bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased sympathetic nervous system activity in rats fed a low-protein diet
Authors: Young J. B. , Kaufman L. N. , Saville M. E. , Landsberg L.
Published: December 2017

To examine the state of sympathetic nervous system (SNS) function in animals fed a protein-restricted diet, [3H] norepinephrine ([3H]-NE) turnover was measured in heart and interscapular brown adipose tissue (IBAT) of rats fed synthetic diets of equal caloric density containing 22% protein (as casein) or 7% protein (the difference being made up by sucrose). Because dietary availability of tyrosine is a potential mediator of SNS responses to protein ingestion, a third diet (7% protein supplemented with tyrosine) was also tested. After 12 days dietary preparation [3H]-NE turnover was increased 35-70% in heart by 7% protein feeding and 93-103% in IBAT. When smaller animals were fed the synthetic diets for 4-5 wk, sympathetic stimulation in those given the protein-restricted formula was also apparent, although demonstration of this response was complicated by comparative problems due to the marked differences in body size between normal and protein-restricted groups. Addition of tyrosine (sufficient to normalize plasma and brain tyrosine levels) was without effect on the stimulation of NE turnover induced by the protein-deficient diet. Similarly, augmented urinary NE excretion observed in animals consuming the 7% protein diet was unaffected by supplemental tyrosine. Urinary dopamine excretion, however, was uniquely and strikingly elevated with restoration of dietary tyrosine to animals fed the low-protein diet. Thus isocaloric substitution of sucrose for casein in the diet activates the SNS in heart and IBAT, a response unrelated to limitation of dietary tyrosine.
Mechanism of inhibition of renin secretion by increased left atrial pressure
Authors: Lee M. E. , Thrasher T. N. , Ramsay D. J.
Published: December 2017

Experiments were designed to elucidate the mechanism of the failure of systemic hypotension to stimulate renin release in the presence of elevated left heart pressure. We conducted a series of graded ascending aortic and suprarenal cuff inflations in dogs with bilateral renal denervation (n = 5). The renal perfusion pressure (RPP) was reduced by 10, 20, and 30% of control by inflation of either cuff. Comparison of the renin response with inflation of the ascending aortic to the suprarenal cuff revealed a clear increase in the threshold required to elicit a renin response to graded reduction of RPP after inflation of the ascending aortic cuff. These results may be explained by differential effects of the two maneuvers on left heart pressure. Left atrial pressure increased during inflation of the ascending aortic cuff but did not change during inflation of the suprarenal cuff. Since the kidneys were denervated, the shift in threshold must be caused by a humoral substance(s). In conclusion, our findings suggest that the efferent pathway of potent inhibition of renin release from the left heart is mediated, at least partially, by a humoral substance.
Central control of expired air temperature and other thermoregulatory effectors in reindeer
Authors: Mercer J. B. , Johnsen H. K. , Blix A. S. , Hotvedt R.
Published: December 2017

Norwegian reindeer (Rangifer tarandus tarandus) were provided with chronically implanted hypothalamic perfusion thermodes to determine to what extent expired air temperature (Tex) is centrally controlled. The effects that alterations of hypothalamic temperature (Thy) had on metabolic heat production, respiratory frequency, respiratory evaporative heat loss, and rectal and leg-skin temperature were simultaneously recorded. Experiments were conducted in conscious animals exposed to ambient temperatures (Ta) of -20, 0, and 20 degrees C in summer, when fur insulation was minimal, and in winter, when it was prime. Altering Thy induced changes in Tex, the degree and direction of which depended on the prevailing Ta, season, and intensity of hypothalamic thermal stimulation. These results indicate that Tex, and hence nasal heat exchange, is under central control. The Thy-induced changes in the other measured parameters confirm that hypothalamic thermosensitivity in these animals is similar to that previously found in other mammalian species.
Influence of age on cardiovascular reflex response in anesthetized rats
Authors: Wei J. Y. , Mendelowitz D. , Anastasi N. , Rowe J. W.
Published: December 2017

To test the hypothesis that aging is associated with an altered hemodynamic response to physiological (nonpharmacological) stimuli, such as postural change and intravascular volume perturbations, we studied the adult (A, 6 mo) and senescent (S, 24 mo) Fischer 344 rat, a mammalian aging model not influenced by atherosclerosis or hypertension. Special emphasis was placed on the afferent limb of the baroreceptor reflex arc, an area not previously studied with respect to age. The base-line heart rate (HR), systemic arterial pressure (SAP), pulmonary arterial pressure (PAP), and carotid sinus nerve activity were not influenced by age. Following postural change (60 degrees upward tilt), the old animals demonstrated a greater drop in systolic pressure (-11 +/- 2, A; -21 +/- 4 mmHg, S; P less than 0.05), but there was no significant change in HR in either group. In response to a controlled withdrawal of 0.5 ml, the A had a greater reduction in systolic pressure (-29 +/- 4, A; -12 +/- 3 mmHg, S; P less than 0.01), whereas HR or PAP did not change; both groups showed a similar decrease in nerve activity. After infusions of 0.5 and 1.0 ml, the systolic and diastolic pressure changes were greater (P less than 0.02), and the changes in nerve activity appeared to be slightly more prolonged in the A compared with the S. Thus the response to changes in intravascular volume and posture are altered with age, and differences in volume-mediated venovasomotor reflex response may contribute to these age-related changes in the rat.
Small male body size in garter snake depends on testes
Authors: Crews D. , Diamond M. A. , Whittier J. , Mason R.
Published: December 2017

In the red-sided garter snake (Thamnophis sirtalis parietalis) adult females are larger than adult males; this difference is apparent within 3 wk of birth, a time coinciding with high circulating levels of androgens. To study the ontogeny and regulation of this sexual dimorphism, male neonates were either castrated, castrated and given Silastic capsules containing testosterone or estradiol, or given a sham operation at 8, 9, or 10 wk of age. Female neonates were either given a Silastic capsule containing testosterone or dihydrotestosterone or given a sham operation at 8, 9, 10, or 14 wk of age. The sex difference in body size and growth rate in neonates was abolished by castration; the pattern of growth of castrated males was similar to sham-operated females. Androgens in the amounts administered failed to reverse the effects of castration, because castrated male and female neonates receiving exogenous androgens grew at the same rate as did sham-operated females. Males castrated as adults grow larger than adult males given a sham operation, indicating the inhibitory role of the testes on body size exists after sexual maturity. Treatment of adult males with testosterone, however, prevented the increase in body size after castration, suggesting that the mechanism regulating weight gain in the garter snake depends on gonadal androgen.
Corticotropin-releasing factor, sauvagine, and urotensin I: effects on blood flow
Authors: Lenz H. J. , Fisher L. A. , Vale W. W. , Brown M. R.
Published: December 2017

Corticotropin-releasing factor (CRF), sauvagine (SVG), and urotensin I (UI) were tested for their effects on superior mesenteric blood flow in conscious dogs. Intravenous (iv) administration of CRF, SVG, and UI induced an immediate rise of mesenteric blood flow that was associated with a decrease in mean arterial pressure and an increase in heart rate. Intracerebroventricular (ICV) injection of SVG and UI, but not CRF, rapidly (within 5 min after injection) elicited a long (90 min) elevation of mesenteric blood flow. Central administration of these peptides induced a delayed rise in heart rate and slightly elevated mean arterial pressure. The finding that CRF given ICV did not increase mesenteric blood flow could not be explained by the release of vasoactive agents such as vasopressin, epinephrine, or norepinephrine. After injection of CRF, SVG, and UI, plasma concentrations of CRF-, SVG-, and UI-like immunoreactivity did not increase as determined by radioimmunoassay. These results indicate that SVG and UI, but not CRF, administered ICV produce a long increase of mesenteric blood flow in conscious dogs. Because iv SVG and UI decrease mean arterial pressure and ICV SVG and UI increase mean arterial pressure and do not cause an increase in SVG- and UI-like immunoreactivity in the peripheral circulation, it is proposed that SVG and UI injected into the third cerebral ventricle act within the central nervous system to increase superior mesenteric blood flow in the dog.
Effects of intracardiac bradykinin on T2-T5 medial spinothalamic cells
Authors: Ammons W. S. , Girardot M. N. , Foreman R. D.
Published: December 2017

Effects of injecting bradykinin (2 micrograms/kg) into the left atrium on spinothalamic tract neurons projecting to medial thalamus (M-STT cells), to the ventral posterior lateral nucleus of the thalamus (L-STT cells), or to both (LM-STT cells) were examined in 18 monkeys (Macaca fascicularis) anesthetized with alpha-chloralose. Bradykinin increased cell activity in 11/16 M-STT cells, 10/15 L-STT cells, and 4/7 LM-STT cells. One M-STT cell was inhibited. Peak responses to bradykinin of the three cell groups were not different. LM-STT cells began to respond and reached peak responses slightly earlier than the other two groups. Six M-STT, four L-STT, and two LM-STT cells became entrained to the cardiac cycle during their responses to bradykinin. Responses to bradykinin were not dependent on the type of somatic input or cell location. Responding cells most often received A delta- and C-fiber sympathetic input, but some responding cells had only A delta-input. These results demonstrate that in addition to L-STT cells STT cells projecting to the medial thalamus respond to a potentially noxious cardiac stimulus. These cells may participate in the motivational-affective component of cardiac pain.
Calcium exchange in isolated cutaneous epithelium of toad Bufo marinus
Authors: Grubb B. R. , Bentley P. J.
Published: December 2017

The Ca content of isolated cutaneous epithelium of toads (Bufo marinus) was 5 mmol/kg wet wt (compared with approximately 300 mmol/kg wet wt for intact skin), of which approximately 1.7 mM is not readily exchangeable with external 45Ca. After incubation in a solution containing 45Ca, loss of the accumulated isotope in an isotope-free medium is almost complete in 2 h. This efflux or washout is reduced by the presence of external Ca- and Na-free media and by La. Loss of Ca from the epithelium may thus reflect the presence of several mechanisms including a Ca-Ca exchange and a Ca-Na exchange. The effect of La (2 mM) was greater than that of a Na- and Ca-free medium, possibly reflecting the presence of an uncoupled Ca extrusion or extrusion by a Ca-ATPase (pump) mechanism. Drugs (ouabain and amiloride) that, respectively, increase or decrease levels of internal Na had no significant effects on efflux or accumulation of Ca. Vasopressin was also without such effects on Ca.
gamma-Aminobutyric acid concentrations are maintained in anoxic turtle brain
Authors: Lutz P. L. , Edwards R. , McMahon P. M.
Published: December 2017

Changes in gamma-aminobutyric acid (GABA) concentrations in the turtle (Pseudemys scripta elegans) brain were studied in situ during prolonged anoxia. With the onset of anoxia, the well-documented rapid increases in GABA found in mammalian brains were not observed in the turtle brain. Although not statistically significant, mean GABA concentrations in the turtle brain were reduced from anesthetized control values during the first 30 min of anoxia. During this initial period brain glutamate content declined. Even after 2 h of nitrogen respiration, GABA in the turtle brain still did not rise above control levels. By the 4th h of anoxia, however, GABA had increased to 147% of control values.
Preliminary isolation of mosquito natriuretic factor
Authors: Petzel D. H. , Hagedorn H. H. , Beyenbach K. W.
Published: December 2017

A natriuretic factor that triggers diuresis in isolated Malpighian tubules of the mosquito was isolated from the head of the yellow-fever mosquito Aedes aegypti by passing a saline extract of mosquito heads through low-pressure and then high-pressure liquid chromatography (HPLC) columns. Three fractions with biologic activity eluted during a reverse-phase HPLC linear acetonitrile gradient run. Fraction I depolarized the transepithelial voltage (Vt) of isolated perfused Malpighian tubules but did not not stimulate fluid secretion in the Ramsay assay (J. A. Ramsay, J. Exp. Biol. 31: 104–113, 1954). Fraction II depolarized and fraction III hyperpolarized Vt, and both stimulated fluid secretion three- to fourfold. Even though the effects of fractions II and III on Vt differed, both stimulated fluid secretion by increasing the rate of NaCl secretion without affecting K secretion. The selective stimulation of active secretory Na transport by fraction III is mimicked by cyclic AMP (cAMP), suggesting the second messenger role of cAMP in the effects of fraction III. Because fraction III stimulates a NaCl-rich, as opposed to KCl-rich, fluid, the term mosquito natriuretic factor is proposed for this active fraction.
Potentiation of nerve-induced bladder contractions after calcium channel blockade
Authors: Carpenter F. G.
Published: December 2017

The potentiation of nerve-induced bladder contractions (NIC) by tetraethylammonium chloride (TEA), K+, or carbachol could result from a greater Ca2+ entry through Ca2+ channels in the muscle or from a greater release of transmitter by nerve terminals. Contractions of equal magnitude by the rat urinary bladder in vitro were initiated by carbachol, K+, or transmural stimulation of urinary bladder motor nerves at 1 Hz. Contractions elicited by K+ or carbachol were drastically reduced by verapamil (0.5 microM), but NICs were unaffected. Thus the role of Ca2+ channels in NICs seems uncertain. NICs are potentiated approximately 50% by K+ (15 mM), carbachol (0.5 microM), or 4-aminopyridine (0.2 mM) and over twofold by TEA (5 mM). Although verapamil (1–5 microM) reduced NICs in a dose-dependent relation, potentiation by each compound was the same. Thus Ca2+ channels probably play no role in potentiation. The resistance of the bladder to distention reflects its viscoelasticity and is Ca2+ sensitive. Because viscoelasticity was decreased by verapamil coincident with the reduction in NICs, both may result from lowered intracellular Ca2+ (Cai2+). However, because the potentiating compounds failed to restore bladder viscoelasticity, they probably did not elevate Cai2+. Therefore, in verapamil-treated preparations potentiation is most probably caused by an enhancement of transmitter release.
Acute volume expansion decreases adrenocortical sensitivity to ACTH and angiotensin II
Authors: Raff H. , Shinsako J. , Wade C. E. , Keil L. C. , Dallman M. F.
Published: December 2017

This study examined the plasma aldosterone and corticosteroid responses to a 60-min infusion of adrenocorticotropin (ACTH) or angiotensin (ANG) II started immediately after an acute isotonic saline volume expansion (0.5 ml . kg-1 . min-1 for 30 min). Five conscious dogs of either sex with exteriorized carotid loops were used in this repeated-design study. Volume expansion per se caused a 10% decrease in hematocrit, a 12.5% decrease in plasma protein, and a 2.7-mmHg increase in central venous pressure with no change in mean arterial pressure, heart rate, or plasma sodium. Volume expansion per se also resulted in significant reductions in vasopressin, plasma renin activity, ACTH, aldosterone, and corticosteroid levels. The aldosterone responses to ACTH and ANG II were significantly inhibited (46-71%) by acute volume expansion. The corticosteroid response to ACTH was 19-29% inhibited by volume expansion. We conclude that acute volume expansion significantly inhibits the adrenocortical sensitivity to its tropic hormones probably via alterations of synergistic factors.
Endogenous cholecystokinin and intestinal satiety
Authors: Collins S. M. , Conover K. L. , Forsyth P. A. , Weingarten H. P.
Published: December 2017

The role of endogenous cholecystokinin (CCK) as a mediator of intestinal satiety is examined. We used rats equipped with a chronic gastric fistula and an indwelling duodenal catheter to assess the effects of direct duodenal stimulation on sham feeding. To evaluate the contribution of endogenous CCK to intestinal satiety we used a specific competitive antagonist of the satiety action of CCK, proglumide. Intraduodenal infusion of 11 or 5 ml liquid diet suppressed sham feeding. Administration of proglumide caused a partial reversal of the suppression of feeding produced by the 11-ml, but not the 5-ml, intraduodenal infusion. Administration of proglumide alone did not influence sham feeding but completely abolished the suppression of sham feeding induced by a maximal dose of exogenous CCK. These results indicate that CCK contributes to intestinal satiety under specific test conditions only. Moreover, since that component of suppression reversed by proglumide was small in comparison with the overall inhibition of eating, these results indicate that factors other than CCK are important in intestinal satiety.
GDP binding to hamster brown fat mitochondria is reduced during hibernation
Authors: Horwitz B. A. , Hamilton J. S. , Kott K. S.
Published: December 2017

Preparation for hibernation is accompanied by increased thermogenic capacity of brown fat (BAT), an important site of thermogenesis during arousal from hibernation. This study examined whether that thermogenic capacity is reduced in hibernation and reactivated during arousal. In one set of experiments, Syrian hamsters were exposed to short photoperiod (10:14 light-dark) and cold (7 degrees C). Those not hibernating at death (n = 10) served as controls for those that were (n = 9). A third group (n = 10) was killed 80–90 min after arousal was initiated by manual perturbation. Mitochondrial GDP binding (nmol/mg mitochondrial protein) was used to estimate thermogenic capacity. In a second experimental series, BAT citrate (si)-synthase and 3-hydroxyacyl-CoA dehydrogenase activities were measured in hibernating and nonhibernating hamsters. Although there were no differences in the maximum activities of these enzymes, GDP binding was markedly lower in the hibernators relative to the nonhibernators (0.214 +/- 0.031 vs. 0.535 +/- 0.039). However, in the partially aroused hamsters, GDP binding had doubled (0.438 +/- 0.04). Thus hibernation is accompanied by a substantial reduction of BAT thermogenic capacity (as manifested by GDP binding), which is reversed during arousal. The rapidity of this reversal indicates that it does not involve the synthesis of new GDP binding sites.
Interaction of light and corticosterone on food intake and brown adipose tissue of the rat
Authors: Fukushima M. , Lupien J. , Bray G. A.
Published: December 2017

The food intake of sham-operated and adrenalectomized rats was measured in 12-h intervals with animals housed in either alternating periods of 12:12 light-dark or in continuous light. The food intake with alternating light and dark was unaffected by adrenalectomy. The maintenance of a constant infusion of corticosterone in adrenalectomized rats also did not disturb the pattern of food intake. In continuous light, food intake was not significantly different in each 12-h period of the daily cycle. Neither adrenalectomy nor the injection of corticosterone, 240 micrograms/day, altered the average 12-h food intake in rats in constant light. The weight of interscapular brown adipose was smaller in adrenalectomized animals, but the protein content was unaffected. Adrenalectomy significantly increased the specific binding of the purine nucleotide GDP to mitochondria from brown adipose tissue. This specific binding was restored to normal by either corticosterone infusion or injection. We conclude that light is the principal entrainer for the average food intake during 12-h periods and that within the framework of these experiments corticosterone plays an insignificant role in controlling food intake. However, adrenalectomy did significantly increase the purine nucleotide binding to mitochondria from brown adipose tissue.
Radioiodide transfer across sheep placenta
Authors: Canning J. F. , Stacey T. E. , Ward R. H. , Boyd R. D.
Published: December 2017

Unidirectional transplacental clearances of radioiodide were calculated from the net radioiodide fluxes after injection into fetal and/or maternal circulations of 33 catheterized conscious sheep. Maternofetal potential difference (PD) was also recorded. Clearance reached a steady state 20 min after bolus injection. Fetomaternal clearance was related to PD. Bidirectional clearance ratios measured in five experiments showed a significant divergence from the value for passive flux predicted from the measured PD, and in four experiments these ratios were also significantly different from unity, this result being incompatible with passive flux even if the transplacental PD is assumed to be zero. Injection of thiocyanate or iodide reduced radioiodide clearance. Fetomaternal clearance of radioiodide was halved by an increase in fetal plasma iodide concentration of approximately 0.1 mM. There appears to be an inhibitable iodide-transporting site capable of active transport in either direction.
Involvement of protein synthesis in circadian clock of Aplysia eye
Authors: Lotshaw D. P. , Jacklet J. W.
Published: December 2017

The effects of the protein synthesis inhibitors anisomycin and puromycin were measured on protein synthesis and phase shifting of the circadian rhythm in the isolated Aplysia eye. Anisomycin pulses induce phase delays proportional in magnitude to the duration and percentage of protein synthesis inhibition. The phase-response curve to anisomycin pulses consisted of delays induced throughout the subjective night. Delays were maximal between circadian times (CT) 18 and CT 2; pulses initiated between CT 2 and CT 12 did not phase shift. Puromycin induced phase delays and advances. Delays were proportional to the duration and percentage of protein synthesis inhibition, occurring with increasing magnitude throughout the subjective night (CT 12-2). Peptidyl-puromycin formation may contribute to the magnitude of the delay. Advances, occurring between CT 2 and CT 8, required a greater drug concentration and pulse duration than delays and appeared to result from an effect other than protein synthesis inhibition. Our results support the hypothesis of a phase-dependent requirement for protein synthesis during the subjective night in this circadian clock.
Fetal renal contribution to amniotic fluid osmolality during maternal hypertonicity
Authors: Woods L. L.
Published: December 2017

The contribution of fetal urine to the increase in amniotic fluid osmolality during maternal hypertonicity was studied in chronically catheterized sheep of 130-135 days gestation. Nine percent NaCl was injected simultaneously into fetal and maternal veins, followed by a continuous infusion into the maternal vein. Maternal and fetal plasma osmolalities rose by 15 +/- 1 (SE) and 13 +/- 1 mosmol/kg, respectively, and remained constant for 4 h. Fetal urine osmolality rose significantly from 188 +/- 31 to 277 +/- 32 mosmol/kg within 1 h and remained constant thereafter. Fetal urine flow rose transiently, fell to normal within 10 min, and averaged 70% of normal beyond 1 h. Amniotic fluid osmolality rose by 10.8 +/- 2.8 mosmol/kg over 4 h. Following hypertonic injection into three fetuses blocked by the arginine vasopressin antagonist d(CH2)5D-tyr(Et)VAVP, urine osmolality did not change, and amniotic fluid osmolality rose by 2.7 +/- 0.3 mosmol/kg. Thus it appears that the increase in amniotic fluid osmolality during maternal hypertonicity may be due largely to an increased fetal urine osmolality coupled with a decreased flow of fetal urine into the amniotic space, rather than to bulk flow of fluid across the membranes and uterine wall.
Effects of sodium depletion and angiotensin II on osmotic regulation of vasopressin
Authors: Wade C. E. , Keil L. C. , Ramsay D. J.
Published: December 2017

After alterations in sodium balance, osmotic reactivity of vasopressin (AVP) release was evaluated in seven conscious dogs during bilateral intracarotid infusions of hypertonic saline. A low-sodium diet reduced plasma sodium concentration by 3%; deoxycorticosterone acetate (30 mg/day for 2 days) elevated the concentration by 1%. Neither treatment altered resting plasma AVP. Hypertonic intracarotid infusions increased jugular plasma osmolality by 20 +/- 2 mosmol/kg independent of manipulations. Plasma AVP values were significantly increased (P less than 0.05) in sodium-depleted dogs compared with values of the control animals. In addition, the osmotic reactivity of AVP release was evaluated during exogenous administration of angiotensin II (ANG II). Intravenous infusion of ANG II (5 ng . kg-1 . min-1) increased plasma concentration of ANG II but did not alter concentration of plasma AVP. The slope for the relationship of jugular plasma osmolality to plasma AVP during hypertonic intracarotid infusions was significantly increased with intravenous infusion of ANG II. Sodium depletion and intravenous ANG II potentiate the relationship of plasma osmolality and plasma AVP when evaluated with intracarotid hypertonic saline infusions in dogs.
Pantothenic acid transport and metabolism in the central nervous system
Authors: Spector R.
Published: December 2017

The mechanisms by which pantothenic acid (PA) enters and leaves brain, choroid plexus, and cerebrospinal fluid (CSF) were investigated by injecting [3H]PA either intravenously or intraventricularly into adult rabbits. [3H]PA, either alone or together with unlabeled PA, was infused at a constant rate into conscious rabbits. At 180 min, [3H]PA readily entered CSF, choroid plexus, and brain. In brain, CSF, and plasma, greater than 90% of the 3H was associated with [3H]PA. The addition of 200 mumol/kg PA to the infusion syringe decreased the penetration of [3H]PA into brain and CSF by approximately 70%. Two hours after the intraventricular injection of [3H]PA, [3H]PA was rapidly cleared from the CSF by a probenecid-sensitive mechanism. No metabolism of the [3H]PA occurred in brain. However, 18 h after the intraventricular injection of 37 microCi (34 nmol) of [3H]PA, approximately 40% of the 3H remaining in forebrain was converted to [3H]CoA. These results show that PA enters and leaves CSF and brain by saturable transport systems. However, [3H]PA is very slowly converted to [3H]CoA in brain in vivo.
Peptide nature of two mosquito natriuretic factors
Authors: Petzel D. H. , Hagedorn H. H. , Beyenbach K. W.
Published: December 2017

High-pressure liquid chromatography (HPLC) of saline extracts of Aedes aegypti heads yields three fractions (from a total of 108) that affect transepithelial voltage and/or fluid secretion in isolated Aedes Malpighian tubules. In this study we investigated the physical and chemical nature of the active materials in these fractions. Gel-filtration chromatography revealed that the molecular weights of the three fractions were between 1,900 and 2,700. To test their thermostability the fractions were repeatedly frozen and thawed over a period of 110 days without loss of biological activity. Boiling at 100 degrees C for 5 min failed to significantly reduce their biological effects in isolated Malpighian tubules. In contrast, treatment with the proteolytic enzyme mixture, pronase, destroyed activity in all three. Fraction I no longer depolarized the transepithelial voltage of in vitro perfused Malpighian tubules, and fractions II and III completely lost their ability to stimulate fluid secretion and to affect transepithelial voltage. We conclude that our HPLC isolation yields a heterogeneous group of three polar low-molecular weight peptides. Expression of their biological activities in Malpighian tubules depends on intact peptide bonds.
Diluting segment in avian kidney. II. Water and chloride transport
Authors: Miwa T. , Nishimura H.
Published: December 2017

The mammalian-type nephrons of avian kidneys contain a Henle's loop that runs parallel to the collecting ducts and the vasa recta. Thus we examined whether the thick ascending limb (TAL) of Henle's loop of the avian kidney acts as a diluting segment by measuring water and Cl transport in the isolated and perfused TAL of the quail, Coturnix coturnix. The TAL showed a lumen-positive transepithelial voltage (Vt) (+9.4 +/- 0.4 mV, n = 28). Net water flux (Jv) was nearly zero when the TAL was perfused and bathed with isosmotic solution. When the osmotic gradient was imposed, Jv increased only slightly, and thus the osmotic water permeability (Lp) was low. Arginine vasotocin (AVT) added to the hyperosmotic bath did not alter either Jv, Lp, or Vt. Cl efflux (lumen to bath, 370.4 +/- 27.7 peq X mm-1 X min-1) was higher than Cl influx (bath to lumen, 98.6 +/- 14.3 peq X mm-1 X min-1) when measured in the different tubules. AVT showed no effect on Cl efflux. These results indicate that in the TAL of the quail osmotic water permeability is low while net Cl reabsorption is present, suggesting that the TAL functions as a diluting segment.
Effects of diet and photoperiod on NE turnover and GDP binding in Siberian hamster brown adipose tissue
Authors: McElroy J. F. , Mason P. W. , Hamilton J. M. , Wade G. N.
Published: December 2017

This experiment examined the effects of diet and photoperiod on food intake, body weight, and brown adipose tissue (BAT) activity in female Siberian hamsters (Phodopus sungorus sungorus). BAT function was assessed by measuring both the sympathetic nervous system activity of BAT [estimated by the rate of norepinephrine (NE) turnover] and BAT thermogenic activity (estimated by GDP binding to BAT mitochondria). Nineteen weeks of high-fat feeding in long photoperiod [16:8 light-dark cycle (LD)] caused a 20% increase in food intake but did not affect body weight. Both NE turnover rate and GDP binding in interscapular BAT (IBAT) were increased four- to eightfold relative to that from chow-fed controls. Thus it appears that in Siberian hamsters BAT can serve the same energy-dissipating function during diet-induced overeating previously established in rats and mice. Nineteen-week exposure to a short photoperiod (LD 8:16) produced a reduction in body weight but did not affect food intake. Both NE turnover rate and GDP binding in IBAT were increased two- to fourfold relative to that from long-photoperiod controls. Thus it appears that in Siberian hamsters the photoperiod-induced improvements in thermogenic capacity are mediated via the same mechanisms as are cold- or diet-induced thermogenesis.
Effect of atrial natriuretic factor in rat pregnancy
Authors: Kristensen C. G. , Nakagawa Y. , Coe F. L. , Lindheimer M. D.
Published: December 2017

Protocols were designed to 1) identify atrial natriuretic factor (ANF) bioactivity in pregnant rats, 2) compare ANF activity in atria from gravid and virgin Sprague-Dawley animals, and 3) assess renal and vascular responsiveness to ANF during gestation. Similar quantities of ANF were extracted from atria of term gravid and age-matched controls (assayed as the natriuretic response in awake virgins). We then purified by high-performance liquid chromatography a peptide identical to the synthetic 23 amino acid atriopeptin II (AP II). With equimolar injections of ANF, gravid rats had a blunted natriuretic response (P less than 0.05). However, when dose was based on estimated extracellular volume, awake virgin and pregnant animals displayed similar highly significant dose-response curves to infused AP II (R's 0.8). When hydropenic rats were assayed, both gravid and virgins required 10 times more ANF to initiate a diuresis; dose-response curves again being similar and highly significant. Decrements in blood pressure were also similar in pregnant and nongravid animals. Thus, despite an increased intravascular volume of 70% during gestation, cardiac content of ANF and the renal and vascular responsiveness to this peptide are similar to those in virgin rats, suggesting resetting of ANF-volume relationships during pregnancy.
Sensitivity of cortisol-induced inhibition of ACTH and renin in fetal sheep
Authors: Wood C. E.
Published: December 2017

Previous experiments demonstrated that increases in ovine fetal plasma cortisol concentration to maximal stress levels suppressed fetal plasma renin activity and completely inhibited fetal adrenocorticotropin (ACTH) responses to subsequent stress. This study was designed to quantitate the suppressive action of cortisol on both ACTH and renin. Fetal sheep between 117 and 131 days gestation were surgically prepared with chronically implanted catheters. At least 4 days after surgery, vehicle or cortisol (0.25, 0.5, 1, 2, or 3 micrograms/min) were infused for 5 h. One hour after the end of the vehicle or cortisol infusion, fetal ACTH and renin secretion were stimulated by intravenous infusion of sodium nitroprusside. Cortisol infusions suppressed basal plasma renin activity (caused by suppression of plasma renin concentration) to degrees that were related to the increases in fetal plasma cortisol concentration. After cortisol infusions, renin responses to hypotension were apparently suppressed to degrees not obviously related to the rate of cortisol infusion. Fetal plasma ACTH responses to hypotension were completely suppressed by increases in total and unbound fetal plasma cortisol concentration 1.6 and 1.7 ng/ml, respectively. These results demonstrate a high sensitivity of the fetal hypothalamopituitary unit and renin-angiotensin system to cortisol.
Ablation of subfornical organ does not prevent angiotensin-induced water drinking in sheep
Authors: McKinley M. J. , Denton D. A. , Park R. G. , Weisinger R. S.
Published: December 2017

The subfornical organ (SFO) and surrounding periventricular tissue were ablated in sheep. Such a lesion did not significantly reduce water drinking in response to intracarotid, intravenous, or intracerebroventricular infusions of [Val5]angiotensin II amide (ANG II) but caused reduced intake of water in response to intracarotid infusion of hypertonic saline. The dipsogenic response of these sheep to water deprivation for 3 days was similar to that of normal sheep subjected to water deprivation. Although the results are not conclusive in excluding the SFO from having a role in ANG II-induced drinking, they show that there are receptors outside the SFO sensitive to blood-borne ANG II that are involved in water drinking in sheep. The results also show that tissue in the SFO or its surroundings may be involved in drinking caused by acute hypertonicity.
Lack of involvement of GABA in baroreceptor-mediated sympathoinhibition
Authors: McCall R. B.
Published: December 2017

The purpose of the present investigation was to determine if gamma-aminobutyric acid (GABA) mediates the baroreceptor-induced inhibition of sympathetic nerve discharge (SND) in dialurethan-anesthetized cats. The GABA antagonists picrotoxin and bicuculline produced marked elevations in arterial blood pressure and inferior cardiac SND. The inhibition of SND observed during pressor responses was occasionally slightly depressed after picrotoxin or bicuculline. Midcollicullar transection blocked or reversed the increase in blood pressure and SND produced by GABA antagonists. Under these conditions, baroreceptor inhibition of SND was not affected by picrotoxin. Microinjections of picrotoxin into the rostral ventrolateral medulla produced increases in arterial blood pressure and SND but failed to affect baroreceptor-induced sympathoinhibition. GABA antagonists given intravenously also failed to affect the baroreceptor-induced inhibition of sympathetically related neurons recorded in the rostral ventrolateral medulla. However, intravenous picrotoxin did antagonize the inhibitory affect of microiontophoretically applied GABA on these neurons. These data provide no evidence to support the contention that GABA mediates the baroreceptor-induced inhibition of SND. The role of GABA in regulating SND is discussed.
Regulation of interacting populations during endocytosis: models of growth factor-tumor promoter dynamics
Authors: Gex-Fabry M. , DeLisi C.
Published: December 2017

A model of growth factor-cell receptor interactions, including internalization, sorting, recycling, and degradation and their modulation by tumor promoters, is developed, analyzed, and tested. In keeping with data and concepts based on a large number of systems, the main assumption is that after receptor-ligand binding the complex associates with a second membrane protein, localized in coated pits, and that this event is a necessary condition for receptor-mediated endocytosis and subsequent intracellular processes. As a consequence of the model, ligands having distinct receptors interfere at the cell surface through competition between their receptor complexes for a limited pool of coated pit proteins. The utility of the model is illustrated by a detailed analysis of binding, endocytosis, and degradation of epidermal growth factor (EGF) and their modulation by phorbol esters. The analysis permits quantitative characterization of the dynamics of the endocytic processes and leads to the following conclusions. The Scatchard plot changes from linear to nonlinear as the ratio of the number of coated pit proteins to the number of receptors decreases. Competition between phorbol ester and EGF-bound receptors for coated pit proteins predicts, in agreement with observation, conversion of nonlinear EGF Scatchard plots to linear plots subsequent to reincubation with phorbol esters. The postulated competition suggests a local homology between the phorbol ester receptor and the EGF receptor. Homologous and heterologous downregulations observed in numerous systems are natural consequences of the model. Preincubation with the heterologous ligand increases the time lag between ligand binding and lysosomal degradation and alters intracellular sorting.
Scaling of physiological responses: a new approach for hemorrhagic shock
Authors: Connett R. J. , Pearce F. J. , Drucker W. R.
Published: December 2017

Standard protocols used to study hemorrhagic shock involve sampling at fixed time intervals and generating a time-based composite curve from each experiment. Although each animal may show the same sequence of responses, the time, rate, and size of the response varies from animal to animal. As a result, sampling times may be inappropriate to identify sharp transitions in the measured parameters, and the composite curves do not reflect the size and shape of the individual responses. This report evaluates several approaches to normalizing hematocrit and blood glucose data obtained from a constant-pressure model of hemorrhagic shock in fed and fasted and dehydrated animals to see if phase relationships and fractional responses from individual animals can be made coherent. Scaling for fractional blood loss on the x-axis and maximal response on the y-axis resulted in convergence of the results from individual animals and different experimental series. Data from a constant rate of hemorrhage model also converged after scaling. A method for prospectively defining the scale and adjusting sampling frequency for individual animals is given.
Validation of doubly labeled water method using a ruminant
Authors: Fancy S. G. , Blanchard J. M. , Holleman D. F. , Kokjer K. J. , White R. G.
Published: December 2017

CO2 production (CDP, ml CO2 . g-1 . h-1) by captive caribou and reindeer (Rangifer tarandus) was measured using the doubly labeled water method (3H2O and H2(18)O) and compared with CO2 expiration rates (VCO2), adjusted for CO2 losses in CH4 and urine, as determined by open-circuit respirometry. CDP calculated from samples of blood or urine from a reindeer in winter was 1-3% higher than the adjusted VCO2. Differences between values derived by the two methods of 5-20% were found in summer trials with caribou. None of these differences were statistically significant (P greater than 0.05). Differences in summer could in part be explained by the net deposition of 3H, 18O, and unlabeled CO2 in antlers and other growing tissues. Total body water volumes calculated from 3H2O dilution were up to 15% higher than those calculated from H2(18)O dilution. The doubly labeled water method appears to be a reasonably accurate method for measuring CDP by caribou and reindeer in winter when growth rates are low, but the method may overestimate CDP by rapidly growing and/or fattening animals.
Water drinking induced by gastric secretagogues in pigs
Authors: Houpt T. R. , Weixler L. C. , Troy D. W.
Published: December 2017

Eleven young pigs, feeding and drinking operantly, were tested for drinking responses to three gastric secretagogues. First, feed was removed for 1 h before the test period, then a continuous intravenous infusion of saline or a secretagogue was begun at a priming rate of 0.6 ml/min for the first 10 min, then at 0.3 ml/min for 50 min. Dose rates were the smallest that would still cause a vigorous gastric secretion. When 0.9% NaCl was infused, the pigs drank a mean of 54 +/- 11 (SE) ml. The comparable volumes for the secretagogues were histamine 174 +/- 41 ml (1 microgram . kg-1 . min-1); pentagastrin 231 +/- 38 ml (0.5 microgram . kg-1 . min-1); and bethanechol 231 +/- 35 ml (1.0-1.5 microgram . kg-1 . min-1). Pretreatment with cimetidine (300 mg iv) depressed the drinking response to histamine to 30 +/- 10 ml and to pentagastrin to 58 +/- 24 ml. Atropine (2 mg iv) depressed the response to bethanechol to 28 +/- 16 ml. Differences between responses to the secretagogues and either control drinking or antagonist-blocked responses were all significant (P less than 0.001). The results indicate that gastric secretion could play a role in stimulation of preprandial water drinking.
ACTH, cortisol, and renin responses to arterial hypotension in sheep
Authors: Wood C. E.
Published: December 2017

This study was designed to investigate adrenocorticotropin (ACTH), cortisol, and renin responses to nitroprusside-induced hypotension in adult sheep. Five sheep were surgically prepared with carotid arterial skin loops at least 1 yr before these experiments. After catheterization of the carotid arteries and external jugular veins the sheep were infused with nitroprusside intravenously at rates of 0, 10, 15, or 20 micrograms . kg-1 . min-1 for 10 min. Nitroprusside produced significantly dose-related decreases in mean arterial pressure and increases in heart rate, plasma ACTH and cortisol concentrations, and plasma renin activity. Hematocrit was significantly increased in the 10- and 20-micrograms . kg-1 . min-1 groups during nitroprusside, probably reflecting contraction of the spleen. After the end of the period of hypotension, hematocrit was significantly decreased in all nitroprusside infusion groups, probably reflecting transcapillary movement of fluid into the vascular space. A posteriori analysis of the data suggests that the ACTH response to nitroprusside infusion was better predicted by the nadir in mean arterial pressure and that the renin activity response was better predicted by the initial rate of decrease of mean arterial pressure during nitroprusside infusion.
Suppression of plasma renin and aldosterone in stress-salt hypertension in dogs
Authors: Anderson D. E. , Gomez-Sanchez C. , Dietz J. R.
Published: December 2017

Plasma renin activity (PRA) and plasma aldosterone concentrations (PAC) of 12 intact chronically instrumented dogs were measured at midday after 1) 7-12 days of normal sodium intake and no behavioral stress, 2) 7-12 days of continuous saline infusion (1.34 l/day) only, and/or 3) 7-12 days of saline infusion and avoidance-conditioning sessions. The saline infusion procedure did not significantly change arterial pressure or heart rate relative to base line but was associated with a consistent decrease in PRA (-0.90 +/- 0.38 ng angiotensin I . ml-1 . h-1) and PAC (-3.6 +/- 1.1 ng/dl). The combination of saline infusion and avoidance conditioning resulted in significant elevations in arterial pressure, but, again, both PRA (-1.46 +/- 0.16 ng angiotensin I . ml-1 . h-1) and PAC (-3.7 +/- 1.1 ng/dl) were significantly decreased. These results show that high sodium intake decreased aldosterone via suppression of renin release but do not rule out a possible hypertensinogenic role for stress-induced adrenocorticotrophic hormone-sensitive corticoids.
Effect of hypophysectomy on dipsogenic stimuli: evidence for angiotensin supersensitivity
Authors: Alper R. H. , Deschepper C. F. , Ganong W. F.
Published: December 2017

The effects of long-term hypophysectomy on renin secretion and the renin and drinking responses to isoproterenol were investigated in male rats. Drinking responses to angiotensin II, hypertonic saline, and water deprivation for 24 h were also measured. Plasma renin activity and plasma angiotensin II were variably lower in rats that had been hypophysectomized for 21 days than in intact controls. Angiotensinogen was also reduced, but plasma renin concentration was not. Isoproterenol produced a smaller increase in plasma renin activity in hypophysectomized rats than it did in controls, but with the one dose of isoproterenol that was tested, the increase in plasma renin concentration was comparable in the two groups. However, the drinking responses to isoproterenol were greater in the hypophysectomized rats. The drinking responses produced by infusion of angiotensin II were also greater, but the responses to infusion of hypertonic saline and to 24 h of water deprivation were not. The data suggest that in rats hypophysectomized for 21 days the circumventricular organs that mediate thirst are hyperresponsive to circulating angiotensin II, possibly because the relatively low circulating angiotensin II levels permit the upregulation of angiotensin II receptors in these structures.
Neurohypophysial peptide potencies in cultured anuran epithelia (A6)
Authors: Lang M. A. , Handler J. S. , Gainer H.
Published: December 2017

To characterize the V2 receptor (for antidiuretic hormone), we have studied the effect of a number of neurohypophysial hormone analogues on cyclic AMP (cAMP) accumulation and short-circuit current in cultured epithelia formed by A6 cells. A6 is the designation of a continuous cell line derived from the kidney of Xenopus laevis. The order of potency for stimulating cAMP accumulation and short-circuit current in A6 epithelia is like that for stimulating water permeability in toad urinary bladder. As anticipated, arginine vasotocin (AVT), the antidiuretic hormone of Amphibia, is more potent than arginine vasopressin (AVP), the antidiuretic hormone of most mammals. The two hormones differ only in the third amino acid (Phe-3 in AVP is a substitution for Ile-3 in AVT). However, there are a number of striking differences in the responsiveness of these amphibian V2 receptors and mammalian V2 receptors to changes in the 7th, 8th, and 9th amino acids where AVT and AVP are identical. 1) Substitution of Lys-8 for Arg-8 in AVP results in marked loss of potency in Amphibia, whereas there is only modest loss of potency in mammals. 2) Desglycinamide AVP is nearly as potent as AVP in Amphibia, whereas it is inactive in mammals. 2) Tocinoic acid, lacking amino acids 7, 8, and 9, has activity in Amphibia, but pressinoic acid, lacking the same three amino acids, is inactive.