bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of naloxone on regional cerebral blood flow during endotoxin shock in conscious rats
Authors: Law W. R. , Ferguson J. L.
Published: December 2017

Maintenance of cerebral blood flow (CBF) is vital during cardiovascular shock. Since opioids have been implicated in the pathophysiology of endotoxin shock and have been shown to alter cerebral perfusion patterns, we determined whether opioids were responsible for any of the changes in regional CBF observed during endotoxin shock and whether the use of naloxone might impair or aid in the maintenance of CBF. When blood flow (BF) is studied with microspheres in rats, the left ventricle of the heart is often cannulated via the right carotid artery. Questions have arisen concerning the potential adverse effects of this method on CBF in the hemisphere ipsilateral to the ligated artery. We measured right and left regional CBF by use of this route of cannulation. Twenty-four hours after cannulations were performed, flow measurements were made using radiolabeled microspheres in conscious unrestrained male Sprague-Dawley rats (300-400 g) before and 10, 30 and 60 min after challenging with 10 mg/kg Escherichia coli endotoxin (etx) or saline. Naloxone (2 mg/kg) or saline was given as a treatment 25 min post-etx. We found no significant differences between right and left cortical, midbrain, or cerebellar BF at any time in any treatment group. After etx, the whole brain received a large share of the depressed cardiac output. Thus global CBF was not significantly reduced below its pre-etx value, an effect unaltered by naloxone. Regionally, BF was reduced to cerebellum and midbrain by 30 min post-etx. Naloxone prevented this depression. No region was affected to a greater or lesser degree than others.(ABSTRACT TRUNCATED AT 250 WORDS)
Size selectivity of blood-brain barrier permeability at various times after osmotic opening
Authors: Robinson P. J. , Rapoport S. I.
Published: December 2017

Recent experiments have shown that after osmotic opening the blood-brain barrier recloses more rapidly to larger than to smaller molecules. Quantitative theoretical analysis of blood-brain barrier permeability to different-sized molecules at different times after osmotic opening supports the concept of pore creation as a result of opening of tight junctions between endothelial cells. Experiments also suggest significant bulk water flow from capillaries into brain within 10 min after opening at an average rate of approximately 1.6 X 10(-4) cm3 X s-1 X g brain-1. A mathematical model of blood-brain barrier permeability based on the creation of pores, together with bulk fluid flow, is presented for both cylindrical pores and rectangular slits. Experimental data are compatible with pore radii of approximately 200 A or slit widths of approximately 220 A. Pore densities of approximately 1 pore per 200 microns 2 of membrane surface are calculated at 6 min after barrier opening, reducing slightly as the barrier recloses. Calculated bulk flow is reduced by an order of magnitude within 35 min of barrier opening and is a major factor in altered blood-brain barrier permeability. Size dependence of blood-brain barrier permeability following osmotic opening is shown to be incompatible with enhanced vesicular transport.
Responses of vasopressin and enkephalins to hemorrhage in adrenalectomized dogs
Authors: Inoue M. , Kimura T. , Matsui K. , Ota K. , Shoji M. , Iitake K. , Yoshinaga K.
Published: December 2017

To study responses of methionine enkephalin-like substance (MELS) and vasopressin (AVP) to hemorrhage, plasma MELS, AVP, and catecholamine levels and mean arterial blood pressure (MAP) and central venous pressure (CVP) were investigated in intact and adrenalectomized dogs (n = 34) under pentobarbital anesthesia. Plasma MELS increased significantly following a hemorrhage-induced rise in plasma epinephrine in intact dogs (n = 6). Plasma AVP rose concomitantly with a fall in CVP before MAP fell, but the subsequent fall in MAP was accompanied by a further elevation in plasma AVP concentration. In nonhemorrhaged control dogs (n = 6) these parameters did not change during the experiment. In adrenalectomized dogs (n = 6) the hemorrhage-induced increase in plasma MELS and AVP was significantly attenuated despite similar decreases in MAP as in intact dogs. In sham-operated dogs (n = 10) changes in these parameters were similar to those in intact dogs. The differences between plasma MELS in the superior vena cava and thoracic aorta did not change during hemorrhage in intact dogs (n = 6), but the differences in plasma AVP rose significantly, indicating a release of the hormone from the head. These results indicate that MELS release elicited by hemorrhage may largely arise from the adrenal gland and not the brain. Adrenalectomy attenuated AVP response to hemorrhagic hypotension.
Glucose-induced norepinephrine levels and obesity resistance
Authors: Levin B. E. , Sullivan A. C.
Published: December 2017

The value of glucose-stimulated sympathetic activation in differentiating rats that would subsequently resist or develop diet-induced obesity (DIO) when chronically fed a high-calorie diet (CM) enriched in fat and sucrose was tested in 3-mo-old male Sprague-Dawley rats. While the rats were on chow the areas under the curve for plasma glucose, insulin, and norepinephrine (NE) levels were measured for 60 min after an intravenous glucose load (1 g/kg). Half of the rats then switched to the CM diet for 14 wk developed DIO with 54% more weight gain and 205% heavier retroperitoneal fat pads; half [diet resistant (DR)] had weight gain and pad weights comparable to chow-fed controls. Caloric intake was comparable in all animals. NE areas after intravenous glucose loads were 54% lower in DR than DIO rats, and there was a positive correlation (r = 0.63) between these NE areas and subsequent weight gain on the CM diet. Areas under the insulin curve correlated with subsequent weight gain on chow (r = 0.71) but not the CM diet. These results suggest that rats predisposed to become DR on the CM diet have dampened sympathetic activation after a glucose load, possibly because of heightened end-organ responsiveness to NE.
Insulin does not influence muscle glycogenolysis in adrenodemedullated exercising rats
Authors: Yang H. T. , Carlson K. I. , Winder W. W.
Published: December 2017

Previous reports have indicated that adrenodemedullated (ADM) rats exhibit an impairment in muscle glycogenolysis and elevated plasma insulin during exercise. This study was designed to determine whether the impaired muscle glycogenolysis in ADM rats is due to absence of epinephrine or to the inappropriately elevated plasma insulin. Fasted ADM rats were infused with saline, with epinephrine (0.045 micrograms . 100 g-1 . min-1), or with epinephrine + insulin (1.6, 3.3, 6.6, and 8.3 ng . 100 g-1 . min-1) during a 30-min run on the treadmill (21 m/min, 10% grade). Soleus muscle glycogen decreased from 5.1 +/- 0.2 mg/g in resting ADM rats to 4.0 +/- 0.2, 0.8 +/- 0.1, and 0.8 +/- 0.1 mg/g in the exercising saline-, epinephrine-, and epinephrine + insulin (8.3 ng . 100 g-1 . min-1)-infused rats, respectively. Glycogen utilization in gastrocnemius and red and white quadriceps muscles during exercise was likewise unaffected by insulin infusion. Blood glucose concentrations were 3.75 +/- 0.08, 2.65 +/- 0.14, 3.93 +/- 0.20, and 2.03 +/- 0.09 mM in the same groups at the end of exercise. Blood lactate was 50% lower and the blood 3-hydroxybutyrate and plasma free fatty acid concentrations were significantly higher in the ADM + saline rats than the other exercising rats. We conclude that inappropriately elevated plasma insulin does not impair epinephrine-stimulated muscle glycogenolysis in fasted ADM rats during exercise.
Calcium content of frog sciatic nerve during chronic hypocalcemia and hypercalcemia
Authors: Wadhwani K. C. , Levitan H. , Rapoport S. I.
Published: December 2017

We examined the calcium contents of desheathed peripheral nerve, perineurial sheath, and whole sciatic nerve in the frog as a function of the steady-state plasma concentration of ionized calcium. Chronic hypocalcemia was induced by parathyroidectomy and by bathing frogs in a phosphate medium. Chronic hypercalcemia was induced by administering vitamin D3 and by bathing frogs for up to 2 wk in medium containing 50 mM CaCl2. Calcium was measured with a calcium-sensitive electrode and by atomic absorption spectroscopy. The calcium contents (mmol/kg wet wt) in whole nerve, desheathed nerve, and the perineurial sheath varied linearly with slopes of 0.72, 0.71, and 1.72, respectively, with plasma concentration (mM) of ionized calcium, which ranged from 0.3 to 8.0 mM. In the same animals the calcium content in the cerebrum was independent of plasma calcium between 0.5 and 1.5 mM but rose at higher plasma concentrations. Our results indicate that net calcium concentration in the frog peripheral nerve is not regulated during chronic hypocalcemia and hypercalcemia, whereas brain calcium is regulated at plasma calcium concentrations less than 1.5 mM. The lack of calcium regulation in the nerve is attributed to the lack of calcium regulation in the endoneurial compartment.
Hormone-controlled cAMP-mediated fluid secretion in yellow-fever mosquito
Authors: Petzel D. H. , Berg M. M. , Beyenbach K. W.
Published: December 2017

Evidence is presented for hormone-controlled adenosine 3',5'-cyclic monophosphate (cAMP)-mediated NaCl diuresis in Malpighian tubules of the blood-feeding yellow-fever mosquito Aedes aegypti. Studies in isolated Malpighian tubules reveal that cAMP added to the peritubular bath selectively stimulates NaCl secretion and not KCl secretion by increasing the Na conductance of the basolateral membrane of primary cells. These effects are duplicated by forskolin and theophylline in parallel with increased intracellular concentrations of endogenous cAMP. Two natriuretic peptides that we have isolated by high-pressure liquid chromatography (HPLC) methods from mosquito heads also increase NaCl and fluid secretion in isolated Malpighian tubules together with increased intracellular levels of cAMP. These results are consistent with a mechanism of NaCl diuresis in which the natriuretic peptides and cAMP are respectively the primary and secondary messengers that couple the ingestion of a blood meal to the excretion of the unwanted salt and water fraction of the meal. This hypothesis is supported by in vivo studies that reveal elevated intracellular cAMP levels in Malpighian tubules at the time of maximum NaCl diuresis.
Diurnal patterns of hemodynamic performance in nonhuman primates
Authors: Engel B. T. , Talan M. I.
Published: December 2017

Heart rate, stroke volume, and intra-arterial blood pressures were monitored continuously in each of four monkeys for 18 consecutive hours, 5 days/wk, for several weeks. Mean heart rate, stroke volume, cardiac output, systolic and diastolic pressure, and total peripheral resistance were calculated each minute, and these averages were analyzed further to yield hourly means and intercorrelations. The main findings from the analyses of mean levels were that cardiac output fell throughout the night and that peripheral resistance rose during the same interval so that arterial pressure fell only slightly; the highest levels of peripheral resistance and lowest levels of cardiac output were recorded between 0500 and 0700. Furthermore, the levels of these responses during the remainder of the morning were higher (peripheral resistance) and lower (cardiac output) than those recorded in the evening.
Selective cooling of the brain in reindeer
Authors: Johnsen H. K. , Blix A. S. , Mercer J. B. , Bolz K. D.
Published: December 2017

Cineangiographic examination of reindeer exposed to local (hypothalamic) or general heating and cooling revealed that the angular oculi veins are constricted during cold stress but dilated during heat stress. Moreover, during heat stress a segment of the facial vein appeared to be occluded, causing the cold venous return from the nasal mucosa to be routed directly to the cavernous sinus for selective cooling of the brain. Histological examination of the vasoactive segment of the facial vein showed unusually thick longitudinal and circular layers of smooth muscle cells. Obstruction of angular oculi blood flow by clamping of the veins in the heat-stressed animal resulted in an immediate rise in brain temperature. When reindeer under heat stress shift from closed- to open-mouth panting, only the expiratory phase of the respiratory cycle takes place through the mouth, whereas inspiration through the nose is continued. In this way, cooling of the nasal mucosa and, hence, cooling of the brain, is maintained.
Nasal heat and water exchange in gray seals
Authors: Folkow L. P. , Blix A. S.
Published: December 2017

Metabolic rate (MR), expired air temperature (Tex), respiratory frequency (f), respiratory minute volume (V), and skin (Ts) and body (Tb) temperatures were recorded in three gray seals (Halichoerus grypus) at ambient air temperatures (Ta) between -40 and +20 degrees C. At Ta within the thermoneutral zone, MR averaged 3.7 W.kg-0.75, while mean V was 0.26 1.min-1.kg-0.75. At Ta below -11 degrees C [apparent lower critical temperature (Tlc)], both MR and V increased linearly with decreasing Ta. Average maximum MR (9.6 W.kg-0.75) and V (0.57 1.min-1.kg-0.75) were both recorded at Ta of -40 degrees C. Tex decreased with decreasing Ta to an average minimum value of 8 degrees C at Ta of -30 degrees C. The highest Tex recorded was 32 degrees C at Ta of +20 degrees C. At Ta of -20 degrees C, both total respiratory heat loss, with one exception, and respiratory evaporative water loss reached their lowest values. At this Ta, 66% of the heat and 80% of the water added to the inspired air were regained on expiration. We suggest that nasal heat exchange may be of considerable importance for thermal and water balance in many pinnipeds.
Ovine fetal and adult atrial natriuretic factor metabolism
Authors: Ervin M. G. , Ross M. G. , Castro R. , Sherman D. , Lam R. W. , Castro L. , Leake R. D. , Fisher D. A.
Published: December 2017

Studies were conducted to quantify ovine fetal and adult atrial natriuretic factor (ANF) metabolism. A total of 14 pregnant ewes with singleton fetuses were prepared with vascular catheters. In protocol 1, six fetuses (mean gestation, 131 +/- 1 days) received intravenous infusions of synthetic human ANF (hANF, 100 ng.min-1.kg-1) for 60 min. Mean basal fetal plasma ANF levels increased from 180 +/- 44 pg/ml to a steady-state level of 1,233 +/- 192 pg/ml. In protocol 2, five fetuses (mean gestation, 130 +/- 1 days) received successive 40-min infusions of hANF at 5, 25, and 100 ng.min-1.kg-1. Although basal fetal plasma ANF levels (522 +/- 135 pg/ml) were greater than those observed in protocol 1, fetal plasma ANF levels increased to 1,580 +/- 295 pg/ml at the highest infusion rate. In both protocols 1 and 2, basal fetal plasma ANF levels were three- to fourfold greater than maternal levels. The fetal plasma ANF clearance rates calculated from protocol 1 and from the 25- and 100-ng.min-1.kg-1 infusions from protocol 2 were similar (89 +/- 10, 120 +/- 31, and 116 +/- 38 ml.min-1.kg-1, respectively) and were combined to yield a mean estimated fetal plasma ANF clearance rate of 102 +/- 11 ml.min-1.kg-1. In protocol 3, adult plasma ANF levels increased from 137 +/- 36 to 4,142 +/- 776 pg/ml in response to ANF infusion at 200 ng.min-1.kg-1. The mean plasma ANF clearance rate calculated for the adult animals was 59 +/- 12 ml.min-1.kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)
Impact of acute corticosterone administration on feeding and macronutrient self-selection patterns
Authors: Kumar B. A. , Leibowitz S. F.
Published: December 2017

Food intake, body weight, and meal patterns in rats are known to be specifically influenced by circulating corticosterone (CORT). The present study examined, in Sprague-Dawley rats, the role of CORT in the regulation of caloric intake and choice of macronutrients during specific periods of the light-dark cycle. Adrenalectomy (ADX) significantly attenuated the ingestion of all three macronutrients, namely, protein, carbohydrate, and fat, in different test periods of the light-dark cycle. This deficit was significantly stronger just before or during the early dark hours, compared with the light period, and it was immediately CORT reversible. During this same early dark period, the stimulatory effect of CORT (0.5 or 2.0 mg/kg sc) on total food intake in ADX animals was also significantly stronger than during the light period. At this time, the CORT-injected ADX animals consumed an even greater amount of total food intake than did the vehicle-injected sham-operated animals and showed a significant preference for carbohydrate, as opposed to no change or a decline in preference for protein or fat. These findings, in light of other evidence, suggest that CORT ensures and stabilizes the ingestion of all three macronutrients but, in particular, stimulates carbohydrate ingestion during the important feeding period at the dark onset when CORT levels normally peak. It is proposed that CORT may provide a critical signal, in conjunction with hypothalamic neurotransmitter systems, in the behavioral and metabolic regulation of body energy balance.
PGI2 attenuates baroreflex control of renal nerve activity by a vagal mechanism
Authors: Zucker I. H. , Panzenbeck M. J. , Barker S. , Tan W. , Hajdu M. A.
Published: December 2017

The present study was undertaken to determine whether left circumflex coronary artery (ic) administration of prostacyclin (PGI2) caused an inhibition of the baroreflex control of renal sympathetic nerve activity (RSNA). RSNA was recorded in 12 dogs. Baroreflex sensitivity of RSNA was assessed by infusion of either sodium nitroprusside or phenylephrine and by determining the slope of the mean arterial pressure-RSNA relationship. During nitroprusside infusion, intracoronary PGI2 depressed the baroreflex sensitivity by nearly 90% compared with intracoronary tris(hydroxymethyl)aminomethane (Tris) (P less than 0.002). In addition, the peak increase in RSNA during nitroprusside infusion was significantly inhibited during intracoronary PGI2 (57.9 +/- 6.4 vs. 21.2 +/- 3.0 spikes/s, P less than 0.05). There was no significant difference in the inhibition of RSNA during phenylephrine infusion when intracoronary PGI2 was compared with Tris. Both bilateral vagotomy and pericoronary lidocaine blocked the inhibitory effects of PGI2 on the baroreflex increase in RSNA. It is concluded from these data that exogenously administered PGI2 stimulates or sensitizes afferent endings within the supply of the left circumflex coronary artery to inhibit the baroreflex control of RSNA during evoked hypotension. These afferents traverse vagal pathways via the pericoronary nerves. The role of endogenous prostaglandins in modulation of baroreflex function via a cardiac reflex remains to be elucidated.
Adrenergic modulation of pancreatic glucagon and insulin secretion in sheep
Authors: Oda S. , Hagino A. , Ohneda A. , Sasaki Y. , Tsuda T.
Published: December 2017

The effect of intravenous infusion of epinephrine, either alone or together with various doses of phentolamine or propranolol, on the secretion of both glucagon and insulin was determined in six sheep. Intravenous infusion of epinephrine alone caused increases in plasma glucagon and glucose concentrations and produced a slight but significant decrease in plasma insulin concentration. The concomitant infusion of propranolol and epinephrine augmented glucagon release and inhibited insulin secretion. Combined propranolol plus epinephrine infusion also caused a marked hyperglycemia. The concomitant infusion of phentolamine and epinephrine produced slight inhibition of glucagon secretion and markedly promoted insulin secretion. Epinephrine-induced hyperglycemia was eliminated by phentolamine infusion. The effects of isoproterenol infusion on plasma glucagon, insulin, and glucose concentrations were similar to that caused by the concomitant infusion of phentolamine and epinephrine. The effects of isoproterenol were abolished by the infusion of propranolol. It is concluded that an alpha-receptor mechanism is the most important component of adrenergic modulation of pancreatic glucagon secretion, whereas beta-receptor activation stimulates and alpha-receptor activation inhibits insulin secretion in sheep.
Role of adrenal medulla in hemodynamic response to hemorrhage and naloxone
Authors: Schadt J. C. , Gaddis R. R.
Published: December 2017

We tested the hypothesis that enkephalins or some other compound(s) released by the adrenal medulla during hemorrhage were responsible for the resultant hypotension. We compared the hemodynamic and plasma catecholamine responses to hemorrhage and subsequent opioid receptor blockade with naloxone in intact, adrenal-denervated (ADD), and adrenalectomized (ADX) rabbits. The studies were done in conscious, chronically prepared, male New Zealand White rabbits. The hemodynamic response to hemorrhage was not different among the three groups. Plasma norepinephrine (NE) increased early in hemorrhage in all groups. In the ADD and ADX animals, NE decreased significantly at the transition to hypotension, suggesting decreased release of NE by peripheral sympathetic nerves as a possible cause of the decrease in pressure. In the intact group, NE did not decrease but reached a plateau possibly due to the release of some NE by the adrenal medulla, which obscured the decreased release by sympathetic nerves. The pressor response to naloxone, though present in all groups, was attenuated by adrenalectomy or adrenal denervation. The plasma NE response to naloxone was similar in all groups and involved a two- to threefold increase after naloxone. We conclude that enkephalins or any other compounds released by the adrenal gland are not responsible for the acute hemodynamic changes during hemorrhage in the conscious rabbit. However, some substance(s) released by the adrenal medulla, perhaps epinephrine, does play a role in naloxone's pressor effect, since this is reduced by adrenalectomy or adrenal denervation.
Atrial natriuretic factor attenuates carotid baroreflex-mediated cardioacceleration in humans
Authors: Ebert T. J. , Cowley A. W.
Published: December 2017

We tested the hypothesis that infusions of atrial natriuretic factor (ANF) attenuate carotid baroreflex-mediated tachycardia in humans. The afferent profile from carotid baroreceptors was altered by repeated, intermittent random applications of neck suction (40 mmHg) and neck pressure (20 mmHg) to healthy volunteers during supine control and during infusions of 15 (n = 6) or 25 ng.kg-1.min-1 (n = 9) of alpha-human ANF or during placebo (n = 9). ANF infusions resulted in five- and eightfold increases of plasma ANF, which did not alter base-line cardiac interval, blood pressure, respiratory sinus arrhythmia, plasma renin activity, vasopressin, or norepinephrine but did reduce central venous pressure. Reflex bradycardic responses were unaltered during these infusions. Reflex tachycardic responses to carotid compression were significantly blunted (up to 40%) during infusions of ANF and were unchanged during placebo. These responses may be due to a sensitization of cardiac receptors and augmentation of cardiac-vagal afferent traffic by ANF, which diminishes reflex cardiac-sympathetic outflow during carotid baroreceptor unloading.
Pattern differences in experimental fevers induced by endotoxin, endogenous pyrogen, and prostaglandins
Authors: Morimoto A. , Nakamori T. , Watanabe T. , Ono T. , Murakami N.
Published: December 2017

To distinguish pattern differences in experimentally induced fevers, we investigated febrile responses induced by intravenous (IV), intracerebroventricular (ICV), and intra-preoptic/anterior hypothalamic (POA) administration of bacterial endotoxin (lipopolysaccharide, LPS), endogenous pyrogen (EP), human recombinant interleukin-1 alpha (IL-1), and prostaglandins E2 and F2 alpha (PGE2 and PGF2 alpha). Intravenous LPS, EP, or IL-1 in high concentrations caused biphasic fever. In low concentrations, they induced only the first phase of fever. Latency to onset and time to first peak of fever induced by IV injection of LPS or EP were almost the same as those after ICV or POA injection of PGE2. Fever induced by ICV or POA administration of LPS, EP, IL-1, or PGF2 alpha had a long latency to onset and a prolonged time course. There were significant differences among the latencies to fever onset exhibited by groups that received ICV or POA injections of LPS, EP, or PGF2 alpha and by groups given IV injections of LPS or EP and ICV or POA injections of PGE2. Present observations indicate different patterns of fever produced by several kinds of pyrogens when given by various routes. These results permit us to consider the possibility that there are several mediators or multiprocesses underlying the pathogenesis of fever.
Regional plasma catecholamine removal and release at rest and exercise in dogs
Authors: Peronnet F. , Beliveau L. , Boudreau G. , Trudeau F. , Brisson G. , Nadeau R.
Published: December 2017

Dynamics of circulating catecholamines (CA) were studied at rest (heart rate = 104 +/- 3 beats/min) and during mild treadmill exercise (heart rate = 168 +/- 5 beats/min) in 60 dogs. Plasma epinephrine (E) and norepinephrine (NE) removal from circulation and release into circulation were estimated from plasma CA arteriovenous differences across the regional vascular beds studied (pulmonary, myocardial, hepatosplanchnic, renal, and skeletal muscle vascular beds) and from regional blood flows. Regional plasma E fractional extraction (PEFE) was used as an index of NE removal from plasma. Arterial plasma CA increased significantly from rest to exercise (P less than 0.05). A significant PEFE was observed at rest and exercise across all studied vascular beds but the pulmonary bed. When plasma flow was taken into account, the largest contributors to plasma CA removal were the hepatosplanchnic vascular bed at rest and skeletal muscle vascular beds during exercise. At rest, the hepatosplanchnic vascular bed was a major contributor to the plasma NE pool. During exercise, main contributors to NE release into plasma were skeletal muscle vascular beds. Circulating CA kinetics did not appear to vary from rest to exercise. Clearance and apparent distribution space were estimated to be, respectively, 1.5 l/min and 2 liters for circulating E and 2 l/min and 5 liters for NE at rest and exercise. Circulating E and NE half times were estimated to be approximately 1 and 1.8 min, respectively.
Kinetics of sodium homeostasis in rats: rapid excretion and equilibration rates
Authors: Holtzman E. J. , Braley L. M. , Williams G. H. , Hollenberg N. K.
Published: December 2017

In normal humans, when sodium intake is abruptly reduced from a high to a very low level, renal sodium excretion falls exponentially (half time approximately 24 h), and several days are required to achieve external sodium balance, where intake equals excretion. Because much of our knowledge of intrarenal mechanisms comes from the rat, we studied their capacity to handle sodium. In two strains of rat, Sprague-Dawley (SD) and Wistar-Kyoto (WKY), whether the sodium load was administered intravenously, by gavage, or by spontaneous feeding, the slope relating sodium excretion to time was 8-10 times more rapid than in humans, reflecting half times of 2-3 h, and external sodium balance was achieved in hours rather than days. The combination of normal rat nocturnal feeding patterns and the rapidity of the response result in a daily spontaneous transition from an expanded state with a high or intermediate level of sodium excretion to a more contracted state, with minimal sodium excretion. Studies designed to assess sodium homeostasis in rats, and related renal and hormonal changes, must consider these rapid transitions, which are related, perhaps, to the rats' persistent and remarkably rapid growth.
Hypocalcin from Stannius corpuscles inhibits gill calcium uptake in trout
Authors: Lafeber F. P. , Flik G. , Wendelaar Bonga S. E. , Perry S. F.
Published: December 2017

Bidirectional whole body flux and branchial Ca2+ influx were measured in freshwater rainbow trout. Intra-arterial injections of homogenates of Stannius corpuscles (CS) as well as of a 54-kDa isolated product (hypocalcin) exerted an inhibitory effect on whole body Ca2+ influx, but did not effect Ca2+ efflux. Hypocalcin was more effective in reducing Ca2+ influx in trout acclimated to low-calcium freshwater than in fish from normal-calcium water. We conclude that the isolated product (hypocalcin) represents the hypocalcemic principle of the CS. Similar doses of hypocalcin caused quantitatively similar decreases in Ca2+ influx in vivo and in the isolated perfused head preparation. This indicates that the gills form the principle target for hypocalcin in trout. The branchial transepithelial potential did not change during hormone treatments. Possible mechanisms of hypocalcin action are suggested.
Renal and endocrine responses in the elderly during head-out water immersion
Authors: Tajima F. , Sagawa S. , Iwamoto J. , Miki K. , Claybaugh J. R. , Shiraki K.
Published: December 2017

After overnight food and fluid restriction, seven healthy old (62-74 yr) and eight young (21-28 yr) men were examined before, during, and after 3-h head-out immersion (HOI) in thermoneutral water (34.5 +/- 0.5 degrees C). On separate days, all subjects remained seated in air for 5 h to obtain the time control data. Although HOI induced a reversible increase in urine flow in all subjects, the response was faster and greater in magnitude in the elderly than in the young. Na excretion and osmolal clearance also followed a response pattern identical to that of urine flow; thus the HOI-induced diuresis was entirely osmotic. Endogenous creatinine clearance increased in the elderly at 2 h of HOI, suggesting an age-related modification in kidney hemodynamics. Although there was virtually the same cephalad blood shift (measured by impedance cardiography), mean arterial pressure significantly increased (P less than 0.05) during HOI in the elderly, which also indicated a different response of peripheral circulation to HOI in the elderly. Control level of plasma atrial natriuretic factor (ANF) was nearly twofold greater in the elderly compared with the young. The HOI induced a nearly fourfold increase in ANF in the elderly, whereas that for the young was threefold. Both plasma aldosterone and ADH responses to HOI were attenuated in the elderly compared with the young, which had no correlation with urine flow or Na excretion. It is concluded that the elderly release more ANF at a given cephalad volume expansion compared with the young, but the vasodilative reaction to ANF was attenuated in the elderly.
Vagal C-fiber blockade abolishes sympathetic inhibition by atrial natriuretic factor
Authors: Schultz H. D. , Gardner D. G. , Deschepper C. F. , Coleridge H. M. , Coleridge J. C.
Published: December 2017

Administration of atrial natriuretic factor (ANF) to anesthetized rats decreases renal nerve activity (RNA), an effect prevented by vagotomy but not by atropine. We sought to determine whether afferent vagal C-fibers mediate the inhibition of sympathetic outflow. ANF (2.5 micrograms/kg iv) decreased mean arterial pressure (MAP) by 25 +/- 2 mmHg, RNA by 11 +/- 5%, and least splanchnic nerve activity (LSNA) by 10 +/- 4% in anesthetized rats with arterial baroreceptors intact, and by 40 +/- 3 mmHg, 28 +/- 7%, and 23 +/- 4%, respectively, in sinoaortic-denervated rats. Inhibition of RNA and LSNA by ANF was reduced slightly by cooling the vagi to 6 or 7 degrees C, a temperature at which conduction in A-fibers was blocked and that in C-fibers attenuated; inhibition was abolished when C-fibers were blocked by cooling to 0 degrees C. We conclude that the inhibition of RNA and LSNA by ANF was mediated by afferent vagal C-fibers. We also obtained evidence that the aortic nerves contribute to ANF-induced inhibition of RNA. Our results support the notion that ANF evokes a generalized decrease in sympathetic tone that contributes to the hypotension, cardiac inhibition, and natriuresis accompanying systemic administration of the peptide.
Penetration of peripheral glucose and insulin into cerebrospinal fluid in rats
Authors: Steffens A. B. , Scheurink A. J. , Porte D. , Woods S. C.
Published: December 2017

In this study the penetration of plasma insulin and glucose into the cerebrospinal fluid (CSF) was investigated. Rats were implanted with cannulas in the cisterna magna and into the left and right jugular veins. Freely moving rats were intravenously infused during 4 h with either glucose solution (10 mg/min) or saline. Before, during, and after the infusions, simultaneous blood and CSF samples were taken. Infusion of glucose led to an immediate rise of both plasma glucose and insulin. Although CSF glucose followed plasma glucose within 10 min, CSF insulin was unchanged until 40 min. After termination of the glucose infusion, levels of all substances returned to base line within 10 min. Twenty-four-hour food deprivation resulted in a significant decrease of plasma glucose, plasma insulin, CSF glucose, and CSF insulin. At the onset of eating after deprivation, an increase of plasma glucose and insulin occurred within 10 min, whereas CSF glucose was delayed between 10 and 40 min, after which ad libitum values were attained or surpassed. CSF insulin always remained below ad libitum levels. It is concluded that 1) glucose and insulin penetrate into the CSF and 2) CSF insulin and glucose can fulfill a putative feedback in homeostatic control of food intake and body weight.
Neural control of shark rectal gland
Authors: Stoff J. S. , Silva P. , Lechan R. , Solomon R. , Epstein F. H.
Published: December 2017

Veratrum alkaloids stimulated salt secretion by the isolated perfused rectal gland of Squalus acanthias. Stimulation by veratrine was prevented by the nerve channel blockers tetrodotoxin and procaine and was not evident in a preparation of dispersed rectal gland cells. Vasoactive intestinal peptide (VIP)-like immunoreactivity was detected by histological techniques in neuronal tissue within the rectal gland. Veratrine stimulation caused the release of immunoreactive VIP into the venous effluent of perfused glands. The stimulatory action of veratrine was inhibited by somatostatin, another neuropeptide known to be present in nerves of Squalus rectal gland. These findings suggest the likelihood of neural modulation of rectal gland function.
Trabecular bone remodeling after seven days of weightlessness exposure (BIOCOSMOS 1667)
Authors: Vico L. , Chappard D. , Palle S. , Bakulin A. V. , Novikov V. E. , Alexandre C.
Published: December 2017

Seven male rats were exposed to 7 days of weightlessness in the Soviet mission COSMOS 1667 and compared with seven control rats by bone histomorphometric methods. In proximal tibial metaphysis, the trabecular bone volume was markedly reduced in flight animals. Trabeculae were decreased in number and thickness; this probably leads to alteration of bone mechanical properties. Formation activity (reflected by measurements of osteoid seams) was decreased at trabecular and endosteal levels. Resorption activity (estimated by count of osteoclast number and active resorption surfaces using a histoenzymologic method) remained unchanged. The imbalance between these cellular activities appears to be responsible for the loss of trabecular bone mass. In proximal femoral metaphysis, measurements were performed in an area located under the muscular insertions. The trabecular bone volume, despite a slight decrease in flight rats, was not significantly different from that of control rats. Furthermore, osteoclastic and osteoid parameters were unchanged. Differential responses between these two long bones need additional investigations. In thoracic and lumbar vertebrae no detectable change in bone mass and bone resorption parameters was found.
Regional neurohypophysial and hypothalamic blood flow in rats during hypercapnia
Authors: Bryan R. M. , Myers C. L. , Page R. B.
Published: December 2017

Regional cerebral blood flow (rCBF) was measured in the neurohypophysis and hypothalamus in normocapnic and hypercapnic rats using [14C]isopropyliodoamphetamine. Rats were surgically prepared using nitrous oxide and halothane and placed in plaster restraining casts. Hypercapnia was produced by increasing the fractional concentration of inspired CO2 (FICO2). rCBF in normocapnic rats was higher in the paraventricular nucleus, supraoptic nucleus, median eminence, and neural lobe than rates previously measured by use of diffusible tracers. During hypercapnia blood flow increased linearly with arterial PCO2 (PACO2) in all regions except the median eminence and neural lobe, which were not affected by hypercapnia. When rats were pretreated with phentolamine (1 mg/kg) to block the alpha-adrenergic receptors, blood flow in the median eminence and neural lobe increased significantly during hypercapnia. We conclude that blood flow in the cell bodies of the paraventricular nucleus and supraoptic nucleus is regulated differently during hypercapnia than blood flow in the nerve terminals in the median eminence and neural lobe. Furthermore, vasodilation produced by increased CO2 is offset by alpha-receptor stimulation in the median eminence and neural lobe.
In vivo transferrin-iron receptor relationships in erythron of rats
Authors: Intragumtornchai T. , Huebers H. A. , Eng M. , Finch C. A.
Published: December 2017

Quantitative measurements of transferrin receptors, tissue transferrin, tissue iron uptake, and erythroid cellularity have been carried out in rats with altered erythropoiesis and altered iron balance. Erythroid receptors increased with erythroid hyperplasia, with the increase in proportion to the increased number of red cell precursors in phenylhydrazine-treated rats. Receptors increased disproportionately in iron deficiency due to both erythroid hyperplasia and an increase in receptors in the individual cell. There was a ratio of 1:1 between cell-related transferrin and receptors in circulating reticulocytes but a disproportionate amount of cell-related transferrin in fixed erythroid tissues (marrow and spleen), suggesting that there was some other reason for the concentration of transferrin in these tissues. Erythron iron uptake was increased in proportion to the increased receptor number in phenylhydrazine-treated animals but was reduced in iron deficiency because of the limited amount of iron-bearing transferrin. These studies demonstrate the dominant role of erythron cellularity and iron status in vivo in determining total receptor number and the importance of receptor number and iron supply in tissue iron uptake.
Effects of melatonin on 2-deoxy-[1-14C]glucose uptake within rat suprachiasmatic nucleus
Authors: Cassone V. M. , Roberts M. H. , Moore R. Y.
Published: December 2017

Previously, we have demonstrated that metabolic activity, shown by autoradiographic determination of 2-deoxy-[1-14C]glucose (2-DG) uptake, within the rat hypothalamic suprachiasmatic nuclei (SCN) was inhibited by subcutaneous injection of 1 mg/kg melatonin. To determine whether this effect was specific to a particular time of day, the effects of melatonin on 2-DG uptake were studied in several hypothalamic areas, including the SCN, supraoptic nuclei (SON), lateral hypothalamic area (LHA), and anterior hypothalamic area (AHA) every 4 h throughout the circadian day. In a second experiment, the effects of different melatonin doses were studied at the time of day at which melatonin had its maximal effect to determine the dose-response relationship of melatonin-induced inhibition of SCN 2-DG uptake. The data indicate that melatonin inhibited 2-DG uptake in the SCN alone at one time of day, primarily at circadian time (CT) 6 and CT10, 2-6 h before subjective dusk, and secondarily at CT22, just before subjective dawn. This effect was dose dependent with a 50% effective dose of 1.49 +/- 2.30 micrograms/kg. The temporal and dose-response characteristics of these effects are similar to those characterizing the entraining effects of melatonin on circadian patterns of locomotion and drinking.
Multiple linear regression is a useful alternative to traditional analyses of variance
Authors: Slinker B. K. , Glantz S. A.
Published: December 2017

Physiologists often wish to compare the effects of several different treatments on a continuous variable of interest, which requires an analysis of variance. Analysis of variance, as presented in most statistics texts, generally requires that there be no missing data and often that each sample group be the same size. Unfortunately, this requirement is rarely satisfied, and investigators are confronted with the problem of how to analyze data that do not strictly fit the traditional analysis of variance paradigm. One can avoid these pitfalls by recasting the analysis of variance as a multiple linear regression problem. When there are no missing data, the results of a traditional analysis of variance and the corresponding multiple regression problem are identical; when the sample sizes are unequal or there are missing data, one can use a regression formulation to analyze data that cannot be easily handled in a traditional analysis of variance paradigm and thus overcome a practical computational limitation of traditional analysis of variance. In addition to overcoming practical limitations of traditional analysis of variance, the multiple linear regression approach is more efficient because in one run of a statistics routine, not only is the analysis of variance done but also one obtains estimates of the size of the treatment effects (as opposed to just an indication of whether such effects are present or not), and many of the pairwise multiple comparisons are done (they are equivalent to t tests for significance of the regression parameter estimates). Finally, interaction between the different treatment factors is easier to interpret than it is in traditional analysis of variance.
Release of atrial natriuretic factor in hypophysectomized rats
Authors: Dietz J. R. , Nazian S. J.
Published: December 2017

The purpose of these studies was to examine the effect of hypophysectomy (HYPOX) on the secretion of atrial natriuretic factor (ANF) and related changes in renal function. Pentobarbital sodium-anesthetized rats received a 20% intravenous blood volume expansion. In intact rats (n = 7), plasma ANF was 39 +/- 3 pg/ml before volume expansion and increased to 71 +/- 10 and 77 +/- 7 pg/ml after volume expansion (P less than 0.01). Volume expansion in HYPOX rats (n = 8) also resulted in an increase in plasma ANF concentration that was significantly less than in the intact group. With volume expansion, sodium excretion rate increased from 0.19 +/- 0.06 to 1.43 +/- 0.43 microM. min-1.100 g body wt-1 (P less than 0.01) in intact rats and from 0.24 +/- 0.08 to 0.74 +/- 0.14 microM.min-1.100 g body wt-1 (P less than 0.05) in HYPOX rats (HYPOX less than intact; P less than 0.05). In an isolated heart-lung preparation, HYPOX rats secreted significantly less ANF than intact rats during two 30-min perfusion periods (P less than 0.02). Atrial ANF concentration was also significantly less in HYPOX rats (P less than 0.05). These results show that hypophysectomy leads to an attenuation of the ANF response to atrial distention and attenuated natriuretic response to blood volume expansion and suggest that the pituitary is required to maintain normal cardiac endocrine function.
Robust conditioned flavor preference produced by intragastric starch infusions in rats
Authors: Sclafani A. , Nissenbaum J. W.
Published: December 2017

Rats were intragastrically infused with hydrolyzed starch (16% Polycose) or water as they drank cherry- or grape-flavored water during 23-h/day tests; chow was available ad libitum. After 4 conditioning days the rats displayed a near-total preference (96%) for the starch-paired flavor over the water-paired flavor in two-choice tests. This conditioned flavor preference persisted during a 4-day extinction test when both flavors were paired with water infusions. The results demonstrate that the postingestive actions of starch are rewarding to nondeprived rats and can condition strong and long-lasting flavor preferences.
Pressor responsiveness to and secretion of vasopressin during the estrous cycle
Authors: Crofton J. T. , Share L. , Brooks D. P.
Published: December 2017

Previously, we observed a sexual dimorphism of the pressor responsiveness to vasopressin in the rat. We have now determined that the pressor action of vasopressin is influenced by the phase of the estrous cycle. Conscious unrestrained male and female rats were given graded intravenous 30-min infusions of vasopressin. The pressor responses of male and estrous female rats were similar, whereas the pressor responses of diestrous, proestrous, and metestrous females were substantially (P less than 0.01) attenuated. This effect could not be attributed to differences in baroreflex sensitivity, which was unaffected by the sex of the rat or phase of the estrous cycle. Baroreflex sensitivity was assessed by the slope of the relationship between changes in heart rate and mean arterial blood pressure in response to graded injections of phenylephrine and nitroprusside. The basal plasma vasopressin concentration was higher (P less than 0.05) in male than in female rats in each phase of the estrous cycle. This was due to a difference in vasopressin release, since there were no sex-related differences in the metabolic clearance rate of vasopressin. These findings suggest that the gonadal hormones influence the cardiovascular actions of vasopressin and its secretion.
Atrial natriuretic hormone effect on renal function and aldosterone secretion in sodium depletion
Authors: Shenker Y.
Published: December 2017

The effects of atrial natriuretic hormone (ANH) on aldosterone secretion and renal function have been well documented, but the physiological role of ANH is still unknown. To address this issue, eight normal men were infused for 4 h with low-dose (1.1 pmol.kg-1.min-1) human [Ser-Tyr28]ANH after 3 days of low-salt (LS) diet. The same subjects were also studied with placebo infusion on LS and high-salt (HS) diet. ANH infusion caused doubling of urine flow, a fourfold increase in urinary sodium excretion, and a slight increase in potassium excretion. Immunoreactive ANH levels increased from 3.1 +/- 0.5 to 21.0 +/- 1.9 pmol/l during ANH infusion. ANH infusion suppressed plasma renin activity (PRA) to one-third of the basal value, and plasma aldosterone was suppressed from 46.5 +/- 6.5 to 20.9 +/- 2.6 ng/dl. Low-dose ANH infusion caused a marked increase in urine flow and urinary sodium excretion and prominent suppression of PRA and plasma aldosterone in sodium-depleted subjects. These results suggest a physiological significance of ANH in regulation of kidney function and aldosterone secretion.
Effects of vasoactive intestinal peptide on vascular conductance are unaffected by anesthesia
Authors: Bouder T. G. , Huffman L. J. , Hedge G. A.
Published: December 2017

In rats anesthetized with ketamine and pentobarbital (KET/PB), vasoactive intestinal peptide (VIP) increases vascular conductance (VC) in the salivary gland, pancreas, and thyroid gland, whereas no changes in VC are observed in a number of other organs. Because anesthesia may alter the responsiveness of physiological systems, we compared the effects of VIP on organ VC in conscious or anesthetized rats. Chronically catheterized rats were studied in the conscious state or 30 min after induction of anesthesia with KET/PB, isoflurane, or Inactin. Blood flows were measured by the reference sample version of the radioactive microsphere (MS) technique using two MS injections (141Ce-MS/85Sr-MS). Mean arterial blood pressure was monitored and used in the calculation of VC. Organ VCs were similar under basal conditions in conscious and anesthetized rats. VIP infusion caused systemic hypotension and increased VCs in the salivary gland, pancreas, and thyroid gland, and these responses were largely unaffected by anesthesia. These results indicate that the anesthetics used do not alter basal VC or the responsiveness of the vasculature to exogenous VIP.