bluuebunny/crossref_metadata_2025 huggingface dataset:
Verapamil blockade of pressor and uterine responses to AVP-OT analogue, oxypressin
Authors: Gazis D. , Gonzalez G. , Mendlowitz M.
Published: December 2017

The effects of the calcium channel blocker verapamil on simultaneously recorded uterine and pressor responses to the equipotent (in eliciting these responses) oxytocin-vasopressin analogue, oxypressin, were studied in urethan-anesthetized and pentolinium- and indomethacin-treated rats during injections and infusions of this analogue. Doses of verapamil that almost completely blocked the pressor response to infused oxypressin had no effect on a pressor response to injected oxypressin of equal magnitude. Larger doses of verapamil blocked the pressor response to injected oxypressin somewhat. Uterine responses were only marginally affected by these doses of verapamil, and there was no significant difference between infusion and injection or between estrus and diestrus.
Angiotensin II facilitation of pressor responses to adrenal field stimulation in pithed rats
Authors: Vollmer R. R. , Corey S. P. , Fluharty S. J.
Published: December 2017

The effects of angiotensin II on pressor responses to electrical field stimulation (1-32 Hz) of the adrenal gland were assessed in pithed male Sprague-Dawley rats. Stimulation elicited frequency-related pressor responses and increments in plasma catecholamines. Interruption of the renin-angiotensin system with the converting enzyme inhibitor captopril or the receptor antagonist saralasin significantly attenuated the pressor responses to adrenal stimulation and injected epinephrine to an equivalent extent. This observation, along with the finding that captopril did not alter the plasma catecholamine increments produced by adrenal stimulation, suggested that endogenously generated angiotensin II was not affecting adrenal catecholamine release. Instead angiotensin II appears to interact at the level of the vascular smooth muscle, because reinfusion of angiotensin II (20 ng.kg-1.min-1 iv) in captopril-treated animals restored responsiveness to stimulation and epinephrine. Infusion of vasopressin also restored pressor activity after captopril; therefore the interaction does not appear to be specific for angiotensin II but may depend on the background tone of the vascular smooth muscle. Moreover, decreasing blood pressure with sodium nitroprusside reversibly attenuated the pressor responses to both adrenal stimulation and epinephrine. The results suggest that endogenously formed angiotensin II facilitates the vasoconstrictor activity of epinephrine by increasing vascular tone.
Model of homeostatic regulation of potassium excretion in sheep
Authors: Rabinowitz L.
Published: December 2017

Based on experimental observations on unanesthetized sheep, a hypothesis is proposed for the homeostatic control of potassium excretion in this ruminant. This hypothesis includes as a novel element a splanchnic sensor of potassium intake. Information provided by the splanchnic sensor contributes to the control of potassium excretion independently of the level of systemic plasma potassium or other conventional control factors. A mathematical model based on this hypothesis successfully simulates the relations between potassium excretion, plasma potassium, and oral and intravenous potassium input observed in sheep.
C-reactive protein, leukocytes, and fever after central IL 1 and alpha-MSH in aged rabbits
Authors: Dao T. K. , Bell R. C. , Feng J. , Jameson D. M. , Lipton J. M.
Published: December 2017

Aged and young unanesthetized rabbits with intracerebroventricular cannulas were tested in experiments designed to determine whether increases in plasma C-reactive protein (CRP) level and leukocytosis can be rapidly induced by central administration of crude buffy-coat supernatant commonly called endogenous pyrogen or interleukin 1 (IL 1). The results indicate that both acute-phase responses occur during fever caused by central administration of this supernatant and that they are generally detectable within 2 h. Although the febrile response was smaller in aged female rabbits, there was no decline in CRP or leukocyte responses, an observation that was not predicted. The antipyretic neuropeptide alpha-melanocyte-stimulating hormone (alpha-MSH) reduced fever caused by central IL 1 more effectively in the aged rabbits. alpha-MSH likewise inhibited the CRP and leukocyte responses to central IL 1. The results confirm that CRP and leukocyte responses can be driven by a central IL 1 signal and further indicate that the response can occur rapidly, consistent with direct central nervous system control of the acute-phase responses. The findings indicate that the acute-phase responses depend in part on the age of the host and that the responses can be modulated by an endogenous central nervous system peptide with known antipyretic and immune modulatory properties.
Plasma catecholamines during E. coli bacteremia in conscious rats
Authors: Jones S. B. , Westfall M. V. , Sayeed M. M.
Published: December 2017

Fasted, conscious male rats, prepared with arterial and venous cannulas, were given doses (10(10)-10(11) organisms/kg) of live Escherichia coli bacteria. Heart rate and blood pressure were recorded, and arterial plasma samples were taken preinjection and at 30, 180, and 360 min after bacterial administration. Plasma was analyzed for lactate, glucose, norepinephrine (NE), and epinephrine (E). Rats given E. coli were normotensive but with significant tachycardia (P less than 0.05 vs. saline). Plasma NE and E levels increased severalfold during bacteremia (P less than 0.05 for all comparisons). Rats were euglycemic but had a sixfold increase in lactate 6 h (P less than 0.05) after E. coli treatment. Additional rats were subjected to the same protocol but had been made tolerant to bacterial endotoxin by multiple injections over the course of several days. Endotoxin-tolerant rats were also tolerant to live E. coli administration (P less than 0.05, 24 h survival) and had significantly reduced levels of E and NE at 6 h compared with nontolerant bacteremic rats (P less than 0.05). Increases in heart rate and plasma lactate were not significant in endotoxin-tolerant rats. These results suggest profound sympathetic activation during acute bacteremia with attenuated activation in endotoxin-tolerant rats. Tolerance appears to reduce the afferent stimuli that are presumably activated during the course of bacteremia.
Role of atrial pressure and rate in release of atrial natriuretic peptide
Authors: Walsh K. P. , Williams T. D. , Spiteri C. , Pitts E. , Lightman S. L. , Sutton R.
Published: December 2017

To investigate whether atrial natriuretic peptide (ANP) release during paroxysmal tachycardia is due to increased atrial rate or increased atrial pressure, plasma ANP concentrations were measured during atrial pacing at increasing rates in six alpha-chloralose-anesthetized dogs whose atrial pressures were maintained artificially low by balloon occlusion of the inferior vena cava (IVC). These ANP concentrations were compared with those seen during identical increasing atrial rates in the same dogs without IVC occlusion. During incremental pacing without IVC occlusion, pulmonary wedge pressure (PWP; mean +/- SE) rose progressively from 5.3 +/- 1.6 at 200 to 20.2 +/- 2.3 mmHg at 350 beats/min (P less than 0.01), and right atrial pressure (RAP) rose progressively from 2.5 +/- 0.9 at 200 to 6.7 +/- 2.1 mmHg at 350 beats/min (P less than 0.05). At the same time, arterial and coronary sinus ANP concentrations rose from 116 +/- 55 and 339 +/- 91 to 1,126 +/- 226 and 1,960 +/- 456 pmol/l, respectively (P less than 0.01). In contrast, incremental pacing with IVC occlusion produced no significant increase in PWP and RAP. Arterial and coronary sinus ANP concentrations during IVC occlusion were, respectively, 208 +/- 126 and 388 +/- 159 at 200 and 261 +/- 83 and 345 +/- 80 pmol/l at 350 beats/min (NS). This study demonstrates that the release of ANP during tachycardia is primarily dependent on increased atrial pressure and not atrial rate.
Ovine fetal adrenal gland and cardiovascular function
Authors: Ray N. D. , Turner C. S. , Rawashdeh N. M. , Rose J. C.
Published: December 2017

Given the necessity of the adrenal gland in maintaining cardiovascular function in adults of various species, these experiments were conducted to determine if fetal bilateral adrenalectomy results in altered resting heart rate, hypotension, and decreased basal blood volume as well as a diminished ability of the fetus to maintain arterial pressure and restore blood volume in response to hemorrhage. We studied heart rate, arterial blood pressure, and blood volume changes in response to hemorrhage of 20% of blood volume at 2%/min in seven adrenalectomized and six intact chronically cannulated unanesthetized lambs between 119 and 133 days of gestation. Blood volumes and percent restitution of shed volume were determined using 51Cr-tagged red blood cells and changes in hematocrit. There was no significant difference between groups in basal heart rate, mean arterial pressure, hematocrit, and blood volume. The two groups were similar to hemorrhage-induced changes in these and restitution of volume. Therefore, fetal adrenal glands are not necessary for basal cardiovascular function or regulation subsequent to moderate hemorrhage in the late gestation ovine fetus.
Proposal for APS-IUPS convention for diagraming physiological mechanisms
Authors: Allweis C.
Published: December 2017

As physiological research reveals the existence of systems of increasing complexity and the existence of important interactions between them, the diagrammatic depiction of those systems and their interactions becomes an essential step in clarifying our own concepts in scientist-to-scientist communication and in teaching. Although control engineers, electronic engineers, and computer programmers long ago established their own diagrammatic conventions, physiologists are only now beginning to feel the need for a uniform convention suited to their own special needs in place of the numerous (and mostly ad hoc) diagram types that have recently proliferated in the literature. The convention proposed here is based on a formal theory of mechanism developed by W. Ross Ashby (An Introduction to Cybernetics, 1956). Its purely mechanistic structure transcends traditional interdisciplinary barriers to communication. Wide acceptance of the convention proposed here would therefore enhance the ability of physiology to encompass mechanisms from molecular and cell biology and integrate them with general and systems physiology in a metadisciplinary effort to comprehend "the wisdom of the body." Among its many advantages is its simplicity; diagrams may be drawn at various levels of detail and complexity by use of a few basic rules, and they can be readily understood without knowledge of the theory.
Hormonal determinants of sodium excretion in rats with experimental high-output heart failure
Authors: Winaver J. , Hoffman A. , Burnett J. C. , Haramati A.
Published: December 2017

The present study evaluates the inter-relationship between the alteration in atrial natriuretic factor (ANF) and the renal handling of Na in rats with chronic aortocaval (a-v) fistula, an experimental model of congestive heart failure. Balance studies in these animals showed two distinct patterns of Na excretion: some rats developed progressive Na retention [urinary sodium excretion (UNaV) less than 100 mueq/24 h], whereas others compensated and returned to normal Na balance (UNaV greater than 1,200 mueq/24 h). Base-line plasma ANF levels were equally elevated in Na-retaining and compensated rats with a-v fistula (588 +/- 70 vs. 621 +/- 114 pg/ml, P, NS). However, the response of the two groups to exogenous administration of synthetic rat ANF-(101-126) in incremental doses varied greatly. ANF infusion increased the fractional Na excretion (FENa) in compensated animals from 0.12 +/- 0.03 to 2.6 +/- 0.5%, whereas the rise in FENa in Na-retaining animals was markedly blunted (0.11 +/- 0.06 to 0.89 +/- 0.35%). A similar pattern of ANF action was observed on the glomerular filtration rate and urine flow. The blunted response to ANF in the Na-retaining animals was associated with a marked increase in plasma renin activity (PRA) (35.6 +/- 6.9 vs. 4.5 +/- 0.7 ng ANG I.ml-1.h-1 in sham control rats, P less than 0.05) and plasma aldosterone levels (729.3 +/- 28.2 vs. 42.6 +/- 18.4 ng/dl in sham control rats, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Osmotically released vasopressin augments cardiopulmonary reflex inhibition of the circulation
Authors: Hasser E. M. , DiCarlo S. E. , Applegate R. J. , Bishop V. S.
Published: December 2017

Exogenous arginine vasopressin (AVP) has been shown to augment the inhibitory influence of arterial and cardiopulmonary baroreflexes. This study examined the influence of osmotically released AVP on the inhibitory responses to activation of cardiopulmonary receptors by administration of veratrum alkaloids. Three groups of conscious dogs, with carotid sinus intact, with prior sinoaortic denervation (SAD), and with prior lesion of the area postrema (AP), were instrumented for monitoring arterial pressure and heart rate and with left circumflex coronary artery or left atrial catheters for administration of veratrum alkaloids. Conscious dogs were administered veratridine (0.5-1.0 microgram.kg-1.min-1) under control conditions, after infusion of hypertonic saline (HS, 6% NaCl), and after HS in the presence of the AVP vascular (V1) receptor antagonist. In carotid sinus-intact dogs, veratridine reduced arterial pressure (-10 +/- 0.4 mmHg). After HS infusion, the depressor response to veratridine was significantly greater (-18 +/- 0.8 mmHg). The enhanced depressor response during HS infusion was prevented by administration of the AVP antagonist (-8 +/- 0.6 mmHg). Responses to veratrum alkaloids in SAD dogs were similar. In AP-lesioned animals, the depressor effects of veratridine (-9 +/- 0.5 mmHg) were similar to intact animals. However, the response to veratridine during HS was not altered (-9 +/- 0.8 mmHg) in AP-lesioned dogs. Results suggest that osmotically stimulated AVP augments the inhibitory effects of cardiopulmonary reflexes and that this effect is mediated through the area postrema via the V1 receptor.
Is adrenergic innervation essential for maintenance of UCP in hamster BAT mitochondria?
Authors: Desautels M. , Dulos R. A.
Published: December 2017

The importance of the neural input for the maintenance of the mitochondrial content of the uncoupling protein (UCP) in hamster brown adipose tissue (BAT) was evaluated by unilateral surgical denervation and chemical sympathectomy with 6-hydroxydopamine. These interventions alone or in combination depleted (by 90-95%) the tissue catecholamine content to the same extent. Injections of 6-hydroxydopamine to hamsters caused reductions in BAT protein content but were without significant effect on [3H]GDP binding to isolated mitochondria or on the mitochondrial content of UCP measured by immunoassay. In contrast, surgical denervation, which had much less effect on BAT composition, caused a significant loss of UCP from the mitochondria. These results differ from those obtained in rats in which both chemical sympathectomy and surgical denervation caused a loss of UCP from the mitochondria. Norepinephrine infusion (with minipumps), which prevented denervation-induced BAT atrophy and reduction in mitochondrial content of UCP in rats, caused pronounced loss of tissue mass and mitochondrial proteins in hamsters and did not prevent the loss of UCP observed in mitochondria isolated from the denervated pad. Thus an intact innervation that may not be adrenergic is required for the expression of UCP in hamster BAT mitochondria.
Effects of denervation and immobilization on collagen synthesis in rat skeletal muscle and tendon
Authors: Savolainen J. , Myllyla V. , Myllyla R. , Vihko V. , Vaananen K. , Takala T. E.
Published: December 2017

The activities of prolyl 4-hydroxylase (PH) and galactosylhydroxylysyl glucosyltransferase (GGT), both enzymes of collagen biosynthesis, and the concentration of hydroxyproline (HYP) were measured in the gastrocnemius, soleus, and tibialis anterior muscles of rats after sciatic nerve neurectomy combined with cast immobilization of the denervated limb for 1 and 3 wk. PH and GGT were also observed in Achilles and tibialis anterior tendons after cast immobilization without neurectomy. After neurectomy the specific PH activity in the denervated gastrocnemius muscle increased by 215% (P less than 0.001). The specific GGT activity increased by 92-110% (P less than 0.01) in the denervated gastrocnemius, soleus, and tibialis anterior muscles. Elevation of the muscular HYP concentration by 118-170% (P less than 0.001) in the denervated muscles was observed. The PH, GGT, and HYP responses of the denervated muscles immobilized at a lengthened or shortened position during denervation atrophy did not generally differ significantly from those of the unfixed denervated ones. The specific PH and GGT activities of the disused tendons decreased by 62 (P less than 0.01) and 25% (P less than 0.001), respectively, in tendons immobilized in a chronically shortened position. The results suggest that denervation atrophy of skeletal muscle is associated with both an increased level of muscular collagen biosynthesis and with an increased muscular collagen concentration. The PH and GGT responses of the cast-immobilized tendons suggest adaptive changes in collagen biosynthesis of the disused tendon.
Cold-induced thermogenesis in younger and older Fischer 344 rats following exercise training
Authors: McDonald R. B. , Horwitz B. A. , Stern J. S.
Published: December 2017

The inability of old rats to maintain body temperature during cold exposure has been well documented. This study evaluated the effect of exercise on the rates of cold-induced O2 consumption and the contribution of nonshivering thermogenesis (NST) to these rates. Younger (12 mo) and older (24 mo) male Fischer 344 (F344) rats were divided into exercised and sedentary groups. Exercised rats were run on a motor-driven treadmill 60 min/day, at 19-24 m/min, 5 days/wk for 6 mo. At the conclusion of the 6-mo training period, O2 consumption of all four groups was measured at thermoneutrality (26 degrees C) and during 6 h of exposure to 6 degrees C. Rectal temperatures were recorded before and after cold exposure. NST was estimated from the ability of isolated brown fat mitochondria to bind guanosine 5'-diphosphate (GDP). Core temperature of older sedentary rats fell 5.1 +/- 0.4 degrees C after cold exposure (36.3 +/- 0.3 vs. 31.2 +/- 0.8 degrees C). Exercise training in older animals prevented this fall from occurring (36.4 +/- 0.2 vs. 35.3 +/- 0.3 degrees C). Core temperatures of cold-exposed younger exercised and sedentary rats did not differ from thermoneutral values. Exercise did not alter the rates of resting body mass-independent (ml.min-1.kg body mass-0.67) O2 consumption in younger or older rats. However, body mass-independent and lean body mass (LBM)-independent (ml.min-1.g LBM-0.67) cold-induced O2 consumptions of older exercised rats were significantly elevated relative to those of older sedentary animals. This effect of exercise was not seen in younger rats.(ABSTRACT TRUNCATED AT 250 WORDS)
Model for evaluating avian renal hemodynamics and glomerular filtration rate autoregulation
Authors: Wideman R. F. , Gregg C. M.
Published: December 2017

Multiple vascular connections in normal avian kidneys make it difficult to experimentally manipulate renal blood flow patterns and perfusion pressures. In this study, hemostatic clips were used to obstruct the ureter of one kidney at the level of the ischiadic artery (IA) in anesthetized 3-wk-old chicks (Gallus domesticus). Kidney tissue upstream from the ureteral obstruction degenerated, leaving an intact caudal renal division with one route of arterial inflow branching from the IA. Renal function studies were conducted, using general anesthesia, when the birds reached 12-15 wk of age. A snare placed around the IA was used to unilaterally decrease renal arterial perfusion pressure (RAPP) for the experimental kidney. Under control conditions (snare loose), urine flow rates (UFR), glomerular filtration rates (GFR), clearance of p-aminohippuric acid, and fractional excretion of Na, K, Ca, and PO4 did not differ significantly, per gram of kidney weight, when experimental and intact contralateral kidneys were compared. Gradual tightening of the IA snare reduced RAPP stepwise. UFR decreased significantly from the initial control value when RAPP reached 40 mmHg, and urine flow ceased completely when RAPP reached 30-35 mmHg. In four of five birds, GFR did not decrease significantly between 110 and 60 mmHg but did decrease significantly below 60 mmHg. Urine osmolality was inversely correlated with UFR. Clearance of PAH did not decrease significantly from control values as RAPP ranged from 100 to 37 mmHg, possibly caused by increased renal portal blood flow. Overall, these results provide the first direct demonstration that in domestic fowl GFR is autoregulated at reduced RAPP.
Control of norepinephrine turnover in brown adipose tissue of Syrian hamsters
Authors: Sigurdson S. L. , Himms-Hagen J.
Published: December 2017

Sympathetic nervous system activity in brown adipose tissue (BAT) of normal and myopathic Syrian hamsters was assessed by measuring norepinephrine turnover rate (NETR) using [3H]norepinephrine. Acute exposure of normal hamsters to cold (4 degrees C) for 4 or 24 h increased norepinephrine secretion but not resynthesis. By 3 days and at 2 wk in the cold, NETR increased but returned to a normal level by 6 wk. Hamsters were initially hypothermic (to 3 days) then normothermic (2 and 6 wk). Adaptation of normal or myopathic hamsters to high-fat diet or short photoperiod (4 h light, 20 h dark) for up to 12 wk did not alter NETR in BAT. Serum triiodothyronine (T3) concentration increased rapidly in the cold to reach a maximum level by 24 h at which it remained for 6 wk and was not correlated with changes in NETR in BAT. The high-fat diet did not alter T3 level in normal hamsters; it increased the low T3 level in myopathic hamsters. Short photoperiod induced a transient increase in T3 level in normal hamsters but not in myopathic hamsters. We conclude that the hypertrophied state of BAT in Syrian hamsters adapted to cold, to high-fat diet, or to short photoperiod is not maintained by elevated norepinephrine secretion and that some other factor(s) must be involved. A selective increase in concentration of BAT mitochondrial uncoupling protein in hamsters may be dependent on raised T3 level in serum and/or production in BAT, since both occur in response to cold acclimation but not in response to high-fat diet or short photoperiod.
Propylthiouracil, but not other antithyroid treatments, lengthens hamster circadian period
Authors: Morin L. P.
Published: December 2017

Two experiments were performed to evaluate the role of the thyroid gland as a mediator of circadian rhythms in the hamster. In experiment 1, the antithyroid drug propylthiouracil (PTU) lengthened the circadian period (tau), increased thyroid weight, and eliminated detectable thyroxine (T4) and triiodothyronine (T3) from blood. A low-iodine diet greatly reduced T4 levels but had no effect on T3 or tau. Treatment with 500 microCi of 131I failed to alter any parameter of physiology or rhythmicity measured. In this experiment, some animals in the low-iodine and PTU groups had greatly reduced testes sizes, and testes size was inversely correlated with change in tau. In experiment 2, T4 and T3 levels detected 11 wk after surgical thyroidectomy were significantly less than those found in sham-operated animals, but concentrations of the two hormones varied widely across the thyroidectomized group. Thyroidectomy did not increase tau either 4 or 11 wk after surgery, nor was there evidence from individuals that level of thyroid function was associated with change in tau. The results from these experiments suggest that diminished thyroid function is not causal of lengthened circadian period.
Progressive activation of paratrigeminal nucleus during entrance to hibernation
Authors: Kilduff T. S. , Sharp F. R. , Heller H. C.
Published: December 2017

The paratrigeminal nucleus (Pa5) undergoes a progressive increase in its uptake of 2-[14C]deoxyglucose (2DG) relative to other brain structures during entrance to hibernation in the ground squirrel. This highly significant increase results in the Pa5 becoming the most highly labeled brain region during hibernation, even though it exhibits one of the lowest levels of 2DG uptake in the brain during the nonhibernating state. The progressive activation of the Pa5 observed during entrance is reversed during arousal from hibernation. These observations and the neuroanatomical projections of the Pa5 implicate this nucleus as playing a role in the entrance and maintenance of the hibernating state.
Comparison of hormonal responses to hypotension in mature and immature fetal lambs
Authors: Rawashdeh N. M. , Ray N. D. , Sundberg D. K. , Rose J. C.
Published: December 2017

We studied norepinephrine (NE) and plasma renin activity (PRA) responses to sodium nitroprusside (NP)-induced hypotension in seven chronically catheterized fetal lambs 0.79-0.94 gestation (mature) and in seven fetuses 0.64-0.72 gestation (immature) 4 or 5 days after surgery. We infused intravenously 5% dextrose in water (DW) or NP in DW to reduce arterial pressure 30% in fetuses for 10 min. Initial infusion choice was random, and the two infusions were separated by 24-48 h. In both groups, basal NE levels were similar and doubled in response to hypotension. In mature fetuses, PRA basal levels were 6.89 +/- 1.80 ng.ml-1.h-1 and increased two- to threefold with hypotension. In immature fetuses, PRA basal levels were 2.42 +/- 0.86 ng.ml-1.h-1 and did not change with hypotension. No changes were observed with DW infusion in either group. Arterial blood gases were normal and remained unchanged. We conclude that in the lamb fetus, NE responses to hypotension are present before and are independent of the development of PRA responses and that before 0.72 gestation there is a functional deficit in the renin-angiotensin system.
Subcellular enzyme binding in glycolytic control: in vivo studies with fish muscle
Authors: Brooks S. P. , Storey K. B.
Published: December 2017

The effect of exercise on the binding of glycolytic enzymes to subcellular structures was examined in rainbow trout (Salmo gardneri). Both “burst” and “endurance” type exercise produced an increase of approximately 50% in the percentage of phosphofructokinase (PFK), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), aldolase, and 3-phosphoglycerate kinase associated with particulate matter in white skeletal muscle. In contrast, cardiac muscle showed no change in enzyme binding when trout were exercised, suggesting that the effects seen in white muscle are related to an increased anaerobic glycolytic flux in this tissue. Modulation of binding by altered pH or calcium ion concentration was tested: a decrease in pH increased PFK binding to subcellular particles, whereas 2 mM CaCl2 decreased GAPDH binding. These results are discussed with respect to the formation of a glycolytic complex during exercise in trout white muscle.
Are fetal adrenocorticotropic hormone and renin secretion suppressed by maternal cortisol secretion?
Authors: Wood C. E.
Published: December 2017

Previous studies from this laboratory have demonstrated that intravenous infusions of hydrocortisone (cortisol) into fetal sheep at rates that produce plasma concentrations achieved during fetal stress inhibit fetal adrenocorticotropic hormone (ACTH) and renin secretion. The present study was designed to test for inhibition of fetal renin and ACTH after maternal adrenal secretion of cortisol. ACTH-(1-24) or saline infusion into 12 pregnant ewes (120-132 days gestation) at rates of 0, 1, 5, or 20 ng ACTH.kg-1.min-1 for 5 h produced dose-related increases in maternal plasma ACTH and cortisol concentrations and fetal plasma cortisol concentration. In the 20-ng.kg-1.min-1 group, increases in fetal plasma cortisol of 8.0 ng/ml (to 24.3 +/- 3.7 ng/ml) did not suppress basal fetal plasma renin activity. One hour after the end of the maternal vehicle or ACTH infusion, fetal ACTH secretion was stimulated by fetal intravenous infusion of sodium nitroprusside. In the 0-, 1-, and 5-ng.kg-1.min-1 groups, fetal ACTH responses to nitroprusside were suppressed in animals infused with ACTH. Together, these results indicate that the maternal adrenal secretion of cortisol inhibits stimulated secretion of ACTH but not renin in 120- to 132-day-gestation fetal sheep.
Membrane potential drives organic cation transport into teleost renal proximal tubules
Authors: Smith P. M. , Pritchard J. B. , Miller D. S.
Published: December 2017

The relationship between organic cation uptake and basolateral membrane potential was studied in renal tubules from two marine teleost fish, Southern flounder (Paralicthys lethostigma) and killifish (Fundulus heteroclitis). Carrier-mediated uptake of the model organic cation, tetraethylammonium (TEA), increased when K+ was changed from 2.5 to 0.2 mM and decreased when medium K+ was increased to 20 mM. Uptake was also reduced by the K+ channel blocker barium (1 mM). Furthermore, basolateral membrane potential hyperpolarized 15-25 mV in low-K+ medium and depolarized 30-40 mV in high-K+ medium. Barium also depolarized. Finally, basolateral membrane potential was depolarized in a concentration-dependent manner by addition of 100-500 microM TEA or Darstine. Thus treatments that hyperpolarize the basolateral membrane potential increase carrier-mediated TEA uptake, whereas those that depolarize basolateral membrane potential reduce uptake. Furthermore, organic cation transport into tubular cells involves the net influx of positive charge. Together, these findings support the argument that carrier-mediated organic cation uptake at the basolateral membrane is a potential-driven, electrogenic process.
Lateral hypothalamus and sympathetic firing rate
Authors: Sakaguchi T. , Takahashi M. , Bray G. A.
Published: December 2017

Measurements of sympathetic firing rate have been made after the acute microinjection of glucose or insulin into the lateral hypothalamic area as well as after ablation of this area with locally injected gold thioglucose. Injection of glucose into the lateral hypothalamus (LH) produced a small but significant and dose-dependent reduction in the firing rate of efferent sympathetic nerves to interscapular brown adipose tissue. Injection of insulin into the same region produced a very short-lived increase in efferent sympathetic firing rate. Bilateral lesions in the lateral hypothalamus produced by microinjection and gold thioglucose lowered body weight more than sham injections into the LH of control animals. There was an increase in basal sympathetic firing rate at 3, 9, and 24 h after LH lesions. There was also an increase in firing rate at 1 and 3 days, but by 7 days firing rate had returned to control levels. The data support the hypothesis that LH lesions enhance sympathetic activity but show only very limited modulation by glucose or insulin.
Beta-receptors in resistance to phosphaturic effect of PTH in respiratory alkalosis
Authors: Hoppe A. , Rybczynska A. , Knox F. G. , Angielski S.
Published: December 2017

Respiratory alkalosis results in a resistance to the phosphaturic effect of parathyroid hormone (PTH) and dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP). The present studies evaluated the role of the beta-adrenergic system in that resistance phenomenon. In clearance experiments on acutely thyroparathyroidectomized male Wistar rats, respiratory alkalosis blunted the PTH-mediated increase in absolute and fractional excretion of phosphate (FEPi). Propranolol infusion restored the phosphaturic response to PTH:FEPi, 0.8 +/- 0.3 vs. 8.1 +/- 2.5% (P less than 0.005). Similarly, the increase of FEPi during cAMP infusion was also diminished by respiratory alkalosis: FEPi, 15.5 +/- 2.2 vs. 5.5 +/- 1.1% (P less than 0.005). This hypophosphaturic effect of respiratory alkalosis in the presence of cAMP was not observed in rats infused with propranolol compared with the period of normal ventilation: FEPi, 21.1 +/- 1.7 vs. 15.3 +/- 1.6 (P less than 0.02). Also, during the infusion of the highly selective beta 2-adrenoceptor antagonist, ICI 118,551, cAMP was phosphaturic in respiratory alkalosis compared with FEPi in the absence of the antagonist: FEPi, 13.0 +/- 2.5 vs. 5.5 +/- 1.1% (P less than 0.02). Finally, the infusion of the beta 2-agonist, fenoterol, to the normally ventilated rats significantly decreased FEPi in cAMP-infused rats in comparison to the absence of the agonist: FEPi, 4.0 +/- 0.7 vs. 22.1 +/- 2.6% (P less than 0.001). We conclude that the resistance to the phosphaturic effect of PTH and cAMP in respiratory alkalosis is mediated by beta-adrenoceptors.
Immunocytochemical distribution of PTH immunoreactivity in vertebrate brains
Authors: Pang P. K. , Kaneko T. , Harvey S.
Published: December 2017

Immunoreactive (IR) cell bodies, reacting with an antiserum specific for the 48-64 region of bovine parathyroid hormone (PTH), were detected in the brains of primitive vertebrates (hagfish), bullfrogs, and higher vertebrates (mice). In each species the IR perikarya were located in the preoptic region, although the precise location and abundance of IR perikarya differed among species. Fiber tracts from these IR perikarya were traced to the neurohypophysis in the hagfish but only to the median eminence in the bullfrog and mouse, where the axonal terminals were in close proximity to hypophyseal portal blood vessels. These results suggest that a novel PTH-like peptidergic system, similar to those secreting hypophysiotropic-releasing factors, is present in the vertebrate brain.
Regional hemodynamic effects of atrial natriuretic peptide or captopril in Brattleboro rats
Authors: Gardiner S. M. , Compton A. M. , Bennett T.
Published: December 2017

The regional hemodynamic effects of rat atrial natriuretic peptide (ANP) (1 and 10 nmol) were measured in the same conscious Brattleboro rats in water-replete and in water-deprived states (14 h). In the latter condition, the effects of ANP were compared with those of captopril (3.2 mumol). In rats in the water-replete state, the low dose of ANP had no significant effects on mean arterial pressure (MAP) or renal, superior mesenteric, or hindquarter vascular resistances, although heart rate (HR) showed a transient increase. The high dose of ANP caused a fall in MAP and an increase in HR. Renal and hindquarter vascular beds showed dilatation followed by constriction; there was a mesenteric vasoconstriction only. In rats in the water-deprived state, the low dose of ANP caused a marked fall in MAP but only a transient increase in HR; there was marked hindquarters vasodilation. The high dose of ANP caused dramatic hypotension and bradyarrhythmia; an initial hindquarter vasodilation gave way to vasoconstriction; renal and mesenteric vasoconstrictions also occurred. The initial effects of captopril on MAP were similar to those of the high dose of ANP, but the regional hemodynamic effects of captopril indicated a potent inhibition of both primary and secondary vasoconstrictor mechanisms.
Evaluation of a blood sample-transfusion protocol in rats: blood gases, renin, and ACTH
Authors: Raff H.
Published: December 2017

The present study evaluated a protocol for drawing large volumes of blood over an acute time frame in conscious cannulated rats with blood from cannulated donor rats simultaneously infused to maintain isovolemia. During time control (n = 6), three successive 1.5-ml blood samples were drawn at 10-min intervals with equal volumes of donor blood infused simultaneously. One milliliter of blood was drawn quickly and saved for analysis followed by an additional 3 ml of blood withdrawal to total a 15-ml/kg hemorrhage. Two subsequent 1.5-ml samples were replaced with autologous (hemorrhage) blood. During hypoxia inspired O2 was decreased to 10% after the first sample-transfusion. The sampling-transfusion protocol (time control) had no effect on blood pressure (MAP), hematocrit (Hct), blood gases, renin, or adrenocorticotropic hormone (ACTH). Hemorrhage resulted in a significant decrease in MAP, Hct, base excess, and arterial PCO2 and an increase in arterial PO2, renin activity, and ACTH. Ten percent O2 resulted in significant hypoxemia, respiratory alkalosis, and a small degree of hypotension at the 20-min sample with no change in renin and a moderate increase in ACTH. The consistency of the results with previous studies confirms the utility and efficiency of large sample-transfusion protocols for the study of blood gas and endocrine dynamics in conscious rats.
Pylorectomy reduces the satiety action of cholecystokinin
Authors: Moran T. H. , Shnayder L. , Hostetler A. M. , McHugh P. R.
Published: December 2017

Rat gastric cholecystokinin (CCK) receptors are localized to the circular muscle layer of the pyloric sphincter, and a role for these receptors in the mediation of CCK satiety has been proposed. To directly assess the contribution of this receptor population in CCK satiety, the area of the pyloric sphincter containing these receptors was surgically removed, and the behavioral responses to CCK were compared pre- and postpylorectomy. The presence of CCK receptors in the gastroduodenal junction was assessed by either in vitro CCK receptor autoradiography or in vitro contractile response to CCK. The results depended on the time after pylorectomy during which testing occurred. Two to 3 wk after pylorectomy rats demonstrated a significant attenuation of CCK satiety such that while the response to 1 and 2 micrograms/kg was intact, any additional inhibition by 4 and 8 micrograms/kg was eliminated. At this time, no evidence of CCK receptors around the gastroduodenal junction was found. In contrast, 2-3 mo after pylorectomy, the normal dose-response inhibition to CCK was intact. Evidence for the presence of CCK binding sites at the gastroduodenal junction was found by both autoradiography and physiological assessment. These results indicate a role for pyloric CCK receptors in the mediation of CCK satiety.
Effects of alpha-MSH on sleep, behavior, and brain temperature: interactions with IL 1
Authors: Opp M. R. , Obal F. , Krueger J. M.
Published: December 2017

Changes in rabbit sleep-wake activity, brain temperature (Tbr), and behavior were studied after intracerebroventricular injections of a putative endogenous antipyretic, alpha-melanocyte-stimulating hormone (alpha-MSH), and of an endogenous pyrogen, interleukin 1 (IL 1-beta). alpha-MSH (0.1-50.0 micrograms) dose dependently increased wakefulness (W) and decreased Tbr, non-rapid-eye-movement sleep (NREMS), and rapid-eye-movement sleep (REMS). NREMS was more sensitive than REMS to the suppressive effects of low alpha-MSH doses. EEG slow-wave activity in NREMS decreased after alpha-MSH treatment. alpha-MSH elicited stretching, yawning, and signs of sexual excitation. IL 1 (20 and 40 ng) induced fever and excess NREMS. alpha-MSH administered 30 min after IL 1 (40 or 20 ng IL 1 + 0.1, 0.5, or 5.0 micrograms alpha-MSH) significantly attenuated IL 1-induced fever and excess NREMS. IL 1 failed to alter the behavioral effects of alpha-MSH. Despite alpha-MSHs effect on rabbit behavior, total motor activity time did not increase, indicating that increased W after alpha-MSH cannot be attributed to behavioral activation. These results suggest that, besides acting as an endogenous antipyretic, alpha-MSH might be involved in regulation of IL 1-induced sleep.
Effects of subpicomolar changes in vasopressin on urinary concentration
Authors: Baerwolff M. , Bie P.
Published: December 2017

The possibility that small amounts of vasopressin (AVP) reduce water excretion without affecting solute excretion was investigated in conscious dogs. AVP was infused intravenously for 120 min at rates of 2 and 5 pg.min-1.kg body wt-1 during water diuresis elicited by a sustained water load of 2% body wt. During control experiments urine osmolality was constantly approximately 60 mosmol/kgH2O; during AVP infusions it increased by factors of 1.36 (P less than 0.01) and 2.12 (P less than 0.01), respectively, concomitant with 39 +/- 6 and 61 +/- 7% reductions in urine flow. Osmolar and free water clearances decreased significantly. Sodium excretion did not change; changes in potassium excretion during AVP were similar to those of the control series, i.e., a gradual decline. During AVP, 5 pg.min-1. kg-1, creatinine and urea clearances decreased (25 +/- 2 and 31 +/- 7%, respectively, both P less than 0.01). With the assumption of metabolic clearance rates of AVP of 15-40 ml.min-1.kg body wt-1, the increase in plasma AVP during the infusion of 2 pg.min-1.kg body wt-1 was 5-13 X 10(-14) M. It is concluded that small increments in plasma AVP may reduce glomerular filtration rate and that with increasing levels of AVP in plasma 1) reduction of free water clearance, 2) reduction in urea clearance, and 3) natriuresis-kaliuresis occur in that order. Apparently AVP cannot reduce water excretion without changing the rate of excretion of solutes.
Antidiuretic and pressor actions of vasopressin in age-dependent DOCA-salt hypertension
Authors: Zicha J. , Kunes J. , Lebl M. , Pohlova I. , Slaninova J. , Jelinek J.
Published: December 2017

The role of antidiuretic and pressor effects of vasopressin (VP) in deoxycorticosterone acetate (DOCA)-salt hypertension was studied in young and adult Brattleboro rats. The antidiuretic VP action was a necessary prerequisite for the development of severe DOCA-salt hypertension. The insufficient expansion of extracellular fluid volume in DOCA-salt-treated VP-deficient (DI) rats was associated with the attenuation of their hypertensive response, although they had highly increased blood volume and extracellular sodium. Chronic [deamino]-D-arginine vasopressin supplementation that restored volume and distribution of body fluids in DI rats permitted the full development of DOCA-salt hypertension. Blood pressure response to DOCA-salt treatment was always greater in young than in adult Brattleboro rats (even in animals lacking pressor or both VP effects). In animals in which antidiuretic VP effects were present, the pattern of body fluid response to DOCA-salt treatment was also age dependent. There was a tendency to intravascular expansion in young hypertensive rats, whereas an increase of interstitial fluid volume was found in adult animals. The elimination of VP pressor action lowered systemic resistance much more in adult than in young hypertensive rats. We conclude that 1) in adult but not in young rats antidiuretic VP effects are essential for the occurrence of blood pressure response to DOCA-salt treatment, 2) the restoration of body fluids due to antidiuretic VP action enables the development of hypertension in both age groups of DI rats, and 3) pressor VP effects contribute to the maintenance of hypertension, especially in adult animals.
Contribution of neurogenic mechanisms to control of intrinsic heart rate
Authors: Machado B. H. , Brody M. J.
Published: December 2017

Altered autonomic tone as well as humoral factors can change the intrinsic rate of the cardiac pacemaker. To study the relationships of neurogenic and humoral factors on intrinsic heart rate (IHR) we used sinoaortic deafferentation (SAD) to increase sympathetic activity, lesion of nucleus ambiguus to reduce central parasympathetic activity, and one-kidney, one-clip (1K1C) renal hypertension to transiently increase the activity of the renin-angiotensin system and the combination of 1K1C hypertension with SAD. In conscious rats, IHR was determined using combined blockade with atropine and propranolol. Rats with 1K1C hypertension (7th day) showed increased mean arterial pressure (MAP), heart rate (HR), and IHR. Rats with SAD (4th day) demonstrated increased MAP and HR, but in contrast, had decreased IHR. Lesion of nucleus ambiguus increased HR and decreased IHR. When 1K1C hypertension was combined with SAD an additional increase in MAP and HR occurred, whereas IHR was reduced compared with renal hypertension alone. These data suggest that IHR is influenced greatly by autonomic tone and that the tachycardia in renal hypertension is linked to increased IHR that is dependent on integrity of the baroreflex.
Biomechanical and biochemical changes in lumbar vertebrae of rapidly growing rats
Authors: Salem G. J. , Zernicke R. F. , Vailas A. C. , Martinez D. A.
Published: December 2017

Although growth-related biochemical, morphological, and biomechanical properties of rat cortical bone have been investigated, similar properties of immature rat vertebral bone have not been well characterized. Information about these properties is necessary, however, for comparative analyses of rat vertebral bone adaptation. Thus a method was developed to characterize growth-related differences in immature rat vertebral bone. The centra of sixth lumbar vertebrae (L6) of 44-day-old and 54-day-old male Sprague-Dawley rats were compressed to 50% of their initial height at a 50%/s strain rate while immersed in a potassium phosphate buffer solution (pH 7.4, 37 degrees C). Structural and material properties for the 54-day-old group that were significantly greater than those for the 44-day-old group included load, stress, and energy at the proportional limit; initial maximum load and stress; and load and energy at 50% strain. The structural stiffness of L6, as well as its elastic modulus, was significantly greater in the older animals. The calcium concentrations and calcium-to-collagen ratios in 54-day-old vertebrae were significantly greater than in younger animals. These results indicated that the specimen preparation and testing protocol developed for rat vertebrae produced reliable biomechanical results, even with the relatively small size of rat vertebrae bodies, and that the quantity and quality of the matrix of immature rat vertebral bone changed significantly during this period of rapid growth. Our test protocol will be useful for investigating the responses of rat vertebral bone to exercise, disease, and spaceflight.
Atrial peptide potentiates renal responses to volume expansion in conscious dogs
Authors: Metzler C. H. , Ramsay D. J.
Published: December 2017

Experiments were performed to compare the renal responses to atrial peptide infusion in conscious dogs with normal and expanded extracellular fluid volumes to test the hypothesis that the renal responses to atrial peptide infusions are dependent on the prevailing fluid and electrolyte status in the animal. Atrial peptide-(99-126) was infused intravenously in doses of either 0, 5, 25, or 100 ng.kg-1.min-1 in conscious dogs prepared with chronic catheters in the femoral artery and vein and the urinary bladder. In dogs with normal extracellular fluid volume, atrial peptide caused small increases in urinary sodium excretion with the high physiological (25 ng.kg-1.min-1) and pharmacological (100 ng.kg-1.min-1) doses. Urine volume and potassium excretion were increased only at the highest pharmacological dose. In contrast, atrial peptide infusion in dogs that were volume expanded by infusion of hypertonic saline showed dramatic, dose-dependent increases in sodium excretion and urine flow with all doses tested. The low, physiological dose of atrial peptide (5 ng.kg-1.min-1) increased sodium excretion and urine flow rate in volume-expanded dogs more than the pharmacological dose in normal dogs (n = 4). These results demonstrate that the renal responses to atrial peptide infusion are potentiated in dogs that are volume expanded and suggest that under conditions where atrial peptide secretion would be enhanced, small changes in plasma atrial peptide concentration can have significant effects on renal function.