bluuebunny/crossref_metadata_2025 huggingface dataset:
beta-Adrenergic receptors in the developing rabbit lung
Authors: Whitsett J. A. , Manton M. A. , Darovec-Beckerman C. , Adams K. G. , Moore J. J.
Published: December 2017

beta-Adrenergic receptors and catecholamine-sensitive adenylate cyclase were identified and partially characterized in membrane fractions of rabbit lungs from day 25 of gestation to adulthood with the beta-adrenergic antagonists (--)-[3H]dihydroalprenolol [(--)-[3H]DHA] and (--)-[125I]iodohydroxybenzylpindolol [(--)-[125I]HYP]. beta-Adrenergic receptor number (Bmax) increased 11.5-fold during this time period, increasing progressively during the latter days of gestation and the early neonatal period, from 37 +/- 10 fmol/mg protein at 25 days gestation to 425 +/- 51 fmol/mg in the adult rabbit lung (mean +/- SD). Receptor affinity for (--)-[3H]DHA (KD = 1.8 nM) or (--)-[125I]HYP (KD - 0.104 nM) and the proportion of beta 1- and beta 2-adrenergic receptor subtypes (60% beta 1 and 40% beta 2) did not change with advancing age. Basal adenylate cyclase activity in lung homogenates decreased significantly with increasing age, whereas the activity in the presence of catecholamine or NaF remained nearly constant. Catecholamines stimulated adenylate cyclase activity at all ages studied supporting a role of the maturation of beta-adrenergic receptors in the regulation of pulmonary function.
Adrenergic regulation of glucagon and insulin secretion during immobilization stress in normal and spontaneously diabetic BB rats
Authors: Nakhooda A. F. , Sole M. J. , Marliss E. B.
Published: December 2017

To test for a possible role of adrenergic mechanisms in the altered glucagon secretion in the spontaneously diabetic "BB" rat, the responses of glucose, insulin, and glucagon to adrenergic blocking agents in diabetic and normal rats were compared at rest and during 2 h of immobilization stress. In unstressed normal rats, phentolamine alone caused a 20 mg/dl fall in glycemia, 1.2 ng/ml rise in insulin (IRI), and no change in glucagon (IRG), whereas the only effect of propranolol was a minor rise in glycemia. Stress caused increments in glycemia of 72 mg/dl and in IRG of 94 pg/ml, and no change in IRI. Phentolamine significantly attenuated the stress-related increments, and IRI increased by the same amount as in the unstressed state. Propranolol exhibited no statistically significant effects on the response to stress. These findings are consistent with alpha-adrenergic stimulation of IRG and suppression of IRI secretion. In unstressed diabetic rats (mean time 0 glycemia, 431 mg/dl), propranolol caused only a small rise in glycemia, whereas phentolamine induced marked increments of glycemia (131 mg/dl) and IRG (116 pg/ml). Stress alone did likewise (189 mg/dl, 122 pg/ml) as did stress with the phentolamine (271 mg/dl, 144 pg/ml). However propranolol significantly attenuated the stress-induced increments in glycemia (88 mg/dl) and IRG (82 pg/ml). Thus both alpha- and beta-adrenergic receptors influence IRG secretion in the diabetic rats. An in vivo model for elucidating neural control of glucoregulation has been developed that is independent of cardiovascular fitness.
Food intake, body weight, and adiposity in female rats: actions and interactions of progestins and antiestrogens
Authors: Gray J. M. , Wade G. N.
Published: December 2017

A series of experiments examined the effects of two progestins, progesterone and R 5020, and two nonsteroidal antiestrogens, nafoxidine and MER-25, on body weight and composition in female rats. Both progesterone and R 5020 increased food intake, body weight, and carcass adiposity in ovariectomized (OVX) rats treated with estradiol benzoate (EB), but neither progestin had any effect on these measures in OVX rats not treated with EB. R 5020 was substantially more effective than progesterone on all end points. Nafoxidine and MER-25 mimicked the actions of estradiol and decreased adipose tissue lipoprotein lipase (LPL) activity by 75–80%. For adipose tissue LPL activity, both nafoxidine and MER-25 were full estrogen agonists and without antiestrogenic activity. Nafoxidine also mimicked the effects of EB by reducing food intake, body weight, and carcass adiposity in OVX rats. In contrast, nafoxidine antagonized the induction of cytoplasmic progestin ([3H]R 5020) binding sites by EB in parametrial adipose tissue of OVX rats. In nafoxidine-treated OVX rats, concurrent progesterone administration had no effect on adipose tissue LPL activity, but progesterone did increase food intake, body weight, and carcass fat content. Some physiological mechanisms by which gonadal steroids may act to influence eating and adiposity are discussed.
Human placental lactogen release in vitro: paradoxical effects of calcium
Authors: Handwerger S. , Conn P. M. , Barrett J. , Barry S. , Golander A.
Published: December 2017

To study the effects of calcium on the release of human placental lactogen (hPL), placental explants were exposed to media containing lower or higher concentrations of calcium than normally available to the placenta. Explants exposed for 2 h to calcium-poor medium or medium containing either 2 mM EDTA or 2 mM EGTA released 160, 248, and 253% more hPL, respectively, than control explants. In contrast, explants exposed to medium containing higher than normal calcium concentrations released the same amounts of hPL as the control explants. At lower than normal extracellular calcium concentrations, the increased hPL release was inversely proportional to the calcium concentration. The increased release in calcium-poor medium was inhibited by subsequent exposure of the explants to medium containing calcium and was prevented by either barium or magnesium. Changes in barium or magnesium concentrations, however, had no effects on hPL release in the presence of normal extracellular calcium concentrations. Methoxyverapamil (D 600), an inhibitor of calcium flux, stimulated hPL release. Because low extracellular calcium and methoxyverapamil both inhibit calcium influx, these experiments suggest that calcium influx inhibits hPL release. The role of calcium in the regulation of hPL release therefore appears to be different from that reported in other release systems.
Coupling of insulin binding and insulin action on glucose transport in fat cells
Authors: Haring H. U. , Biermann E. , Kemmler W.
Published: December 2017

The initial lag phase of insulin action on glucose transport in adipocytes reflects an unknown process that couples receptor binding and glucose transport activity. The influence of temperature, cellular ATP, cyclic AMP, and calcium on this process and a possible relation to internalization of insulin were studied. The Arrhenius plot of the coupling shows a break in slope at 30 degrees C; the activation energy below 30 degrees C is 17.5 kcal/mol. Reduction of cellular ATP by 70% prolongs the coupling process; initial binding and final maximal response of the glucose transport remain unaffected. Further reduction of ATP (greater than 90%) before addition of insulin abolishes the coupling completely. Reduction of ATP at different time points after addition of insulin blocks further activation; however, the actual state of activity is preserved. Calcium depletion by EDTA prolongs the coupling and decreases the maximal response. Internalization of insulin as determined in chloroquine-treated cells begins later than transport activation and is in contrast to transport activation not observable at 15 degrees C. In conclusion, the coupling is not related to internalization; it is ATP-dependent, whereas the initial binding and the activated transport system are ATP-independent. Calcium but not cyclic AMP might be second messenger or cofactor in the coupling process.
Perifused pituitary cultures: a model for LHRH regulation of LH secretion
Authors: Loughlin J. S. , Badger T. M. , Crowley W. F.
Published: December 2017

In this paper, a dispersed anterior pituitary cell system that is continuously perifused and suitable for the study of luteinizing hormone-releasing hormone (LHRH)-anterior pituitary physiology is described. Adult male Sprague-Dawley rats were decapitated and the anterior pituitaries removed, dispersed using collagenase, mixed with Biogel P2, and packed into 0.9-cm columns using sterile technique. All experiments were conducted using Krebs-Ringer-bicarbonate-glucose buffer, and a stable base line was achieved. A constant dose of LHRH (50 ng) administered several times at 1-h intervals stimulated the same quantal release of LH. LH secretion is linear in response to LHRH over the range of 1-50 nM and to rat hypothalamic extracts over a range of 1/32 to 1/2 hypothalamic equivalents, regardless of whether the extracts are administered in ascending or descending order. These results indicate that perifusion of dispersed pituitary cells provides a useful model for the study of LHRH physiology, combining the advantages of the long-term viability of pituitary cells in culture with the dynamic nature afforded by perifusion.
Direct measurement of gluconeogenesis from [2,3]13C2]alanine in the human neonate
Authors: Frazer T. E. , Karl I. E. , Hillman L. S. , Bier D. M.
Published: December 2017

The functional integrity of the gluconeogenic pathway was measured in nine term infants, four appropriate-for-gestational age (AGA), and five normoglycemic small-for-gestational age (SGA), by determination of 13C2 enrichment in blood glucose during the constant infusion of tracer [2,3]13C2]alanine between 4 and 8 h of postnatal age. Alanine flux, calculated from the steady-state blood [2,3-13C2]alanine enrichment was 16.6 +/- 1.3 (SE) (mumol.kg-1.min-1 in the AGA infants and not statistically different from the value of 15.3 +/- 0.7 mumol.kg-1.min-1 in the SGA infants. Alanine flux did not correlate with blood alanine level in either group. By 6 h of age, the earliest sampling time, there was 13C2 enrichment of blood glucose in every infant studied, indicating that the gluconeogenic pathway was functionally intact by that time and implying that it was operative sooner. At 8 h of age, 9.3 +/- 2.3% of blood glucose was derived from alanine in the AGA group and 12.9 +/- 2.4% in the SGA group, values not statistically different. These data indicate that the term human newborn has a functional gluconeogenic pathway very early in postnatal life and that intrauterine growth retardation per se does not impair maturation of the system. Furthermore, the plasma alanine level alone is a poor index of gluconeogenic carbon flow in these infants.
Developmental changes in rabbit and dog adrenal function: a possible homologue of adrenarche in the dog
Authors: Schiebinger R. J. , Albertson B. D. , Barnes K. M. , Cutler G. B. , Loriaux D. L.
Published: December 2017

Histologic, hormonal, and enzymatic studies were performed in the rabbit and dog to identify maturational changes similar to human adrenarche. Development of an adrenal reticular zone was observed in both the rabbit and dog, analogous to the change in the man. Plasma dehydroepiandrosterone (DHA) and androstenedione (delta 4-A) increased significantly in postpubertal compared to prepubertal male rabbits and dogs, but the increases were much smaller than those reported in man. Orchiectomy reduced plasma DHA and delta 4-A of adult rabbit and dog to near undetectable levels, suggesting a primarily testicular origin. The activities of adrenal microsomal 17-hydroxylase and 17,20-desmolase in the orchiectomized rabbit and dog were subsequently measured to explain this apparent low adrenal contribution to DHA and delta 4-A. Adrenal 17-hydroxylase activity in the rabbit ad 17,20-desmolase activity in both the rabbit and dog were significantly lower than in an adrenal androgen-secreting primate (cynomolgus macaque). Adrenal 17-hydroxylase activity in the dog, measured 1 wk after castration, doubled after sexual maturation (P less than 0.001). This change was paralleled by a significant rise in basal and ACTH-stimulated plasma 17-hydroxyprogesterone in the intact dog (P less than 0.05). Because adrenal 17-hydroxylase activity has been shown to increase during adrenarche in man, this change may be homologous to human adrenarche.
Amino acid disposition by liver and gastrointestinal tract after protein and glucose ingestion
Authors: Bloomgarden Z. T. , Liljenquist J. , Lacy W. , Rabin D.
Published: December 2017

Hepatic uptake and gut and splanchnic output of amino acids were determined after administration of protein and glucose loads in conscious dogs with indwelling catheters in the femoral artery and portal and hepatic veins. Oral or parenteral glucose given with a beef meal blunted the rise in arterial amino acids relative to that seen with ingestion of beef alone. Gut amino acid output was considerably delayed with oral hypertonic glucose, but was unchanged with parenteral glucose and with oral isotonic glucose. Ingestion of beef with oral hypertonic mannitol, a nonabsorbable sugar alcohol, delayed the rise in gut amino acid output in a manner similar to that seen with beef plus oral hypertonic glucose. We have evaluated the relationship between circulating amino acids, circulating hormone concentrations, and amino acid metabolism. Significant correlations with hepatic amino acid uptake were found for insulin, for arterial and portal amino acid levels, and for gut amino acid output. Partial correlation analysis suggests that gut amino acid output is the major determinant of hepatic amino acid uptake.
Effects of phosphate-induced hyperparathyroidism and parathyroidectomy on rat kidney calcium in vivo
Authors: Borle A. B. , Clark I.
Published: December 2017

The effects of a high-phosphate diet on the calcium metabolism of kidney cells were studied in intact and parathyroidectomized (PTX) rats. The control and the PTX rats were pair-fed a normal diet with a Ca/P of 2:1 or a high-phosphate diet with a Ca/P of 1:8 for 6 wk (chronic experiments) or 1, 3, and 6 days (acute experiments). Renal cell calcium metabolism was studied by chemical and kinetic analyses in kidney slices incubated in vitro. In the control rats the high-phosphate diet significantly increased kidney and mitochondrial calcium, the cytosolic and mitochondrial exchangeable calcium pools, and all calcium fluxes. In these controls, the plasma phosphate was not significantly elevated, but the parathyroid hormone (PTH) levels tended to be high. In PTX rats fed the same high-phosphate diet, the plasma phosphate was significantly elevated, but no change in renal calcium metabolism occurred. These results suggest that nephrocalcinosis was caused by elevated PTH levels and not by the elevated plasma phosphate and that the first step in the development of nephrocalcinosis is a stimulation of cellular calcium metabolism and transport.
Effects of arginine-free meals on ureagenesis in cats
Authors: Stewart P. M. , Batshaw M. , Valle D. , Walser M.
Published: December 2017

Cats given a single arginine-free meal have been reported to develop severe hyperammonemia, attributed to impaired function of ornithine aminotransferase (OAT). We found that cats that developed hyperammonemia following an arginine-free meal had low hepatic ornithine levels. However, the average sum of hepatic ornithine plus arginine plus citrulline rose, indicating that some ornithine synthesis via OAT took place, and hyperammonemia failed to occur in cats with higher hepatic ornithine levels. OAT activity and kinetic constants were comparable to values reported in the rat. Furthermore, dietary supplementation with ornithine caused only occasional and transient hyperornithinemia. Thus, OAT can function in the cat. The Ka of N-acetylglutamate (AGA) synthetase for arginine was 5 times higher in cats than in rats, but AGA content and citrullinogenesis by intact mitochondria were the same following arginine-free or arginine-containing meals. Other kinetic parameters of AGA synthetase and carbamoylphosphate synthetase were similar to values in the rat. We conclude that low levels of hepatic ornithine are probably responsible for making some cats susceptible to hyperammonemia following this stimulus.
Adaptation to prolonged starvation in the rat: curtailment of skeletal muscle proteolysis
Authors: Goodman M. N. , McElaney M. A. , Ruderman N. B.
Published: December 2017

Previous studies have established that 16-wk-old nonobese and obese rats conserve body protein during prolonged starvation. To determine the basis for this, protein synthesis and degradation in skeletal muscle were evaluated in the isolated perfused hindquarters of these rats, in the fed state and when starved for 2, 5, 10, and 11 days. Rats aged 4 and 8 wk were used as a comparison. The results indicate that the response to starvation depends on several factors: the age of the rat, its degree of adiposity, and the duration of the fast. An early event in starvation was a decline in muscle protein synthesis. This occurred in all groups, albeit this reduction occurred more slowly in the older rats. A later response to starvation was an increase in muscle proteolysis. This occurred between 2 and 5 days in the 8-wk-old rats. In 16-wk-old rats it did not occur until between 5 and 10 days, and it was preceded by a period of decreased proteolysis. In 16-wk-old obese rats, a decrease in proteolysis persisted for upwards of 10 days and the secondary increase was not noted during the period of study. The data suggest that the ability of older and more obese rats to conserve body protein during starvation is due, in part, to a curtailment of muscle proteolysis. This adaptation seems to correlate with the availability of lipid fuels.
Importance of cholinergic innervation of the pancreas for glucose tolerance in the rat
Authors: Trimble E. R. , Berthoud H. R. , Siegel E. G. , Jeanrenaud B. , Renold A. E.
Published: December 2017

Because cholinergic innervation of the pancreas is of importance in control of oral glucose tolerance, it seems important to determine whether transplanted pancreatic tissue becomes reinnervated with cholinergic fibers. Oral and intravenous glucose tolerance tests (ivGTT) were performed with and without atropine treatment on streptozotocin-diabetic rats treated by intraportal transplantation of isogenic islets 13-15 wk previously and on sham-operated nondiabetic controls. Atropine had no effect on the ivGTT of transplanted rats or controls. In controls atropine caused a deterioration of the oral glucose tolerance, abolished the preabsorptive insulin release, and also diminished the early part of the glucose-induced insulin release in these animals. In the absence of atropine, transplanted rats had pathological oral glucose tolerance, preabsorptive insulin release was absent, and glucose-induced insulin release was diminished compared to controls. Atropine had little effect on the oral GTT of transplanted rats. The present results underline the importance of the vagus nerve in the control of oral glucose tolerance and show that the vagus nerve in rats, at least under these experimental conditions, does not modulate the insulin response to intravenous glucose. The results suggest that intraportally transplanted islets remain functionally vagotomized.
Carbohydrate metabolism in isolated, working newborn pig heart
Authors: Werner J. C. , Whitman V. , Fripp R. R. , Schuler H. G. , Morgan H. E.
Published: December 2017

Metabolic activity of the newborn pig heart was observed by means of a preparation that allowed isolated hearts to perform a physiologic work load. A 10-min period of retrograde aortic perfusion was followed by 60 min of recirculating perfusion in which bicarbonate buffer was infused into the right atrium and ejected from both ventricles at measured pressures and flow rates. The buffer was supplemented with either glucose (10 mM), lactate (20 mM), or pyruvate (20 mM), or was unsupplemented. Pressure development and ventricular outputs were stable through 60 min of perfusion with glucose, pyruvate, or lactate supplementation. Myocardial high-energy phosphate and glycogen contents were also stable. In hearts perfused without substrate supplementation, mechanical performance deteriorated after 30 min. Rates of substrate uptake and oxygen consumption indicated that either glucose, lactate, or pyruvate could serve as a primary source of metabolic energy. Minimal lactate production was observed when either glucose or pyruvate were present. These findings indicate that, despite recent emergence from the relatively hypoxic intrauterine environment, the well-oxygenated newborn pig heart did not depend on anaerobic metabolism of glucose for energy production at physiologic work loads.
Rapid fluctuations in plasma catecholamines in monkeys under undisturbed conditions
Authors: Hansen B. C. , Schielke G. P. , Jen K. L. , Wolfe R. A. , Movahed H. , Pek S. B.
Published: December 2017

We have demonstrated in monkeys and in man sustained synchronous oscillations in plasma levels of insulin, C-peptide, glucagon, and glucose that have periods ranging from 8 to 11 min. To identify the mechanisms of these oscillations, we studied plasma levels of catecholamines in search for periodic fluctuations. Blood was obtained at 2-min intervals from fasting, undisturbed, chair-adapted male rhesus monkeys via chronically implanted central venous catheters. Plasma levels of epinephrine, norepinephrine, and dopamine were measured by a radioenzymatic assay. Large fluctuations in plasma epinephrine were observed with an average peak-to-trough amplitude of 34 pg/ml at a mean level of 122 pg/ml. Similar fluctuations in norepinephrine and dopamine occurred and were correlated to those of epinephrine: r = 0.51 and 0.35, respectively. The most common periodicity in all three catecholamines was 6-13 min/cycle as determined by spectral analyses. Cross-correlation analyses indicated that fluctuations in the catecholamines were significantly negatively correlated with oscillations in insulin and were unrelated to fluctuations in glucagon. These fluctuations in plasma catecholamines may be related to mechanisms controlling the periodicity observed in plasma insulin and glucose.
Evidence for two distinct modalities of CA2+ influx into pancreatic B cell
Authors: Lebrun P. , Malaisse W. J. , Herchuelz A.
Published: December 2017

The pathways through which glucose stimulates Ca2+ inflow into islet cells were investigated by comparing the inhibitory effect of verapamil, a selective blocker of voltage-sensitive Ca2+ channels, on glucose- and K+-stimulated insulin release and 45Ca efflux from perifused rat pancreatic islets. The islets stimulated by K+ (20 mM) were more sensitive to verapamil than those exposed to glucose (27.8 mM). The stimulation of 45Ca efflux by a low concentration of glucose (8.3 mM) was extremely resistant to verapamil, whereas that induced by a rise in the glucose concentration from 8.3 to 27.8 mM displayed the same sensitivity towards verapamil as that characterizing the response to K+. Because the increase in 45Ca efflux evoked by glucose or K+. Because the increase in 45Ca efflux evoked by glucose or K+ reflects a stimulation of Ca2+ entry into islet cells, it is proposed that the B cell may be equipped with two populations of Ca2+ channels that differ in their sensitivity towards verapamil and possibly their voltage-dependency. Glucose apparently stimulates Ca2+ inflow through both types of channels. At low concentrations, glucose may stimulate Ca2+ inflow, in part, by gating the voltage-insensitive pathway.
Responses to mixed meals in pancreatectomized dogs deprived of postprandial insulin
Authors: Goriya Y. , Bahoric A. , Marliss E. B. , Zinman B. , Albisser A. M.
Published: December 2017

Insulin plays a central role in metabolic control after a mixed meal. In the absence of adequate meal insulin release, abnormal circulating concentrations of most meal-derived metabolic substrates can be expected. To quantify these abnormalities in depth, responses of six pancreatectomized dogs on long-term intravenous insulin replacement were compared to those of five normal control dogs. Blood samples were drawn hourly for 24 h via a chronic indwelling catheter, and all animals ate a single mixed meal. To establish whether there were route-related differences, insulin was delivered into either the portal or the peripheral circulation of the diabetic animals at constant rates. These insulin infusion rates resulted in premeal fasting normoglycemia and in normal levels of insulin, glucagon, lactate, pyruvate, 3-hydroxybutyrate, nonesterified fatty acids, and 9 of 13 amino acids. In the absence of enhanced meal insulin infusion, the subsequent responses of glucose, lactate, pyruvate, alanine, and 10 of 13 other blood amino acids were exaggerated in terms of both amplitude and duration. Only minor or transient differences were attributable to the routes of insulin infusion. Remarkably, in spite of these abnormal postmeal responses, basal insulin alone (with constant circulating levels) succeeded in restoring all metabolite and hormonal levels during the postabsorptive period 16-23 h after the meal. Thus, with intravenous insulin infusions, the requirements for fasting metabolic normalization may be considered independently of those for metabolic control following caloric intake. It remains to be shown how prolonged deprivation of the postprandial insulin supplement results in metabolic decompensation under these conditions.
Absorption and disposition of a glucose load in the conscious dog
Authors: Abumrad N. N. , Cherrington A. D. , Williams P. E. , Lacy W. W. , Rabin D.
Published: December 2017

The quantitative disposition of an intragastrically administered glucose load was studied in eight conscious 18-h fasted dogs using isotopic and arteriovenous (A-V) techniques. During the control period, the gut utilized 25% of the basal net hepatic glucose output (2.8 +/- 0.2 mg.kg-1.min-1). After glucose ingestion, 80% of the load was absorbed as glucose, 11% was converted across the gut to lactate and alanine, and 4% was oxidized to CO2. Two percent of the load remained in the gut 4 h after glucose administration and 3% was unaccounted for. During the absorptive period, net hepatic glucose balance (NHGB) varied considerably (mean range = output of 1.8 to uptake of 9.1 mg.kg-1.min-1), while endogenous hepatic glucose production (Ra hp) showed a consistent 80% suppression. The total net hepatic glucose uptake during the absorptive period (150 +/- 10 min) accounted for the disposal of 24 +/- 10% of the ingested load, and the amount of glucose escaping the splanchnic bed was 40 +/- 3%. Overall NHGB correlated positively with basal arterial glucose and insulin levels and negatively with basal arterial glycerol and FFA and with peak absorptive arterial glucose and insulin levels. These data suggest that the hepatic response to an ingested glucose load depends in part on the degree of metabolic fast of the animal at the time of glucose ingestion; the latter may be a major determinant of the roles played by the tissues in glucose disposal.
Glucoregulation during insulin and glucagon deficiency: role of catecholamines
Authors: Koerker D. J. , Halter J. B.
Published: December 2017

Glucose production decreases markedly following acute reduction in insulin and glucagon secretion (induced by somatostatin). After about an hour, however, glucose production is restored nearly to basal rates. To study the mechanism by which this occurs, islet hormone deficiency was superimposed on beta-adrenergic blockade. It was found that the hypoglycemia that accompanies insulin and glucagon deficiency is an adequate stimulus for catecholamine secretion. During combined hormone deficiency and beta-blockade, glucose production fell and remained very low for 2-3 h. This resulted in a profound hypoglycemia (glucose less than 30 mg/dl). We conclude from these studies that restoration of glucose production during sustained insulin and glucagon deficiency is not attributable to a) onset of insulin deficiency because insulin is equally depressed in both experimental settings, b) glucose autoregulation even though adequate substrate is available, or c) an alpha-adrenergic mechanism because plasma catecholamines were very high and alpha-receptors were not blocked. Rather, the glucose counterregulation during insulin and glucagon deficiency must be heavily dependent on a beta-adrenergic mechanism.
Algorithms for the study of episodic hormone secretion
Authors: Merriam G. R. , Wachter K. W.
Published: December 2017

There is no generally accepted procedure for identifying ultradian pulsations in hormonal time series. We suggest an approach based on removing long-term trends, such as diurnal rhythms, from the series of observations; identifying peaks in the residual series; and resolving each peak, if appropriate, into overlapping secretory episodes. The first step uses a robust smoothing technique to generate a smoothed series that omits peaks or trends with time constants less than 6--12 h. The smoothed series is subtracted from the original, and in the second step their difference, the residual series, is examined for the presence of peaks. The standard deviation of the assay is calculated at each point, and the residuals are rescaled in terms of this unit. Peaks are identified as individual subseries elevated above the base line of duration n, all the points in which have magnitude at least G(n), where the values of G are cut-off criteria based on the width of the peak. Thus the algorithm selects both narrow high peaks and broader peaks that may be lower. The user selects the G(n) for each hormone based on theoretical considerations or a set of calibration data series. Points that meet these criteria are identified as belonging to peaks and flagged. To assure that the smoothing process is not influenced by runs of closely spaced peaks, these flagged points are then assigned a reduced weight, and the smoothing is repeated; the revised residuals are then reexamined. After these two steps are iterated until there are no further changes, each peak is examined once more to determine whether it can be resolved into more than one overlapping peak. Finally, the process collects statistics on the average frequency and amplitude of the peaks. We have developed computer programs to carry out these algorithms.
Follicle dominance and ovarian asymmetry after luteectomy in rhesus monkeys
Authors: Goodman A. L. , Koering M. J. , Nixon W. E. , Williams R. F. , Hodgen G. D.
Published: December 2017

Previous work demonstrated that asymmetrical ovarian activity accompanies morphological asymmetry during the ovarian cycle in rhesus and cynomolgus macaques. This study was designed to determine whether functional ovarian asymmetry could be used to detect the upcoming dominant follicle (DF) even before it was grossly visible. Revealing a latent DF in this manner would permit a better estimate of the time when dominance of the follicle selected to ovulate is attained. To accomplish this, rhesus monkeys were luteectomized at midluteal phase to synchronize subsequent follicle growth, and 4 or 8 days later either the ipsilateral or contralateral ovary was removed. Unilateral ablation at day 4 (when no DF is grossly apparent) of either ovary produced symmetrical responses: the interval from luteectomy (CLX) to the next luteinizing hormone (LH) surge was extended by about 4 days in both groups (P less than 0.01), i.e., from about 12.5 days to 16.7 +/- 1.6 and 17.0 +/- 1.5 days (mean +/- SE). In contrast, hemiovariectomy at day 8 produced markedly divergent asymmetrical responses. Removal of the ipsilateral ovary 8 days after CLX did not affect the timing of the next LH surge (13.2 +/- 0.6 days), which ordinarily occurs about 12.5 days after CLX alone. However, ablation of the contralateral ovary (bearing the next DF) on day 8 extended the interval from CLX to the next LH surge from about 12.5 to 26.6 +/- 1.3 days. These findings indicate that, during the normal ovarian cycle when menses occurs 2--4 days after luteolysis, the follicle destined to ovulate becomes dominant between the 2nd and 6th day and that attainment of dominance signals the completion of a follicle selection process that begins or resumes promptly after luteolysis.
Modulation of corticosteroid secretion by dopaminergic mechanisms in rhesus monkeys
Authors: Sowers J. R.
Published: December 2017

This study was designed to investigate dopaminergic mechanisms in the control of corticosteroid secretion. Ten rhesus monkeys received metoclopramide (1.25 mg iv) or domperidone (1.25 mg iv) with 5% dextrose (vehicle) or with dopamine (4 micrograms.kg-1.min-1) infusions begun 60 min before administration of the dopamine antagonist. Metoclopramide, in the presence of vehicle, increased plasma 18-hydroxycorticosterone from 11.2 +/- 1.0 ng/dl to a maximum concentration of 50 +/- 5.1, plasma aldosterone from 5.4 +/- 0.7 ng/dl to a maximum of 38.2 +/- 4.9, and prolactin (PRL) concentrations from 8.5 +/- 1.2 ng/ml to a maximum of 114.6 +/- 7.2. Domperidone, in the presence of vehicle, increased plasma PRL concentrations from 8.6 +/- 1.2 ng/ml to a maximum of 148.7 +/- 7.8 but had no effect on plasma corticosteroids. Dopamine infusion inhibited the 18-hydroxycorticosterone, aldosterone, and PRL response to metoclopramide and the PRL response to domperidone. These results demonstrate that 18-hydroxycorticosterone and aldosterone responses to metoclopramide and PRL responses to metoclopramide and domperidone are mediated by their antagonist activity at dopamine receptors. Domperidone may fail to stimulate aldosterone secretion because it does not cross the blood-brain barrier or fails to act as an antagonist at the glomerulosa dopamine receptor through which dopaminergic modulation of corticosteroid secretion is mediated. A parallel time course of stimulation of 18-hydroxycorticosterone and aldosterone secretion without changes in other aldosterone precursors suggests that dopamine modulates the activity of the glomerulosa 18-hydroxylase enzyme.
Effect of antimicrotubule agents on microtubules and steroidogenesis in luteal cells
Authors: Azhar S. , Reaven E.
Published: December 2017

This report represents an effort to reinvestigate the relationship of steroid hormone processing with microtubule protein, using the highly active progesterone-producing cells of superovulated immature rats as a model steroid hormone system. For the most part, gonadotropin-primed rats were used at 6 days and were reinjected with saline or various doses of colchicine and vinblastine: after 3 h the animals were injected with human chorionic gonadotropin (hCG, 10 IU) or saline for an additional hour. Subsequently, the ovaries were perfused with fixative for morphological studies or luteal cells were isolated for in vitro incubation with various additives. The results are as follows: 1) luteal cell progesterone synthesis is reduced in a dose- and time-dependent manner after treatment with antimicrotubule drugs; 2) additional stimulating agents given in vitro (hCG, Bt2cAMP, epinephrine) do not overcome the reduction produced by treatment with antimicrotubule drugs; 3) luteal cells show normal protein synthesis after treatment with antimicrotubule drugs; 4) luteal cells have microtubules of unusual appearance that are insensitive to the action of antimicrotubule agents. These results show that in the luteinized ovary, both colchicine and vinblastine interfere with hormone-stimulated steroidogenesis. Although the mechanism for the effect is not yet understood, it does not appear to be related to the content of the intact microtubules in luteal cells. Whether the drugs exert their action by binding to the unassembled form of microtubule protein in the cells remains to be determined.
Physical training of lean and genetically obese Zucker rats: effect on fat cell metabolism
Authors: Wardzala L. J. , Crettaz M. , Horton E. D. , Jeanrenaud B. , Horton E. S.
Published: December 2017

The effects of 6-wk treadmill training program on the metabolism of isolated adipose cells from obese (fa/fa) and lean (Fa/?) Zucker rats were studied. Glucose metabolism and transport, insulin binding, and lipolysis were measured in adipose cells prepared from sedentary control and exercise-trained (ET) lean and/or obese rats. Two- to threefold increases in glucose metabolism were observed in cells from lean and obese ET rats compared with their respective controls. However, the insulin concentrations giving half-maximal stimulation (measuring insulin sensitivity) did not change (approximately 8 microunits/ml in lean and approximately 45 microunits/ml in obese rats). In lean ET rats, glucose transport and maximal glucose metabolic capacity (transport not rate-limiting) were increased twofold and sensitivity of lipolysis to epinephrine was increased three- to fourfold. These were not measured in obese rats. The results suggest that training of both lean and obese Zucker rats increases glucose utilization in adipose cells by increasing both glucose transport and intracellular glucose metabolism. Increased triglyceride turnover is also suggested by the increased sensitivity of lipolysis to epinephrine.
Stimulus-secretion coupling in beta-cells: modulation by pH
Authors: Pace C. S. , Tarvin J. T. , Smith J. S.
Published: December 2017

We have examined the influence of changes in pH on the oscillatory pattern of electrical activity (EA) in the beta-cell by altering medium pH (pHo) and using permeable weak buffers to alter intracellular pH (pHi). A decrease in pH in the presence of glucose elicited depolarization to the active phase and constant spike activity, whereas an increase in pH elicited a decrease in spike activity or silent hyperpolarization. On inhibition of HCO3:Cl antiport by addition of DIDS (4,4'-diisothiocyano-2,2'-stilbene disulfonic acid), probenecid, or withdrawal of medium HCO-3, there was an increase in the duration of the active phase. A similar result was obtained on the inhibition of Na:H antiport by the addition of amiloride or the reduction of medium [Na+]. The influence of H+ and glucose has been proposed to decrease K+ permeability (PK). However, the influence of pH on 86Rb+ efflux was most effective at subthreshold or 4.2 mM glucose; only a moderate decrease in PK occurred at 8.3 mM glucose, and no effect was obtained at 16.7 mM glucose. Alteration of pHi, and not pHo, induces similar effects on glucose-induced electrical and secretory events. There is a clear dissociation between the influence of inhibitors of the Na:H and HCO3:Cl antiporters on the electrical and secretory events. DIDS and amiloride increased glucose-induced EA, but markedly inhibited the secretory response to glucose. It is evident that pH modulates the electrical events and cationic fluxes and ultimately influences the transduction of information to the mechanisms controlling the secretory process in the beta-cell.
Vasopressin and angiotensin II receptors in rat aortic smooth muscle cells in culture
Authors: Penit J. , Faure M. , Jard S.
Published: December 2017

Rat aortic smooth muscle cells were isolated and maintained in primary culture. After 2-3 days, cells recovered their contractile phenotype and could be induced to contract in response to vasopressin and angiotensin II. Vasopressin- and angiotensin-specific binding sites were detected on these cells, using tritiated Lys8-vasopressin, Asn1-Val5-angiotensin II, and Sarc1-Ile8-angiotensin II. Vasopressin binding sites had Kd values of 30 and 12 nM for Lys8-and Arg8-vasopressin, respectively, and a maximal binding capacity of 25,000 sites/cell. They displayed several of the expected characteristics of vasopressin receptors involved in the vasopressor response in vivo. A highly significant correlation was found between the relative agonistic or antagonistic vasopressor potencies of a series of vasopressin structural analogues and their relative abilities to inhibit [3H]vasopressin binding to aortic smooth muscle cells. Specific binding sites for Asn1-Val5-angiotensin II and Sarc1-Ile8-angiotensin II had the following characteristics: Kd = 2.3 and 1.3 nM, respectively; maximal capacity: 50,000 sites/cell. Vasopressin and angiotensin did not modify the intracellular cyclic AMP content of aortic smooth muscle cells.
Zinc, iron, and copper absorption in the streptozotocin-diabetic rat
Authors: Craft N. E. , Failla M. L.
Published: December 2017

Altered tissue levels of trace metals have been reported in streptozotocin-diabetic (STZ) rats. To determine whether increased hepatic and renal levels of Cu and Zn were associated with enhanced intestinal absorption, trace metal absorption was studied in control (C) and STZ rats using dietary balance and in situ ligated-loop techniques. The apparent daily absorption of dietary Zn and Cu per 100 g body wt was threefold higher in STZ than C rats. In comparison, dietary Fe absorption per day was not altered. Increased Zn absorption was closely correlated with diabetes-associated polyphagia. The initial rate of injected 65Zn excretion was more rapid in STZ rats, although the rate of excretion beyond day 7 was similar from C and STZ animals. The quantity of Zn, Fe, and Cu absorbed per 20 cm duodenal loop was similar for C and STZ rats. Zn, Fe, and Cu absorption per gram dry mucosa were reduced 45-53% in STZ rats due to the 50% increase in mucosal mass. Moreover, the quantity of radioisotopes accumulated per gram dry mucosa and the concentration of metallothionein per gram mucosal cytosol protein were similar in C and STZ animals. Together, these data demonstrate that increased absorption of dietary Zn and Cu is in part responsible for accumulation of these elements in STZ tissues and suggest altered metal transport at the luminal (brush border) surface of the intestinal epithelium.
Progestin increases cathepsin D synthesis in uterine luminal epithelial cells
Authors: Moulton B. C. , Koenig B. B.
Published: December 2017

Early in blastocyst implantation, cells of the uterine luminal epithelium deteriorate and die in response to the presence of the blastocyst. Destruction of the epithelial cells appears to depend on control of the autophagic activity and enzyme content of lysosomes in these cells. Concentrations of the lysosomal proteinase, cathepsin D, have been identified in luminal epithelial cells, and these studies examined changes in epithelial cathepsin D activity and their hormonal control during early pseudopregnancy in the rat. Cathepsin D activity in luminal epithelial cells increases during early pseudopregnancy to maximal levels at the time of sensitivity to deciduogenic stimuli. Rates of cathepsin D synthesis in luminal epithelial cells also increase during early pseudopregnancy, but neither enzyme activity nor rates of synthesis increase in stromal-myometrial tissues. In ovariectomized rats, progestins rather than estradiol increase cathepsin D activity and rates of synthesis in luminal epithelial cells. These studies suggest that cell death in the luminal epithelium during blastocyst implantation may depend in part on the accumulation of lysosomal cathepsin D in these cells in response to progesterone secretion during early pregnancy.
Osmoregulation of thirst and vasopressin secretion in human subjects: effect of various solutes
Authors: Zerbe R. L. , Robertson G. L.
Published: December 2017

Various hypertonic solutions were infused in healthy human volunteers to determine their effect on thirst and vasopressin secretion. Hypertonic saline and mannitol produced prompt and parallel increases in plasma osmolality and vasopressin concentration. For both of these solutes, there was a high degree of correlation between these measurements. The slope describing this relationship varied considerably between individuals, but the same subjects showed similar slopes with either saline or mannitol. Both solutions stimulated thirst. Hypertonic urea infusions produced a comparable rise in osmolality but produced a smaller increase in plasma vasopressin and stimulated thirst in only one of the subjects. With urea, the correlation between plasma osmolality and vasopressin was significantly lower. Within individuals, the slope describing this relationship was significantly correlated with that seen during hypertonic saline. Hypertonic glucose significantly increased plasma osmolality but decreased plasma vasopressin and had no detectable effect on thirst. We conclude that osmoregulation of vasopressin in humans is mediated by a selective osmoreceptor that is located primarily outside of the blood-brain barrier and that individual differences in osmoregulatory sensitivity are not solute specific.
In vitro TSH and PRL secretion from eutopic and heterotopic rat pituitaries: effects of hypothyroidism
Authors: Ikeda H. , Greer M. A.
Published: December 2017

Five adenohypophyses from donors of the same strain, age, and sex were transplanted under the renal capsule of young adult female rats. At least 3 wk later, enzymatically dispersed cells from eutopic or heterotopic adenohypophyses from the same rat were perifused in vitro in a small chamber. Thyrotropin (TSH) and prolactin (PRL) secretion per 10(6) cells were significantly less from heterotopic than from eutopic cells under all conditions. In cells from euthyroid animals, TRH induced TSH secretion only in the eutopic cells but induced PRL secretion in both eutopic and heterotopic cells. Hypothyroidism increased TRH-induced TSH secretion and content in the cell lysate in both eutopic and heterotopic cells but increased TRH-induced PRL secretion only in the eutopic cells. The increase in TSH secretion induced by hypothyroidism in the heterotopic cells was of borderline statistical significance. The inability of TRH to induce TSH secretion in heterotopic pituitary cells from euthyroid rats may be due to a lower set point for thyroid hormone inhibition of TSH secretion in the heterotopic thyrotrophs. Heterotopic pituitary TSH secretion is probably suppressed by the normal plasma thyroid hormone concentration maintained by the eutopic pituitary and may be stimulated by TRH only in the presence of a subnormal plasma thyroid hormone concentration.
Effects of beta-blockade on glycogen metabolism in human subjects during exercise
Authors: Chasiotis D. , Brandt R. , Harris R. C. , Hultman E.
Published: December 2017

The effect of beta-blockade on glycogen metabolism during isometric and dynamic exercise in humans has been investigated. Isometric exercise increased the glycogenolytic rate in muscle but had no effect on the cAMP content. Neither the metabolic pattern nor the time of contraction was affected by beta-blockade. Dynamic exercise increased the cAMP content in muscle by about 100%. The cAMP content at rest was significantly reduced after propranolol infusion and did not increase during exercise. Total hexosemonophosphates increased sixfold during exercise but little or no increase occurred after administration of propranolol. The accumulation of lactate in muscle was slightly reduced during exercise following beta-blockade. The fraction of phosphorylase in the alpha form was 22.5% of the total at rest but decreased to 16% at exhaustion. Synthetase I was similarly decreased. During exercise with propranolol phosphorylase alpha decreased further to 3%, whereas synthetase I was unchanged. It is concluded that beta-blockade has no effect on muscle glycogenolysis during isometric contraction but decreases the rate of glycogen degradation during dynamic exercise at high work loads due to changes in the phosphorylase-synthetase system.