bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma level, urinary excretion, and metabolic production of cGMP during gestation in rats
Authors: Conrad K. P. , Vernier K. A.
Published: December 2017

We postulated that guanosine 3',5'-cyclic monophosphate (cGMP), a cellular mediator of vascular smooth muscle relaxation, might mediate maternal renal and cardiovascular hemodynamic adaptation to pregnancy. Because extracellular levels of cGMP most likely reflect intracellular production, we began our investigation of this hypothesis by measuring the plasma concentration, urinary excretion, and metabolic clearance rates of cGMP during pregnancy in rats. Plasma cGMP was significantly elevated during mid- and late pregnancy, whereas urinary excretion of cGMP was increased throughout pregnancy. The fractional excretion of cGMP by the kidneys was 0.90 +/- 0.15 in the nonpregnant condition. In contrast, plasma levels of adenosine 3',5'-cyclic monophosphate were unchanged during pregnancy, and its urinary excretion rose slightly, reaching significance only on gestational day 20. There was also a significant rise in urinary excretion of cGMP throughout pseudopregnancy. The metabolic clearance rate of cGMP measured in chronically instrumented rats before, during, and after pregnancy was not significantly altered during gestation. The elevated plasma level of cGMP during gestation in rats, in the face of an unchanged metabolic clearance, reflects augmented tissue(s) production of cGMP, although enhanced cellular efflux may contribute. Because cGMP is a second messenger for several vasodilatory hormones, our data are consistent with the hypothesis that vascular production of cGMP may increase during pregnancy and thereby contribute to maternal renal and cardiovascular vasodilation. (Most investigators have not observed increment of plasma atrial natriuretic peptide in rat gestation; therefore this hormone is an unlikely first messenger for the elevated extracellular levels of cGMP that we have observed. Finally, pseudopregnant rats also showed enhanced urinary excretion of cGMP, which suggests that the proliferative activity that accompanies fetoplacental maturation, as well as hormones elaborated by the fetoplacental unit, is not necessary for the rise in urinary excretion of cGMP observed during pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)
Release of atrial natriuretic factor during infusion of isoproterenol and angiotensin II
Authors: Christensen G. , Ilebekk A. , Kiil F.
Published: December 2017

Release of atrial natriuretic factor (ANF) is related to atrial pressure and heart rate and may be influenced by beta-adrenergic stimulation and angiotensin II. Experiments in five closed-chest dogs showed lower plasma immunoreactive (ir) ANF during intravenous (iv) isoproterenol (0.2-0.3 micrograms.kg-1.min-1) and higher plasma ir-ANF during iv angiotensin II (0.2-0.3 micrograms.kg-1.min-1) than during blood volume expansion measured at equal mean right atrial pressure (RAP) and heart rate. This indicated that the agents may affect ANF release differently, possibly through their effects on left atrial pressure (LAP). In five open-chest dogs with right atrial pacing at 216 +/- 1 beats/min, blood volume was expanded until mean RAP was 9 mmHg. Mean LAP rose to 16.8 +/- 2.0 mmHg, and plasma ir-ANF rose from 57 +/- 6 to 219 +/- 39 pg/ml. At a constant mean RAP of 9 mmHg, iv isoproterenol infusion reduced mean LAP to 12.6 +/- 1.4 mmHg and reduced plasma ir-ANF by 115 +/- 31 to 105 +/- 13 pg/ml. During iv angiotensin II infusion at a mean RAP of 9 mmHg, mean LAP rose to 23.2 +/- 2.2 mmHg and plasma ir-ANF averaged 281 +/- 77 pg/ml. The correlation between plasma ir-ANF and LAP (r = 0.83) indicates that the different effects of isoproterenol and angiotensin II on ANF release can be accounted for by the effects on LAP.
Heterogeneous renal responses to atrial natriuretic factor. I. Chronic caval dogs
Authors: Maher E. , Cernacek P. , Levy M.
Published: December 2017

Atrial natriuretic factor (ANF) (175 ng.kg-1.min-1) was administered to 14 normal, alert dogs and again after constriction of the thoracic vena cava. The average natriuresis observed in the dogs when they were normal was blunted by 55% when they developed ascites and were avidly retaining sodium. Of the 14 caval dogs, 7 showed a natriuretic response no different from the control phase while 7 showed no natriuresis at all in response to the ANF. Ten dogs were restudied when they entered a phase of sodium balance despite the persistence of ascites. All 10 dogs now responded to ANF, and 5 dogs previously not responding now showed a mean change of urinary sodium excretion rate (delta UnaV) of 204 mu eq/min. The two groups could not be differentiated in terms of plasma volume, systemic or renal hemodynamics, or plasma levels of renin and aldosterone. We conclude that there is reversible attenuation of the ANF natriuretic effect in 50% of chronic caval dogs, which disappears when they lose avidity for sodium retention.
Response to palatability after area postrema lesions: a result of learned aversions
Authors: Tomoyasu N. , Kenney N. J.
Published: December 2017

The role of palatability, novelty, and food aversion in determining changes of food choice after ablation of the area postrema and caudal-medial aspect of the nucleus of the solitary tract (AP/cmNTS) is examined through a series of studies utilizing 24-h, two-food choice tests. On test days, the food that the animal has ingested since the time of lesioning or sham surgery is presented along with a novel food that varies in palatability. The results indicate that postlesion diet history is the major determinant of food choice by lesioned rats. Lesioned rats consistently take less of their familiar postlesion food than diet-matched controls, suggesting that the lesioned rats have developed an aversion to that food. Over-ingestion of the novel food may occur, but this outcome is not reliable. No indication that the animals' response to food palatability is affected by AP/cmNTS ablation was found. Learned aversion to a food ingested after AP/cmNTS ablation may account not only for changes of food preference after the lesion but also may be involved in the hypophagia and weight loss resulting from the ablation.
Turtles and rats: a biochemical comparison of anoxia-tolerant and anoxia-sensitive brains
Authors: Suarez R. K. , Doll C. J. , Buie A. E. , West T. G. , Funk G. D. , Hochachka P. W.
Published: December 2017

When temperature differences are taken into account, turtle brains use glucose at one-sixth the rate reported in rat brains. Na+-K+-ATPase activities are 2- to 2.5-fold higher in rat than in turtle brains. Maximal activities of hexokinase and lactate dehydrogenase are similar, whereas citrate synthase activities are two- to threefold higher in rat than turtle brains at the respective biological temperatures. Voltage-dependent Ca2+ channel densities, when compared between the two species, showed no consistent pattern. These data, along with the threefold differences in density of voltage-dependent Na+ channels reported by Lutz et al., are consistent with the idea that lower rates of channel and pump-mediated Na+ and K+ fluxes result in lower rates of aerobic energy metabolism in turtle brains compared with rat brains.
Effects of simulated weightlessness on rat osteocalcin and bone calcium
Authors: Patterson-Buckendahl P. , Globus R. K. , Bikle D. D. , Cann C. E. , Morey-Holton E.
Published: December 2017

Some of the musculoskeletal changes that occur in growing rats during spaceflight are simulated by a model that selectively unloads the hindlimbs while maintaining normal weight bearing on the forelimbs. Using this model we studied the response of mineral and the mineral-binding protein osteocalcin (OC) in the third lumbar vertebra (L3) and the femoral midshaft to periods of unweighting from 2 to 28 days. Serum OC decreased by 25%, consistent with a decreased rate of bone growth, during the first week of suspension and returned toward control values after 15 days. The L3 and femur weighed 20% less than control bones after 10-28 days. OC content of L3 and femur diaphysis were lower after 7 days of suspension and returned to normal levels at 28 days, whereas Ca content rose slightly at 5 days then decreased sharply. OC:Ca ratio was also affected. The data suggest that unweighting affects formation and deposition of OC and Ca differently depending on bone location and duration of unweighting. Both serum and bone OC are highly sensitive indicators of disruption of osteoblast activity by altered skeletal loading.
Bombesin affects feeding independent of a gastric mechanism or site of action
Authors: Hostetler A. M. , McHugh P. R. , Moran T. H.
Published: December 2017

Peripherally administered bombesin has been demonstrated to inhibit food intake in a variety of species. Although the behavioral actions of bombesin are well characterized, neither the site of action nor mechanism through which bombesin affects feeding has been demonstrated. To test the hypothesis that bombesin's feeding effects are through a gastric inhibitory mechanism or a gastric site of action we examined the potential relationship between the inhibition of gastric emptying and the inhibition of intake produced across a dose range of bombesin and compared the relative potency of bombesin analogues for inhibiting feeding with their affinity for gastric bombesin receptors. Comparisons of the inhibitions of gastric emptying and feeding produced by 2, 4, 8, or 16 micrograms/kg of bombesin revealed no relationship, and, in fact, no gastric inhibitory action was evident. The feeding inhibitory actions of dose ranges (100 pmol-100 nmol) of litorin, ranatensin, acetylated gastrin-releasing peptide-(20-27) [AcGRP-(20-27)] and bombesin-(8-14) fragment were assessed and compared with bombesin. These compounds inhibited feeding with a relative potency of bombesin greater than AcGRP-(20-27) greater than ranatensin greater than litorin greater than bombesin-(8-14). This rank order of potency differed from the relative affinity of these compounds for gastric bombesin receptors for which all of these compounds except bombesin-(8-14) have a greater affinity than does bombesin. The results of these two experiments suggest that bombesin's satiety actions are not mediated by a gastric inhibitory mechanism or through a gastric site of action.
Response of rainbow trout to constant-pressure and constant-volume hemorrhage
Authors: Duff D. W. , Olson K. R.
Published: December 2017

Plasma oncotic pressure (OC), protein concentration (P), osmolality (Osm), and hematocrit (Hct) were measured in conscious rainbow trout subjected to 120 min of constant-pressure (CPH) or constant-volume (CVH) hemorrhage. Blood volume, tissue red cell, and plasma space were determined in control and CPH trout with 51Cr-labeled red cells and 125I-albumin. At the onset of CPH, blood loss exceeded 1.5 ml.min-1.kg-1 but quickly dropped to a constant rate of 0.1 ml.min-1.kg-1 by 15 min. After 2 h, 73% of the initial blood volume was lost, and Hct, OC, and P were reduced by 55 +/- 3, 39 +/- 4, and 19 +/- 9%, respectively; Osm did not change. Calculated blood volume was reduced by 39% (51Cr method) or by 56% (125I method). Red cell space was reduced in all tissues except brain. Plasma space decreased in stomach, increased in liver and kidney, and was unchanged in other tissues. CVH had similar effects on Hct, OC, and P, while Osm and plasma sodium increased. The time required for arterial pressure to recover to within 90% of control increased with successive bleeding from 39 to greater than 160 min. Twenty-four hours after CVH, Hct remained depressed, while all other parameters were returning toward control levels. Trout incorporate a variety of mechanisms to respond to hemorrhage, including mobilization of stored blood and reabsorption of fluid from interstitial and probably intracellular sources. High permeability of trout capillaries to protein may facilitate the restoration of protein and fluid and allow fish to survive extensive hypovolemia.
Lateral hypothalamic injection of 2-deoxy-D-glucose suppresses sympathetic activity
Authors: Egawa M. , Yoshimatsu H. , Bray G. A.
Published: December 2017

To investigate the effects of glucoprivation on sympathetic nerve activity to interscapular brown adipose tissue (IBAT), 2-deoxy-D-glucose (2-DG) was injected into the third cerebral ventricle (icv), lateral hypothalamic area (LHA), and ventromedial hypothalamic nucleus (VMN) of rats. The multiunit discharges of sympathetic nerves to IBAT were recorded electrophysiologically. The icv injection of high and low doses of 2-DG (5.0 and 2.5 mg/rat) suppressed sympathetic nerve activity by 76.9 and 49.8% respectively, 30 min after injection compared with preinjected base line. After the low dose of 2-DG, there was a gradual recovery, but after the high dose recovery did not occur. The unilateral microinjection of 2-DG (0.25 mg/rat) into the LHA induced a similar suppression of sympathetic nerve activity to that observed after icv injection of 10 times as much 2-DG (-25.3%). The injection of vehicle or sucrose into the LHA did not suppress sympathetic nerve activity. The microinjection into the VMN either unilaterally or bilaterally did not suppress sympathetic nerve activity to IBAT. We conclude that the LHA but not the VMH is one site of action of 2-DG. The data are consistent with the hypothesis that the brain senses glucoprivation in the LHA and reduces sympathetic drive to thermogenic tissues such as IBAT.
Axons of passage may be responsible for fastigial nucleus pressor response
Authors: Henry R. T. , Connor J. D.
Published: December 2017

Bilateral destruction of perikarya in the fastigial nucleus (FN) of the rat with the cytotoxic agent kainic acid (0.5 mg) did not alter the blood pressure (BP) increases observed during monopolar electrical stimulation (100 microA, 50 Hz, 0.5-ms pulse width) of this region. BP increases in control animals were 30 +/- 8 mm Hg, whereas BP increased 30 +/- 7 mmHg in kainic acid-lesioned rats. Furthermore, picrotoxin (100 ng) and muscimol (25 ng) microinjected unilaterally into the FN of conscious, unrestrained rats produced postural asymmetry but no change in BP or heart rate. These data suggest that the FN pressor response may be due, at least in part, to stimulation of axons of passage.
Effect of hepatic portal glucose concentration on food intake and metabolism
Authors: Tordoff M. G. , Tluczek J. P. , Friedman M. I.
Published: December 2017

To examine the effect of different hepatic portal glucose concentrations on food intake and metabolism, rats were given hepatic portal or jugular infusions (83 microliters/min for 2 h) of 0.3, 0.6, and 1.2 M glucose, equiosmotic NaCl, or a mock control infusion. Food intake was decreased to the same extent by the three concentrations of glucose infused into the hepatic portal vein and unaffected by any concentration of glucose infused into the jugular vein. Parallel to the changes in food intake, hepatic glycogen content was increased by glucose infused into the hepatic portal vein but not jugular vein. Conversely, systemic plasma glucose levels were increased by glucose infused into the jugular vein but not hepatic portal vein. Plasma insulin levels increased to the same extent irrespective of the route of infusion. Food intake was unaffected by the osmolarity of glucose infused into the hepatic portal vein, but was decreased by hyperosmotic NaCl control infusions. Hyperosmotic NaCl infusions also elevated levels of circulating fat fuels, indicating a stress response. The results show that the critical metabolic event in the liver that influences food intake is only indirectly coupled to the concentration of glucose in the hepatic portal vein.
Methane production in ruminants: its effect on the doubly labeled water method
Authors: Midwood A. J. , Haggarty P. , McGaw B. A. , Robinson J. J.
Published: December 2017

The doubly labeled water (DLW) technique for measuring CO2 production (rCO2) in free-living animals requires an assessment of the elimination of both 2H and 18O from the body over a long period of time. To calculate rCO2, it is necessary to calculate water turnover (rH2O) from the 2H flux rate. In ruminant animals, the accuracy of this calculation is affected by the loss of 2H in methane. We have quantified the effect of methane production (rCH4) on the 2H flux rate, determined in four sheep given 2H2O. The methane produced was depleted in 2H relative to the urine. A relationship between the enrichment of the methane and urine was established. The ratio of urine to methane enrichment was found on average to be 0.6536, and this value was unaffected by the level of rCH4 but showed some dependence on the absolute concentration of 2H in urine. For this reason, the ratio value obtained from four sheep not given 2H2O was different, a mean of 0.6886 was measured, this ratio was unaffected by changes in the diet supplied to the animals. Computer modeling was used to illustrate the dependence of the isotopically derived value for rCO2 on not only rCH4 but also the magnitude of rCO2 itself. The effect of rCH4 on the DLW method can be predicted from the observed ratio of rCO2 to rCH4 and the value of 0.6536 obtained for the ratio of methane to urine enrichment. With the use of data from several studies at this Institute, a limited range of 10 to 20 was found for rCO2/rCH4 in animals fed at or above maintenance.(ABSTRACT TRUNCATED AT 250 WORDS)
Bladder contractions and micturition in fetal sheep: their relation to behavioral states
Authors: Wlodek M. E. , Thorburn G. D. , Harding R.
Published: December 2017

Fetal bladder contractions, indicative of micturition (voiding), and behavioral states were monitored in unanesthetized fetal sheep in utero during the last third of gestation. Fetal voids began during low-voltage electrocortical activity (LV ECoG) at a greater frequency (91.4 +/- 1.0%) than expected (57.2%) and began during high-voltage electrocortical activity (HV ECoG) with a lower frequency (8.7 +/- 1.0%) than expected (42.8%). Fetal voids began significantly sooner after the onset of LV ECoG (5.84 +/- 0.13 min) than after the onset of HV ECoG (10.88 +/- 0.04 min). Electroocular and nuchal muscle activities were associated with 96.2 and 66.0% of the voids, respectively, but there was no significant association between fetal voiding and swallowing episodes. Abolition of spontaneous voiding, by urine drainage (24 h), caused no significant differences, relative to a 24-h control period, in the duration or number of episodes of LV or HV ECoG or percentage of time spent in these states. Also, induction of voiding by infusing saline into the bladder did not significantly alter the time to the next change of ECoG state. However, the mean time to the next void and the mean volume of saline infused into the bladder to induce voiding tended to be less during LV ECoG than HV ECoG, although not significantly less. Our data show that most spontaneous voids in the fetus begin during LV ECoG, suggesting that voiding is regulated by descending information from the brain. Furthermore, these experiments demonstrate that fetal bladder contractions and voiding, either spontaneous or induced, do not influence the normal cycling of fetal ECoG states.
Mobilization of calcium, phosphorus, and magnesium by embryonic alligators (Alligator mississippiensis)
Authors: Packard M. J. , Packard G. C.
Published: December 2017

The yolk of an alligator (Alligator mississippiensis) egg contains approximately 115 mg of Ca, 180 mg of P, and 17 mg of Mg at oviposition. This compartment is the primary (or sole) source of P and Mg for the forming embryo. Both of these elements are depleted rapidly from the yolk once the embryo enters the growth phase of development. The yolk also is an important source of Ca for the embryo, particularly during the first two-thirds of incubation. During the last trimester of development, however, the embryo supplements Ca from the yolk with Ca mobilized from the eggshell. Indeed, more Ca is withdrawn from the eggshell during the last 2 wk of incubation than can be used by the embryo in skeletogenesis. The excess Ca is stored in the yolk, thereby causing net transfer of Ca to shift from withdrawal from the yolk to deposition in the yolk. Consequently, the residual yolk in the hatchling alligator contains a substantial reserve of Ca to support skeletal growth during the neonatal period. The pattern of mobilization and deposition of Ca during embryogenesis in alligators is similar to that characterizing avian embryos, but is distinct from that characterizing embryos of all other oviparous reptiles.
Regional hemodynamic effects of neuromedin U in conscious rats
Authors: Gardiner S. M. , Compton A. M. , Bennett T. , Domin J. , Bloom S. R.
Published: December 2017

In conscious unrestrained Long-Evans rats, chronically instrumented with miniaturized pulsed Doppler flow probes, intravenous administration of porcine neuromedin U-8 by bolus (0.1 and 1.0 nmol) or infusion (1 and 10 nmol/h) exerted potent constrictor effects on the superior mesenteric vascular bed. With the choice of an appropriate dose, the reduction in superior mesenteric blood flow was not accompanied by any changes in systemic arterial blood pressure, heart rate, and renal or hindquarters blood flows. Porcine neuromedin U-25 had similar effects to neuromedin U-8, but was generally more potent. In Brattleboro rats the pattern of response to neuromedin U-25 was similar to that seen in Long-Evans rats, indicating that mesenteric vasoconstriction was not dependent on release of endogenous vasopressin. In Long-Evans rats the regional hemodynamic actions of rat neuromedin U were comparable with those of porcine neuromedin U-25. The latter peptide at a dose of 1.0 nmol caused a rise in total peripheral resistance and a reduction in cardiac output, with an inconsistent change in heart rate. The results raise the possibility that the high concentration of neuromedin U in the rat intestine is associated with the control of local blood flow.
Atrial appendectomy reduces ANF but not sodium excretion in acute vasopressin hypertension
Authors: Zimmerman R. S. , Barbee R. W. , Martinez A. , MacPhee A. A. , Trippodo N. C.
Published: December 2017

The present study was designed to determine whether atrial appendectomy would decrease the sodium excretion associated with pressor doses of arginine vasopressin (AVP) infusion in rats by decreasing circulating levels of atrial natriuretic factor (ANF). Ten to 21 days after either sham (n = 9) or bilateral atrial appendectomy (n = 13) AVP (19 ng.kg-1.min-1) was infused for 90 min in anesthetized Sprague-Dawley rats. Atrial appendectomy decreased circulating ANF levels from 469 +/- 70 pg/ml in sham-operated animals to 259 +/- 50 pg/ml (P less than 0.05) in atrial-appendectomized animals after 90 min of AVP infusion. Despite a reduction in circulating levels of ANF, sodium excretion, potassium excretion, and urine flow increased and were not affected by bilateral atrial appendectomy. Glomerular filtration rate and mean arterial pressure significantly increased in both groups of rats. The present study supports non-ANF factors such as increases in renal perfusion pressure and/or glomerular filtration rate as potential mechanisms in AVP-induced natriuresis.
Brain glucoprivation and ketoprivation do not promote ingestion in the suckling rat pup
Authors: Leshem M. , Flynn F. W. , Epstein A. N.
Published: December 2017

We examined the possibility that brain glucose or ketone availability may control suckling or precocious feeding in the preweanling rat. Brain glucoprivation induced by 5-thio-D-glucose injection into the 4th ventricle did not increase feeding on orally infused milk until 30 days of age, although hyperglycemia was evoked as early as 9 days by the same treatment. Plasma ketone levels varied with suckling status, but pharmacological blockade of hepatic free fatty acid oxidation, which restricts ketone availability (ketoprivation), failed to increase suckling. Because the suckling rat can switch energy substrates under nutritional duress, we combined glucoprivation and ketoprivation. Feeding was suppressed, and suckling was not affected. Finally, we injected ketones into the 3rd brain ventricle and found that they increased feeding. Thus, in contrast to the adult rat, reduced glucose or ketone utilization by the brain does not increase food intake in the preweanling, but increased circulating and brain ketone concentrations may arouse feeding.
Renin response to hemorrhage in conscious rats: effect of acute reductions in hematocrit
Authors: Raff H.
Published: December 2017

This study examined the effect of prior exchange transfusion and acute reduction in hematocrit on the subsequent plasma renin concentration (PRC) response to 15 ml/kg hemorrhage in conscious cannulated rats. Long-Evans rats (400-500 g) were assigned to one of eight groups (6-8 rats/group). Rats were exchanged transfused (5 ml total) with whole blood, red blood cells and saline, plasma, or isotonic saline, with the two latter groups showing a decrease in hematocrit of 10-20%. Thirty minutes after exchange transfusion, rats were either subjected to a 0- (control) or 15-ml/kg hemorrhage. Control rats showed no change in mean arterial pressure or PRC regardless of exchange transfusion. The rats exchange transfused with saline had a significant decrease in arterial pH and a more profound hypotension after hemorrhage. PRC ranged from 7 +/- 1 to 11 +/- 1 ng.ml-1.h-1 after exchange transfusion. Subsequent hemorrhage resulted in an increase in PRC that was significantly greater in the saline-transfused group (45 +/- 16 ng.ml-1.h-1) 10 min after hemorrhage. We conclude that exchange transfusion with saline leads to an augmented renin response to hemorrhage in part due to a decrease in arterial pH and more severe hypotension.
Influence of atrial natriuretic factor on autonomic control of heart rate
Authors: Atchison D. J. , Ackermann U.
Published: December 2017

Atrial natriuretic factor (ANF) may prevent reflex tachycardia. To determine whether this action occurs in the central or peripheral nervous system, Sprague-Dawley rats, anesthetized with Inactin (100 mg/kg ip), underwent surgical cardiac denervation and subsequent vagus nerve and stellate ganglion stimulation. We compared the change in heart rate (delta HR) in response to high- and low-frequency stimulation in a group receiving a vehicle infusion with a group receiving an ANF infusion (0.28 microgram.kg-1.min-1). We found that ANF had no effect on delta HR in the absence of all stimulation or during sympathetic stimulation at any frequency. There was no significant interaction between ANF enhancement of parasympathetic activity and the level of sympathetic stimulation. ANF acted peripherally to significantly (P less than 0.05) increase the magnitude of delta HR in response to parasympathetic stimulation at high (5 Hz) and low (2 Hz) frequencies. We speculate that a common step in mechanism of action of ANF and acetylcholine may be responsible for the enhancement of cardiac parasympathetic effects by ANF.
Decreased availability of metabolic fuels induces anestrus in golden hamsters
Authors: Schneider J. E. , Wade G. N.
Published: December 2017

Food deprivation inhibits ovulation and estrous behavior in golden hamsters. In experiment 1, the effects of phasic starvation (food deprivation on days 1 and 2 of the 4-day estrous cycle) depended on prior body weight and fat content. Starvation-induced anestrus, which occurs after only one cycle of phasic starvation in lean hamsters, did not occur until after three or more cycles in fat hamsters. None of the fat hamsters became anestrous until their body weights had declined to the level of lean hamsters. However, in experiment 2, we found evidence that changes in reproductive status were not signaled by any dimension of body size per se but instead by the general availability of metabolic fuels. Estrous cycles of thin hamsters were not significantly affected by food deprivation and weight loss when the hamsters were provided with either a 25% glucose solution or with vegetable shortening. In experiment 3, simultaneous pharmacological reduction of both fatty acid oxidation and glycolysis inhibited estrous cycles in hamsters fed ad libitum. Estradiol treatment restored estrous behavior, but not ovulation, in food-deprived, lean hamsters and in hamsters in which both fatty acid oxidation and glycolysis were reduced. Decreased availability of utilizable metabolic fuels may inhibit follicular development, which may in turn lead to circulating estradiol levels that are insufficient to stimulate estrous behavior.
Deuterium and oxygen-18 abundance in birds: implications for DLW energetics studies
Authors: Tatner P.
Published: December 2017

The doubly labeled water (DLW) technique for measuring energy expenditure may employ one (18O) or two (18O and deuterium) stable isotopes as tracers. These occur naturally in the environment, so when they are used as tracers it is necessary to subtract the background levels. Few studies report data on background concentrations. This work provides such data for a range of avian species. Overall, there was a strong positive correlation (r = 0.63) between the 18O and deuterium concentrations in birds' body water. Variation in the deuterium concentration was less extensive than in the 18O concentration (1:2.7 parts/million). In the European robin, there was a linked, seasonal variation in 18O and deuterium abundance producing high summer and low winter values. Throughout the year, a high individual variability was greater in 18O than in deuterium. A difference between the European robin and the dipper suggests that habitat may also influence background abundance. Investigation of the effect of variation in background abundance on measures of energy expenditure for small passerines (20 g) revealed that employing estimates, instead of direct measurements, had a minor influence over an experimental period of 1 day but could potentially introduce errors as large as 54% over a 2-day period.
Association of DOCA hypertension with induction of atherosclerosis in rats with short-term diabetes mellitus
Authors: Hebden R. A. , Todd M. E. , Tang C. , Gowen B. , McNeill J. H.
Published: December 2017

We investigated the effect of deoxycorticosterone acetate (DOCA)-induced hypertension on plasma lipid and cholesterol levels and the development of vascular atherosclerotic changes in male Wistar rats injected with streptozotocin (STZ) or saline (CON). Rats given STZ alone demonstrated a mild hyperlipidemia and hypercholesterolemia without any change in blood pressure. One week of DOCA administration was without effect on blood pressure in CON and STZ groups, but at 3 and 6 wk caused a significant and similar elevation in both groups. This DOCA-induced elevation in blood pressure appeared to be associated with the increase in plasma lipid and cholesterol levels seen in both CON and STZ groups at 3 and 6 wk, although the elevation in lipid and cholesterol levels was significantly more pronounced in the STZ rats. Both CON and STZ groups injected with DOCA developed significant pathological changes in all vessels under investigation. However, the degree of atherosclerosis appeared, from a semiquantitative analysis, to be worse in the thoracic aortas and renal arteries of the STZ group. Neither normotensive group developed any atherosclerosis. It is concluded that hypertension is associated with atherosclerosis in normal rats and rats with short-term STZ-induced diabetes mellitus, although the higher plasma lipid and cholesterol levels of the latter group may potentiate the degree of vascular damage.
Micropuncture study of the avian kidney: infusion of mannitol or sodium chloride
Authors: Roberts J. R. , Dantzler W. H.
Published: December 2017

Renal function was studied in anesthetized starlings by micropuncture and clearance techniques. The effects of intravenous infusions of isosmotic sodium chloride and hyposmotic mannitol solutions were compared. In the proximal tubules of the superficial reptilian-type nephrons, there is net reabsorption of sodium, chloride, and potassium; net secretion of calcium and urate; and either net secretion or no net secretion or reabsorption of magnesium and phosphate. The fractional delivery of ions and urate to the site of micropuncture, the percent of fluid reabsorbed, and the single nephron glomerular filtration rate (SNGFR) were not significantly different between the two infusion treatments. However, in the sodium chloride-infused birds, whole kidney GFR and the fractional excretion of sodium and chloride by the whole animal were higher, and fractional excretion of magnesium and potassium were lower. The data for each infusion group were further subdivided on the basis of whether the birds were in molt. In starlings, molt is associated with elevated levels of plasma prolactin. For the sodium chloride infusion, sodium and water reabsorption to the site of micropuncture was greater in the birds in molt than in those not in molt.
Glycogenesis from lactate in rabbit skeletal muscle fiber types
Authors: Pagliassotti M. J. , Donovan C. M.
Published: December 2017

The path of glycogen synthesis from three-carbon precursors was studied via single-pass perfusions in three distinct rabbit skeletal muscle preparations, i.e., glycolytic (greater than 99% type IIb), oxidative (greater than 97% type I), and mixed (type I, IIa, and IIb). The extent of interaction between the Krebs cycle and glycogenesis was assessed utilizing [1-14C]- or [2-14C]lactate at basal (1.1 +/- 0.1 mM) and elevated (8.1 +/- 0.3 mM) lactate concentrations (protocols 1 and 2). Under conditions in which the net balance of glucose and lactate, [14C]lactate removal, and venous lactate-specific activity were similar, the yields of 14CO2 and [14C]glycogen were not significantly influenced by position of the label. Additional perfusions were performed with lactate (8.0 +/- 0.1 mM) and acetate (1.0 +/- 0.1 mM) as sole substrates and either [U-14C]lactate or [2-14C]acetate as the tracer. Under conditions of net glycogen synthesis, the incorporation of [14C]lactate into glycogen [in disintegrations/min (dpm).g-1.2 h-1] was 40,940 +/- 3,320, 1,540 +/- 320, and 32,600 +/- 4,100 in the glycolytic, oxidative, and mixed preparations, respectively. However, no incorporation of [2-14C]acetate into glycogen was observed in any preparation, despite a significant yield of 14CO2. Mercaptopicolinic acid, a potent inhibitor of phosphoenolpyruvate carboxykinase (PEPCK), demonstrated no significant effect on net substrate balance, tracer uptake, net glycogen synthesis, incorporation of [14C]lactate and [3H]-glucose into glycogen, or 14CO2 yield. Current results suggest an extramitochondrial route for net glycogen synthesis from three-carbon precursors, exclusive of PEPCK, that is consistent across all mammalian skeletal muscle fiber types.
Alteration of antioxidant enzymes with aging in rat skeletal muscle and liver
Authors: Ji L. L. , Dillon D. , Wu E.
Published: December 2017

Maximal activities of antioxidant enzymes involved in oxygen free radical metabolism in skeletal muscle and liver were investigated in 4-, 26-, and 31-mo-old male Wistar-Furth rat at rest and after a single bout of treadmill exercise. In skeletal muscle, cytosolic (Cu-Zn) and mitochondrial (Mn) superoxide dismutase (SOD) specific activities were significantly higher in the aged rats and at 31 mo reached 135 and 218%, respectively, of those at 4 mo. Resting catalase activity was doubled at 31 mo compared with that at 4 mo. Glutathione peroxidase (GPX) activity increased twofold in muscle cytosol and by 47% in mitochondria of aged rats. Glutathione S-transferase (GST), glutathione reductase (GR), and glucose-6-phosphate dehydrogenase (G-6-PDH) activities in muscle were also significantly elevated. Hepatic antioxidant enzymes were altered differentially with aging. Cytosolic SOD and GST activities were decreased, whereas mitochondrial GPX, GR, and G-6-PDH activities were increased. Lipid peroxidation was greater in skeletal muscle homogenate and mitochondria but lower in liver homogenate in the aged rats. An acute exercise bout had little effect on muscle or liver antioxidant enzymes regardless of the animal's age. It is concluded that aging is accompanied with an elevation of antioxidant enzyme activities and lipid peroxidation in skeletal muscle probably due to the increased oxygen free radical production and reaction.
Estrogen-induced modulation of hypothalamic osmoregulation in female rats
Authors: Akaishi T. , Sakuma Y.
Published: December 2017

Estrogen treatment of ovariectomized female rats for a week decreased plasma osmolality from 294 to 278 mosmol/kgH2O, but recordings from the whole animal preparation under urethan anesthesia failed to detect any change in the activity of 76 vasopressinergic neurons in the supraoptic nucleus (SON) of the hypothalamus. In brain slice preparations, neuronal discharge of 74 presumed vasopressinergic SON cells increased linearly as the osmolality of the perfusate was increased from 278 to 320 mosmol/kgH2O, each 10 mosmol/kgH2O fraction corresponding to a 0.7-Hz change. This osmolality-neuronal activity relationship was similar in the slices taken from the estrogen-treated and the control ovariectomized animals, except that the neurons in the former fired twice as frequently as those in the control throughout the osmolality range. This difference explains the estrogen-induced decrease in the osmolality threshold to elicit antidiuresis and the resultant water retention in estrogen-treated animals. It was reasoned that the estrogen-induced neuronal activation was offset by the decreased plasma osmolality in the animal as a whole.
Relation of plasma norepinephrine and sympathetic traffic during hypotension in humans
Authors: Rea R. F. , Eckberg D. L. , Fritsch J. M. , Goldstein D. S.
Published: December 2017

We compared changes in antecubital venous plasma levels of norepinephrine (NE) and peroneal nerve muscle sympathetic activity (MSA) during and after nitroprusside (NP)-induced hypotension in nine healthy volunteers. During NP, MSA increased at 98.7%/min, peaked at 4 min at 399 +/- 77% (SE) of base line, and then decreased, so that at the end of the infusion MSA was 298 +/- 39% of base line. NE increased at 9.2%/min and peaked at 14.5 min at 231 +/- 31% of base line just before the end of the infusion. Percent increases of MSA and NE near the end of NP were not significantly different. The time-to-peak NE lagged the time-to-peak MSA by nearly 10 min. These results suggest that during increases of sympathetic outflow diffusion and washout of NE from neuroeffector junctions result in delayed increases in NE in the venous drainage; percent changes in MSA and NE during prolonged stable mild hypotension are similar. The findings provide conditional support for the use of changes in NE to indicate changes in sympathetic traffic.
Blood flow and oxygen delivery to fetal organs and tissues during sustained hypoxemia
Authors: Rurak D. W. , Richardson B. S. , Patrick J. E. , Carmichael L. , Homan J.
Published: December 2017

To examine the fetal cardiovascular responses to a sustained reduction in O2 delivery (DO2), studies were conducted on 13 chronically instrumented fetal lambs (128-138 days gestation) made hypoxemic for 7.9 +/- 0.5 h by lowering maternal inspired O2 concentration to 9-10%. Fetal descending aortic PO2 fell initially from 18.0 +/- 1.0 to 10.7 +/- 0.6 mmHg, whereas pH decreased progressively from 7.326 +/- 0.006 to 6.843 +/- 0.023. Blood flow to the cerebral hemispheres, myocardium, and adrenal glands rose maximally by 110.2 +/- 22.5, 253.7 +/- 41.1, and 338.7 +/- 55.0%. Cerebral hemispheric DO2 fell progressively, whereas DO2 to the myocardium and adrenal was maintained until 7.9 h, when it fell significantly. There was also a rise in blood flow to brown adipose tissue. Blood flow to the gut and skeletal muscle was maintained, whereas flow to the spleen and kidney fell. DO2 to all these tissues fell markedly because of the progressive decline in blood O2 content. It is concluded that fetal cardiovascular function was well maintained in the face of severe hypoxemia and marked acidemia.
Central effects of angiotensins I and II in conscious streptozotocin-treated rats
Authors: Tomlinson K. C. , Gardiner S. M. , Bennett T.
Published: December 2017

Responses to intracerebroventricular (icv) angiotensin II (ANG II) were measured in Long-Evans rats treated with the diabetogenic agent, streptozotocin (STZ), or saline 28 days earlier. STZ-treated Long-Evans rats showed normal pressor responses to ANG II in the absence of drinking water, but bradycardic responses were impaired although there was no reduction in baroreflex sensitivity. When allowed to drink, saline-treated, but not STZ-treated, rats showed an enhanced pressor response to icv ANG II and a tachycardia. Peripheral V1-receptor antagonism attenuated the pressor response to icv ANG II, leaving a residual response that was greater in saline-treated than in STZ-treated rats. STZ-treated rats had attenuated pressor and heart rate responses to icv angiotensin I (ANG I). Although some cardiovascular responses to icv ANG I and ANG II were reduced in STZ-treated rats, these animals showed enhanced sensitivity to the dipsogenic effects of the peptides. Vasopressin-deficient Brattleboro rats showed little pressor response to icv ANG II unless drinking was allowed, in which case the pressor response was less in STZ-treated than in saline-treated Brattleboro rats, although there was no difference in drinking response.
Renal and systemic hemodynamic responses to sustained submaximal exertion in horses
Authors: Hinchcliff K. W. , McKeever K. H. , Schmall L. M. , Kohn C. W. , Muir W. W.
Published: December 2017

We investigated the effects of 1 h of sustained submaximal exertion on the renal and systemic hemodynamics of six horses. The horses ran on a treadmill at a speed that produced heart rates of 55-60% of each horse's maximum heart rate. Exertion produced heart rates of 121 +/- 6.6 and 126 +/- 6.1 (SE) beats/min after 15 and 60 min, respectively. Cardiac output increased significantly (P less than 0.05) from 70.1 +/- 3.1 to 246.2 +/- 4.7 ml.min-1.kg body wt-1 after 15 min of exertion and thereafter did not change. There was no significant change from rest in p-aminohippuric acid and creatinine clearances, filtration fraction, or renal blood flow during exertion. Plasma total solid concentration and hematocrit increased by 3.8 and 8.6%, respectively, between 20 and 60 min of exertion. Pulmonary artery temperature increased significantly from 37.6 degrees C at rest to 38.6 degrees C at 60 min of exertion. This study demonstrates the ability of the horse to maintain renal hemodynamics similar to resting values and systemic hemodynamics at steady-state values despite hemoconcentration and increased body temperature during sustained submaximal exertion.
Arrest of cytochrome-c oxidase synthesis coordinated with catabolic arrest in dormant Artemia embryos
Authors: Hofmann G. E. , Hand S. C.
Published: December 2017

We have examined cytochrome-c oxidase (COX) biosynthesis in brine shrimp (Artemia franciscana) embryos during preemergence development (PED), as well as its inhibition under anaerobic dormancy, to determine whether transitions in intracellular pH (pHi) have a regulatory influence on anabolic processes. Under control aerobic conditions (embryo pHi greater than or equal to 7.9), incorporation of radiolabeled amino acids shows that substantial biosynthesis of COX occurs during 12 h of PED (500% increase when corrected for enzyme turnover). This anabolic process is blocked under anoxia, a condition known to foster intracellular acidification (pHi less than or equal to 6.8). The arrest of COX synthesis is quantitatively identical when embryos are incubated aerobically during artifical acidification with CO2 (pHi = 6.8). The data suggest that pHi, directly or indirectly, is a regulator of protein synthesis in Artemia embryos during anaerobic dormancy. Previous work has established a fundamental role for pHi in the arrest of carbohydrate catabolism under anoxia. Thus there appears to be a coordinated suppression of energy-producing and energy-utilizing events as Artemia embryos enter quiescence that involves pHi as the common intracellular signal.
Cell volume regulation by skate erythrocytes: role of potassium
Authors: Dickman K. G. , Goldstein L.
Published: December 2017

The role of K transport during cell volume regulation in response to extracellular osmolality, protein kinase C activation, and cellular Ca was examined in skate (Raja erinacea) red blood cells (RBC). Reduction of medium osmolality from 960 to 660 mosmol/kgH2O had no effect on K uptake or efflux despite a 25% increase in cell volume. Further reduction to 460 mosmol/kgH2O caused K uptake to double and K efflux to triple resulting in net K loss. Net K efflux in 460 mosmol/kgH2O medium was correlated with the presence of a regulatory volume decrease, which was sensitive to the anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and insensitive to chloride replacement. K-K exchange was absent in both isotonic and hypotonic media. Treatment with the Ca ionophore A23187 in the presence of Ca had no effect on either cell volume or K efflux in isotonic medium, indicating the absence of Ca-activated K transport. In contrast, phorbol ester treatment caused cell volume, Na content, and proton and K efflux to increase. Consistent with activation of Na-H exchange, phorbol ester effects were inhibited by dimethylamiloride. This study constitutes the first demonstration of volume-sensitive K transport in RBC from the most primitive vertebrate studied to date.
Central administration of atrial peptide decreases sympathetic outflow in rats
Authors: Schultz H. D. , Steele M. K. , Gardner D. G.
Published: December 2017

Previously, we reported that intravenous (iv) administration of atrial natriuretic peptide (ANP) evokes a decrease in sympathetic outflow. This effect requires an afferent input from vagal C-fibers. Here, we examined the effect of intracerebroventricular (icv) administration of ANP on sympathetic outflow, as well as the potential role of central mechanisms in mediating the sympathoinhibitory effects evoked by systemic administration of the peptide. In anesthetized rats with arterial baroreceptors intact, injection of ANP (100-500 ng) into the third ventricle did not affect renal and least-splanchnic sympathetic nerve activities, heart rate, and mean arterial pressure. After sinoaortic denervation, however, icv injection of ANP (100 ng) decreased these variables by 8 +/- 1 and 9 +/- 2% of control nerve activity, 9 +/- 3 beats/min, and 13 +/- 2 mmHg, respectively (P less than 0.05). The inhibitory sympathetic and cardiovascular effects of icv ANP were dose dependent, with responses seen after doses too small to produce systemic effects (less than 100 ng). Vagal blockade did not abolish the effects evoked by icv ANP. In addition, iv administration of ANP did not alter reflex responses to graded electrical stimulation of afferent vagal C-fibers. Furthermore, central administration of an antiserum directed against rat ANP did not alter the inhibitory sympathetic responses evoked by iv administration of the peptide. Taken together, these results indicate that centrally administered ANP, like systemic ANP, decreases sympathetic outflow, heart rate, and blood pressure; however, the central and peripheral actions of the peptide can be distinguished and appear to be independent.