bluuebunny/crossref_metadata_2025 huggingface dataset:
Lymphatic and vascular responses to fluid infusion in castrated and noncastrated sheep
Authors: Valenzuela G. J. , Brace R. A. , Longo L. D.
Published: December 2017

Estrogen administration produces blood volume expansion and interstitial fluid retention. We decided to study the effect of estrogen withdrawal on blood volume and determine whether oophorectomy has an effect on lymph flow or protein concentration. The rate of left thoracic duct lymph flow averaged 0.041 +/- 0.005 (SE) and 0.071 +/- 0.008 ml X min-1 X kg-1 in castrated (n = 9) and noncastrated (n = 9) female sheep, respectively (P = 0.006). After three serial intravenous infusions of Ringer lactate solution (2% body wt/infusion) the thoracic duct lymph flow in the castrated animals increased 358, 457, and 498% over the base-line rate, compared with increase of 200, 235, and 353% in the nonpregnant ewes. However, with the lower control values in the castrated animals, the lymph flow rate reached the same absolute values as those seen in the noncastrated ewes. Lymph protein concentration and the lymph-to-plasma protein concentration ratio, as well as arterial and venous pressures, were unaltered by oophorectomy. Base-line whole blood volumes were 58.2 +/- 1.9 (n = 9) and 64.8 +/- 2.6 ml/kg (n = 9) in the castrated and noncastrated ewes, respectively (P less than 0.05). Systemic vascular compliance averaged 4.5 +/- 0.7 and 7.1 +/- 1.7 ml X kg-1 X mmHg-1 in the castrated and noncastrated ewes, respectively (P less than 0.05), whereas interstitial fluid compliance values were 12 and 32 ml X kg-1 X mmHg-1, respectively. The capillary filtration coefficients were not different in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)
3-O-methylglucose transport in soleus muscle of bacteremic rats
Authors: Westfall M. V. , Sayeed M. M.
Published: December 2017

Basal and insulin-stimulated soleus muscle 3-O-[14C]methylglucose ([14C]-3-O-MG) transport was studied in vitro and in vivo during bacteremia in rats. Fasted rats were injected with Escherichia coli to produce bacteremia (B), and controls (C) received saline. In vitro studies using soleus muscles were carried out 8 or 12 h after bacterial injection, and transport was measured using the rate coefficient (lambda = min-1). Although insulin-stimulated (10 mU/ml) [14C]-3-O-MG transport was decreased in 12-h bacteremic rat muscles (lambda B = 0.041 +/- 0.003; lambda C = 0.055 +/- 0.002), the basal [14C]-3-O-MG transport rate coefficient was elevated (lambda B = 0.027 +/- 0.004; lambda C = 0.019 +/- 0.001). For in vivo studies, [14C]-3-O-MG with or without insulin was injected into rats 10-40 min prior to removing soleus muscles at 12 h postbacterial or postsaline injection. Transport was measured as the ratio of [14C]-3-O-MGintracell/[14C]-3-O-MGextracell. Basal ratios were not different and muscles from both control and bacteremic rats responded comparably to insulin with increased [14C]-3-O-MG transport during the initial 30 min. At 35-40 min postinsulin injection there was a further stimulation of [14C]-3-O-MG transport in control but not in 12-h bacteremic rat muscles. The changes in [14C]-3-O-MG transport observed in vitro and in vivo after 12 h of bacteremia may be due to circulating mediators and/or changes in membrane function.
Sympathetic alterations after midline medullary raphe lesions
Authors: McCall R. B. , Harris L. T.
Published: December 2017

The present study was designed to determine the functional importance of the midline medullary raphe nuclei in the autonomic regulation of the cardiovascular system in the anesthetized cat. Baroreceptor and somatosympathetic reflexes as well as the effects of electrical stimulation of vagal afferents and pressor and depressor sites in the hypothalamus and spinal trigeminal tract were determined before and after midline medullary lesions that extended from 2 to 7 mm rostral to the obex. Midline medullary lesions failed to affect baroreceptor reflexes as judged by the lack of effect on the sympathoinhibition associated with the pressor response to phenylephrine and the degree of slow-wave locking of sympathetic activity to the cardiac cycle. However, the lesion did significantly increase spontaneous sympathetic activity recorded from the inferior cardiac nerve. Blood pressure and heart rate were not altered by midline lesions. In addition, the computer-summed sympathoexcitatory response to electrical stimulation of somatic afferents in the sciatic nerve and the sympathoinhibitory response to stimulation of vagal afferent fibers were not affected by midline lesions. In contrast, the decrease in blood pressure and inhibition of sympathetic nerve activity elicited by electrical stimulation of the spinal trigeminal tract were completely abolished by the lesion. Depressor responses evoked from the anteroventral third ventricle region of the hypothalamus but not pressor responses elicited from the posterior hypothalamus were eliminated following midline medullary lesions. Finally, the sympathoinhibitory actions of the serotonin antagonist methysergide were blocked by medullary raphe lesions. These data indicate that neural elements in the medial medullary area function to provide a tonic inhibition of sympathetic nerve activity that is of nonbaroreceptor origin. Depressor responses evoked from the anterior hypothalamus and the spinal trigeminal tract also are mediated through this area of the medulla. Finally, the data support our contention that medullary serotonergic neurons have a sympathoexcitatory function.
Body composition, food intake, and brown fat thermogenesis in pregnant Djungarian hamsters
Authors: Schneider J. E. , Wade G. N.
Published: December 2017

Strategies for balancing energy storage and expenditure during pregnancy were examined in the Djungarian hamster. In expt 1, pregnant hamsters lost nearly 50% of their body lipid stores, even though they showed significant increases in body weight and food intake during the latter half of pregnancy. The increase in body weight was accounted for by the growth of the uteri, fetuses, and placentas. The water and fat-free dry contents of the maternal carcasses did not differ from those of the unmated controls. In expt 2, brown fat cytochrome-c oxidase activity (mitochondrial content) was significantly lower in the late- but not early-pregnant females relative to the nonpregnant controls. Specific GDP-binding levels did not differ significantly among these groups. Thus an overall decrease in total thermogenic activity in brown fat would be expected during late pregnancy. The loss of carcass lipid, despite decreased brown fat thermogenesis and increased food intake, suggests that substantial increases in energy expenditure occur in pregnant females that are not related to heat production in brown fat. The present results are not consistent with traditional models of energy balance during pregnancy. Some of the inconsistencies may be related to differences between hoarding and nonhoarding families of rodents, whereas others may be due to the fact that the traditional model is based on a possibly exceptional species, the laboratory rat.
Further evidence for hepatic control of salt intake in rats
Authors: Tordoff M. G. , Schulkin J. , Friedman M. I.
Published: December 2017

We examined the contributions of oral and hepatic factors to the control of salt intake in rats made "salt hungry" by combined dietary sodium restriction and furosemide treatment. A 7.5-ml preload of 0.5 M NaCl, which was either voluntarily ingested or slowly infused (7.5 ml/90 min) into the hepatic portal vein, decreased subsequent 0.5 M NaCl intake by approximately 7.5 ml in both cases. Hepatic portal infusions were probably acting in the liver because slow jugular infusions (7.5 ml/90 min) did not influence salt drinking, although rapid (7.5 ml/5 min) infusions by both routes reduced salt intake. If salt was ingested but drained through a gastric cannula, rats showed little sign of reducing salt in a 2-h test. These results suggest that the quantity of salt ingested by salt-hungry rats is regulated by a postabsorptive mechanism that is probably located in the liver.
Roles of gill and red cell carbonic anhydrase in elasmobranch HCO3- and CO2 excretion
Authors: Swenson E. R. , Maren T. H.
Published: December 2017

We studied the roles of gill and erythrocyte carbonic anhydrase in normal CO2 transfer (metabolic CO2 elimination) and in HCO3- excretion during metabolic alkalosis in the resting and swimming dogfish shark, Squalus acanthias. Gill carbonic anhydrase was selectively inhibited (greater than 98.5%) by 1 mg/kg benzolamide, which caused no physiologically significant red cell carbonic anhydrase inhibition (approximately 40%). Enzyme in both tissues was inhibited by 30 mg/kg methazolamide (greater than 99%). Both drugs caused equivalent reductions in HCO3- excretion following an infusion of 9 mmol/kg NaHCO3 as measured by the rate of fall in plasma HCO3- and by transfer into seawater. Methazolamide (red cell and gill carbonic anhydrase inhibition) caused a respiratory acidosis in fish with normal acid-base status, whereas benzolamide (gill carbonic anhydrase inhibition) did not. The only effect observed with benzolamide in these fish was a small elevation in plasma HCO3-. These findings, taken together, suggest that red cell carbonic anhydrase is required for normal metabolic CO2 elimination by the gill. Although carbonic anhydrase is located in the respiratory epithelium, it appears to have no quantitative role in transfer of metabolic CO2 to the environment, a pattern similar to all terrestrial vertebrates. However, carbonic anhydrase in the gill is crucial to this organ's function in acid-base regulation, both in the excretion of H+ or HCO3- generated in normal metabolism and in various acid-base disturbances.
Cardiovascular and fluid responses to atrial natriuretic factor in sheep fetus
Authors: Brace R. A. , Cheung C. Y.
Published: December 2017

Presently little is known about the effects of atrial natriuretic factor (ANF) in the fetus. In this study we explored the effects of ANF on vascular pressures and fluid dynamics in the chronically catheterized sheep fetuses averaging 133 days gestation (term = 145-150 days). Under resting conditions plasma ANF concentration was positively correlated with fetal heart rate (P less than 0.001) and was not correlated with arterial pressure, venous pressure, or plasma osmolality. The weight-normalized fetal urine flow rate correlated positively with ANF concentration (P less than 0.01). After a bolus injection of 8 micrograms/kg of synthetic human ANF into the inferior vena cava, fetal arterial pressure decreased by 2 mmHg and remained at this level for 60 min, venous pressure was unchanged, and heart rate increased transiently by 15 beats/min. Urine flow rate increased to 250% of control 5 min after the injection and returned to control at 20 min even though ANF was four times control levels. Fetal blood volume decreased significantly by 5% within 10 min and remained low for 60 min. This decrease in blood volume was greater than the increase in urine flow. A kinetic analysis revealed that ANF disappearance from the plasma could not be adequately characterized with a single rate constant due to exchange between plasma and interstitial fluid.(ABSTRACT TRUNCATED AT 250 WORDS)
Differential effects of spinal transection on sympathetic nerve activities in rats
Authors: Taylor R. F. , Schramm L. P.
Published: December 2017

We measured renal, splenogastric, and lumbar multiunit sympathetic activities in chloralose-anesthetized, paralyzed, and artificially respired Sprague-Dawley rats. Acute spinal transection reduced arterial pressure and lumbar sympathetic activity. However, renal and splenogastric activities were doubled after transection. We conclude that spinal systems exist in the rat that are capable of maintaining renal and splenogastric, but not lumbar, sympathetic activities after spinal transection. Cross-correlation and power spectral analysis of simultaneously recorded sympathetic activities indicated that renal and splenogastric activities often, but not always, shared periodicities near the respiratory rate. These shared periodicities were responsible for high correlations between renal and splenogastric activities. After spinal transection, the shared periodicities usually disappeared, and correlations were reduced. Renal and lumbar activities were rarely strongly correlated, and they rarely shared major periodicities. We conclude that brain stem systems often provide synchronization of abdominal sympathetic activities. However, these activities can be independently generated in both intact and spinally transected rats.
Pancreatic glucagon and cholecystokinin synergistically inhibit sham feeding in rats
Authors: Le Sauter J. , Geary N.
Published: December 2017

Pancreatic glucagon (PG) elicits satiety in normally feeding rats but fails to inhibit sham feeding in rats with open gastric cannulas. This suggests that a gastric or postgastric food stimulus is necessary for PG's satiating action. To determine whether bombesin or cholecystokinin might provide such a stimulus, sham-feeding rats received simultaneous intraperitoneal injections of 100-800 micrograms/kg of PG and doses of bombesin or cholecystokinin (CCK) that were near the threshold for inhibition of sham feeding. PG and 0.15-to 0.30-micrograms/kg CCK combinations inhibited sham feeding potently (37.6 +/- 7.0 and 62.0 +/- 9.4%, respectively). In contrast, PG and 0.25- to 0.50-microgram/kg bombesin combinations did not significantly affect sham feeding. Behavioral observations indicated that the inhibition of sham feeding by PG plus CCK did not disrupt the normal postprandial satiety sequence of behavior, PG, 400 micrograms/kg, plus 0.15 micrograms/kg of CCK did not inhibit sham drinking in 18-h water-deprived rats. PG, 400 micrograms/kg, plus 0.30 microgram/kg of CCK did inhibit sham drinking, although the effect (34.6 +/- 6.6%) was significantly less than the effect on sham feeding (75.5 +/- 9.7%) in the same rats. These data indicate that CCK is a sufficient food stimulus to permit PG to inhibit sham feeding. Furthermore, this inhibitory effect appears to result from a functional synergism of PG and CCK.
Transplacental clearance and blood flows of bovine gravid uterus at several stages of gestation
Authors: Reynolds L. P. , Ferrell C. L.
Published: December 2017

Rates of uterine and umbilical blood flows and transplacental clearance of deuterium oxide (D2O) were determined for cows on 137 +/- 1.0 (SE, n = 9), 180 +/- 0.5 (n = 8), 226 +/- 0.4 (n = 9), and 250 +/- 1.8 (n = 5) days of gestation. From days 137 to 250, rates increased 4.5-fold for uterine blood flow, 21-fold for umbilical blood flow, and 14-fold for clearance of D2O. Changes in rates of umbilical blood flow and D2O clearance paralleled increased rates of fetal growth and metabolism, which have previously been reported to occur during the last half of gestation. The regressions of D2O clearance on uterine and umbilical blood flows were significant (P less than 0.01) and explained 94-99% of the variation in placental clearance of D2O. Because the rate of D2O clearance was always less than that of uterine and umbilical blood flows, and because a relatively simple statistical model explained most of the variation in clearance, it was suggested that a concurrent or countercurrent arrangement of maternal and fetal placental microvasculatures is not adequate to explain clearance of highly diffusable substances across the bovine placenta. In addition, a placental exchange diagram of the data showed the existence of severe uneven distribution of maternal and fetal placental blood flows and/or significant shunting of maternal and fetal placental flows away from areas of exchange. Taken together, these data indicate that the placenta of the cow, like those of the sheep and goat, represents a relatively inefficient system of transplacental exchange.
Cardiac arrhythmias during arousal from hibernation in three species of rodents
Authors: Eagles D. A. , Jacques L. B. , Taboada J. , Wagner C. W. , Diakun T. A.
Published: December 2017

Cardiac activity was monitored during arousal from deep hibernation in three species of hibernators (Citellus tridecemlineatus, Marmota monax, and Mesocricetus auratus). Individuals of each species showed marked arrhythmias, and these were confined to a body temperature range of between 11 and 20 degrees C, measured orally or rectally. The arrhythmias consisted of intermittent periods of asystole and bradycardia and were sometimes marked by the appearance of premature ventricular contractions and elevated or depressed S-T segments. Surgical manipulation of euthermic M. monax, under pentobarbital sodium anesthesia, indicated that none of the arrhythmias observed was inducible by injections of cold saline into the vena cava.
Nonshivering thermogenesis and the thermogenic capacity of brown fat in fasted and/or refed mice
Authors: Trayhurn P. , Jennings G.
Published: December 2017

The effects of fasting and refeeding on nonshivering thermogenesis and the properties of brown adipose tissue have been investigated in mice. Fasting for 48 h led to a substantial reduction in the capacity for nonshivering thermogenesis, and there was no recovery of thermogenic capacity during the first 5 days of refeeding. A period of 10-15 days of refeeding was required for full restoration of thermogenic capacity. The mice were hyperphagic during the first 6 days of refeeding, but body weight was recovered after 24 h. The amount of interscapular brown adipose tissue decreased substantially on fasting, but it recovered 24 h after the initiation of refeeding. Cytochrome oxidase activity, the level of mitochondrial GDP binding, and the specific mitochondrial concentration of uncoupling protein in brown adipose tissue were each reduced by fasting. Although both GDP binding and the specific concentration of uncoupling protein rapidly returned to normal on refeeding, the activity of cytochrome oxidase was not normalized until 10 days after the end of the fast. These results indicate that a prolonged period of refeeding is required for the recovery in the capacity for nonshivering thermogenesis following a fast, a similar time course being evident for the recovery of cytochrome oxidase activity in brown adipose tissue. It is suggested that the fasting-induced reduction in the capacity for nonshivering thermogenesis is linked primarily to a loss of mitochondria from brown adipose tissue and that the normalization of thermogenic capacity is dependent on the restoration of mitochondrial mass.
Role of atrial peptide system in renal and endocrine adaptation to hypotensive hemorrhage
Authors: Edwards B. S. , Zimmerman R. S. , Schwab T. R. , Heublein D. M. , Burnett J. C.
Published: December 2017

Hypotensive hemorrhage (HH) is characterized by intravascular volume depletion, avid renal sodium retention, and activation of the renin-angiotensin-aldosterone system (RAAS). The current studies were designed to investigate whether intravascular volume depletion would modulate circulating atrial natriuretic factor (ANF) and, further, to examine what contribution, if any, a decrease in ANF would have in mediating the antinatriuresis and RAAS stimulation associated with HH. Two groups of anesthetized dogs underwent controlled arterial hemorrhage to reduce mean arterial pressure by 15-20 mmHg. Data were collected before and immediately after HH. One group (n = 6) underwent hemorrhage alone, whereas a second group (n = 5) underwent HH with simultaneous administration of alpha-human ANF (2.5 ng.kg-1.min-1), a dose calculated to prevent a reduction in ANF. In the untreated group, circulating ANF was significantly reduced after hemorrhage (79.4 +/- 7.4 to 57.2 +/- 3.4 pg/ml, P less than 0.05), whereas in the treated group ANF increased significantly (73.5 +/- 12.2 to 147.4 +/- 17.2 pg/ml, P less than 0.05). Despite differences in circulating ANF, both groups had similar reductions in urinary sodium excretion and renal blood flow, and similar increases in plasma renin activity. These studies demonstrate that circulating ANF is significantly reduced in HH; however, the mechanism of antinatriuresis and activation of the RAAS is independent of the reduction in circulating ANF.
Effect of clonidine on the thermic effect of feeding in humans
Authors: Schwartz R. S. , Jaeger L. F. , Veith R. C.
Published: December 2017

Previous studies in humans attempting to assess the role of the sympathetic nervous system (SNS) in the thermic effect of feeding (TEF) have investigated the effect of oral or intravenous propranolol on TEF. This approach is potentially limited, however, because of the direct effects of propranolol on catecholamine and thyroid metabolism. In the present study we chose instead to evaluate the effect of clonidine, a centrally acting alpha 2-adrenergic receptor agonist that inhibits SNS outflow, on TEF and SNS activity as reflected by both plasma catecholamines and norepinephrine (NE) kinetics. The TEF and SNS response to an 800-kcal high-carbohydrate liquid meal (85% carbohydrate, 15% protein) was studied in eight healthy male subjects (27 +/- 6 yr) on two separate occasions with the subjects wearing either a clonidine or placebo skin patch for 48 h prior to study. Clonidine significantly suppressed base-line plasma NE concentration (-46%, P less than 0.01) and NE appearance rate (-47%, P = 0.01) compared with placebo, whereas there was no significant effect on epinephrine concentrations, NE clearance rate, or base-line energy expenditure. The expected increments in plasma NE and NE appearance after a meal were also reduced by 54% (P less than 0.05) and 70% (P less than 0.01) of placebo values, respectively, after clonidine. Associated with this reduced SNS response to the meal was a blunting of the expected TEF by 33% (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Hemodynamic and renal effects of low-dose infusions of atrial peptide in awake dogs
Authors: Bie P. , Wang B. C. , Leadley R. J. , Goetz K. L.
Published: December 2017

The effects of alpha-human atrial natriuretic peptide (alpha-hANP) on cardiovascular and renal function in conscious dogs were evaluated in two experimental protocols. In one protocol, alpha-hANP was infused intravenously at increasing rates of 50, 100, and 200 ng.min-1.kg-1 (stepup infusion) during successive 20-min periods. The greatest responses occurred during the final 20-min period of the stepup infusion when the plasma concentration of immunoreactive atrial natriuretic peptide (irANP) was increased by 44-fold over preinfusion values; pressures in the aorta and both atria were decreased at this time, whereas glomerular filtration rate, urine flow, and sodium excretion were increased. In a second protocol, alpha-hANP was infused for 1 h at constant rates of either 12.5, 25, or 50 ng.min-1.kg-1; these constant infusions increased plasma irANP by 3-, 7-, and 12-fold, respectively. Each infusion rate decreased left and right atrial pressures and increased urine flow and sodium excretion. The two lowest infusion rates elevated plasma irANP to levels that would be expected to occur only during unusual physiological, or perhaps pathophysiological, conditions. The two highest infusion rates decreased plasma renin activity. Nevertheless, the accompanying maximal increases in sodium excretion were modest (41-72%). These data imply that small changes in circulating atrial peptides that presumably occur under normal physiological conditions would not have a dominant effect on the regulation of sodium excretion; the peptides may, however, play a modulatory role on sodium excretion under these conditions. It remains to be determined whether the ability of atrial peptides to lower cardiac filling pressures is of physiological significance.
Fasting in king penguin. II. Hormonal and metabolic changes during molt
Authors: Cherel Y. , Leloup J. , Le Maho Y.
Published: December 2017

The coincidence of fast and molt in penguins is an interesting condition for investigating the factors controlling protein metabolism; avian molt involves the utilization of amino acids for synthesis of new feathers, whereas a major factor for adaptation to fasting in birds, as for mammals, is reduction in net protein breakdown. Hormonal and biochemical changes were studied in seven molting king penguins. Their initial body mass was 18 kg. It decreased by 58% over 41 days of fasting. Feather synthesis lasted for the first 3 wk of the fast. It was marked by plasma concentrations of alanine and uric acid 1.5 to 2 times those for nonmolting fast, and plasma thyroxine was increased five times. At the completion of molt all these values returned to levels comparable to those in nonmolting fast. As indicated by high plasma levels of beta-hydroxybutyrate, lipid stores were mobilized readily during molting. The fast ended by a phase of enhancement in protein utilization that was characterized by a fivefold increase in uricacidemia and coincided with an 80% drop in plasma beta-hydroxybutyrate and a fourfold increase in plasma corticosterone. These data suggest that two different hormones control the two successive periods marked by an increased protein mobilization during the molting fast, i.e., thyroxine during feather growth and corticosterone toward the end of the fast, when the molt is completed.
Renin, ACTH, and aldosterone during acute hypercapnia and hypoxia in conscious rats
Authors: Raff H. , Roarty T. P.
Published: December 2017

The control of aldosterone secretion may be altered during acute changes in arterial blood gases. We studied the blood gas, plasma electrolyte, renin (PRA), adrenocorticotropic hormone (ACTH), and aldosterone (ALDO) responses to acute hypercapnia (4 and 8% CO2), acute hypocapnic hypoxia (10% O2), acute severe normocapnic hypoxia (7% O2-4% CO2), and acute hypercapnic hypoxia (7% O2-8% CO2) in conscious, cannulated Long-Evans rats. Normoxia resulted in normal levels of PRA (6.9 +/- 2.0 ng.ml-1.h-1), ACTH (96 +/- 32 pg/ml), and ALDO (10 +/- 3 ng/dl). Hypercapnia had no effect on PRA but did lead to an increase in ACTH (to 298 +/- 69 pg/ml) and ALDO (to 33 +/- 7 ng/dl) during 8% CO2 exposure. Normocapnic hypoxia resulted in a significant increase in ACTH (to 196 +/- 14 pg/ml) and ALDO (to 30 +/- 3 ng/dl). Hypercapnic hypoxia resulted in the greatest increases in PRA (to 30 +/- 2 ng.ml-1.h-1), ACTH (to 397 +/- 114 pg/ml), and ALDO (to 41 +/- 5 ng/dl). We conclude that in conscious rats 1) hypercapnia (less than 80 Torr) had no significant effect on PRA, 2) isocapnic, severe hypoxia (Po2 approximately 34 Torr) increased ACTH, and 3) the combination of hypercapnia and hypoxia was a very potent stimulus to PRA, ACTH, and ALDO. The ALDO responses to increases in endogenous ACTH and angiotensin II appear to be normal in conscious rats during acute hypoxia and/or hypercapnia.
Effect of feeding on renin-angiotensin-aldosterone system of the horse
Authors: Clarke L. L. , Ganjam V. K. , Fichtenbaum B. , Hatfield D. , Garner H. E.
Published: December 2017

The effect of feeding frequency and associated meal size on the renin-angiotensin-aldosterone system (RAAS) in seven horses was examined. A daily maintenance ration of hay-grain pellets was provided either as a multiple feeding regimen (MF), in which the ration was divided into six equal portions fed at 4-h intervals, or as a single large feeding (SF) given from 9 A.M. until 11 A.M. Plasma renin activity (PRA), aldosterone (PAC), cortisol (PCC), protein concentration (TP), packed cell volume (PCV), and serum sodium and potassium were measured serially. To prevent significant RAAS stimulation due to strenuous exercise or by assuming orthostatism after a period of recumbency, the horses were trained to stand in 1 X 4-m tie stalls during the experiments. Changes in Na intake were prevented by disallowing nonration salt sources. A 12:12 light-dark interval was maintained. During the MF experiment, only serum Na changed diurnally, with concentrations lowest in early morning and highest before midday. In contrast, during the SF experiment, PRA was increased at 0.5, 1.0, and 3.0 h and PAC was increased at 3.0, 5.0, and 7.0 h after onset of feeding (P less than 0.005). Increased TP and PCV suggested transient hypovolemia was responsible for renin release. Significant increases in Na and decreases in K occurred while eating; however, K increased postprandially to be coincident with aldosterone. Except for a transient increase during feeding in SF, PCC demonstrated a similar circadian rhythm in both experiments. It was concluded that 1) episodic feeding (SF) causes significant diurnal variation of the RAAS in the horse, and 2) spontaneous circadian activity of the RAAS cannot be demonstrated in this species during a steady-state feeding regimen (MF).
Placental oxygen transport in sheep with different hemoglobin types
Authors: Wilkening R. B. , Molina R. D. , Meschia G.
Published: December 2017

To study the effect of genetic differences in the maternal oxyhemoglobin dissociation curve on fetal O2 supply, we compared eight pregnant ewes homozygous for high O2 affinity hemoglobin (A) with eight pregnant ewes homozygous for low O2 affinity hemoglobin (B). Each ewe carried a single fetus. Fetal weights were not significantly different (A, 3,000 +/- 170 g; B, 3,070 +/- 270 g). The A ewes had significantly higher arterial O2 saturation (95 vs. 89.4%), uterine blood flow per kilogram of fetus (464 vs. 374 ml/min), uterine venous O2 saturation (78.1 vs. 67.5%), and placental-to-fetal weight ratio (0.107 vs. 0.085). Uterine venous PO2 was significantly less in A ewes (41.7 vs. 47.6 Torr), but umbilical venous and arterial PO2 and fetal O2 uptake were virtually equal in the two groups. We conclude that the difference in O2 affinity between A and B hemoglobins is fully compensated for by differences in arterial O2 saturation, in the rate of perfusion of the pregnant uterus, and in the degree of PO2 equilibration between the uterine and umbilical circulations so that the single fetuses of A and B hemoglobin carriers have equal levels of oxygenation.
Effect of selective hepatic vagotomy on plasma FFA levels in resting and exercising rats
Authors: Lavoie J. M. , Lord M. , Paulin A.
Published: December 2017

Metabolic effects of a selective hepatic vagotomy (HV) were investigated in nonfasted (N) and 24-h fasted (F) rats, at rest and immediately after a 50-min exercise period (26 m/min, 0% grade). In nonfasted rats, no significant differences between HV and sham-operated (SHM) groups were found in blood substrates [free fatty acids (FFA) or glucose], insulin, and muscle glycogen levels, either at rest or after exercise. In F rats, liver glycogen was almost completely depleted at rest. This depletion was associated with a significantly (P less than 0.05) lower plasma FFA concentration at rest in HV compared with SHM rats (mean +/- SE, 0.57 +/- 0.04 vs. 0.83 +/- 0.1 mmol/l). No differences in FFA levels were observed between the same two groups after the exercise period. Exercise, however, resulted in a 2.5 times greater glycogen breakdown in the soleus muscle of HV compared with SHM rats. Hepatic vagotomy in the F condition was also associated with lower resting and exercising insulin concentrations. It is concluded that HV, when followed by a 24-h fast, may influence metabolic substrate regulation at rest and to a certain extent during exercise. These data support the concept of the existence of hepatic glucoreceptors responsive to a decrease in liver glycogen content.
Effects of exercise, detraining, starvation, and refeeding on lipogenic capacity of Osborne-Mendel rat
Authors: Lowney P. , Lee V. M. , Hansen R. J. , Stern J. S.
Published: December 2017

Both starvation and refeeding and exercise and detraining are procedures that result in lowered lipid stores followed by their refilling. Rats subjected to these procedures were evaluated for their ability to produce hepatic biosynthetic reducing equivalents. Five-week-old male Osborne-Mendel rats were exercised on a motorized treadmill for 6 wk (final speed 27 m/min, 60 min/day, 6 day/wk) or kept sedentary. Exercised and sedentary rats were starved for 48 h or fed ad libitum. After treatments, some rats in each group were killed. Remaining exercised animals were detrained or detrained and refed. Remaining sedentary rats were refed. Activities of hepatic glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and malic enzyme were evaluated. Plasma glucose, triglyceride, insulin, liver triglyceride, and body composition were determined. Results indicate that changes in lipids stores associated with starvation and refeeding and exercise and detraining are not associated with similar changes in enzyme activity. Starvation resulted in lowered plasma glucose, triglyceride, and insulin. Starvation and all exercise treatments resulted in lowered carcass fat. Exercised rats who were starved for 48 h and then detrained and refed for 72 h had the greatest liver weights and percent liver triglycerides. This was not associated with similar changes in enzyme activity. Increased liver lipid and decreased carcass fat may indicate a redistribution of lipid stores in these animals.
Role of central nervous system in renal nerve activity during prolonged hemorrhagic shock in dogs
Authors: Koyama S. , Aibiki M. , Kanai K. , Fujita T. , Miyakawa K.
Published: December 2017

The contribution of sympathetic efferent outflow through the central nervous system (CNS) during prolonged hemorrhagic hypotension of 50 mmHg was examined in anesthetized dogs. Mean blood pressure, heart rate, and renal nerve activity (RNA) were recorded simultaneously after arterial bleeding for 2 h. In animals with an intact neuraxis, hemorrhage to approximately 50 mmHg increased RNA to 180 +/- 12% of control level at 5 min after bleeding, but returned close to control level after 10 min. A secondary increase in RNA followed, with its maximum (280 +/- 12%) at 30 min after bleeding. Then RNA gradually decreased so that at end of experiment (120 min after bleeding) RNA was 10 +/- 9% of control. The initial increase in RNA was abolished by denervation of afferents from carotid sinus and cardiopulmonary regions, but secondary RNA response during hemorrhagic hypotension was similar to that in the intact group and occurred when the head region of animals was exposed to a hypotension of 50 mmHg, and perfusion to peripheral regions of the body was maintained near normal range. However, when perfusion to the head was maintained at a steady level and peripheral regions were exposed to hypotension of 50 mmHg, RNA response did not change significantly. These results provide evidence that prolonged hemorrhagic hypotension, which induces severe brain ischemia, causes biphasic sympathetic outflow via the CNS. The increase in sympathetic activity was followed by decrease with time. This decrease may contribute to the pathogenesis of vasomotor paralysis occurring at the irreversible stage of hemorrhagic shock.
Interrelationships among atrial peptides, renin, and blood volume in pregnant rats
Authors: Nadel A. S. , Ballermann B. J. , Anderson S. , Brenner B. M.
Published: December 2017

To determine how changes in intravascular volume are sensed by atrial and renal volume receptors during pregnancy and the puerperium, circulating atrial natriuretic peptide (ANP) levels and plasma renin activity (PRA) were measured in conscious chronically catheterized rats on days 9-10, 15-16, 19-20, and 22 of pregnancy, on the first postpartum day, and in nonpregnant controls. Blood volume measured in a separate group of anesthetized rats increased progressively during pregnancy, and circulating ANP levels tended to decline, although not significantly below the nonpregnant value of 132 +/- 9 pg/ml (mean +/- SE). PRA remained similar to the nonpregnant value of 5.5 +/- 0.6 ng angiotensin I.ml-1.h-1 until day 22 of pregnancy, when it rose to 14.1 +/- 1.8 ng angiotensin I.ml-1.h-1 (P less than 0.001 vs. nonpregnant). In pregnant rats, PRA was suppressed after uninephrectomy and chronic administration of deoxycorticosterone and saline, demonstrating the ability of this hormonal system to respond appropriately to further increments in volume induced during pregnancy. On the first postpartum day plasma ANP rose to 268 +/- 26 pg/ml, and PRA fell to 3.6 +/- 0.4 ng angiotensin I.ml-1.h-1 (P less than 0.005 and P less than 0.05 vs. nonpregnant values, respectively). Thus it appears that the increased blood volume in normal pregnancy is not sensed by renal or atrial volume sensors, presumably because it is accommodated by an enlarged maternal vascular compartment. In the puerperium, however, due to the decreased size of the maternal vascular compartment, atrial and renal volume sensors recognize the intravascular volume as expanded.(ABSTRACT TRUNCATED AT 250 WORDS)
In vitro secretion of atrial natriuretic factor: receptor-mediated release of prohormone
Authors: Veress A. T. , Milojevic S. , Yip C. , Flynn T. G. , Sonnenberg H.
Published: December 2017

Secretion of atrial natriuretic factor (ANF) in vivo is thought to be mediated by atrial distension. We have shown previously that nonstretched atria can release natriuretic activity in vitro when stimulated by certain agonists. In the present study atrial appendages from freshly excised rat hearts were incubated at 37 degrees C for up to 1 h in the presence of either vasopressin (5 X 10(-9) mol/l) or angiotensin II (2.5 X 10(-7) mol/l). Aliquots of postincubation media were injected intravenously into anesthetized bioassay rats to determine natriuretic activity. Control media, in which atria had been incubated without agonist, did not cause natriuresis. Significant increases in sodium excretion were seen after injection of media in which atria had been incubated in the presence of either agonist. Injection of medium with the same agonist concentration did not result in comparable natriuresis. Radioimmunoassay (RIA) indicated a high concentration of immunoactive ANF in the natriuretic media. However, radioreceptor assay (RRA) of the same media gave apparent ANF concentrations that were lower by about three orders of magnitude. Because the antibody used in the RIA cross reacts with ANF prohormone, whereas the RRA is sensitive only to the active form, we concluded that agonist-induced, stretch-independent release of ANF is in the form of prohormone, which can be converted to the active hormone in the circulation of the bioassay animal. The conclusion of prohormone release was confirmed by liquid chromatography. The data thus suggest that receptor-mediated as well as stretch-induced ANF secretion may be important in regulating the activity of the ANF system.
Aldosterone and renin inhibition by physiological levels of atrial natriuretic factor
Authors: Brands M. W. , Freeman R. H.
Published: December 2017

This study was designed to examine, in the rat, the inhibition of renin release and aldosterone secretion by physiological plasma levels of atrial natriuretic factor (ANF). Intravascular volume expansion over 30 min with donor blood equal to 3% body weight increased plasma ANF concentration from a base line of 216 +/- 28 to 1,590 +/- 240 pg/ml (P less than 0.001) in sodium-replete rats. Basal plasma ANF levels were decreased to 125 +/- 9 pg/ml in animals fed a low-sodium diet, and the infusion of synthetic ANF into separate groups of these rats at doses of 15 or 45 ng.kg-1.min-1 elevated plasma ANF to 346 +/- 38 and 720 +/- 96 pg/ml, respectively (P less than 0.001 for both values). Infusion of ANF at 15 ng.kg-1.min-1 resulted in a significantly lower plasma renin activity [30 +/- 3 vs. 69 +/- 5 ng angiotensin I (ANG I).ml-1.h-1, P less than 0.05], but there was no difference in aldosterone secretion between control and infused groups (7.00 +/- 0.49 vs. 7.29 +/- 0.95 ng/min, P greater than 0.05). However, the higher ANF dose of 45 ng.kg-1.min-1 did reduce aldosterone secretion approximately 40% to 4.18 +/- 0.36 ng/min (P less than 0.001) with no further suppression in plasma renin activity. In sodium-replete rats, infusion of ANF at 45 ng.kg-1.min-1 resulted in lower plasma renin activity compared with the control noninfused group (14 +/- 4 vs. 22 +/- 2 ng ANG I.ml-1.h-1, P less than 0.05), but aldosterone secretion was not different (P greater than 0.05) between the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Baroreflex unimpaired by operant avoidance or classical aversive conditioning in dogs
Authors: Shammas R. A. , Denison A. L. , Pfennig T. W. , Hemker D. P. , Stephenson R. B.
Published: December 2017

Previous studies showed that baroreflex control of heart rate is impaired during operant shock avoidance conditioning and classical aversive conditioning. However, the effects of such "emotionally stressful" paradigms on the ability of the baroreflex to control arterial pressure have not been directly assessed. We prepared the carotid sinus regions of dogs for reversible isolation from the systemic circulation, and we derived complete stimulus-response relations for the effects of carotid sinus pressure on both heart rate and arterial pressure. For any given carotid sinus pressure, arterial pressure and heart rate were higher during operant shock-avoidance conditioning and during classical aversive conditioning than in a neutral environment, which indicates an upward resetting of the baroreflex. However, threshold and saturation carotid sinus pressures were unaffected by operant conditioning or classical conditioning, which indicates that the baroreceptors themselves were not reset. The ranges over which the carotid baroreflex could vary arterial pressure and heart rate were significantly increased during both operant conditioning and classical conditioning. Baroreflex gain was unchanged during operant conditioning and was significantly increased during classical conditioning. We conclude that the baroreflex is not impaired during operant shock-avoidance conditioning or classical aversive conditioning in dogs. However, the baroreflex is reset and regulates blood pressure at an elevated level.
Hypotension produced by vagal block in primates
Authors: Cornish K. G. , Barazanji M. , Ryberg A. , Gilmore J. P.
Published: December 2017

In many species, the vagus has been reported to contain afferents that inhibit sympathetic tone. Vagal block (VB) increases blood pressure in both the intact and sinoaortic-denervated (SAD) dog. In the present study, VB was produced in intact and SAD monkeys by infiltrating the vagi with a local anesthetic. This was done in conjunction with blood volume expansion or head-out water immersion. The cardiovascular parameters monitored were heart rate (HR), blood pressure (BP), and left atrial pressure (LAP). VB decreased BP (-13 +/- 2.8 mmHg) in the control group and the SAD animals (-47 +/- 6.7 mmHg) without changing HR. Volume expansion decreased BP in the SAD animals (-6 +/- 3.4) but not in the intact monkeys (1.8 +/- 2.27), whereas HR did not change. Volume expansion after VB increased BP in both the SAD and the intact animals while producing a decrease in HR. Volume expansion caused LAP to increase in all groups (SAD 13.9 +/- 6.3; control VB 11.6 +/- 1.8, control 9.3 +/- 0.89, SAD VB 7.66 +/- 3.46). Immersion in the VB SAD animals increased BP to a greater extent than volume expansion. VB in the monkey must be removing input from peripheral receptors, which maintain sympathetic tone. Because immersion with VB increases BP more than volume expansion with VB, it is concluded that VB causes predominantly venous pooling. Because cardiopulmonary receptors generally inhibit sympathetic tone, it is concluded that those receptors responsible for the observed hypotension are located in the venous system, probably in the chest or the abdominal cavity.
Basis for apparent saturation kinetics of Na+ influx in freshwater hyperregulators
Authors: Kirschner L. B.
Published: December 2017

Uptake of Na+ by intact frogs has been reported to show saturation kinetics at low external concentrations (less than 2 mM); yet other evidence shows that the transport system is far from saturated in this concentration range. The saturation behavior was reproduced here in isolated frog skins that were then used as appropriate models for investigating the paradox. When the skin was bathed by 2 mM Na+ outside and open circuited, influx (JNain) was near maximum. If, under these conditions, the skin was short circuited, JNain increased threefold. Alternatively, if Cl- permeability was increased in the open-circuited skin, JNain doubled. Both perturbations uncouple JNain from the efflux of a cation (nominally H+), which normally maintains electrical neutrality under open-circuit conditions. This suggests that the apparent saturation of JNain is caused by limiting efflux of the counterion. In confirmation of this prediction, stimulation of proton efflux markedly increased JNain. Thus the apparent Michaelis-Menten kinetics observed in frogs, and probably in other freshwater animals as well, do not represent saturation of an element in Na+ transport, either the amiloride-sensitive apical channel or the basolateral Na+-K+-ATPase.
Cold-induced thermogenesis in younger and older Fischer 344 rats following exercise training
Authors: McDonald Roger B. , Horwitz Barbara A. , Stern Judith S.
Published: December 2017

Pages R908–R916: Roger B. McDonald, Barbara A. Horwitz, and Judith S. Stern. “Cold-induced thermogenesis in younger and older Fischer 344 rats following exercise training.” Page R912: the y-axis label of Fig. 4 should read: VO2 [ml/(min x kg body mass0.67)]. Page R913: substitute corrected Table 3:

(See PDF)
Cardiorenal endocrine dynamics during volume expansion in hypothyroid dogs
Authors: Zimmerman R. S. , Ryan J. , Edwards B. S. , Klee G. , Zimmerman D. , Scott N. , Burnett J. C.
Published: December 2017

To address the role of atrial natriuretic factor (ANF) in hypothyroidism in the control of cardiorenal-endocrine function during volume loading, the relationships between atrial pressure, ANF, the renin-angiotensin-aldosterone system, and renal hemodynamic and excretory function were examined during and after acute 10% body wt saline volume infusion in pentobarbital-anesthetized hypothyroid dogs (n = 8). Hormonal changes before and after thyroidectomy were also evaluated. Four to 6 wk after thyroidectomy, ANF decreased and arginine vasopressin (AVP) and plasma renin activity (PRA) increased. Acute saline volume expansion caused an increase in ANF and decreases in AVP and PRA. Atrial pressure increased throughout volume expansion. Despite the absence of an increase in glomerular filtration rate (GFR) during volume expansion, urinary sodium excretion increased due to a marked rise in fractional excretion of sodium. These studies demonstrate that in hypothyroidism 1) ANF is decreased; 2) despite the decrease in basal ANF, increases in atrial pressure can stimulate relase of ANF; 3) despite the absence of an increase in GFR during volume expansion, fractional excretion of sodium increases associated with an increase in ANF; and 4) a lack of an increase in GFR during volume expansion is not related to an inability to increase ANF.
Integrated metabolic control of food intake after 2-deoxy-D-glucose and nicotinic acid injection
Authors: Even P. , Coulaud H. , Nicolaidis S.
Published: December 2017

We measured the minute-to-minute respiratory quotient (RQ), total metabolic rate, and the intensity and energy cost of locomotor activity in unrestrained rats with a recently developed open-circuit metabolic device. These measures permitted calculation of the resting metabolic rate (designated metabolisme de fond or MF). Simultaneous monitoring of the meal patterns of the animals allowed correlations between MF and feeding behavior. The major hypotheses proposed to account for the onset of feeding were challenged by pharmacological inhibition of the utilization of glucose and/or lipids. When injected together, 2-deoxy-D-glucose, which blocks glucose utilization, and nicotinic acid, which blocks lipid utilization, had a synergistic effect on MF and on the feeding response. The RQ, which reflects the relative rate of glucose-to-lipid utilization, showed that neither the inhibition of utilization of glucose nor the inhibition of utilization of lipids could account for the magnitude of the feeding response. The signal that best accounted for these examples of experimentally induced feeding is ischymetric (power or rate of energy) in nature rather than solely glucostatic or solely lipostatic.