bluuebunny/crossref_metadata_2025 huggingface dataset:
Compensatory cell proliferation and growth in the rat heart after postnatal hypothyroidism
Authors: Moussavi R. , Meisami E. , Timiras P. S.
Published: December 2017

Measurement of total DNA, RNA, and protein as well as weight of the heart in male rats at 10, 25, 50, and 90 postnatal days revealed that hypothyroidism, as induced by administration from birth of the goitrogen propylthiouracil (PTU), results in highly significant reductions in cardiac cell proliferation and cell growth. These inhibitory effects on hyperplastic and hypertrophic growths were less drastic during the suckling period than during the postweaning period. In the latter period, heart growth of the hypothyroid animals was found to remain at a standstill with regard to all the parameters measured. When, after 25 days of hypothyroidism, PTU treatment was discontinued, the retarded heart showed marked signs of rehabilitation and compensatory development. Indeed, by day 90, total DNA content had essentially compensated for its deficit but total RNA, protein content, and weight, though showing marked compensatory surges (from 80-90% deficit to 20-30%), were not yet fully compensated. The results clearly indicate that the growing heart has a marked ability to be rehabilitated from severe hypothyroid retardation, showing within 2 mo full compensation of cell number and nearly complete compensation of cell growth. It is suggested that rehabilitation of the heart is brought about by physiological restoration not only of the thyroid hormones but also of growth hormone and possibly other thyroid-dependent growth factors.
Steroid secretion by rat testes perfused with perfluorochemicals as oxygen carriers
Authors: Chubb C. , Draper P.
Published: December 2017

Organs perfused in vitro are important experimental models for physiological studies. Perfusion medium supplemented with artificial oxygen carriers would at physiological flow rates supply sufficient oxygen to organs and would be superior to medium containing erythrocytes because it is more defined. Perfluorotributylamine (FC-43), a perfluorochemical, is an artificial oxygen carrier that has been previously reported to be ineffective in maintaining endocrine organs perfused in vitro. The purpose of this study was to determine the efficacy of FC-43 as an oxygen carrier for rat testes perfused in vitro. The effects of FC-43 on testicular function and structure were assessed by comparing the results of experiments using perfusion medium containing either FC-43 or erythrocytes. The results suggest that perfusion medium containing perfluorochemicals must be prepared by standardized procedures and defined as to its physiochemical parameters. The study resulted in the first successful in vitro perfusion of an endocrine organ with perfluorochemicals as oxygen carriers. The results not only provide the basis for an improved perfusion medium but also support in vitro perfused testes as effective experimental tools for testing perfluorochemical-based blood substitutes.
Immunoreactive ACTH and gamma-MSH in rat plasma during early stages of adrenal regeneration
Authors: Alfano J. , Dressler L. G. , Brownie A. C.
Published: December 2017

Recent evidence suggests that in addition to ACTH the pro-gamma-melanotropins play a role in controlling both the steroidogenic activity and growth of the adrenal cortex. By using the regenerating gland as a model for rapid adrenal growth, studies were carried out to monitor plasma ACTH and pro-gamma-melanotropins during the acute phase following adrenal enucleation. Adrenal enucleated rats (experimental group) were uninephroadrenalectomized; controls were uninephrectomized or uninephroadrenalectomized. At intervals up to 96 h after surgery, animals from each of the three groups were killed under quiescent conditions at the low and high points of their circadian rhythm. The plasma concentrations of both ACTH and 11 K gamma-melanocyte-stimulating hormone (MSH) in the adrenal enucleated rats were markedly elevated as compared with either control group at each time point monitored. However, there were no significant differences in plasma ACTH or 11 K gamma-MSH between the two control groups, and the levels of plasma 6 K gamma-MSH remained unchanged in all three groups throughout the experiment. These data are consistent with a role for pro-gamma-melanotropins in adrenal regeneration.
Mechanism for glycogenolysis in nonexercising human muscle during and after exercise
Authors: Ahlborg G.
Published: December 2017

Arterial-deep venous differences for glucose and lactate across the nonexercising forearm were determined in healthy subjects during 3 h of leg exercise at 50% of maximum oxygen uptake and during 20-min recovery. At 160 min of exercise 0.5 mg propranolol was infused into the brachial artery. The results were compared with a control group that did not receive propranolol during exercise. Exercise stimulated to increased forearm lactate release which was higher than that which could be accounted for by the simultaneous blood glucose uptake. After propranolol forearm lactate production decreased during and after exercise while the controls still showed increasing lactate release. In contrast to the control values the lactate production by the blocked forearm could be accounted for by the glucose uptake. It is concluded that the stimulating effect of prolonged exercise on nonexercising muscle that persists during recovery is characterized by increased lactate release derived from beta-adrenergically stimulated glycogenolysis.
Biphasic changes in 3-methylhistidine excretion in humans after exercise
Authors: Dohm G. L. , Israel R. G. , Breedlove R. L. , Williams R. T. , Askew E. W.
Published: December 2017

We previously reported that 3-methylhistidine excretion was increased in human subjects after a strenuous bout of exercise. Because other investigators have not corroborated this finding, we undertook the present study to investigate the conditions that result in decreased and increased 3-methylhistidine excretion in human subjects after exercise. Four experiments were performed: a cross-sectional study comparing 3-methylhistidine excretion in endurance-trained subjects with untrained controls, a longitudinal study of 3-methylhistidine excretion by female basketball players before the start of the season and again during the competitive season, an experiment to determine changes in 3-methylhistidine excretion as a result of 2 h of exercise each day for 7 consecutive days, and a study to determine changes in 3-methylhistidine excretion during 4-h intervals after a strenuous exercise bout. The 3-methylhistidine-to-creatinine ratio was approximately 20% higher for trained than nontrained subjects. In three separate experiments a biphasic change of 3-methylhistidine excretion was observed in response to exercise with an immediate decrease in the 3-methylhistidine-to-creatinine ratio during exercise followed by a prolonged increase. The magnitudes of the negative and positive responses determine whether one observes an increase, no change, or a decrease in the total daily excretion of 3-methylhistidine.
Hypothalamic obesity, brown adipose tissue, and sympathoadrenal activity in rats
Authors: Vander Tuig J. G. , Kerner J. , Romsos D. R.
Published: December 2017

Obesity-producing, hypothalamic knife cuts and ventromedial hypothalamic (VMH) lesions in ad libitum-fed adult rats increased intake of a high-fat diet (123 and 130%) and energy retention (880 and 1,099%) during the 4-wk period postsurgery; even when pair fed to control rats, energy retention of the knife-cut and lesioned rats was still elevated (105 and 155%). Thermogenic capacity of brown adipose tissue (BAT), estimated from guanosine diphosphate (GDP) binding to BAT mitochondria, was unchanged in hyperphagic knife-cut and VMH-lesioned rats and was reduced approximately 50% when these rats were pair fed to controls. Urinary excretion of norepinephrine (NE) was approximately twofold higher in ad libitum-fed, knife-cut, and lesioned rats than in control rats; restriction of energy intake decreased NE excretion to control values. Rates of NE turnover in heart paralleled urinary NE excretion, whereas NE turnover in BAT was generally not increased in the hyperphagic rats. Urinary epinephrine excretion, an index of adrenal medullary activity, was depressed in all knife-cut and VMH-lesioned rats. Hyperphagia coupled with a lack of increased heat production in BAT causes gross obesity in ad libitum-fed, knife-cut, and VMH-lesioned rats, whereas obesity in pair-fed rats develops in part at least as a result of reduced heat production by BAT.
Mitochondrial thermogenin content is unchanged during atrophy of BAT of fasting mice
Authors: Desautels M.
Published: December 2017

The objectives of this study were to evaluate the rate at which brown adipose tissue (BAT) from mice atrophies when its thermogenic activity is suppressed during fasting or exposure to a thermoneutral environment (33 degrees C) and whether such atrophy is accompanied by loss from BAT mitochondria of "thermogenin," the GDP binding protein associated with the calorigenic proton conductance pathway. Atrophy of mouse BAT was characterized by rapid loss of protein but unchanged tissue DNA content. The rate of protein loss varied from 2 to 6 mg protein/day depending on the environmental and feeding status of the mice. In synchrony with tissue protein loss, there was a marked reduction in the tissue content of mitochondrial proteins and of thermogenin, measured by immunoassay. However, the concentration of thermogenin in isolated mitochondria was unchanged by fasting or exposure of the mice to 33 degrees C for 48 h. By contrast, marked reduction in [3H]GDP binding to isolated mitochondria were observed after exposure of the mice to 33 degrees C. Mice acclimated at 4 but not those acclimated at 21 degrees C showed reduction in GDP binding to isolated mitochondria during fasting. These results clearly indicate that changes in purine nucleotide binding to isolated mitochondria can occur in the absence of changes in the mitochondrial concentration of thermogenin. Thus rapid decrease in BAT thermogenic capacity (e.g., during fasting or 33 degrees C exposure) appears dependent on extensive loss of tissue protein, probably whole mitochondria, rather than rapid and selective removal of thermogenin from the mitochondria.
Apparent decreased oxidation and turnover of leucine during infusion of medium-chain triglycerides
Authors: Beaufrere B. , Tessari P. , Cattalini M. , Miles J. , Haymond M. W.
Published: December 2017

A potential effector of the protein-sparing adaptation to fasting could be the increased availability of endogenous long-chain fatty acids. Were this hypothesis correct, infusion of medium-chain triglycerides to increase the plasma concentration of medium-chain fatty acids might also result in protein sparing. However, in most in vitro studies in rat muscle, octanoate increases the oxidation of the essential amino acid leucine. Therefore leucine metabolism was assessed with infusions of [3H]leucine and a-[14C]ketoisocaproate ([14C]KIC) before and during an infusion of trioctanoin in conscious dogs. Plasma octanoate increased from less than 30 to 528 microM over the 3 h of infusion. Plasma leucine and KIC concentrations decreased by 65-70% (P less than 0.01) over the first 2 h of infusion. Leucine oxidation, estimated from the expired 14CO2 and the plasma [14C]KIC specific activity, as well as from an open two-pool model, decreased. By use of these isotope models, the rates of leucine coming from and going to protein decreased (P less than 0.05 to P less than 0.01). Interconversion of leucine and KIC estimated from the open two-pool model decreased by 80% (P less than 0.01). These changes were accompanied by a 36% decrease in the plasma concentration of total plasma amino acids. Within the confines of the isotope models employed, these data are consistent with the hypothesis that increased fatty acid oxidation decreases protein turnover and may spare essential amino acids.
Regulation of iodothyronine 5'-deiodination in lean and obese (ob/ob) mice
Authors: Hillgartner F. B. , Romsos D. R.
Published: December 2017

Obese (ob/ob) mice exhibit impaired cold- and diet-induced thermogenesis, which may result in part from a defect in thyroid hormone action at the level of peripheral deiodination of thyroxine (T4) to 3,5,3'-triiodothyronine (T3). The latter possibility was examined by comparing kinetic parameters of 5'-deiodination (5'-D) in hepatic and renal microsomes of lean and obese mice during various physiological conditions. 5'-D Was adaptive to changes in age (1 to 8-10 wk), environmental temperature (14, 25, and 33 degrees C), and thyroid hormone status in both lean and obese mice. The magnitude of enzyme response, however, varied between phenotypes. 5'-D Response to age and environmental temperature was also dependent on tissue type, indicating that different isozymes for 5'-D may exist in liver and kidney. Under basal conditions at 25 degrees C, maximal hepatic and renal 5'-D was lower in obese mice than in lean mice. Differences in Vmax were observed as early as 1 wk of age. Km values for 5'-D were similar in lean and obese mice. These findings suggest that T3 availability to thermogenic target tissues may be impaired in obese mice, which may contribute to diminished thyroid hormone expression and heat production in these animals.
Influence of subdiaphragmatic vagotomy and brown fat sympathectomy on thermogenesis in rats
Authors: Andrews P. L. , Rothwell N. J. , Stock M. J.
Published: December 2017

Infusion of rats with insulin (8 U/day via implanted minipump) for 7 days caused a 22% rise in resting oxygen consumption, which was inhibited by acute injection of the beta-adrenergic antagonist propranolol. Insulin treatment produced significant increases in brown fat mass, protein content, and total thermogenic activity (assessed from binding of guanosine diphosphate to isolated brown fat mitochondria), but these responses were inhibited by prior surgical sympathectomy of the tissue. Animals subjected to subdiaphragmatic vagotomy gained more weight than pair-fed, sham-operated controls and showed reductions in total energy expenditure, the acute thermogenic response to a meal and brown adipose tissue activity. Daily injections of insulin (1 U/day) prevented all of these effects of vagotomy. These data demonstrate that the changes in brown fat activity induced by exogenous insulin are mediated by the sympathetic nervous system and that the depressed thermogenesis and brown fat activity associated with vagotomy appear to be due to a relative insulin deficiency and can be reversed by treatment with the hormone.
Amniotic fluid ionic concentration in response to chronic fetal vasopressin infusion
Authors: Ross M. G. , Ervin M. G. , Leake R. D. , Fisher D. A.
Published: December 2017

Chronically prepared, third trimester fetal lambs were administered 72-h intravenous infusions of arginine vasopressin (AVP) (65 or 130 mU/kg h) or 0.9% saline. Saline infusion preceding the AVP infusion did not change amniotic fluid (AF) composition. During the AVP infusion, there were significant increases in amniotic fluid osmolality (278.8 +/- 4.9 to 302.1 +/- 4.5 mosm) and in sodium (122.7 +/- 3.3 to 135.3 +/- 3.6 meq/l) and potassium (9.7 +/- 2.6 to 13.8 +/- 1.3 meq/l) concentrations. Saline infusion after the AVP infusion resulted in return of AF osmolality, sodium, and potassium toward normal levels. Fetal plasma and amniotic fluid AVP levels measured by radioimmunoassay significantly increased during AVP infusion and decreased during the subsequent saline infusion. There were no changes in maternal or fetal plasma osmolality in response to AVP. These results suggest that fetal AVP released in response to intrauterine stress may alter the composition and osmolality of amniotic fluid in a reversible manner.
Calcium, cAMP, and dopamine affect single mammotrophs assayed by hemolytic plaques
Authors: Anderson J. M. , Keefer D. A. , Koritnik D. D. , Yasumoto T. , Cronin M. J.
Published: December 2017

We investigated the effects of dopamine, forskolin, and maitotoxin on prolactin release from individual rat and monkey mammotrophs. Forskolin increases cAMP levels, whereas maitotoxin amplifies the influx of extracellular calcium. Prolactin secretion from single mammotrophs was visualized by the reverse hemolytic plaque assay and then quantified by measuring the proportion of plaque-forming cells and the mean plaque area. In the presence of dopamine alone both the plaque proportion and mean area of the plaques formed by rat mammotrophs decreased by 50 and 40%, respectively. This inhibition of secretion was blocked by the dopaminergic antagonist spiperone as well as forskolin and maitotoxin. Forskolin and maitotoxin alone significantly elevated both the proportion (+30%) and area (+180% for forskolin and +250% for maitotoxin) of the plaques. These actions of maitotoxin were neutralized by D-600, a calcium channel blocker. All of these agents induced similar trends with monkey prolactin cells. We conclude that single mammotrophs in culture respond to perturbations in a differential manner and in a way predicted by earlier results based on macropopulation measurements.
By 94 days of gestation plasma cortisol increases block ACTH response to hypotension in lamb fetuses
Authors: Hargrave B. Y. , Rose J. C.
Published: December 2017

By use of a crossover design, we studied the effects of increasing plasma cortisol concentration on ACTH responses to a standardized stress in 14 lamb fetuses between 94 and 108 days gestation. On a random basis we assigned the animals into two groups of seven. Animals in groups I and II received infusions of cortisol (5 and 1 microgram/min, respectively) or saline for 4 h. After the cortisol or saline pretreatment, we reduced arterial pressure approximately 40-50% in both groups of animals with nitroprusside. After saline pretreatment, hypotension in the group I animals produced an increase in the fetal plasma ACTH from 15 +/- 3 to 200 +/- 20 pg/ml (P less than 0.001), and in the group II animals pretreated with saline plasma ACTH increased from 21 +/- 4 to 141 +/- 19 pg/ml (P less than 0.001) with hypotension. Cortisol pretreatment elevated fetal plasma cortisol levels from 7 +/- 3 to 36 +/- 5 ng/ml in group I and from 8 +/- 4 to 20 +/- 2 ng/ml in group II. The ACTH response to hypotension in both groups was abolished by the cortisol pretreatment. We conclude that by 94 days gestation increases in plasma cortisol within a physiological range block ACTH responses to hypotension in lamb fetuses.
Regulation of hepatic gluconeogenesis in newborn rabbit: controlling factors in presuckling period
Authors: Brennan W. A. , Aprille J. R.
Published: December 2017

We have previously shown (Comp. Biochem. Physiol. 77B: 35-39, 1984) that a rapid postnatal increase in hepatic mitochondrial adenine nucleotide content activates pyruvate carboxylation and gluconeogenesis in the newborn rabbit. This study investigated factors limiting flux through the gluconeogenic pathway and examined the physiological stimuli responsible for the activation phenomenon. There is a 2.3-fold increase in total mitochondrial adenine nucleotides, along with a threefold increase in the matrix ATP/ADP ratio, by 2 h after birth, resulting overall in a sixfold increase in the amount of ATP/mg mitochondrial protein. Analysis of gluconeogenic intermediates, measured in freeze-clamped livers between birth and 4 h postnatal, suggests that pyruvate carboxylase controls gluconeogenic flux during this period. Newborn rabbits reared in an hypoxic environment (5% O2) exhibited decreased mitochondrial adenine nucleotide content, decreased rates of pyruvate carboxylation, and depressed blood glucose levels compared with littermates reared in room air or 95% O2. Manipulation of the insulin-to-glucagon ratio in vivo by injecting insulin at birth significantly delayed postnatal increases in the mitochondrial adenine nucleotide content and the rate of pyruvate carboxylation. Conversely, glucagon injection produced a supranormal increase in both mitochondrial adenine nucleotide content and pyruvate carboxylation. In addition, insulin injection prevented, whereas glucagon enhanced, the normal postnatal increase in tissue ATP/ADP. These results suggest that tissue oxygenation and a decreased insulin-to-glucagon ratio promote the rapid influx of adenine nucleotides from the liver cytosol into the mitochondrial matrix, thereby activating pyruvate carboxylation and gluconeogenesis during the presuckling period.
GIP increases insulin receptor affinity and cellular sensitivity in adipocytes
Authors: Starich G. H. , Bar R. S. , Mazzaferri E. L.
Published: December 2017

Glucose ingestion has been previously shown to rapidly increase both the affinity of the insulin receptor and the cellular sensitivity of target tissues for insulin. We now demonstrate that gastric inhibitory polypeptide (GIP), a gastrointestinal hormone released by glucose ingestion, can mimic these effects in vitro. Incubation of rat adipocytes with GIP (10-100 ng/ml) resulted in both a displacement to the left of the insulin binding isotherm (i.e., increased receptor affinity) and potentiated insulin-mediated glucose uptake at insulin concentrations less than 1 ng/ml (i.e., increased cellular insulin sensitivity). Cholecystokinin, another gastrointestinal hormone, did not alter the insulin receptor binding characteristics or glucose uptake of the adipocytes in vitro. We suggest that GIP, a known potentiator of glucose-stimulated insulin secretion, may also modulate the effects of insulin by directly altering target tissue sensitivity to insulin.
Cephalic phase of insulin secretion and food stimulation in humans: a new perspective
Authors: Bellisle F. , Louis-Sylvestre J. , Demozay F. , Blazy D. , Le Magnen J.
Published: December 2017

Insulinemia and glycemia were measured at a 1-min interval at the hour of a lunch meal in human subjects. When no food was presented to naive subjects (n = 4), cyclic oscillations of insulinemia were found (period, 12-20 min; amplitude, 2.8-10.3 microU/ml). It is proposed that these spontaneous oscillations must be taken into consideration when evaluating the insulin response on cephalic contact with food stimuli; they might otherwise constitute a source of artifacts. Four subjects were then submitted to a series of four test meals scheduled at a 1-wk interval. Although their prandial glycemia remained comparable with preprandial values for the first 16 min of the meals, insulinemia often exhibited early peaks (within a few min after meal onset) whose amplitude appeared related to palatability conditions. Evidence suggests that the insulin peaks triggered by cephalic stimulation are Pavlovian reflexes that become conditioned to the test situation. A typical neuroendocrine response to alimentary frustration is also described. The results are discussed in perspective with animal works, in terms of the effects of neuroendocrine events on feeding behavior.
Potentiation of hemorrhage-evoked catecholamine release by prior blood loss in cats
Authors: Bereiter D. A. , Gann D. S.
Published: December 2017

The effect of prior blood loss on the plasma catecholamine response to acute hemorrhage (H) was assessed in alpha-chloralose-urethane anesthetized cats. Animals sustained an initial H period of 0 (samples only), 10, or 20% H total blood volume. Ninety minutes after reinfusion of the shed blood, all animals sustained a rapid 20% H. The catecholamine and arterial pressure responses to this second 20% H were assessed every 2 min for 20-min duration. Plasma norepinephrine increased modestly in the 0/20% group (+0.63 +/- 0.13 ng/ml) and 10/20% group (+0.66 +/- 0.07 ng/ml), whereas the 20/20% group showed a much larger (P less than 0.01) mean increase of 3.58 +/- 1.16 ng/ml. Plasma epinephrine did not increase after 0/20% (+0.05 +/- 0.02 ng/ml), increased slightly after 10/20% H (+0.10 +/- 0.05 ng/ml), and demonstrated a large significant increase after 20/20% H (+0.48 +/- 0.18 ng/ml). The differential effect of 20% H on catecholamine release, depending on the magnitude of prior blood loss, was not the result of altered mean arterial or pulse pressure responses to H. Correlation analyses revealed that the mean increases in epinephrine and norepinephrine during the post-H sampling period were well correlated in each animal (r = 0.864, P less than 0.001). The data indicate that the priming effect of prior blood loss on H evoked catecholamine release: requires an initial blood loss of 20% of total blood volume; occurs rapidly, as it is seen by 90 min after the initial H period; and affects epinephrine and norepinephrine similarly. We conclude that the immediate past secretory history of the sympathoadrenal system affects its responsiveness to subsequent blood loss.
Amino acid metabolism after lambda-carrageenan injury to rat skeletal muscle
Authors: Albina J. E. , Shearer J. , Mastrofrancesco B. , Caldwell M. D.
Published: December 2017

To evaluate whether the alterations in amino acid (AA) metabolism that follow the lambda-carrageenan injury are direct consequences of wounding and are therefore independent of food intake, plasma AA, in vivo muscle intracellular free AA, and AA release during isolated hindlimb perfusions were determined in pentobarbital-anesthetized rats with lambda-carrageenan-induced hindlimb muscle wounds (W) and in pair-fed (PFC) and ad libitum-fed (ALC) non-wounded controls. Both PFC and W animals showed different plasma and muscle intracellular AA composition that ALC. The alterations observed in these compartments in W animals may not have resulted exclusively as a consequence of the wound. Wounded hindlimbs released more AA during perfusion than either control group. The marked increase in net protein catabolism of W muscle appeared to be related to wounding and not a consequence of partial starvation. The normalized release (amino acid/phenylalanine ratio) of glutamine (W less than ALC), alanine (W less than PFC and ALC), and the branched-chain amino acids (W greater than PFC and ALC) differed among groups, suggesting an alteration in the metabolism of these AA in W tissue.
Secretin and its C-terminal hexapeptide potentiates insulin release in mouse islets
Authors: Kofod H. , Hansen B. , Lernmark A. , Hedeskov C. J.
Published: December 2017

Peptides representing the C-terminal end of secretin were synthetized and their effects tested along with secretin on column-perifused isolated mouse pancreatic islets. Insulin release induced by 10 mmol/l D-glucose was potentiated by secretin tested in a concentration range of 0.01-10 micrograms/ml; the maximal effect was obtained with 1 microgram/ml secretin. This effect was mimicked by 50-500 micrograms/ml NH2-Leu-Leu-Gln-Gly-Leu-Val-NH2, [S-(22-27)], which represents an amidated C-terminal sequence of the secretin molecule. The consecutive smaller secretin C-terminal peptides had either no effects [Val-NH2, S-(24-27)] or only marginally [S-(26-27), S-(23-27)] potentiating effects on insulin release in the presence of 10 mmol/l D-glucose. The effects of secretin and S-(22-27) were not influenced by 2 mmol/l glutamine. The intact hormone and the five synthetic peptides as well as Val-NH2 had no stimulatory effect on islet glutamate dehydrogenase activity. In fact, S-(23-27), S-(24-27), and S-(25-27) inhibited the islet glutamate dehydrogenase activity, the activation by which amino acids and amino acid derivatives are known to elicit a potentiation of insulin release. Our results suggest that the C-terminal part is important to the marked potentiation of glucose-induced insulin release in vitro by secretin.
Body composition of two human cadavers by neutron activation and chemical analysis
Authors: Knight G. S. , Beddoe A. H. , Streat S. J. , Hill G. L.
Published: December 2017

In vivo neutron activation analysis (NAA) is currently used to measure body composition in metabolic and nutritional studies in many clinical situations, but has not previously been validated by comparison with chemical analysis of human cadavers. Total body nitrogen (TBN) and chlorine (TBCl) were measured in two human cadavers by NAA before homogenization and chemical analysis (CHEM) after (cadaver 1: TBN, 1.47 NAA, 1.51 CHEM; TBCl, 0.144 NAA, 0.147 CHEM; cadaver 2: TBN, 0.576 NAA, 0.572 CHEM; TBCl, 0.0227 NAA, 0.0250 CHEM). The homogenates were also analyzed by NAA, and no significant differences were found, indicating that the effects of elemental inhomogeneity on the measurement of TBN and TBCl are insignificant. Total body water, fat, protein, minerals, and carbohydrates were measured chemically for each cadaver and compared with estimates for these compartments obtained from a body composition model, which when used in vivo involves NAA and tritium dilution. The agreement found justifies the use of the model for the measurement of changes in total body protein, water, and fat in sequential studies in groups of patients.
Norepinephrine inhibition of pulsatile LH release: receptor specificity
Authors: Bergen H. , Leung P. C.
Published: December 2017

Infusion of norepinephrine (NE) into the third ventricle of ovariectomized (OVX) adult rats inhibits pulsatile luteinizing hormone (LH) secretion. This study examines the effects of pretreatment with specific alpha- and beta-adrenergic blockers on the subsequent NE-induced suppression of LH release. Unanesthetized long-term OVX rats were injected ip or iv with phenoxybenzamine (alpha-adrenergic receptor blocker), propranolol (beta-adrenergic blocker), or an equal volume of saline (as controls). Approximately 1-1.5 h later, the animals were given an intraventricular (ivt) administration of NE. Infusion of acidified saline into the third ventricle of OVX rats failed to affect the pulsatile pattern of LH release characteristic of these animals. After ivt of NE, the control rats showed a significant decrease in mean blood LH level of ca. 30%. Pretreatment of OVX rat with propranolol either ivt or ip failed to affect pulsatile LH release. Subsequent ivt infusion of NE either at 1 h or 15 min after propranolol treatment also caused a 28-30% decrease in the mean LH levels and suppressed pulsatile discharge of LH, an effect that lasted for approximately 45-50 min. In sharp contrast to the saline and propranolol-treated groups, rats pretreated with phenoxybenzamine had sporadic or no LH pulses during the 70-min postphenoxybenzamine period and had significantly lower mean LH levels when compared with control animals (P less than 0.05). Moreover, a drop in mean blood LH levels after NE infusion was not observed in the rats pretreated with phenoxybenzamine.(ABSTRACT TRUNCATED AT 250 WORDS)
Different production and decay rates of six renin forms isolated from rat plasma
Authors: Sessler F. M. , Jacquez J. A. , Malvin R. L.
Published: December 2017

Rat kidney contains six forms of renin, which are in different proportion from those found in plasma. We tested the hypothesis that differential removal and production of the forms might explain the differences between stored and circulating renins. In one group of rats, the six forms of renin were measured in plasma, 10 min after hemorrhage, or after aortic constriction. Plasma was run on an isoelectric focusing gel, and the six peaks of renin activity were expressed either as angiotensin I per hour per milliliter or as a percentage of the total plasma renin concentration. After hemorrhage or aortic constriction, the concentration of each form was significantly increased; the profile of circulating renin was significantly modified, showing an increase in proportion of form 2 and a decrease of forms 4, 5, and 6. In a second group, the disappearance of each form was measured 0 to 100 min after nephrectomy and fitted a two-exponential decay curve. Interpreted as a two-pool system with degradation from pool 1, the degradation rate decreased progressively, going from form 1 to 6. In a third group, arterial and renal venous blood were collected. The profile of secreted renin was calculated from the arterial venous difference. This profile fitted the prediction of the two-compartment model. Our data support the hypothesis that the proportion of each circulating renin form is the result of a balance between the rate of production of renin of constant composition and the degradation of the six forms at different rates.
Leucine and isoleucine activate skeletal muscle branched-chain alpha-keto acid dehydrogenase in vivo
Authors: Aftring R. P. , Block K. P. , Buse M. G.
Published: December 2017

The response of rat skeletal muscle branched-chain alpha-keto acid dehydrogenase to administration of branched-chain amino acids in vivo was determined using a soluble preparation of the enzyme. After detergent extraction of the complex in the presence of kinase and phosphatase inhibitors, initial in vivo activity was typically 1 nmol X min-1 X g muscle-1, with 0.1 mM alpha-[1-14C]ketoisocaproate as substrate. Total activity of the dephosphorylated complex, measured after preincubation with 15 mM Mg2+, typically reached a maximum of 29 nmol X min-1 X g-1. Thus in overnight-fasted rats the complex was 2-3% active. Initial activity increased three- to fivefold after leucine or isoleucine (at higher concentrations) but not valine administration in vivo. After intravenous leucine injection (0.25 mmol/kg) initial muscle enzyme activity increased rapidly and subsequently decreased, paralleling plasma leucine concentrations, while plasma valine and isoleucine decreased. In conclusion, muscle branched-chain alpha-keto acid dehydrogenase complex is rapidly activated when circulating leucine is increased to concentrations that may occur after meals. During hyperleucinemia accelerated valine and isoleucine degradation by muscle may account for the observed "antagonism" among the branched-chain amino acids.
Changes in leucine kinetics during meal absorption: effects of dietary leucine availability
Authors: Nissen S. , Haymond M. W.
Published: December 2017

Whole-body leucine and alpha-ketoisocaproate (KIC) metabolism were estimated in mature dogs fed a complete meal, a meal devoid of branched-chain amino acids, and a meal devoid of all amino acids. Using a constant infusion of [4,5-3H]leucine and alpha-[1-14C]ketoisocaproate (KIC), combined with dietary [5,5,5-2H3]leucine, the rate of whole-body proteolysis, protein synthesis, leucine oxidation, and interconversion of leucine and KIC were estimated along with the rate of leucine absorption. Ingestion of the complete meal resulted in a decrease in the rate of endogenous proteolysis, a small increase in the estimated rate of leucine entering protein, and a twofold increase in the rate of leucine oxidation. Ingestion of either the meal devoid of branched-chain amino acids or devoid of all amino acids resulted in a decrease in estimates of whole-body rates of proteolysis and protein synthesis, decreased leucine oxidation, and a decrease in the interconversion of leucine and KIC. The decrease in whole-body proteolysis was closely associated with the rise in plasma insulin concentrations following meal ingestion. Together these data suggest that the transition from tissue catabolism to anabolism is the result, at least in part, of decreased whole-body proteolysis. This meal-related decrease in proteolysis is independent of the dietary amino acid composition or content. In contrast, the rate of protein synthesis was sustained only when the meal complete in all amino acids was provided, indicating an overriding control of protein synthesis by amino acid availability.
Role of vasopressin in stimulation of ACTH secretion by angiotensin II in conscious dogs
Authors: Klingbeil C. K. , Keil L. C. , Chang D. , Reid I. A.
Published: December 2017

Three series of experiments were performed in conscious dogs to test the possibility that the stimulation of adrenocorticotropin (ACTH) release by angiotensin II (ANG II) is mediated by arginine vasopressin (AVP). In the first protocol, the effect of ANG II on ACTH release was studied in dogs in which endogenous AVP levels had been increased by water deprivation. Water deprivation for 24 h increased plasma AVP concentration from 3.0 +/- 0.5 to 7.7 +/- 0.5 pg/ml (P less than 0.01) and increased the AVP response to the highest dose of ANG II (20 ng X kg-1 X min-1). Despite these changes, water deprivation failed to increase the ACTH response to ANG II. Next, the contribution of endogenous AVP to the stimulation of ACTH release by ANG II was examined using the V1-receptor antagonist, d(CH2)5Tyr[Met]-AVP (10 micrograms/kg iv). The ACTH response to ANG II in the presence of the AVP antagonist (66.4 +/- 3.1 to 100.1 +/- 15.9 pg/ml) was not significantly less than that in its absence (53.0 +/- 4.8 to 72.2 +/- 11.1 pg/ml). Finally, ANG II and AVP were infused in combination to determine whether there is a synergism between these two peptides in the release of ACTH. In one protocol, AVP and ANG II were infused separately and in combination. The ACTH response to ANG II and AVP in combination (48.7 +/- 6.5 to 61.5 +/- 8.5 pg/ml) was not enhanced compared with the responses to ANG II (59.8 +/- 7.3 to 71.0 +/- 10.1 pg/ml) or AVP (48.8 +/- 5.7 to 55.6 +/- 6.5 pg/ml) alone.(ABSTRACT TRUNCATED AT 250 WORDS)
Importance of calcium in renal renin release
Authors: Henrich W. L. , Campbell W. B.
Published: December 2017

The sequence of intracellular events that lead to renin release is incompletely defined. Accordingly, we examined the interrelationship of two important factors in the process: renin release coupled to cAMP and renin release related to a decrease in intracellular calcium activity (Cai). Rat renal cortical slices were used to study these relationships in vitro. In the initial studies, cAMP-coupled renin release was established for isoproterenol (10(-5) M), prostacyclin (PGI2; 10(-6) M), and forskolin (10(-5) M). Each agent caused an increase in renin release and tissue cAMP levels, which were inhibited by the addition of the adenyl cyclase inhibitor 2',5'-dideoxyadenosine (DDA, 10(-5) M) to the media. Diltiazem (10(-4) M) and 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8; 0.6 X 10(-4) M) are believed to decrease Cai by different mechanisms; each of these agents caused a significant increase in renin release. Renin release stimulated by diltiazem, and TMB-8 was not inhibited by either DDA or indomethacin. The calcium ionophore A23187 (17 X 10(-6) M) and vanadate (10(-3) M) were next added to produce an increase in Cai. Both of these agents blunted renin release produced by isoproterenol, PGI2, and forskolin. These results provide strong indirect support for an inverse relationship between Cai and renin release in the juxtaglomerular cell. The results also imply that changes in Cai occupy a step that is distal to cAMP-coupled events in the sequence of intracellular events which culminate in renin release.
Chronic DOCA treatment increases Ca absorption: role of hypercalciuria and vitamin D
Authors: Zikos D. , Langman C. , Gafter U. , Delahaye B. , Lau K.
Published: December 2017

To examine the effects of mineralocorticoidism on calcium (Ca) absorption and to define the mechanism, rats received a high-salt diet and injections of vehicle or deoxycorticosterone acetate (DOCA). Net (44.2 vs. 31.4 mg/day) and percent Ca absorption (28.1 vs. 20.1%) was increased after 5 days of DOCA. This was associated with increased duodenal 45Ca uptake. Thus despite the hypercalciuria, Ca balance was similar. Although the hypercalciuria persisted chronically, the gut effects were sustained, which maintained normal ionized Ca, bone Ca, and Ca balance. Urinary cyclic adenosine monophosphate was elevated by DOCA. Compared with appropriate controls, neither DOCA alone nor polydipsia (elicited by dextrose) produced similar magnitudes of hypercalciuria as DOCA plus high-salt diet. These maneuvers also failed to increase Ca absorption. Neutralization of the metabolic alkalosis neither attenuated the DOCA-induced hypercalciuria nor abolished the Ca hyperabsorption. In vitamin D-deprived rats, the hypercalciuria but not the intestinal effects of DOCA were reproduced. Serum 1,25-dihydroxyvitamin D3 levels were increased during chronic DOCA treatment (224 vs. 139 pg/ml). These data best fit the hypothesis that increased Ca absorption is secondary to the calciuric effects of DOCA and high-salt diet and is mediated via the increased parathyroid hormone and 1,25-dihydroxyvitamin D3 activities.
Bone changes due to pregnancy and lactation: influence of vitamin D status
Authors: Marie P. J. , Cancela L. , Le Boulch N. , Miravet L.
Published: December 2017

The effects of pregnancy and lactation on endosteal bone formation and resorption were evaluated in vitamin D-depleted (-D) and vitamin D-repleted (+D) rats. Pregnancy induced a marked stimulation of osteoclastic bone resorption and of static and dynamic parameters of bone formation and mineralization. Bone resorption increased independently of vitamin D status and did not correlate with plasma 1,25-dihydroxyvitamin D3 [1,25(OH)2D] levels, but it was associated with increased plasma immunoreactive parathyroid hormone (iPTH) concentrations. Stimulation of the endosteal bone formation rate was mainly impaired in D-depleted rats, resulting in trabecular bone loss, which, in -D mother rats, was associated with decreased bone ash and total bone calcium. Lactation further stimulated bone resorption and reduced the trabecular bone volume; ash weight and bone calcium content were also decreased independently of the vitamin D status and changes in plasma iPTH levels. In presence of vitamin D, the bone formation rate increased fourfold during lactation but was unchanged in -D lactating rats. During lactation, vitamin D-depleted rats lost twofold more calcified bone than +D rats because of impaired mineralization. Thus, the present study shows that both the endosteal bone resorption and formation are stimulated by pregnancy and lactation and that vitamin D is required for normal bone mineralization during the reproductive period.
Continuous ovine fetal hemorrhage: sensitivity of plasma and urine arginine vasopressin response
Authors: Ross M. G. , Ervin M. G. , Leake R. D. , Humme J. A. , Fisher D. A.
Published: December 2017

Intravascular hemorrhage of the ovine fetus is a potent stimulus for arginine vasopressin (AVP) secretion. However, the method (acute, continuous) and rate of blood withdrawal may influence the fetal response. To determine the hemorrhage threshold for AVP secretion in response to slow continuous hemorrhage, five chronically catheterized ovine fetuses were continuously hemorrhaged (0.6% blood vol/min) to 24-30% blood volume withdrawal. Immediately after hemorrhage fetal blood was reinfused at an equivalent rate. In addition to AVP measurements by radioimmunoassay, fetal urinary responses were monitored as an index of fetal AVP secretion. Significant increases in plasma AVP occurred during hemorrhage (1.0 +/- 0.1 to 8.0 +/- 2.0 pg/ml). The fetal plasma AVP-hemorrhage threshold, as defined by regression analysis, occurred at withdrawal of 13.0% blood volume. Fetal urine volume significantly decreased from a mean basal rate of 0.59 +/- 0.03 to 0.21 +/- 0.06 ml/min at the completion of hemorrhage. Urinary sodium, potassium, and osmolar excretion also significantly decreased at the completion of hemorrhage. Urinary AVP excretion, urine osmolality, sodium, and potassium concentrations did not change significantly during the hemorrhage period but increased significantly during the reinfusion period; the delay a result of renal and catheter dead space. Reinfusion of blood resulted in a return of plasma AVP to basal levels. These results define a threshold for AVP secretion and demonstrate significant urinary effects in response to slow continuous hemorrhage.
Exogenous vasopressin modulates activity of oxytocin neurons in homozygous Brattleboro rats
Authors: Cheng S. W. , North W. G.
Published: December 2017

We studied the effects of chronic replacement with arginine vasopressin (AVP) or 1-desamino-D-arginine vasopressin (DDAVP), as well as acute replacement with AVP or DDAVP, on the responsiveness of oxytocin (OT) neurons as indexed by plasma oxytocin-associated neurophysin concentration [( OT-RNP]) during acute salt loading in conscious, chronically catheterized homozygous Brattleboro (DI) rats. Salt loading was carried out on days 5 and 12 of AVP (3,000 ng/day) or DDAVP (50 ng/day) treatment or 60 min after intraperitoneal injection of 1 microgram AVP or 25 ng DDAVP. All vasopressin treatments did not significantly alter the basal [OT-RNP]. In response to infusion of 18% saline, there were corresponding significant increases in plasma osmolality (Posmol) and [OT-RNP] in all animals. The increases in [OT-RNP] in vasopressin-treated DI rats were markedly reduced compared with those observed earlier for untreated DI animals despite similar rises in Posmol. The slopes of the relationship between delta [OT-RNP] and delta Posmol were 9.0 and 9.8 fmol X ml-1 X mosmol-1 X kg for chronically AVP-treated DI rats, 8.9, and 8.8 fmol X ml-1 X mosmol-1 X kg for chronically DDAVP-treated DI animals, 10.7 fmol X ml-1 X mosmol-1 X kg for acutely AVP-treated DI rats, and 8.3 fmol X ml-1 X mosmol-1 X kg for acutely DDAVP-treated animals compared with that of 34.9 fmol X ml-1 X mosmol-1 X kg for untreated DI rats.(ABSTRACT TRUNCATED AT 250 WORDS)
A simple efficient method for separating murine uterine epithelial and mesenchymal cells
Authors: Bigsby R. M. , Cooke P. S. , Cunha G. R.
Published: December 2017

A simple, and very efficient, method for isolating pure uterine epithelium from neonatal, immature, or adult mice and pure uterine mesenchyme from neonatal mice is described. The technique uses mild tryptic digestion of the tissues to loosen the adherence of the epithelium to its underlying mesenchyme followed by gentle mechanical manipulation to effect removal of the luminal epithelium as an intact tube of cells. The epithelial fraction collected by this method was free of stromal cell contamination as judged by microscopic examination of the freshly isolated cells and of cell cultures made from that fraction. The mesenchymal fraction was consistently devoid of epithelium when collected from neonatal mice (5 days old or younger), but mesenchyme from uteri of mice greater than or equal to 10 days old was usually contaminated with epithelial cells due to retention of glandular epithelial crypts in the mesenchyme following removal of the luminal epithelium. Both epithelial and mesenchymal cells obtained by this method are viable, as judged by their ability to attach, spread, and synthesize DNA in vitro. Epithelial cells isolated from 20-day-old or adult animals have a full complement of estrogen receptors, as assessed by whole cell uptake of [3H]estradiol. The technique described here has clear advantages over previously described methods for obtaining pure uterine epithelium and in addition allows mesenchymal tissue free of epithelial contamination to be obtained when applied to uteri of animals less than or equal to 5 days old.
Complete inhibition of creatine kinase in isolated perfused rat hearts
Authors: Fossel E. T. , Hoefeler H.
Published: December 2017

Transient exposure of an isolated isovolumic perfused rat heart to low concentrations (0.5 mM) of perfusate-born iodoacetamide resulted in complete inhibition of creatine kinase and partial inhibition of glyceraldehyde-3-phosphate dehydrogenase in the heart. At low levels of developed pressure, hearts maintained mechanical function, ATP, and creatine phosphate levels at control values. However, iodoacetamide-inhibited hearts were unable to maintain control values of end diastolic pressure or peak systolic pressure as work load increased. Global ischemia resulted in loss of all ATP without loss of creatine phosphate, indicating lack of active creatine kinase. These results indicate that isovolumic perfused rat hearts are able to maintain normal function and normal levels of high-energy phosphates without active creatine kinase at low levels of developed pressure.