control rats, PANF measured 122.0 +/- 12.1 pg/ml, whereas it averaged 389.4 +/- 30.3 pg/ml for volume-expanded and 368.1 +/- 22.3 pg/ml for ANF-infused rats. GFR was also comparable and significantly increased (P less than 0.05) in volume-expanded and ANF-infused groups compared with control rats. Infusion of ANF at a dose to mimic PANF obtained during acute volume expansion resulted in a fourfold increase in the fractional excretion of sodium. The results of these studies suggest that ANF may play an important quantitative role in promoting natriuresis during acute volume expansion.
Membrane-associated carbonic anhydrase in gills of the blue crab, Callinectes sapidus
Authors: Henry R. P.
Published: December 2017

The presence of the enzyme carbonic anhydrase (CA) on the basal membrane of the branchial endothelial cells in the blue crab and its physiological significance were studied in vivo using a membrane-impermeant CA inhibitor, quaternary ammonium sulfanilamide (QAS). Injection of QAS into the hemolymph of Callinectes sapidus resulted in the rapid development of a respiratory acidosis; PCO2 rose almost 2 Torr, pH was lowered by approximately 0.25 units, and total CO2 rose by 2 mM. These results support the hypothesis that membrane-associated CA exposed to hemolymph is present in the crustacean gill and that it is physiologically significant in mobilizing hemolymph HCO-3 to CO2 to facilitate CO2 excretion across the gill. The recovery from this acidosis coincides with the clearance of the inhibitor from the hemolymph. Hemolymph osmotic and ionic parameters were unaffected by QAS, reconfirming the role of branchial cytoplasmic CA in ion regulation and also providing a convenient bioassay for determining CA inhibitor permeability in the intact organism.
Regulation of drinking and vasopressin secretion: role of organum vasculosum laminae terminalis
Authors: Thrasher T. N. , Keil L. C.
Published: December 2017

We have proposed that the organum vasculosum laminae terminalis (OVLT) contains osmoreceptors involved in the regulation of drinking and secretion of arginine vasopressin (AVP) in the dog. By use of the technique of electrolytic ablation, conscious dogs were evaluated for their responses to acute peripheral challenges of hypertonic NaCl and angiotensin II (ANG II) and hemorrhage (20 ml/kg) before and after destruction of the OVLT (n = 7) or adjacent tissue (n = 9) as a control. Lesions confined to the tip of the optic recess and destroying greater than 90% of the OVLT caused a dramatic increase in the threshold to drink and increase plasma AVP levels and a significant (P less than 0.01) reduction in the magnitude of these responses to an osmotic stimulus. Drinking and secretion of AVP in response to ANG II, but not the rise in peripheral corticosteroids, were also blocked (P less than 0.01) by ablation of the OVLT. In contrast responses to hemorrhage were not affected by the lesion. These results support the hypothesis that the OVLT contains osmoreceptors involved in physiological responses to cellular dehydration and suggest involvement in drinking and secretion of AVP in response to ANG II. The results also indicate that forebrain mechanisms which depend on the OVLT are independent of mechanisms responding to hemorrhage in conscious dogs.
Adipocyte blood flow is decreased in obese Zucker rats
Authors: West D. B. , Prinz W. A. , Francendese A. A. , Greenwood M. R.
Published: December 2017

Blood flow to five adipose tissue depots and five other organs was measured in unanesthetized free-moving obese and lean male Zucker rats using the radiolabeled microsphere technique. Cardiac output and blood pressure were also measured. Obese rats were significantly heavier and had larger fat depots characterized by more and larger adipocytes. Cardiac output and blood pressure were similar in lean and obese rats. Blood flow to adipose tissue was substantially reduced in all five depots of obese rats when expressed per square millimeter of cell surface. When blood flow was expressed per cell, it was reduced in obese rats in the dorsal subcutaneous and inguinal depots and significantly elevated in the obese mesenteric adipose depot. Significant interdepot differences in blood flow were observed in both lean and obese rats. Nonadipose organ blood flow was not different between obese and lean rats, but when expressed on a per gram basis, blood flow through triceps surae muscle, epididymis, and testis was elevated in obese rats. These findings suggest that there is a substantial alteration of hemodynamics in obesity that may contribute to or reflect the altered metabolism of adipose tissue in obese rats. Furthermore, interdepot differences of adipose tissue blood flow also parallel reported interdepot differences in metabolism.
Fetal heart rate, arterial pressure, and blood volume responses to cortisol infusion
Authors: Wood C. E. , Cheung C. Y. , Brace R. A.
Published: December 2017

The purpose of this study was to determine whether physiological amounts of cortisol affect the fetal cardiovascular system. Cortisol (4 micrograms/min) or the vehicle was infused intravenously for 5 h into six chronically catheterized sheep fetuses at 127-143 days gestation (term = 145-150 days). In the cortisol-infused animals, plasma cortisol concentration increased from 2.0 +/- 0.6 (SE) to 8.3 +/- 0.9 ng/ml. There was a concomitant decrease in fetal heart rate of 38 beats/min (P less than 1 X 10(-6)) and an increase in arterial pressure. Estimated blood volume decreased by 6% in the cortisol-infused fetuses compared with the vehicle-infused animals (P less than 1 X 10(-4]. In addition, plasma norepinephrine and epinephrine concentrations decreased to 70% of control at the end of the 5-h cortisol infusion, whereas plasma renin concentration decreased to 34% of control. The simultaneous increase in fetal arterial pressure and decrease in estimated blood volume suggest that fetal vascular resistance increased, whereas vascular compliance and/or nonstressed vascular volume decreased. However, this does not appear to be mediated by increases in circulating vasoconstrictor hormone concentrations or increased sympathetic tone. Thus the present study shows that physiological amounts of cortisol have significant effects on the fetal cardiovascular system but the mechanisms are unknown.
Effect of continuous infusions of CCK-8 on food intake and body and pancreatic weights in rats
Authors: Lukaszewski L. , Praissman M.
Published: December 2017

The ability of cholecystokinin (CCK) to act as a long-term satiety factor was assessed by its continuous infusion into the jugular veins of rats. Animals receiving a low dose of cholecystokinin octapeptide (CCK-8) (0.6 microgram CCK-8.kg body wt-1.h-1) did not show any significant differences in body weight changes or in food consumption from rats receiving saline and a group of unoperated controls over the 7-day infusion period. A 19.3-fold greater dose of CCK-8 (11.6 micrograms.kg body wt-1.h-1) did cause a significant decline in food consumption for the first 4 days compared with saline-infused rats (P less than 0.05) and unoperated controls (P less than 0.01). Rats receiving a high dose of CCK gained weight at a slower rate than rats receiving saline, but this effect lasted only 2 days and was not significant. Pancreatic growth was used as an indirect measure of elevated CCK levels in these animals. The infusion of 0.6 microgram CCK-8.kg body wt-1.h-1 did not lead to sufficiently elevated peptide levels to promote pancreatic growth. In contrast, those rats receiving a high dose of CCK-8 had significantly greater pancreatic weights (P less than 0.01) compared with saline-treated rats and unoperated controls. These results indicate that CCK-8, when administered continuously and in a large enough dose, can suppress food intake in rats for a period of several days before losing its effectiveness.
Renal nerve and cardiovascular responses to cardiac receptor stimulation in rabbits
Authors: Niitani S. , Tomomatsu E. , Ohba H. , Yoshida Y. , Yagi S.
Published: December 2017

It has been shown that a species difference exists among cats, dogs, and monkeys in the reflex response to cardiac sympathetic afferent stimulation with bradykinin (BK). This study was performed to determine the arterial blood pressure (ABP), heart rate (HR), and renal nerve activity (RNA) responses to epicardial BK applications in the intact and sinoaortic-denervated and vagotomized (SAD + Vx) rabbits. Eight rabbits were anesthetized with pentobarbital sodium. The heart was exposed and suspended in the epicardial cradle. The ABP, HR, and RNA responses were determined when 1 and 10 micrograms/ml BK were applied to the anterior surface of the left ventricle in the intact and SAD + Vx state. In both the intact and SAD + Vx rabbits, ABP, HR, and RNA were significantly reduced with epicardial BK. In the SAD + Vx rabbits, BK evoked small decreases in ABP and HR and no change in RNA after topical lidocaine. These results show the existence of a depressor response and decreases in HR and RNA in the rabbit mediated by the action of BK on cardiac sympathetic afferents.
Hormonal response to exercise in humans: influence of hypoxia and physical training
Authors: Kjaer M. , Bangsbo J. , Lortie G. , Galbo H.
Published: December 2017

Hypoxia and physical training alter the responses of glucoregulatory hormones to absolute work loads in opposite directions. These effects have tentatively been ascribed to changes in maximal O2 consumption (VO2 max) and ensuing changes in relative work loads. However, hypoxia as well as training may more specifically influence the hormonal response. We therefore differentiated the influence of hypoxia, training, and VO2 max, respectively, on the hormonal response to bicycle exercise. Responses to hypoxia in a low-pressure chamber (PB = 465 vs. 730 Torr) were studied at given absolute and relative (85% VO2 max) work loads in seven endurance-trained athletes (T) and 7 age and weight-matched sedentary subjects (C). Concentrations in plasma of norepinephrine, growth hormone, adrenocorticotropic hormone, and cortisol were always closely related to the relative work load. However, the epinephrine response in T, but not in C, was at the same relative work load higher during hypoxia (5.84 +/- 0.83 nmol/l) than during normoxia (4.26 +/- 0.44, P less than 0.05). These results indicate that the hormonal response is influenced by hypoxia and physical training, mainly via changes in the relative work load. However, in trained subjects both at rest and during exercise, an enhancing effect of hypoxia per se on the epinephrine response is seen, probably due to an increased adrenal medullary secretory responsiveness in long-term endurance-trained subjects.
Septal neurons respond to activation of baro- and chemoreceptors in the rat
Authors: Miyazawa T. M. , Gelsema A. J. , Calaresu F. R.
Published: December 2017

Because it has recently been shown that selective activation of neuronal perikarya in the septal area elicits arterial depressor responses, it seems reasonable to expect that information from receptors in the cardiovascular system may be related to the septum. This possibility was investigated by searching for single units in the medial and lateral septal nuclei responding to activation of baroreceptors, elicited either by electrical stimulation of the aortic depressor nerve (ADN) or by systemic injection of phenylephrine (PE), or responding to activation of chemoreceptors, elicited by intracarotid injection of sodium cyanide. Fifty-four male Wistar rats weighing 300-400 g were anesthetized with urethan (1.4 g/kg ip) or alpha-chloralose-urethan (35 and 400 mg/kg ip, respectively) and allowed to breathe spontaneously. One-third of spontaneously firing units tested responded to ADN stimulation; these 93 units were divided into two groups according to their response patterns; 62 (67%) showed an increase and 31 (33%) a decrease in their discharge. Of 35 units tested, 6 responded to intravenous injection of PE. The majority of the units (48 of 60) affected by chemoreceptor activation were excited, and the remaining 12 were inhibited. These experiments suggest that sensory information from cardiovascular receptors may play an important role in the control of the circulation by the septum.
Cold- and norepinephrine-induced thermogenesis in younger and older Fischer 344 rats
Authors: McDonald R. B. , Horwitz B. A. , Hamilton J. S. , Stern J. S.
Published: December 2017

Older rats exposed to low environmental temperatures show attenuated thermogenesis. However, the mechanisms responsible for this attenuation are not clear. This investigation evaluated the possibility that reduced nonshivering thermogenic capacity is associated with this attenuation. O2 consumption was measured in male Fischer 344 rats ages 7 and 24 mo at thermoneutrality (26 degrees C), during exposure to cold (6 degrees C) for 2 h, and during norepinephrine (NE) infusion (an in vivo measure of nonshivering thermogenesis). In addition, the binding of GDP to isolated mitochondria of brown fat, an in vitro estimate of nonshivering thermogenesis, was also measured. Resting mass-independent O2 consumption (ml.min-1.g body mass -0.67) was not different between the two age groups. However, mass-independent O2 consumption was significantly greater in the younger vs. older rats during 2 h of cold exposure (younger, 2.86 +/- 0.19 l/kg body mass 0.67; older, 2.39 +/- 0.10 l/kg body mass 0.67) and during 20 min of maximum NE infusion (younger, 410.4 +/- 15.1 ml/kg body mass)] was greater in younger than ml/kg body mass 0.67). Brown fat mass [absolute (g) as well as relative (g tissue/kg body mass)] was greater in younger than in older rats. Furthermore, younger rats had significantly greater binding of GDP to isolated mitochondria of brown fat than did the older rats. This effect was true whether the data were expressed as nanomoles bound per milligram mitochondrial protein (32% lower in older rats), bound nanomoles recovered (57% lower), or bound picogram per kilogram body mass 0.67 (59% lower).(ABSTRACT TRUNCATED AT 250 WORDS)