bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of renal perfusion pressure on alpha- and beta-adrenergic stimulation of renin release
Authors: Blair M. L. , Chen Y. H. , Izzo J. L.
Published: December 2017

Experiments were performed in pentobarbital-anesthetized dogs to 1) determine if neural stimulation of renin release can be mediated by renal alpha-adrenoceptors at renal nerve stimulation (RNS) frequencies that have little or no effect on total renal blood flow (less than or equal to 1.2 Hz) and 2) ascertain whether alpha-adrenergic control of renin release is affected by renal perfusion pressure (RPP). The renal nerves were electrically stimulated both in the absence of RPP control and with RPP controlled near 85 mmHg. Decreased RPP lowered the threshold for neurogenic stimulation of renin release from less than or equal to 1.2 to 0.3 Hz. beta-Adrenoceptor blockade with propranolol blunted the renin secretion rate (RSR) response to graded RNS (0.3-5.0 Hz), but the extent of inhibition during low-frequency RNS was dependent on RPP. Propranolol prevented increased RSR at 0.6-1.2 Hz RNS when RPP was 111-120 mmHg but not when RPP was 85 mmHg. Combined alpha- and beta-blockade with prazosin and propranolol totally prevented increased RSR during 0.6-1.2 Hz RNS at reduced RPP. In summary, both alpha- and beta-adrenoceptors mediate neural stimulation of renin release at RNS frequencies that do not decrease total renal blood flow when RPP is 85 mmHg.
GRF increases release of growth hormone and arachidonate from anterior pituitary cells
Authors: Judd A. M. , Koike K. , MacLeod R. M.
Published: December 2017

Arachidonate and its metabolites increase growth hormone release in vitro. A study was designed to determine whether arachidonate release from anterior pituitary cells is modified by growth hormone-releasing factor (GRF) or somatostatin (SRIF). Cultured pituitary cells were incubated with [3H]arachidonate to esterify the long-chain fatty acid into cellular lipids. The cells were extensively washed with medium containing no [3H]arachidonate and then incubated with GRF and/or SRIF for 30 min. The incubation medium was then extracted with ethyl acetate, and following thin-layer chromatographic separation, the radioactivity in the [3H]arachidonate band was measured. GRF in a concentration-dependent manner (1-30 nM) stimulated growth hormone and arachidonate release, whereas SRIF (100 nM) blocked the GRF-induced increase of growth hormone and arachidonate release. The effects of GRF on growth hormone and arachidonate were evident at time intervals as brief as 5 min. These findings support the hypothesis that arachidonate may play a role in the GRF-induced growth hormone release.
Do hypoglycemic sulfonylureas inhibit Na+,K+-ATPase activity in pancreatic islets?
Authors: Lebrun P. , Malaisse W. J. , Herchuelz A.
Published: December 2017

The view that the insulinotropic response to hypoglycemic sulfonylureas is somehow related to an inhibitory action of these drugs on either the Ca2+-activated K+ permeability or the Na+,K+-ATPase activity in pancreatic islet cells was investigated by measuring the effect of tolbutamide on 86Rb outflow and uptake, 45Ca outflow, and insulin release in rat pancreatic islets. Although tolbutamide inhibited 86Rb efflux from glucose-deprived islets, whether in the absence or presence of extracellular Ca2+ or ouabain, a primary action of the sulfonylurea on the Ca2+-responsive K+ channels appeared unlikely, because tolbutamide failed to suppress the increase in 86Rb outflow evoked by either the ionophore A23187 or ouabain. Glibenclamide also failed to suppress the increase in 86Rb outflow evoked by the ionophore. Moreover, tolbutamide itself stimulated quinine-sensitive 86Rb outflow from glucose-stimulated islets. Likewise, although tolbutamide inhibited an ouabain-resistant modality of 86Rb inflow into the islet cells, an inhibitory action of the sulfonylurea on the Na+,K+-ATPase appeared improbable, because tolbutamide failed to minimize and instead favored the cationic and secretory response to ouabain. It is concluded, therefore, that the capacity of tolbutamide to cause under suitable conditions continuous electrical activity in islet cells cannot be attributed to inhibition of either the Ca2+-sensitive K+ permeability or ouabain-sensitive Na+,K+-ATPase.
Perturbation of insulin oscillations by nerve blockade in the in vitro canine pancreas
Authors: Stagner J. I. , Samols E.
Published: December 2017

The in vitro canine pancreas produces an oscillatory pattern of insulin secretion during a constant glucose concentration despite the lack of external nervous modulation or recirculating hormone feedback. The normal period of insulin fluctuations (7.4 +/- 0.34 min) is unaffected by combined adrenergic and cholinergic blockade by 5 microM atropine, 4 microM propranolol, and 4 microM phentolamine (8.0 +/- 0.31 min, P less than 0.20). To test the theory that the coordination of islet secretion may be controlled by an intrapancreatic nervous system (nonadrenergic, noncholinergic), nerve blockade was attempted by the infusion of tetrodotoxin (TTX) on a background of combined autonomic blockade. TTX infusion resulted in a change in the oscillatory pattern of insulin release by increasing net insulin release and shifting the period of oscillation to 4.5 +/- 0.29 min (P less than 0.0005) at both 88 and 200 mg/dl glucose. These results suggest that an intrinsic autonomously functioning pancreatic nervous system is responsible for the coordination of islet secretion and the production of periodic fluctuations of insulin secretion.
Incorporation of glucose carbons into rat lung lipids after exposure to 0.6 ppm ozone
Authors: Bassett D. J. , Rabinowitz J. L.
Published: December 2017

Continuous exposure to low concentrations of ozone has previously been associated with proliferation of lung alveolar type II epithelial cells. In this study, 14C incorporation into tissue lipids was determined in isolated rat lungs by perfusion with [U-14C]glucose, at a time of maximal hyperplasia brought about by 3 days continuous exposure to 0.6 ppm ozone. Ozone exposed lungs exhibited increased rates of glycolytic energy production, indicated by an 89% increase in 3H2O generation on perfusion with [5-3H]glucose, from a control value of 17.5 +/- 2.1 mumol X h-1 X g-1 X dry wt-1 (+/- SE, n = 4). Ozone exposure resulted in enhanced 14C incorporations into glyceride-glycerol and fatty acid moieties of lung lipids of 95 and 180%, respectively, with a greater proportion of label being recovered in shorter chain fatty acids. Although increased labeling was observed in both neutral and phospholipids, the pattern of 14C recovery suggested a relative increased glucose carbon incorporation into lung free fatty acids, phosphatidic acid, and such membrane associated lipids as phosphatidylinositol and those containing sphingosine. These results are consistent with the needs of a dividing cell population for enhanced energy production and synthesis of new lipids.
cAMP-independent stimulation of glycogen phosphorylase in newborn rat hepatocytes
Authors: Noguchi A. , Jett P. A. , Gold A. H.
Published: December 2017

Postnatal development of glycogen phosphorylase activation by the cAMP-independent pathway was examined in isolated rat hepatocytes from control and propylthiouracil-treated congenital hypothyroid rat pups. At 5 days postnatum there was complete phosphorylase activation by beta-adrenergic stimulation, glucagon, and the calcium ionophore A23187, but no activation by alpha-adrenergic stimulation. Activation of phosphorylase by angiotensin or vasopressin was less than in hepatocytes from adult rats (P less than 0.01). At 28 days postnatum activation by all of these hormones was complete. In the propylthiouracil-treated group hormone responsiveness was similar to the control at 5 days postnatum. However, alpha-adrenergic (P less than 0.025), angiotensin, and vasopressin (P less than 0.05) activation was decreased at 28 days postnatum, and beta-adrenergic, glucagon, and A23187 activation was complete. The attenuated responses were restored by thyroxine replacement from 15 days postnatum. [32P]Pi incorporation into phosphatidylinositol by epinephrine and vasopressin in 28-day propylthiouracil-treated rats was lower than the control (P less than 0.01). We speculate that the diminished phosphorylase response of hepatocytes to alpha-adrenergic, vasopressin, or angiotensin stimuli in the early neonatal period could be related to low receptor numbers and the weaker phosphoinositide response during this period. Also, the depressed phosphorylase response to alpha-adrenergic, vasopressin, and angiotensin stimulation in congenital hypothyroidism at 28 days postnatum could be related to a decrease in number of plasma membrane receptors for these agonists.
Muscle glucose metabolism in exercising rats: comparison with insulin stimulation
Authors: James D. E. , Kraegen E. W. , Chisholm D. J.
Published: December 2017

We describe here a technique using bolus 2-[3H]deoxyglucose (2-[3H]DG) administration for estimating the glucose metabolic rate (R'g) in individual tissues of the rat during exercise. After 50 min of treadmill running at a moderate work load various tissues were analyzed for accumulation of phosphorylated 2-[3H]DG and/or glycogen mass. There was considerable heterogeneity in R'g in response to exercise among different muscles, despite similar basal values. R'g increased 32-fold above basal in soleus (to 90.4 +/- 5.7 mumol X 100 g-1 X min-1), 42-fold in red gastrocnemius (to 71.2 +/- 1.6), 5-fold in white gastrocnemius (to 7.0 +/- 0.8), and 2-fold in extensor digitorum longus (to 4.1 +/- 1.0) during exercise. There was a close relationship between muscle glycogen depletion and R'g within different muscles. In view of the magnitude of the increase in R'g during exercise, this method provides a very sensitive index of muscle fiber recruitment during exercise. The pattern of exercise-stimulated R'g in muscles of different fiber composition was similar to that seen with insulin stimulation. However, moderate exercise alone produced increments in R'g (soleus and red gastrocnemius) that were significantly higher (P less than 0.005) than that observed during maximal insulin stimulation even though whole body glucose utilization was slightly higher during maximal insulin stimulation. These data emphasize the heterogeneity of the response in different muscles during exercise and suggest that intracellular events beyond glucose transport may be rate limiting under the influence of one or both of these stimuli.
Prolactin increases lipid fluidity and prolactin binding of rat prostatic membranes
Authors: Dave J. R. , Witorsch R. J.
Published: December 2017

The objective of these studies was to determine whether prolactin could modify the lipid fluidity of rat ventral and dorsolateral prostate membranes and subsequently modify the availability of prolactin receptors. Additional studies were also undertaken to determine the effects of prolactin on serum lipid fluidity. Adult male rats were injected with 0, 100, or 400 micrograms ovine prolactin/day subcutaneously for a period of 5 days. Serum and prostatic membrane lipid fluidity was measured by a fluorescence polarization method using a lipid probe 1,6-diphenylhexatriene. Prolactin binding in dextran-coated charcoal-pretreated prostatic membranes was determined by radioreceptor assay. This pretreatment has been reported by us to remove the endogenous substances that interfere with prolactin binding assay (J. R. Dave and R. J. Witorsch, Endocrinology 111: 2144-2146, 1982). Prolactin binding increased by approximately 44 and 72% in dorsolateral prostate and 16 and 39% in ventral prostate in 100- and 400-micrograms groups, respectively. Membrane fluidity increased by approximately 16 and 19% in dorsolateral prostate and 10 and 13% in ventral prostate in 100- and 400-micrograms groups, respectively. Serum lipid fluidity increased 50 and 79% in 100- and 400-micrograms groups, respectively.
Effect of redox potential on protein degradation in perfused rat heart
Authors: Chua B. H. , Kleinhans B. J.
Published: December 2017

The effect of redox potential on protein degradation was assessed in rat hearts supplied either glucose or pyruvate, and the correlation between redox state and proteolysis was examined after the addition of insulin and leucine. In hearts supplied glucose as the sole energy source, the inhibition of protein degradation by a range of concentrations of insulin was associated with increased ratios of perfusate lactate to pyruvate and intracellular lactate to pyruvate, malate to pyruvate, and NADH to NAD. However, the extent of inhibition did not correlate with the redox state. The inhibitory effect of leucine on protein degradation was not accompanied by any change in redox state of the hearts. In hearts provided with pyruvate, rates of protein degradation continued to be inhibited by insulin even though the perfusate lactate to pyruvate was decreased by 14-fold and the calculated cytosolic NADH-to-NAD ratios were only 3% of those seen in hearts supplied glucose. These results indicated that a correlation between redox state and protein degradation was not apparent in myocardium under the experimental conditions examined.
Insulin stimulation of an electrogenic pump at high extracellular potassium concentration
Authors: Wu F. S. , Zierler K.
Published: December 2017

There is no agreement about the immediate mechanism by which insulin hyperpolarizes skeletal muscle, adipocytes, and myocardium. Of three candidates, one has been eliminated; the hyperpolarization is not secondary to an increase in intracellular [K]. There are reports that insulin hyperpolarizes by increasing relative permeability to K compared with that to Na ions, and other reports that insulin stimulates an ouabain-sensitive electrogenic Na-K exchange pump. Our evidence has been interpreted to support the former and deny the latter, when rat skeletal muscle is bathed at normal [K]. Crucial evidence for the latter has not been reported: insulin hyperpolarizes to a potential more negative than the K equilibrium potential. We now report that when rat caudofemoralis muscle is incubated with insulin at normal extracellular [K], then depolarized by increasing extracellular [K] to 38.4 mM, by equimolar substitution of KCl for NaCl, there is hyperpolarization compared with potentials of muscles treated similarly with respect to [K] but without insulin. Under these circumstances, the membrane potential in the presence of insulin is more negative than the new K equilibrium potential, and, in contrast to our previous experience with muscles bathed only in normal [K], the hyperpolarization in high [K] is reduced or eliminated by ouabain.
Secretory patterns of glucoregulatory hormones in prehepatic circulation of dogs
Authors: Sirek A. , Vaitkus P. , Norwich K. H. , Sirek O. V. , Unger R. H. , Harris V.
Published: December 2017

The temporal organization of patterns of secretion of insulin, glucagon, and somatostatin was studied in basal conditions in normal or pancreatectomized dogs fitted with an indwelling hepatic portal catheter. Portal and peripheral blood samples were collected at a 7.5- or 15-min frequency, which covered the medium range of the ultradian period. The raw data were studied using spectral analyses employing fast Fourier transformation (FFT) techniques. The results indicate that in normal dogs: 1) endogenous physiological periodicities, statistically significant at a level of alpha = 0.05 (i.e., 95% confidence interval), were found to exist for the three pancreatic hormones in portal blood between 0.54 and 1.78 h/cycle and in peripheral blood between 0.59 and 1.84 h/cycle; 2) the portal levels of the hormones are significantly higher than peripheral ones; and, 3) whereas pancreatic hormones oscillated, glucose was found to maintain a steady level. In pancreatectomized dogs, no regular rhythm was detected. Thus, whereas endogenous periodicities exist for the secretion of pancreatic hormones in the normal dog, in the pancreatectomized dog the extrapancreatic glucagon and somatostatin are secreted in nonperiodic, randomly occurring pulses.
Effects of hypophysectomy and GH administration on bovine and human GH binding to rat liver membranes
Authors: Messina J. L. , Eden S. , Kostyo J. L.
Published: December 2017

Experiments were conducted to investigate the specific binding of highly purified bovine and human growth hormones (bGH and hGH) to purified liver plasma membranes of male rats at various times after hypophysectomy and after the acute intravenous administration of bGH. Liver membranes prepared from hypophysectomized male rats showed a two- to threefold increase in the specific binding of either [125I]iodo-bGH or [125I]iodo-hGH, when compared with membranes prepared from the livers of age-matched normal male rats. The increase in GH binding was apparent within 3 days after hypophysectomy and persisted for a number of weeks after the operation. The increase in GH binding produced by hypophysectomy appeared to be due to an increase in the number of binding sites present on the membranes. The intravenous injection of 200 micrograms of bGH into hypophysectomized male rats 5-60 min before they were killed markedly reduced the ability of liver membranes prepared from these animals to bind [125I]iodo-bGH specifically. This decrease in GH binding seen after the injection of bGH may have been due to the development of a slowly dissociating hormone-binding site complex, which thereby reduced the number of available binding sites. This conclusion is supported by the finding that bGH, which is bound in vitro to isolated liver membranes, dissociates slowly and incompletely in the presence of an excess of unlabeled hormone. Moreover, the degree to which the bound hormone can dissociate appears to depend on the length of time that association is allowed to occur.(ABSTRACT TRUNCATED AT 250 WORDS)
Metabolic adaptation to reduced muscle blood flow. II. Mechanisms and beneficial effects
Authors: Elander A. , Idstrom J. P. , Holm S. , Schersten T. , Bylund-Fellenius A. C.
Published: December 2017

Increased mitochondrial enzyme activities are induced in rat muscles after common iliac artery ligation, giving a 76-93% blood flow reduction, and 6 days of intermittent muscle stimulation. To elucidate the trigger for this enzyme induction, the acute alterations in the metabolite pattern during contractions were evaluated. More pronounced changes in intramuscular PO2, creatine phosphate, ATP/ADP, lactate/pyruvate, and glycogen were observed in the ligated leg. The benefit of this enzyme alteration was investigated with the hindlimb perfusion technique. Enzymatically adapted and control legs were perfused at reduced flow during contractions. Similar oxygen consumption and glucose uptake but a significantly lower lactate release were observed in the adapted legs. A lower lactate level, lactate/pyruvate, and a better maintained creatine phosphate/creatine were found in the adapted soleus muscle. The results demonstrate that the increase of mitochondrial enzymes is preceded by acute alterations in energy metabolites due to intermittent hypoxia during contractions at reduced flow and that this enzyme adaptation allows the muscle tissue to maintain a lower anaerobic metabolism and a better energy state during exercise.
Synthesis and release of luteinizing hormone in vitro: manipulations of Ca2+ environment
Authors: Liu T. C. , Jackson G. L.
Published: December 2017

We determined if luteinizing hormone (LH) synthesis is Ca2+ dependent and coupled to LH release. We monitored LH synthesis when LH release was stimulated either by specific [gonadotropin-releasing hormone (GnRH)] or nonspecific stimuli (50 mM K+ and 2 or 20 microM Ca2+ ionophore A23187) and inhibited by Ca2+-reduced medium. LH synthesis was estimated by measuring incorporation of [3H]glucosamine (glycosylation) and [14C]alanine (translation) into total (cell and medium) immunoprecipitable LH by cultured rat anterior pituitary cells. Both GnRH (1 nM) and 50 mM K+ significantly stimulated LH release and glycosylation, but had no effect on LH translation. A23187 also stimulated LH release, but significantly depressed glycosylation of LH and total protein and [14C]alanine uptake. Deletion of Ca2+ from the medium depressed both GnRH-induced LH release and glycosylation. Addition of 0.1 mM EGTA to Ca2+-free medium not only inhibited GnRH-induced release and glycosylation of LH but also uptake of precursors and glycosylation and translation of total protein. Thus glycosylation and release of LH are Ca2+ dependent. Whether parallel changes in LH release and glycosylation reflect a cause and effect relationship remains to be determined.
Hemorrhagic shock and the central vasopressin and opioid peptide system of rats
Authors: Feuerstein G. , Molineaux C. J. , Rosenberger J. G. , Zerbe R. L. , Cox B. M. , Faden A. I.
Published: December 2017

The effect of hemorrhagic shock (40% of blood vol) on the distribution of immunoreactive dynorphin A (Dyn A-IR), [Arg8]vasopressin (AVP-IR), and [Leu5]enkephalin (LE-IR) in the pituitary and brain nuclei was studied in the conscious rat. At 24 h after hemorrhage, the neurointermediate lobe (NIL) showed a reduction in Dyn A-IR (52%) and AVP-IR (32%) and an increase in LE-IR (72%); at this time, the anterior lobe also showed decreased Dyn A-IR (50%) and increased LE-IR (210%). Dyn A-IR, but not LE-IR, was also significantly depleted in some forebrain nuclei in all experimental groups as compared with intact controls, whereas Dyn A-IR in the hypothalamic ventromedial nucleus was elevated only in the sham-control rats. AVP-IR was elevated in the supraoptic nucleus and median eminence (200 and 31%, respectively) 2 and 24 h after bleeding, although plasma AVP returned to normal levels. These data indicate that stress and hypovolemic hypotension produce site and time-dependent change in distribution of dynorphins, AVP, and LE in the central nervous system.
Effect of intragastric triglyceride administration on glucose homeostasis in newborn pigs
Authors: Pegorier J. P. , Simoes-Nunes C. , Duee P. H. , Peret J. , Girard J.
Published: December 2017

The fasting hypoglycemia (1.78 +/- 0.29 mmol/l) which develops in 48-h-old pigs is partially reversed (3.85 +/- 0.55 mmol/l) after gastric administration of long-chain triglycerides (LCT). The increase in blood glucose induced by LCT feeding was not secondary to a decreased glucose utilization because glucose disappearance rate increased in LCT-fed piglets but resulted from a twofold increase in glucose appearance. By using the crossover-plot technique, the stimulation of hepatic gluconeogenesis induced by LCT feeding has been localized at 1) the level of pyruvate carboxylase owing to the twofold increase in hepatic acetyl-CoA concentration and 2) the level of glyceraldehyde-3-phosphate dehydrogenase secondary to the increase in reducing equivalents (NADH), which displaces this equilibrium reaction in the direction of gluconeogenesis. As blood lactate, pyruvate, and alanine concentrations increased after LCT feeding, the possible effects of LCT on pyruvate dehydrogenase in peripheral tissues are discussed. These data demonstrate that fatty acids stimulate hepatic gluconeogenesis in 48-h-old fasting piglets and underline the role of fat provision in the regulation of glucose homeostasis during the neonatal period in the pig.
Nutritional efficiency of alpha-ketoisocaproate relative to leucine, assessed isotopically
Authors: Kang C. W. , Walser M.
Published: December 2017

The efficiency of alpha-ketoisocaproate as a dietary substitute for leucine was assessed in rats by two techniques: first, the minimal dose of alpha-ketoisocaproate required, as a supplement to a leucine-free diet, to achieve a growth rate as great as animals receiving leucine was found to be between 2.2 and 4.4 times larger. Therefore the nutritional efficiency of alpha-ketoisocaproate lies between 0.23 and 0.46. Second, alpha-[1-14C]-ketoisocaproate and [3H]leucine were administered orally and the ratio of 14C/3H incorporated into the leucine of whole-body protein and fibrin was measured. This ratio, divided by the ratio 14C/3H injected, was the same in fibrin as in whole-body protein and averaged 0.39. Thus both techniques yield the same value, within the error of measurement, for the relative nutritional efficiency of alpha-ketoisocaproate. We also found that alpha-ketoisocaproate feeding at varying dosage did not alter this ratio in whole-body protein (measured in rats fasted overnight), suggesting that neither wide variations in growth rate nor exposure for 10 days to alpha-ketoisocaproate (in a diet of constant protein content) alters the relative rates of utilization (or oxidation) of alpha-ketoisocaproate vs. leucine.
Short-term, mixed-diet overfeeding in man: no evidence for "luxuskonsumption"
Authors: Ravussin E. , Schutz Y. , Acheson K. J. , Dusmet M. , Bourquin L. , Jequier E.
Published: December 2017

After 13 days of weight maintenance diet (13,720 +/- 620 kJ/day, 40% fat, 15% protein, and 45% carbohydrate), five young men (71.3 +/- 7.1 kg, 181 +/- 8 cm; means +/- SD) were overfed for 9 days at 1.6 times their maintenance requirements (i.e., +8,010 kJ/day). Twenty-four-hour energy expenditure (24-h EE) and basal metabolic rate (BMR) were measured on three occasions, once after 10 days on the weight-maintenance diet and after 2 and 9 days of overfeeding. Physical activity was monitored throughout the study, body composition was measured by underwater weighing, and nitrogen balance was assessed for 3 days during the two experimental periods. Overfeeding caused an increase in body weight averaging 3.2 kg of which 56% was fat as measured by underwater weighing. After 9 days of overfeeding, BMR increased by 622 kJ/day, which could explain one-third of the increase in 24-h EE (2,038 kJ/day); the remainder was due to the thermic effect of food (which increased in proportion with excess energy intake) and the increased cost of physical activity, related to body weight gain. This study shows that approximately one-quarter of the excess energy intake was dissipated through an increase in EE, with 75% being stored in the body. Under our experimental conditions of mixed overfeeding in which body composition measurements were combined with those of energy balance, it was possible to account for all of the energy ingested in excess of maintenance requirements.
Effects of parathyroid hormone on puppies during development of Ca and vitamin D deficiency
Authors: Wong K. M. , Klein L. , Hollis B.
Published: December 2017

The acute effects of parathyroid extract (PTE) were studied repeatedly in young dogs (prelabeled with 45Ca and [3H]tetracycline) during the development of calcium (Ca) and vitamin D deficiency. Blood Ca and radioactivity changes were monitored sequentially after subcutaneous PTE, injected seven times over 63 days. In control dogs, all sequential responses to acute PTE challenges were constant in both magnitude of increase and time at which maximum response occurred over the entire experiment. Under chronic Ca and D deficiency, plasma 25-hydroxyvitamin D in experimental dogs decreased continuously to very low levels at 63 days, whereas 1,25-dihydroxyvitamin D initially increased to a maximum at 32 days and thereafter decreased. In response to an acute challenge of PTE, dogs on the deficient diet for 3 and 10 days showed a greater response of blood Ca and 45Ca than the controls but subsequently showed a smaller response than controls after 49 and 63 days on the deficient diet. Compared with control dogs, the time of maximal response of blood Ca and 45Ca to PTE occurred much earlier in dogs that were on the deficient diet for 35-63 days. The blood [3H]tetracycline response (index of bone resorption) to exogenous PTE in the deficient dogs, however, was constant and similar to that of the control dogs during the entire period. The data suggest that the bone resorption response to PTE was normal in Ca- and D-deficient puppies with hypocalcemia.(ABSTRACT TRUNCATED AT 250 WORDS)
Rate-limiting steps for insulin-mediated glucose uptake into perfused rat hindlimb
Authors: Kubo K. , Foley J. E.
Published: December 2017

To determine the glucose and insulin concentrations at which glucose transport is rate limiting for insulin-mediated glucose uptake and metabolism in muscle, glucose clearance was determined in the presence of glucose concentrations ranging from trace to 20 mM and in the absence or presence of insulin in the perfused rat hindlimb. In the absence of insulin and at submaximally stimulating insulin concentrations glucose clearance was constant up to 7 mM glucose and then decreased as the glucose concentration was raised. At maximally stimulating insulin concentrations glucose clearance was constant up to 2 mM glucose and then decreased. The decrease in glucose clearance between 2 and 7 mM glucose in the presence of maximally stimulating insulin concentrations could not be accounted for by competition among glucose molecules for the glucose transport system. The results suggest that at physiological glucose concentrations in the presence of maximally stimulating insulin concentrations the rate-limiting step for insulin-mediated glucose uptake and metabolism in muscle shifts from glucose transport to some step beyond transport.
Dog inactive renin: biochemical characterization and secretion into renal plasma and lymph
Authors: Dzau V. J. , Wilcox C. S. , Sands K. , Dunckel P.
Published: December 2017

It has been suggested that the dog is a useful model for studies of inactive renin (IR). However, the nature and origin of the trypsin-activated angiotensin-forming activity in dog plasma have not been fully defined. We characterized dog IR using renin-specific antibody, immunoaffinity, and Affigel blue chromatography. Activated IR resembles renal and plasma active renin in biochemical and immunological properties. IR was detected in renal lymph, arterial and venous plasma, as well as renal extracts. At basal state, there was a significant renal venous-arterial gradient of IR indicating secretion from the kidney. Furthermore, a sixfold higher concentration of IR was demonstrated in renal lymph than in plasma. Our data provides evidence for two possible routes of IR secretion from the kidney and supports the contention that the dog is a good model for studies of IR secretion and regulation.
Changes in protein turnover in rat uterus during pregnancy
Authors: Morton A. J. , Goldspink D. F.
Published: December 2017

The adaptive growth and protein turnover of the rat uterus were studied during the 21 days of gestation and up to 3 days after parturition. Despite large increases (13-fold) in uterine size during gestation, the fractional rate of protein synthesis (measured in vivo) remained unchanged when compared with nonpregnant tissue values of 44 +/- 5%/day. However, decreases were found in the rate of protein breakdown after implantation (i.e., 75% on day 7 and 28% on day 11) and in the activity of cathepsin D (i.e., 33 and 85% on days 8 and 16 of gestation). Changes in the degradative processes would therefore appear to be primarily responsible for the massive uterine growth during pregnancy. In contrast to the uterus the fractional rates of synthesis in the placenta and fetus progressively decreased during gestation. After parturition the uterus rapidly returned to its normal size by a combination of cellular atrophy and cell loss. After 2 days, a complementary decrease in the fractional rate of synthesis (30%) and an increase in protein degradation (2-fold) explained the process of involution.
Acute exercise, epinephrine, and diabetes enhance insulin binding to skeletal muscle
Authors: Webster B. A. , Vigna S. R. , Paquette T.
Published: December 2017

We measured insulin binding to crude membranes from rat skeletal muscle, with binding expressed relative to the sarcolemmal marker, cholesterol ester (CE). The amount of CE in the sarcolemma remained constant after streptozotocin-induced diabetes and acute exercise (swam for 90 min). Soleus (predominantly slow-twitch fibers) had higher insulin binding capacity than extensor digitorum longus (predominantly fast twitch). Both diabetes and acute exercise enhanced insulin binding. The shape of the enhanced insulin binding curve differed, however, between diabetes and acute exercise. Diabetes elicited a uniform increase in binding across the insulin concentrations measured (0.04-166 nM); acute exercise elicited the largest increase at the lower concentrations, suggesting different mechanisms cause the enhanced binding. Addition of 13.1 nM epinephrine to the perfusate in a rat hindlimb preparation increased insulin binding in a pattern similar to acute exercise. In contrast, muscular contraction stimulated by the sciatic nerve (1 Hz) or reduction of perfusate insulin from 100 to 40 pM, two additional correlates of acute exercise, had no effect. The increased insulin binding after acute exercise, therefore, appears to be mediated through elevated levels of catecholamines and not upregulation of the insulin receptor.
Involvement of glutathione oxidation reduction in parathyroid hormone secretion
Authors: Morrissey J. J.
Published: December 2017

This study determines whether calcium affects glutathione metabolism and whether glutathione metabolism may influence parathyroid (PTH) secretion in collagenase dispersed bovine parathyroid cells. Reduced glutathione (GSH) and glutathione disulfide (GSSG) were measured fluorometrically and enzymatically while PTH secretion was determined by radioimmunoassay. The total GSH and GSSG content of parathyroid cells was found to range from 1.59 to 1.71 micrograms/mg cell protein, and this did not vary significantly with changes in extracellular calcium. An increase in the medium calcium concentration from 0.5 to 2.0 mM did, however, cause an increase in GSSG from 0.43-0.54 to 1.19-1.20 micrograms/mg protein with a concomitant decrease in GSH. The compound 2-cyclohexen-1-one was used to deplete the cells of GSH at a low-calcium medium (0.5 mM) to levels seen in high-calcium medium (2.0 mM). This treatment was found to inhibit PTH secretion in the low-calcium medium, as if the cells were incubated in high medium calcium. Both 2-cyclohexen-1-one and calcium caused a rapid decrease in reduced GSH levels and in hormone secretion. The ketone was not found to affect cellular protein synthesis, indicating that there was no nonspecific toxic effect of this treatment on the cells. These results suggest that changes in the calcium concentration of the medium affect the GSH/GSSG ratio of dispersed parathyroid cells. Changes in the GSH/GSSG ratio induced by calcium may be related to changes in PTH secretion.
Insulin metabolism by liver, muscle, and kidneys from spontaneously diabetic rats
Authors: Rabkin R. , Reaven G. M. , Mondon C. E.
Published: December 2017

The in vivo metabolism of insulin is a complex process in which liver, kidney, and muscle are major participants. In this study we evaluated the effect of spontaneous hyperglycemic nonketoacidotic diabetes (DH) and ketoacidotic diabetes (DKA) on insulin clearance and degradation by these organs. Livers, hindlimbs, and kidneys from nondiabetic controls and DH and DKA Bio-Breed rats were isolated and perfused with artificial media. Liver clearance of immunoreactive insulin (ml/min) was significantly higher in DH rats, 6.0 +/- 0.2, but significantly lower in DKA rats, 3.4 +/- 0.5, compared with controls, 4.6 +/- 0.2. Acidosis alone induced by ammonium chloride loading, did not impair liver insulin clearance (4.8 +/- 0.4 ml/min). Muscle responded differently to the diabetic state in that insulin clearance was not altered by DH and DKA. Renal (organ) clearance of insulin was significantly depressed in the DKA state when compared with controls (0.52 +/- 0.04 and 0.75 +/- 0.07 ml X min-1 X g-1, respectively). This could largely be explained by a lower glomerular filtration rate. Fractional urinary insulin clearance was increased twofold above control values in DH kidneys and fourfold in DKA kidneys, indicating that tubular luminal absorption of insulin was impaired in both states. By contrast contraluminal uptake (peritubular clearance) did not differ significantly from controls. 125I-insulin degrading activity of the 100,000 g supernate fraction from muscle homogenates was similar in the diabetic and control groups. However in liver and kidney, degrading activity did not correspond to whole organ insulin clearance in a consistent manner.(ABSTRACT TRUNCATED AT 250 WORDS)
Relation between plasma and tissue parameters of leucine metabolism in fed and starved rats
Authors: Vazquez J. A. , Paul H. S. , Adibi S. A.
Published: December 2017

By use of a primed continuous infusion of [1-14C]leucine, we investigated parameters of leucine metabolism in plasma, expired air, and tissues of fed and 48-h starved rats. The ratios of muscle to plasma specific activity of alpha-ketoisocaproate (KIC) in fed and starved rats were not significantly different from 1. The ratio of muscle to plasma specific activity of leucine was also not significantly different from 1 in fed rats, but was significantly lower than 1 in starved rats. The rate of leucine oxidation was 28-34% higher when calculation was based on plasma KIC rather than leucine specific activity. However, starvation significantly increased the rate of leucine oxidation with either specific activity. The rates of leucine incorporation into whole-body protein, calculated as the difference between plasma leucine turnover and oxidation, were unaffected by starvation, but the incorporations into total protein measured directly were significantly decreased in liver and muscle. We conclude that leucine or KIC specific activity in muscle is better predicted by plasma KIC than leucine specific activity, and the difference between rates of plasma leucine turnover and oxidation does not appear to be a valid measurement of leucine incorporation into whole-body protein.
Role of glutamine in adaptations in nitrogen metabolism during fasting
Authors: Cersosimo E. , Williams P. E. , Radosevich P. M. , Hoxworth B. T. , Lacy W. W. , Abumrad N. N.
Published: December 2017

The present study examines the effect of glutamine infusion on the interorgan fluxes of glutamine, alanine, urea, and ammonia with progressive fasting. Experiments were carried out in two groups of conscious dogs with catheters previously implanted in an artery and in the hepatic, portal, and renal veins. Group I (n = 12) was fasted for 24 h, and group II (n = 10) was fasted for 96 h. On the day of the study, seven animals of group I and five of group II received a constant infusion of glutamine (3.0 mumol . kg-1 . min-1) for 1 h, and the rest (controls) received saline. Four-day fasting produced ketosis with a compensated metabolic acidosis. The demand for glutamine by the kidneys and gut increased, and the liver switched from net glutamine utilization to that of net production. The kidneys (33%) and gut (230%) increased their production of ammonia, while their release of alanine decreased. The estimated efflux of glutamine by skeletal muscle, however, did not change. All of the infused glutamine was cleared by the splanchnic and renal tissues. In group I, there was increased gut production of alanine, which was matched by increased hepatic alanine uptake and urea production. No such changes were observed in Group II. There was, however, an increase in hepatic uptake of ammonia. Finally, glutamine infusion did not alter glutamine or alanine output by skeletal muscle in group I, while it decreased efflux of alanine but not that of glutamine in group II. The data emphasize the complex interdependence of the liver, gut, kidneys, and skeletal muscle in nitrogen sparing.(ABSTRACT TRUNCATED AT 250 WORDS)
Peripheral venous catecholamines versus adrenal secretory rates after brain stem stimulation in cats
Authors: Bereiter D. A. , Engeland W. C. , Gann D. S.
Published: December 2017

The relationship between adrenal catecholamine secretion and peripheral venous catecholamine concentration was assessed in samples collected before and after brief (15-s) periods of brain stem electrical stimulation in cats anesthetized with alpha-chloralose-urethan. Adrenal blood flow from the left lumboadrenal vein averaged 0.75 +/- 0.05 ml/min (means +/- SE, n = 56). Peripheral norepinephrine (NE) concentration (1.19 +/- 0.07 ng/ml) was not well correlated with adrenal NE secretion (38.18 +/- 3.99 ng/min) before stimulation (r = 0.334, P less than 0.025). Although brain stem sites that evoked large increases in adrenal NE secretion often caused an increase in peripheral NE, sites that evoked significant decreases in adrenal NE secretion were not accompanied by decreases in peripheral NE. Peripheral epinephrine (E) concentration (0.11 +/- 0.01 ng/ml) was well correlated with adrenal E secretion (23.72 +/- 2.33 ng/min) before stimulation (r = 0.468, P less than 0.001). Brain stem stimulation-evoked changes in adrenal E secretion were generally reflected in changes of peripheral E concentration, although many exceptions were seen. Peripheral dopamine (DA) concentration (0.23 +/- 0.02 ng/ml) was well correlated with adrenal DA secretion (0.94 +/- 0.11 ng/min) before stimulation (r = 0.505, P less than 0.001). However, stimulus-evoked changes in adrenal DA secretion were not reflected in changes of peripheral DA concentration. The data indicate that, whereas brief periods of brain stem stimulation evoke a wide range of adrenal secretory responses, peripheral catecholamine responses best reflected adrenal secretion only when large increases in adrenal secretion were evoked and were poor indicators of decreased adrenal catecholamine secretion.(ABSTRACT TRUNCATED AT 250 WORDS)
Net substrates balance across hindlimb in conscious rabbit during late pregnancy
Authors: Bouisset M. , Pere M. C. , Gilbert M.
Published: December 2017

The present work performed in rabbits was designed to investigate whether changes in skeletal muscle metabolism could contribute to glucose homeostasis during late pregnancy a time at which there is a large glucose demand of the gravid uterus. We therefore studied the net substrate balance of glucose, lactate, free fatty acids, and ketone bodies across the hindlimb of pregnant animals (days 24 and 30) and virgin animals. Our data show that on day 24 the basal rate of glucose uptake is similar to that observed in virgin rabbits, but it decreases by approximately 60% on day 30 despite comparable levels of blood glucose and plasma insulin at both gestational ages. A moderate hyperglycemia (20% above basal level) and hyperinsulinemia (2- to 3-fold above basal level) sustained for 80 min failed to increase glucose uptake except in virgin animals. Estimates of the contribution of substrates to oxidative metabolism indicate that free fatty acids could represent the major fuel in all groups, whereas glucose would be of minor importance especially at term. It is concluded that in pregnancy a) under normoglycemia there is a reduced insulin effect on glucose uptake and b) under moderate hyperglycemia and hyperinsulinemia the insulin resistance results from an impaired stimulation of glucose uptake. Sparing glucose from the skeletal muscle, the mother can direct more glucose toward the uterus without marked increase in her production rate.
Relationship between nerve blood flow and intercapillary distance in peripheral nerve edema
Authors: McManis P. G. , Low P. A. , Yao J. K.
Published: December 2017

Some human and experimental neuropathies are characterized by endoneurial edema and increased intercapillary distance (ICD). This may potentially produce chronic endoneurial ischemia. To examine the relationship between nerve blood flow (NBF) and ICD we measured NBF in rats with experimental galactose neuropathy (EGN), a model where ICD is known to be increased. Simultaneous measurements of NBF in the center and subperineurial region were made in normal and edematous tibial nerves using hydrogen-sensitive microelectrodes and hydrogen polarography. NBF was significantly reduced in rats with EGN when compared with controls. A second finding was that in half the rats with EGN there was a greater reduction in NBF in the subperineurial region, a site of maximal ICD increase. In contrast, NBF was similar in central and peripheral regions in control rats. These findings support the hypothesis that an increase in ICD produces a reduction in NBF. Further support for the hypothesis is derived from a computer model of the effect of changes in ICD on endoneurial oxygen tension. We conclude that a chronic reduction in NBF may participate in the pathogenesis of edematous neuropathies.
Rapid changes in number of GDP binding sites on brown adipose tissue mitochondria
Authors: Swick A. G. , Swick R. W.
Published: December 2017

GDP binding to brown adipose tissue (BAT) mitochondria increased more than twofold in 20 min when rats were moved from 27 to 4 degrees C. When animals housed at 4 degrees C for 2 h were returned to 27 degrees C, GDP binding decreased sharply in 20 min and returned to control levels in 2 h. These results are consistent with a rapid unmasking and remasking of GDP binding sites. GDP binding to mitochondria from warm and acutely cold treated rats was not modified by prior swelling, by freeze-thawing, nor by sonication of the mitochondria before assay. GDP-inhibitable proton conductance, as measured by passive swelling, was unaffected by this brief exposure to cold but more than doubled in rats kept at 4 degrees C for 10 days. We hypothesize that the rate of GDP-inhibitable swelling may be a reflection of uncoupling protein concentration in the BAT mitochondria, whereas physiological thermogenic activity is more appropriately indicated by GDP binding. The alterations in binding activity appear not to be due to changes in the mitochondrial membrane integrity.
Increased formation and keeping of ribosomes during dietary recovery of mouse kidney
Authors: Iapalucci-Espinoza S. , Bur J. A. , Pucciarelli M. G. , Conde R. D.
Published: December 2017

In the kidney of 5-day protein-depleted mice there is a decrease of 23% in the rRNA mass. When these animals are fed with a complete diet, rRNA content is restored to its normal value after 24 h of refeeding. The mechanisms that underlie this phenomenon were studied. It was found that the activity of rRNA polymerase I in the nuclei of kidneys from refed mice showed an increase of about twofold compared with the activity in normal and protein-depleted nuclei. The in vivo incorporation of a large dose (nontrace) of [14C]orotic acid into rRNA was also twofold enhanced in kidneys from refed mice. Ribosome degradation (measured by the disappearance of radioactivity from either ribosomal proteins or rRNA previously labeled by the injection of NaH14CO3 and [14C]orotic acid to the mice, respectively) stopped during the 1st day after refeeding. The estimation of the difference between the rRNA synthesis rate and the net rRNA increase also demonstrated a decrease in the rRNA degradation rate in refed mice.