bluuebunny/crossref_metadata_2025 huggingface dataset:
In vitro localization of thermosensitive neurons in the rat diencephalon
Authors: Dean J. B. , Boulant J. A.
Published: December 2017

Many thermosensitive neurons in the preoptic area-anterior hypothalamus (POAH) are believed to function in thermoregulation. Although many other diencephalic regions are implicated in thermoregulation, measurements of single-cell activity during localized thermal stimulation in these regions are lacking. Utilizing horizontal tissue slices, we have recorded single-unit activity throughout the rat diencephalon in response to localized thermal stimulation. Thermosensitive cells were identified in 18 nuclei. The proportions of each subpopulation inside vs. outside the POAH were similar: POAH (n = 83 cells); warm = 31%, cold = 4%, warm-cold = 1%, and temperature insensitive = 64%, outside POAH (n = 198 cells; warm = 39%, cold = 6%, warm-cold = 4%, and temperature insensitive = 51%. However, nuclei located rostral and lateral to POAH contained a large percentage of warm-sensitive cells (49-63%). Caudal nuclei contained approximately half of the cold-sensitive cells studied. This wide distribution of thermo-sensitive cells suggests that many diencephalic areas, besides the POAH, are capable of thermoreception and thermointegration. Moreover, many of these thermosensitive cells may function in other systems (e.g., reproduction, feeding, and water balance) which central and environmental temperatures are known to influence.
Protein metabolism and beta-myosin heavy-chain mRNA in unweighted soleus muscle
Authors: Thomason D. B. , Biggs R. B. , Booth F. W.
Published: December 2017

To investigate the relative influence of protein synthetic and degradative control mechanisms in vivo during skeletal muscle atrophy, we measured myofibril and total mixed protein synthesis rates in muscles of rats prevented from hindlimb weight-bearing for 5 h and 7 days. Protein synthesis rates were determined by infusing the animals with [3H]Leu for 5 h and measuring the specific activity of [3H]Leu in the aminoacyl-tRNA precursor and protein product fractions of the muscles. In the soleus muscle, myofibril protein synthesis rates decreased from a control value of 5.9 to 4.6%/day during 5 h of hindlimb unweighting and to 2.4%/day after 7 days of hindlimb unweighting. The relatively more phasic muscles (plantaris, medial gastrocnemius, quadriceps) showed a tendency for increased myofibril protein synthesis rates (117-127% of control) during the first 5 h followed by a decrease (46-62% of control) at 7 days of hindlimb unweighting. A predicted time course of soleus muscle myofibril protein degradation rate was obtained from a numerical model of the decrease in soleus myofibril protein synthesis rate as a first-order process [half-time (t1/2) = 0.3 day by least-squares fit] and the time course of soleus muscle myofibril protein previously observed with hindlimb unweighting (Thomason et al., J. Appl. Physiol. 63: 130-137, 1987). The degradation rate model makes specific, testable predictions for the mechanism of myofibril protein degradation during soleus muscle atrophy: 1) the first-order degradation rate constant does not obtain a fixed value over a 24-day period but is continuously changing throughout atrophy, and 2) the first-order degradation rate constant changes on a time scale slower than protein synthesis rate.(ABSTRACT TRUNCATED AT 250 WORDS)
Catecholamine activity in paraventricular hypothalamus after hemorrhage in cats
Authors: Thrivikraman K. V. , Bereiter D. A. , Gann D. S.
Published: December 2017

Temporal changes in catecholamine activity within the paraventricular nucleus (PVN) of the hypothalamus were assessed using in vivo voltammetry after moderate hemorrhage in chloralose-anesthetized cats. Oxidation current was measured with carbon microelectrodes, and the change at +250 mV was used as an estimate of catecholamine activity. The magnitude and directional change in catecholamine activity was assessed for each site during the initial 3 min of blood loss. Of 62 recording sites, 45 sites were located along the rostrocaudal extent of the medial PVN. Fifteen of these 45 sites exhibited an increase, 15 others exhibited a decrease, and the remaining 15 sites exhibited no change in catecholamine activity. The magnitude of change in oxidation current was independent of the magnitude of the decrease in arterial pressure after hemorrhage. Twelve of the 15 sites that exhibited increases in catecholamine activity were located in the caudal PVN along its dorsomedial aspect, whereas the location of sites that exhibited decreases in catecholamine activity were more widely distributed throughout the nucleus. These data are consistent with the hypothesis that an increase in the release of catecholamines within the caudal PVN in response to hemorrhage is facilitatory for the release of adrenocorticotropin and/or vasopressin.
Cardiovascular responses during feeding in newborn lambs
Authors: Langille B. L. , Adamson S. L. , Jones S. A.
Published: December 2017

We examined the cardiovascular responses to bottle feeding in newborn lambs. Feeding induced a persistent rise in blood pressure, from 76.3 +/- 1.9 mmHg to 114 +/- 3.8 mmHg, that lasted for the duration of the feeding episode. This was accompanied by a transient tachycardia that lasted for approximately 10 s at the beginning of each feeding episode. Vasoconstriction of the hindlimb circulation, the gastrointestinal tract, kidneys, and adrenal and thyroid glands contributed to the pressor response, whereas changes in skeletal muscle resistance were not statistically significant. Of tissues assessed, only those actively involved in feeding (tongue and esophagus) vasodilated. Feeding tachycardia was greatly inhibited or abolished by the beta-blocker propranolol but the alpha-blocker phentolamine caused only moderate inhibition of the pressor response. Furthermore, chemical sympathectomy with 6-hydroxydopamine delayed the onset of the pressor response but did not abolish the ultimate rise in pressure. These findings indicate that feeding causes a significant pressor response in newborn lambs that is only partially mediated by sympathetic innervation.
Subregions of rostral ventral medulla control arterial pressure and regional hemodynamics
Authors: Cox B. F. , Brody M. J.
Published: December 2017

The cardiovascular effects of inactivating rostral ventromedial medulla (RVMM) under conditions of normal (2.5 ml) and reduced (1.5 ml) tidal volume were studied in urethan-anesthetized rats. Bilateral microinjection of lidocaine (200 nl, 4%) reduced mean arterial pressure (MAP), renal, mesenteric, and particularly hindquarter vascular resistance. These effects were not significantly altered by reducing tidal volume. Electrical stimulation of RVMM increased MAP and regional vascular resistances, again with the hindquarter change most prominent. The integrated cardiovascular response to stimulating rostral ventrolateral medulla (RVLM) appears to require integrity of RVMM; however, the converse is not true. Overall, these studies indicate that 1) the potential for RVMM to maintain neurogenic control of arterial pressure is as great as RVLM; 2) RVMM is capable of playing a proportionally greater role in the controlling hindquarter vascular resistance; 3) the integrity of RVMM appears to be important for responses elicited from RVLM; and 4) unlike RVLM, neural control of arterial pressure is sustained by RVMM under conditions of reduced tidal volume. We conclude that RVLM and RVMM are functionally and anatomically distinct subregions of rostral ventral medulla with equivalent capacity to maintain vasomotor tone.
Reduced renal responses to volume expansion in streptozotocin-induced diabetic rats
Authors: Patel K. P. , Zhang P. L.
Published: December 2017

To determine whether the volume reflex is defective in the diabetic state, the diuretic and natriuretic responses to acute volume expansion (VE) were measured in streptozotocin (STZ)-induced diabetic (Dia) rats. Urine flow (UV) and sodium excretion (UNaV) were measured before and after VE from innervated and denervated kidneys in anesthetized (Inactin 0.1 g/kg, ip) control and Dia rats (Sprague-Dawley rats injected with vehicle or STZ 65 mg/kg ip, respectively, 2 wk before the experiment). Blood glucose levels were significantly elevated in the Dia group compared with the control group. A VE of 1.2 ml/min for 15 min produced a significantly greater diuresis and natriuresis in control rats compared with Dia rats. In addition, reducing the hyperglycemia in Dia rats (third group) by treatment with insulin reversed the blunted UV and UNaV responses to VE. Ratios of UV (innervated-denervated, I/D) before and after VE indicate significant increases in UV by the innervated kidneys, relative to the denervated kidneys in all three groups. I/D ratios of UNa V were not different between the three groups before VE, but were significantly smaller in the Dia rats compared with both control and STZ plus insulin groups after VE. This study demonstrates that 1) there is an abnormal volume reflex in the STZ-induced Dia rats; 2) the natriuresis due to renal sympatho-inhibition is blunted in response to VE in Dia rats; and 3) restoring the glucose levels to normal by insulin treatment in the Dia rats normalizes the volume reflex.
ACTH-(4-10) through gamma-MSH: evidence for a new class of central autonomic nervous system-regulating peptides
Authors: Gruber K. A. , Callahan M. F.
Published: December 2017

Examination of the cardiovascular effects produced by peripheral administration of peptide sequences derived from adrenocorticotropic hormone (ACTH) led to the discovery of the pressor, cardioaccelerator, and natriuretic actions of intravenous (iv) ACTH-(4-10). Based on pharmacological studies in rats with alpha- and beta-adrenergic receptor antagonists, the cardiovascular effects of this peptide appeared to be mediated by the release of catecholamines. A peptide sequence analogous to ACTH-(4-10), gamma-melanocyte-stimulating hormone (gamma-MSH), possesses greater than 100-fold more cardiovascular activity and 1,000-fold more natriuretic activity than ACTH-(4-10). The pressor effect of iv gamma-MSH peptides appears to be dependent on the maintenance of preganglionic sympathetic drive, with no significant contribution of circulating vasopressin or angiotensin II. However, the presence of central vasopressinergic, and perhaps angiotensinergic, pathways appears to be crucial for expression of the full pressor effect of circulating gamma-MSH. Further evidence for the potential importance of the central nervous system (CNS) in these cardiovascular effects was obtained from central lesion experiments and a comparison of intracarotid vs. intrajugular infusions. Structure-activity studies suggested that the cardiovascular effects of ACTH-(4-10) or gamma-MSH are dependent on an Arg-hydrophobic amino acid sequence, located at or near their COOH-terminal. A similar requirement for biological activity is found in molluscan cardioexcitatory peptides, and the molluscan peptides have cardiovascular effects in rats, which resemble ACTH-(4-10) or gamma-MSH. This suggests that peptides of the gamma-MSH family are the pharmacological analogues, and perhaps the physiological homologues, of a cardioexcitatory family of peptides found in molluscs and birds. Elevated circulating levels of peptides derived from the NH2-terminal of pro-opiomelanocortin (POMC) have been found in psychological stress, cardiovascular distress, and hemorrhage. Increases in central sympathetic drive are common to all of these states. gamma-MSH peptides have been localized to POMC neurons in the arcuate nucleus and nucleus commissuralis of the rat. Projections from the latter nucleus innervate hindbrain vasomotor centers. Intraventricular administration of gamma-MSH produces prolonged elevation of mean arterial pressure. gamma-MSH peptides may provide a link between humoral and neurogenic mechanisms in cardiovascular regulation and could potentially be important neurotransmitters for central control of the cardiovascular system.
Prostaglandin fevers in rats: regulated change in body temperature or change in regulated body temperature?
Authors: Feng J. D. , Price M. , Cohen J. , Satinoff E.
Published: December 2017

Experiments examining the effects of central injections of E-series prostaglandins (PGE) on body temperature have only been done in the light part of a light-dark cycle. The present experiments examined the characteristics of fevers in rats after intraventricular PGE2 injections in both light and dark in a 12:12 h photoperiod. In the light, the change in body temperature (Tb) after 0.5 microgram was not significantly different from the change after vehicle injection. After injection of PGE2 (1, 2, 4, and 8 micrograms), Tb rose in a dose-dependent fashion. Mean initial Tb in the light was 36.4-36.6 degrees C. Tb rose a mean of 1.5 degrees C after 1 microgram, 1.9 degrees C after 2 micrograms, 2.7 degrees C after 4 micrograms, and 3.5 degrees C after 8 micrograms PGE2. A dose of 16 micrograms gave almost identical results as 8 micrograms. In the dark, mean initial Tb was 37.4-37.7 degrees C. Tb rose less than 0.8, 1.1, 1.4, and 2.3 degrees C after 1-8 micrograms PGE2, respectively. Thus there were two distinct dose-response curves for day and night. Nevertheless, peak Tb values attained in the two conditions were not significantly different from each other at any given dose. These results show that a particular dose of PGE2 raises Tb to a particular level, largely independent of either the Tb at the time of the injection or the phase of the light-dark cycle. However, the change in Tb at any dose depends strongly on initial Tb. Therefore, we urge researchers in the pharmacology of thermoregulation to report initial and final Tb values as well as changes in Tb.
Benzodiazepines acting on ventral surface of medulla cause airway dilation
Authors: Haxhiu M. A. , van Lunteren E. , Cherniack N. S. , Deal E. C.
Published: December 2017

The benzodiazepines that have anxiolytic, anticonvulsant, muscle-relaxant, and sedative-hypnotic properties affect respiration possibly by acting on gamma-aminobutyric acid (GABA)ergic receptors. This study investigated the effects of benzodiazepines diazepam and midazolam) applied topically to or microinjected just beneath the ventrolateral medullary surface (VMS) on airway tone in alpha-chloralose-anesthetized, paralyzed, and artificially ventilated cats. Trachealis smooth muscle tension was assessed by measuring the changes in pressure in a balloon placed in a bypassed rostral segment of the trachea. In 21 cats ventilated with 7% CO2 in O2, surface application of benzodiazepines caused a significant decrease in tracheal tone. Similar to topical application, microinjection of midazolam (1 microgram) in the ventral medulla (0.1-0.2 mm from the surface) in six cats decreased tracheal pressure by 13.2 +/- 2.1 cmH2O (P less than 0.01). In addition, application of benzodiazepines on the VMS in animals ventilated with 12% O2 in N2 (n = 5) decreased tracheal pressure from 15.9 +/- 2.2 to 5.2 +/- 2.7 cmH2O (P less than 0.05). Furthermore, in all cats studied (n = 6), the magnitude of lung deflation-induced tracheal contraction was reduced after application of benzodiazepines on the ventral surface of the medulla (from 11.4 +/- 1.6 to 2.2 +/- 0.9 cmH2O; P less than 0.01). The effects of benzodiazepines on tracheal tone were reversed and blocked by application of Ro 15-1788, a specific benzodiazepines antagonist. However, when parasympathetic activity was abolished by atropine and tracheal tone was restored with 5-hydroxytryptamine, benzodiazepines applied on the VMS had no effect on tracheal pressure. These results suggest that benzodiazepines acting centrally, on structures located near the VMS, can cause a decrease in airway smooth muscle tone by diminishing the activity of parasympathetic neurons which project to the airways.
Relationship between atrial granularity and release of atrial natriuretic factor in rats with diabetes mellitus
Authors: Hebden R. A. , Todd M. E. , McNeill J. H.
Published: December 2017

We examined the effect of a 25% blood volume expansion on the release of atrial natriuretic factor (ANF) in conscious Wistar rats (13-15 wk old) injected 6 wk earlier with streptozotocin (55 mg/kg iv, diabetic) or saline (1 ml/kg iv, control). The diabetic rats demonstrated a significant (P less than 0.05) resting hypotension (132 +/- 2/91 +/- 1 mmHg, systolic/diastolic) and bradycardia (340 +/- 5 beats/min) compared with the controls (145 +/- 2/98 +/- 2 mmHg, 377 +/- 8 beats/min). Resting plasma immunoreactive (IR) ANF levels were significantly (P less than 0.05) elevated in the diabetic rats (control: 72 +/- 4 pg/ml; diabetic: 87 +/- 4), although resting right atrial pressures were not different (control: 6.0 +/- 0.8 cmH2O; diabetic: 5.2 +/- 0.6). Volume expansion with donor blood from similarly treated animals significantly (P less than 0.05) elevated IR ANF levels in both groups, but the increase in the saline-injected group (+527 +/- 80 pg/ml) was significantly (P less than 0.05) greater than that of the streptozotocin-injected group (+323 +/- 45 pg/ml). Both groups showed similar elevations in right atrial pressure (control: +1.8 +/- 0.3 cmH2O; diabetic: +1.6 +/- 0.4). Morphological examination of tissue taken from right atria demonstrated no difference in cardiocyte volume percent per unit of tissue but a significant (P less than 0.05) reduction in the relative frequency of occurrence of atrial granules in the diabetic group. The cause of the reduction in atrial granularity in these animals is as yet unknown.
Rats eating and hoarding as a function of body weight and cost of foraging
Authors: Cabanac M. , Swiergiel A. H.
Published: December 2017

Rats were trained to forage 2 h daily in a zigzag alley at -15 degrees C. On experimental days food was placed in large amounts at a 1-, 4-, or 16-m distance from a warm shelter. The mass of food ingested and hoarded in the shelter by the rats was then recorded. The rats' body weights were depressed progressively by spacing the sessions with access to food, and then the animals were allowed to recover their initial body weight. The results showed that 2-h food intake was constant and did not vary as a function of body weight loss or the distance to reach the food (cost). On the other hand, the mass of food hoarded was a linear increasing function of body weight loss below the hypothetical set point for body weight and a decreasing linear function of the distance to the food. The linear regression of the mass of food hoarded on body weight with a negative slope (b) adequately depicted the rat's hoarding behavior: mass hoarded = a + b (body wt). The slope of this function decreased with increasing cost of food procurement. It is concluded that 1) the main response of the rat to starvation is food hoarding rather than ingestion and 2) the estimation of the body weight set point from hoarding is not affected by the costs of food procurement.
Microprocessor-based analysis of sympathetic nerve traffic
Authors: Brown D. R. , Randall D. C.
Published: December 2017

Two systems based on microcomputers with analog-to-digital (A/D) converters were developed to measure sympathetic nerve activity. The first utilized a relatively inexpensive computer and A/D converter and an analog technique to count nerve traffic "spikes" above a reference voltage. The second system, which required a more expensive microcomputer and A/D converter, used digital methods exclusively to count spikes and integrate nerve activity. These systems produced accurate and reliable indexes of nerve traffic. The digital system could also be used to store the nerve signal to magnetic disk, thereby allowing the later use of more complex analytical procedures and the possibility of comparing the results of different analyses performed upon a single data set.
Lack of effect of vasopressin replacement on renin hypersecretion in Brattleboro rats
Authors: Golin R. M. , Gotoh E. , Keil L. C. , Shackelford R. L. , Ganong W. F.
Published: December 2017

To determine how the vasopressin deficiency in homozygous Brattleboro rats with diabetes insipidus produces increased renin secretion, homozygous and heterozygous Brattleboro rats were infused through subcutaneously implanted Alzet minipumps for 1 wk with a dose of arginine vasopressin that restored plasma vasopressin to normal in the homozygous animals. In the homozygous animals, plasma renin activity (PRA) and the PRA response to immobilization remained elevated compared with Long-Evans controls. Propranolol reduced PRA to normal and markedly reduced the PRA response to immobilization. PRA was normal in heterozygous Brattleboro rats. The data indicate that the increased renin secretion in homozygous rats is a result of increased sympathetic activity, and because circulating vasopressin does not cross the blood-brain barrier, it seems likely that the increased sympathetic activity is central in origin.
Effect of baroreceptor denervation on vasopressin and cortisol responses to angiotensin II infusion in conscious dogs
Authors: Brooks V. L. , Klingbeil C. K. , Quillen E. W. , Keil L. C. , Reid I. A.
Published: December 2017

Recent studies suggest that the pressor response to exogenous angiotensin II infusion may, through baroreceptor-dependent mechanisms, counteract the stimulatory effect of the peptide on vasopressin and adrenocorticotropic hormone (ACTH) secretion. To test this hypothesis, the effect of combined cardiac and sinoaortic baroreceptor denervation on the increases in plasma concentrations of vasopressin and cortisol (used as an index of ACTH secretion) produced by angiotensin II infusion was studied in conscious dogs. In eight intact dogs, 30-min angiotensin II infusions at 5, 10, and 20 ng.kg-1.min-1 increased mean arterial pressure from 108 +/- 5 to 126 +/- 5 mmHg, from 101 +/- 4 to 130 +/- 4 mmHg, and from 99 +/- 3 to 138 +/- 4 mmHg, respectively (P less than 0.001). Plasma cortisol concentration increased from 19 +/- 4 to 27 +/- 4 ng/ml, from 19 +/- 4 to 43 +/- 4 ng/ml, and from 19 +/- 4 to 71 +/- 6 ng/ml (P less than 0.01), and plasma vasopressin concentration increased from 2.2 +/- 0.3 to 3.1 +/- 0.3 pg/ml, from 2.3 +/- 0.3 to 3.5 +/- 0.4 pg/ml, and from 2.2 +/- 0.4 to 5.0 +/- 0.5 pg/ml (P less than 0.01). In five to six baroreceptor-denervated dogs, angiotensin II infusion produced increases in mean arterial pressure, plasma vasopressin concentration, and plasma cortisol concentration that were not consistently different from those in the intact dogs. These results demonstrate that baroreceptor denervation does not enhance the vasopressin or cortisol responses to angiotensin II infusion in conscious dogs.
Tumor necrosis factor enhances glucose uptake by peripheral tissues
Authors: Evans D. A. , Jacobs D. O. , Wilmore D. W.
Published: December 2017

Anesthetized dogs received a constant intravenous infusion of tumor necrosis factor (TNF) or saline over 6 h. Glucose kinetics were studied by determining the rate of glucose turnover and hindlimb substrate flux. Cardiovascular responses were monitored and concentrations of counterregulatory hormones were also measured. TNF infusion caused a fall in blood glucose concentration from 4.6 +/- 0.1 to 3.9 +/- 0.2 mmol/l by 6 h (P less than 0.05). This mild hypoglycemia was associated with increased circulating levels of cortisol, glucagon, and epinephrine. The rate of glucose production increased from 26.5 +/- 2.1 to 32.5 +/- 0.7 mumol.min-1.kg body wt-1 (P less than 0.05) over the 6-h infusion period; this response was associated with increased glucose disappearance (26.4 +/- 2.2 to 32.7 +/- 0.9 mumol.min-1.kg body wt-1, P less than 0.05) and enhanced clearance (5.7 +/- 0.5 to 9.0 +/- 0.6 ml.min-1.kg body wt-1, P less than 0.05). As blood glucose levels fell, hindlimb glucose uptake and glucose clearance increased markedly in TNF-infused animals as compared with controls despite a 50% fall in mean serum insulin concentration. The exchange of lactate, pyruvate, and total amino acid nitrogen across the hindlimbs was similar in both groups of animals. However, arterial concentrations of lactate and pyruvate rose to two to three times their initial values. The hypoglycemia associated with the infusion of TNF results from a disparity between the rate of glucose appearance and disappearance. There is an increased uptake of glucose across the hindlimb; this response appears to be independent of insulin concentrations and may be related to direct effects of TNF.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of ovariectomy and estradiol on unity of female rat circadian rhythms
Authors: Thomas E. M. , Armstrong S. M.
Published: December 2017

Sixteen rats were ovariectomized and given either a 1-cm implant of crystalline estradiol-17 beta (eight rats) or an empty implant (eight rats). A further six rats were sham ovariectomized and given empty implants, and eight rats were left unoperated. The rats were exposed to 70 days of constant dim light (LL) with a maximum illumination level of 20 lx, and circadian running and drinking rhythms were monitored. In LL, both the running and drinking activity rhythms of the ovariectomized, blank-implanted rats became markedly disrupted, whereas unoperated and sham-operated rats maintained unified rhythms. Estradiol-implanted rats developed fewer rhythm desynchronies, and the majority displayed a single band of free-running activity. Rather than being arrhythmic, the activity of the LL-exposed ovariectomized rats appeared to contain several free-running components. Thus these data are consistent with the concept of a multioscillatory basis to the circadian system and support a role for the ovary and its hormone estradiol in the maintenance of coherence between component oscillators.
Membrane dynamics in relation to fluid absorption in reptilian proximal renal tubules
Authors: Dantzler W. H.
Published: December 2017

Net fluid absorption (Jv), cell volume, and cell membrane area have been studied in isolated, perfused snake (Thamnophis spp.) proximal tubules. With Na+ in both perfusate and bathing medium, Jv averages approximately 0.9 nl.min-1.mm-1. When choline replaces Na+ in perfusate, Jv nearly ceases. When choline also replaces Na+ in bathing medium, so that both solutions are identical, Jv returns to the control rate. The results are the same when tetramethylammonium replaces Na+, when sucrose replaces Na+ and the equivalent amount of Cl-, and when methyl sulfate replaces Cl- alone. However, when Li+ replaces Na+ in perfusate alone or in both perfusate and bathing medium, Jv is unchanged. Jv at control rates is isosmotic and can be partially inhibited by cold and cyanide. When choline replaces Na+ in perfusate and bathing medium, cell volume doubles, and intercellular space volume nearly quintuples. The areas of the lateral and apical cell membranes also approximately double, so that the surface area-to-volume ratio remains constant. These morphological changes in the absence of Na+ occur concomitantly with maintenance of Jv, suggesting that they may play a permissive role in such maintenance.
Ambient temperature and food costs: effects on behavior patterns in rats
Authors: Collier G. H. , Johnson D. F. , Naveira J. , Cybulski K. A.
Published: December 2017

Eating, drinking, wheel running, and nesting were recorded continuously in animals living in cages where they foraged for and consumed food by completing operant bar-press requirements. The ambient temperature was either 24 or 0 degrees C. Two food costs, that of initiating meals and that of pellets within meals, were separately manipulated at each temperature. Compared with room temperature, the cold temperature produced a doubling of food and water intake and a greater than twofold increase in nesting time each day. Running behavior was not altered. Regardless of temperature, the cost of initiating meals influenced the frequency and size of meals but did not affect total food intake or time spent feeding, and this cost had no effect on any other activity. As the cost of pellets within meals increased, the time spent feeding increased and there was a decline in daily food intake. The change in intake was greater at the cold temperature because in the cold the rats did not increase daily feeding time sufficiently to maintain intake as pellet cost increased. Such an increase in feeding time would have required that less time be spent in one of the other activities.
Aldosterone and renin inhibition by atrial natriuretic factor in potassium-loaded rats
Authors: Brands M. W. , Freeman R. H.
Published: December 2017

This study was designed to determine the effects of synthetic rat atrial natriuretic factor (ANF) on plasma renin activity (PRA) and aldosterone secretion in separate groups of normal and potassium-loaded anesthetized rats. Control rats were fed a normal diet of sodium and potassium and had base-line levels of PRA and aldosterone secretion of 25 +/- 3 ng angiotensin I (ANG I).ml-1.h-1 and 0.56 +/- 0.09 ng/min, respectively. Chronic oral potassium loading for 10 days elevated the plasma potassium concentration, stimulated aldosterone secretion to 1.80 +/- 0.18 ng/min (P less than 0.05), and attenuated PRA to 13 +/- 2 ng ANG I.ml-1.h-1 (P less than 0.05). Infusion of ANF at 45 ng.kg-1.min-1 in potassium-loaded rats lowered aldosterone secretion to 1.32 +/- 0.21 ng/min (P less than 0.05) but did not significantly reduce PRA (11 +/- 2 ng ANG I.ml-1.h-1 (P greater than 0.05). A higher ANF infusion dose of 100 ng.kg-1.min-1 produced a further decrement in aldosterone secretion to 1.15 +/- 0.26 ng/min (P less than 0.05) and also reduced PRA to 3 +/- 1 ng ANG I.ml-1.h-1 (P less than 0.05). In the control rats, aldosterone secretion and PRA were decreased significantly during infusion with both low and high ANF doses. Base-line arterial pressures among experimental groups were not different (P greater than 0.05) and did not change during infusion of ANF in any group. These results indicate that ANF can inhibit chronic potassium-stimulated aldosterone secretion in the rat independently of its inhibitory actions on renin release.
Weight cycling in female rats subjected to varying meal patterns
Authors: Wheeler J. , Martin R. , Lin D. , Yakubu F. , Hill J. O.
Published: December 2017

The effect of weight cycling on energy balance was examined in female rats. Two groups of adult female rats were subjected to three bouts of weight cycling, each bout consisting of 8 days of food restriction (9 g/day or approximately 50% of usual intake) followed by 16 days of refeeding. During refeeding animals were given 22.8 g/day of food so that they were offered, during the 24-day cycle, the same amount of food offered to control rats that were not subjected to weight cycling. One group of weight-cycled rats (gorgers) was given its daily intake in a few large meals (i.e., allowed to gorge). The other weight-cycled group (nibblers) was fed by automated feeders in several small meals during each 24-h period (i.e., prevented from gorging). Neither weight-cycled group displayed an increased food efficiency or an increased body fatness compared with noncycled controls. Weight-cycled rats allowed to gorge did have an increased food efficiency and a greater carcass energy content compared with weight-cycled rats not allowed to gorge. These results suggest a pattern of gorging promoted food efficiency and body energy gain compared with a pattern of nibbling, but gorging during refeeding cannot account for reports of increased food efficiency in weight-cycled rats.
Somnogenic, pyrogenic, and hematologic effects of bacterial peptidoglycan
Authors: Johannsen L. , Toth L. A. , Rosenthal R. S. , Opp M. R. , Obal F. , Cady A. B. , Krueger J. M.
Published: December 2017

Bacterial infections and certain muramyl peptides elicit a variety of pathophysiological effects including increases in body temperature and slow-wave sleep. Bacterial cell wall peptidoglycan is composed of muramyl peptides. To investigate the ability of isolated bacterial cell walls to enhance slow-wave sleep, rabbits were injected intravenously with cell walls isolated from Staphylococcus aureus or with soluble peptidoglycan prepared from Neisseria gonorrhoeae. These injections increased slow-wave sleep, electroencephalographic delta-wave amplitudes, and body temperature, reduced rapid-eye-movement sleep, and induced neutrophilia and lymphopenia. The somnogenic and pyrogenic effects of S. aureus cell walls developed within 1 h and persisted throughout the recording period. Injections of N. gonorrhoeae peptidoglycan induced similar effects but of larger magnitude and shorter duration. We conclude that peptidoglycan is a bacterial component that mediates the increased sleep observed during infectious disease.
Counteracting effects of urea and betaine in mammalian cells in culture
Authors: Yancey P. H. , Burg M. B.
Published: December 2017

Urea and methylamines, such as betaine, are among the major organic osmotic effectors accumulated by organisms under hyperosmotic (high NaCl) stress; the mammalian renal medulla also accumulates such compounds in antidiuresis. Studies on isolated proteins show that urea generally destabilizes protein structure, whereas methylamines are generally stabilizers capable of offsetting the effects of urea. The counteracting-osmolytes hypothesis predicts that cells exposed to high urea concentrations require methylamines for optimal function. In this study, urea, betaine, and other solutes (NaCl, glycerol, sorbitol) were added to growth medium of cultured mammalian cells under conditions in which most solutes entered the cells. For two renal [Madin-Darby canine kidney (MDCK) and PAP-HT25] and one nonrenal (Chinese hamster ovary) cell line, urea (greater than 100 mM) or betaine (greater than 50-100 mM) alone inhibited cell growth and survival, measured as colony-forming efficiency. However, the addition of betaine (up to 120 mM) to media with urea (50-300 mM) greatly increased colony-forming efficiency above that with urea alone. A similar, although less marked effect, was seen on colony sizes with MDCK cells. These results support the counteracting-osmolytes hypothesis.
Extracellular pH and suppression of electrical activity during anoxia in turtle and rat brain
Authors: Feng Z. C. , Sick T. J. , Rosenthal M.
Published: December 2017

To evaluate the contribution of extracellular H+ activity toward depression of brain electrical activity during anoxia, extracellular pH (pHe) and field potentials were measured in turtle and rat olfactory bulbs with ion-selective microelectrodes. This study tests the hypothesis that unique regulation of pHe contributes to the remarkable tolerance of turtle brain to prolonged anoxia. Hypercapnea (20% CO2 ventilation) depressed olfactory bulb evoked potentials 25-30% in both rat and turtle. During anoxia, evoked potentials were completely abolished within 1 min in rat olfactory bulb but decreased to only 40% of control after 4 h in the turtle despite similar changes in brain pHe. Anoxia-induced acidification of turtle brain was exacerbated by hypercapnea and was attenuated by hypocapnea or by hypocapnea plus intravenous infusion of sodium bicarbonate. However, these manipulations of pHe during anoxia in turtle brain had little effect on depression of evoked potentials. We conclude that energy failure, rather than extracellular acidification, is the major contributor toward suppression of electrical activity in mammalian brain and that preservation of energy balance, rather than unique pH regulation, is responsible for protection of turtle brain during anoxia.
Stimulation of H+ secretion by CO2 in turtle bladder: role of intracellular pH, exocytosis, and calcium
Authors: Arruda J. A. , Dytko G. , Talor Z.
Published: December 2017

We studied the interaction of intracellular pH, exocytosis, and cell calcium on the stimulation of H+ secretion by CO2 in turtle bladder. Intracellular pH was continuously monitored by the fluorescent dye 6-carboxyfluorescein and exocytosis was monitored by the release of mucosal fluorescein dextran. The initial stimulation of H+ secretion by 1 or 5% CO2 added to the serosal solution was accompanied by a similar and temporally related increase in exocytosis. Furthermore, a decrease in intracellular pH seems necessary for the early increase in H+ secretion and exocytosis. Because calcium plays an important role in exocytosis, we measured intracellular calcium in isolated cells with the fluorescent dye quin2. An increase in intracellular calcium (from 50 to 100 nM) was observed in isolated turtle bladder epithelial cells gassed with 5% CO2. To further evaluate the role of intracellular calcium on H+ secretion and exocytosis we utilized agents that alter cell calcium such as trifluoperazine and lanthanum. In the presence of CO2 these agents blocked partially the increase in H+ secretion and exocytosis but did not affect the decrease in intracellular H+. In conclusion, exocytosis, intracellular pH, and intracellular calcium play a key role in mediating CO2-stimulated H+ secretion in the turtle bladder.
ANF and postprandial control of sodium excretion in dogs with compensated heart failure
Authors: Villarreal D. , Freeman R. H. , Brands M. W.
Published: December 2017

The changes in plasma immunoreactive atrial natriuretic factor (iANF) and urinary Na excretion that occur in response to an oral load of Na and to infusion of synthetic atrial natriuretic factor (ANF) were examined in conscious dogs with an arteriovenous (AV) fistula and chronic compensated high-output heart failure. After ingestion of a meal containing 125 meq Na, plasma iANF and right atrial pressure increased from high basal levels of 506 +/- 46 pg/ml and 96 +/- 5 mmH2O to peak responses of 728 +/- 43 pg/ml (P less than 0.05) and 104 +/- 6 mmH2O (P less than 0.05). These increases were associated with a brisk postprandial natriuresis and diuresis of a magnitude previously observed in normal dogs. Synthetic ANF infusions that achieved plasma iANF levels of similar and higher magnitude to those observed during the feeding experiments did not produce a significant natriuresis in these AV fistula dogs. In separate series of experiments, chronic effects of normal and low-Na diets on daily Na excretion and postabsorptive plasma iANF, renin, and aldosterone were studied in normal and AV fistula dogs. During the normal Na diet of 40 meq/day, both groups had normal levels of renin and aldosterone, but Na balance was achieved in AV fistula animals in the presence of a fourfold elevation in plasma iANF compared with normal dogs (P less than 0.05). During 2 wk of Na restriction, cumulative negative Na balance and marked stimulation of renin and aldosterone were similar in normal and AV fistula animals, but plasma iANF did not change significantly in either group.(ABSTRACT TRUNCATED AT 250 WORDS)
Body size, medullary thickness, and urine concentrating ability in mammals
Authors: Beuchat C. A.
Published: December 2017

B. H. Blake (Comp. Biochem. Physiol. A Comp. Physiol. 58: 413-419, 1977.) and W. A. Calder and E. J. Braun (Am. J. Physiol. 244 (Regulatory Integrative Comp. Physiol. 13): R601-R606, 1983.) have predicted that urine concentrating ability of mammals should decline with increasing body mass (M, in kg) as M-0.08. Edwards (29), on the other hand, speculated that concentrating ability should be independent of body mass. Using information compiled from the literature for 245 species of mammals, I examined the scaling of urine concentrating ability with body mass. Maximum urine concentration (Uosm, in mosmol/kgH2O) declined exponentially with body mass as Uosm = 2,564 M-0.097, and generally only the smallest species (less than 400 g) could produce urine with an osmolality greater than 4,000 mosmol/kgH2O. Medullary thickness (MT, in mm) and, therefore, the length of the loop of Henle, increased with body mass as MT = 8.147 M0.129. The thickness of the medulla relative to the size of the kidney (RMT), however, declined with body size (RMT = 5.408 M-0.108). The relative thickness of the medulla accounted for only 59% of the variability among species in concentrating ability, indicating that there are other morphological or physiological factors that significantly influence urine concentrating ability.
Effect of water or saline intake on heat-induced limb vasodilation in dehydrated baboons
Authors: Ryan K. L. , Proppe D. W.
Published: December 2017

Dehydration markedly attenuates the increase in hindlimb blood flow elicited by environmental heating (EH) in baboons. This study sought to determine the importance of gradually produced increases in body fluid osmolality and decreases in body fluid volume in producing this attenuation. The hindlimb blood flow increases during EH of seven unanesthetized chronically instrumented baboons were examined during euhydration, dehydration (64-68 h of water deprivation), and after ad libitum oral rehydration with either water or a hyperosmotic saline solution. EH consisted of acute exposure to ambient temperatures of 38-42 degrees C until internal temperature reached 39.5 degrees C. Dehydration depressed the maximal external iliac artery blood flow (MIBF) and iliac vascular conductance (IVC) attained during EH in the euhydrated state by 37 and 43%, respectively. Rehydration with either water or saline solution, however, restored maximal MIBF and IVC to euhydrated levels. Because plasma osmolality remained at dehydrated levels after rehydration with saline, hyperosmolality does not produce the dehydration-induced attenuation in hindlimb blood flow.
Inhibitory effect of renal nerve activity during canine anaphylactic hypotension
Authors: Koyama S. , Fujita T. , Uematsu H. , Shibamoto T. , Aibiki M. , Kojima S.
Published: December 2017

We have examined baroreceptor regulation of renal nerve activity (RNA) during anaphylactic hypotension that affects renal nerve activity. In anesthetized dogs, mean blood pressure (MBP), heart rate (HR), and RNA were simultaneously measured. To test for a normally functioning baroreceptor reflex in each animal, a transient hypotension was induced by an intravenous injection of sodium nitroprusside (4 micrograms/kg). Nitroprusside produced a reflex increase in RNA (+63 +/- 12% at -20 mmHg and +139 +/- 8% at -40 mmHg) and HR (+13 +/- 1 beats/min at -20 mmHg and +21 +/- 2 beats/min at -40 mmHg). However, intravenous administration of Ascaris suum antigen in animals with an intact neuraxis caused a decrease in RNA (-15 +/- 14% at -20 mmHg and -42 +/- 11% at -40 mmHg blood pressure during the antigen-induced hypotension) in parallel with a fall in systemic blood pressure. HR responses were -5 +/- 2 beats/min at -20 mmHg and -10 +/- 1 beats/min at -40 mmHg during the hypotension induced by the antigen. In animals with combined denervation of the carotid sinus and vagal nerves, HR did not change significantly during anaphylactic hypotension. However, a decrease in RNA remained (-60 +/- 4% at -20 mmHg and -72 +/- 4% at -40 mmHg of hypotension). The decrease in RNA after antigen administration was significantly greater after denervation than in animals with an intact neuraxis. These results indicate that systemic baroreceptor reflex control of RNA is reduced during anaphylactic hypotension. Impaired reflex control of sympathetic nerve activity may result from an impairment of sympathetic outflow through the central nervous system.
Diluting segment in kidney of dogfish shark. II. Electrophysiology of apical membranes and cellular resistances
Authors: Hebert S. C. , Friedman P. A.
Published: December 2017

Diluting segments from the bundle zone of the dogfish shark kidney were perfused in vitro and the electrophysiological characteristics of this segment investigated using conventional microelectrodes and cable analysis. In 21 tubules perfused with symmetrical Ringer solutions the average transepithelial voltage (Vte), transepithelial conductance (Gte), and equivalent short circuit current (Isc) were 8.7 +/- 0.6 mV, 91.3 +/- 10.2 mS/cm2, and 641 +/- 48 microA/cm2, respectively. Microelectrode impalements in 52 cells yielded values for the basolateral membrane voltage (Vb) and an estimated apical membrane fractional resistance (fRa) of -57.5 +/- 1.3 mV and 0.896 +/- 0.008, respectively. All of these parameters were distributed in a Gaussian manner. Liminal furosemide (10(-4) M) abolished Isc, hyperpolarized apical membrane voltage (Va) and Vb, increased Gte, and reduced fRa. The apical membrane was predominantly conductive to K+: increasing luminal K+ from 5 to 49.7 mM resulted in an apical depolarization of 41.2 mV and a fall in fRa and luminal Ba2+ (1 mM) depolarized Va by 14.3 mV and increased fRa. The apical transference number for K+ was 0.74 +/- 0.07. The cellular and paracellular resistances were estimated from the effects of luminal Ba2+ on fRa and Gte. The cell conductance represented approximately 45% of Gte, with the primary resistance barrier located at the apical membrane: apical membrane resistance was 59.7 +/- 16.0 and basolateral membrane resistance was 5.9 +/- 2.3 omega.cm2. From these resistance values together with the passive permeability (PNa/PCl) of 2.5 determined previously, the ratio of net Cl- absorption to net transcellular Na+ absorption was determined to be 2.(ABSTRACT TRUNCATED AT 250 WORDS)
Temporal relationships among fetal urine flow, ANF, and AVP responses to hypertonic infusions
Authors: Miner L. K. , Brace R. A. , Cheung C. Y.
Published: December 2017

The fetal urine flow response to acute increases in osmolality may be mediated by changes in the plasma concentrations of atrial natriuretic factor (ANF), arginine vasopressin (AVP), and/or angiotensin II (ANG II). To explore this, hypertonic NaCl or mannitol was infused intravascularly over 10 min into chronically catheterized fetal sheep and their mothers simultaneously, followed by a 2-h maternal infusion at 1-2 ml/min to maintain the elevated osmolality. Fetal osmolality rose by 16 mosmol/kgH2O during 13% mannitol and 2.5% NaCl infusions and by 57 mosmol/kgH2O during 7% NaCl infusions. Large increases in fetal urine flow occurred in the three groups with peak flows (average of 304%, P less than 10(-6)) at 0-4 min after the end of the infusion. Flow declined to preinfusion values in all groups at 30-40 min. These changes in urine flow occurred in parallel with a rise (to 223%, P less than 10(-6)) and fall in plasma ANF concentrations. One hour after the infusions, urine flow declined to 50% of control concomitant with elevations in plasma AVP (to 414%, P less than 10(-6)), whereas plasma ANG II concentration did not change. Thus the initial increase in fetal urine flow in response to acute hypertonic infusions is temporally related to a rise in fetal plasma ANF, whereas the subsequent fall in urine flow is temporally related to a fall in plasma ANF and a simultaneous rise in AVP concentration. This suggests that ANF may contribute to the acute urine flow increase after hypertonic infusion, whereas AVP appears to be more important for the long-term regulation of fetal urine flow.