bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance of LH pulse-detection algorithms at rapid rates of venous sampling in humans
Authors: Veldhuis J. D. , Evans W. S. , Rogol A. D. , Drake C. R. , Thorner M. O. , Merriam G. R. , Johnson M. L.
Published: December 2017

To assess the influence of the sampling rate on the quantitative characterization of pulsatile luteinizing hormone (LH) release, we withdrew blood at 4-min intervals for 8 h in five men and at 1-min intervals for 2 h in six other men. For comparative purposes, significant LH pulses were enumerated by three independent, computerized pulse-detection algorithms currently available. Our results indicate that, although the absolute number of LH pulses detected was influenced by the particular algorithm used and the estimate of intra-assay variance, all three analyses yielded increased pulse-frequency estimates at more intensive rates of venous sampling. Moreover, using a fourth, modified pulse-detection algorithm intended to maximize recognition of true-positive LH pulses while minimizing both false-positive and false-negative pulses, we observed that venous sampling at 4- and 1-min intervals exposed 4- and 12-fold more LH pulses, respectively, than could be discerned at conventional sampling rates. At rapid rates of venous sampling, the pattern of LH pulses comprised high-frequency, low-amplitude LH pulsations superimposed on lower-frequency LH peaks. This pattern suggests that the pituitary gland is responsive to high rates of intermittent neural stimulation. Moreover, these observed profiles are consistent with rapid initial rates of LH disappearance and/or distribution that we could demonstrate after intravenous bolus injections of purified LH in hypogonadotropic volunteers. In conclusion, we have compared results from three different pulse-detection algorithms at various rates of venous sampling and demonstrated a critical influence of sampling rate on apparent LH pulse frequency in humans.
Stimulation of pituitary cAMP accumulation by human pancreatic GH-releasing factor-(1-44)
Authors: Culler M. D. , Kenjo T. , Obara N. , Arimura A.
Published: December 2017

This study seeks to determine whether hpGRF-(1-44) stimulates pituitary growth hormone (GH) secretion and cAMP accumulation in a manner that is consistent with the concept of cAMP as an intracellular mediator of GH release. Addition of 10 nM hpGRF-(1-44) to rat anterior pituitary cell cultures stimulated a rapid elevation of intracellular cAMP that preceded or coincided with increases in GH and cAMP secretion. A dose-related increase in GH and cAMP release and in intracellular cAMP accumulation was observed in response to increasing concentrations of hpGRF-(1-44). Stimulation of cAMP accumulation and release, however, occurred over a hpGRF-(1-44) concentration range that was approximately one order of magnitude higher than required for dose-related GH release. Simultaneous addition of 0.05 nM hpGRF-(1-44) and 0.2, 0.5, or 1.0 mM 3-isobutyl-1-methylxanthine (MIX) to the cultures resulted in a significant potentiation of intracellular cAMP accumulation and release. Potentiation of GH release was not observed, however, probably due to attainment of maximal or near maximal GH release by MIX alone. The addition of increasing doses of exogenous N6-O2'-dibutyryladenosine 3',5'-cyclic monophosphate (DBcAMP) to cell cultures resulted in a dose-related increase in GH secretion. The results of this study are consistent with the concept of cAMP as a second messenger for hpGRF-(1-44) in stimulating GH release. Additionally, a novel method for cAMP extraction that utilizes trifluoroacetic acid is described.
Evidence for an intestinal mechanism in hypercalciuria of spontaneously hypertensive rats
Authors: Lau K. , Zikos D. , Spirnak J. , Eby B.
Published: December 2017

To define the mechanism for the hypercalciuria in spontaneously hypertensive rats (SHR), Ca clearance was evaluated in fasted 23-wk-old SHR and normotensive Wistar Kyoto (WKy) controls. There was no exaggerated calciuria before or after parathyroidectomy. Ca balance was therefore measured in the nonfasted animals, which revealed hyperabsorption in SHR of both sexes with increments 10-fold that of Ca excretion, supporting the primacy of intestinal hyperabsorption. In situ duodenal Ca uptake was also increased in the SHR. Parathyroidectomy did not affect the hyperabsorption. Hypercalcemia (total and ionized) and hypercalciuria in SHR associated with reduced adenosine 3',5'-cyclic monophosphate excretion, were abolished by fasting. Correction of hypertension for 6 mo failed to abolish the hypercalciuria. Bone Ca deposits were increased in 1-yr-old SHR. Ten-week-old SHR, in contrast, displayed mild malabsorption. Our data do not support the "renal leak" hypothesis. Instead, the adult SHR is characterized by increased Ca retention due to primary hyperabsorption, absorptive hypercalciuria, and increased bone Ca deposition. These phenomena are independent of sex, parathyroid hormone, and treatment of the established hypertension.
Alanine kinetics in humans: influence of different isotopic tracers
Authors: Yang R. D. , Matthews D. E. , Bier D. M. , Lo C. , Young V. R.
Published: December 2017

Whole-body alanine kinetics were studied using continuous infusions of [15N]-, [3,3,3-2H3]-, [1-13C]-, and [3-13C]alanine tracers in healthy male subjects in the postabsorptive state. Alanine kinetics were highly dependent on the choice of isotopically labeled alanine. Highest rates of alanine flux (mean +/- SE) were obtained with the [3,3,3-2H3]alanine (474 +/- 41 mumol X kg-1 X h-1). [1-13C]- and [3-13C]alanine tracers gave intermediate values (297 +/- 12 and 317 +/- 22 mumol X kg-1 X h-1, respectively). The slowest rates of alanine turnover were measured with [15N]alanine (226 +/- 7 mumol X kg-1 X h-1). These results emphasize the heterogeneous metabolism of different portions of the alanine molecule and the importance of choosing an appropriate alanine tracer for studying different aspects of alanine metabolism.
Pituitary LH responsiveness to GnRH in vitro as related to GnRH receptor number
Authors: Baldwin D. M. , Bourne G. A. , Marshall J. C.
Published: December 2017

The objective of this in vitro study was to determine whether the increase in the augmented phase of the biphasic luteinizing hormone (LH) response to gonadotrophin-releasing hormone (GnRH) and its enhancement by estradiol (E2) were associated with GnRH-stimulated increases in pituitary GnRH receptor concentration. Pituitary glands from 72 h ovariectomized (OVX), OVX + E2, or proestrous rats were perifused continuously with GnRH (12 ng/h). LH release was measured at 10-min intervals, and pituitary GnRH-binding capacity (GnRH-BC) was assessed at 0, 40, 80, 120, and 240 min after addition of GnRH. All treatment groups exhibited a biphasic pattern of LH release; initial (20-70 min) and augmented (120-240 min) mean rates of LH secretion (micrograms/h) were 1.78 and 3.92 (OVX), 6.40 and 16.67 (OVX + E2), and 2.79 and 18.64 (proestrus), respectively. Total LH release was significantly greater in the OVX + E2 and proestrous groups (44.0 and 45.8 micrograms) vs. the OVX group (12.4 micrograms). Throughout the GnRH infusion period, GnRH-BC did not change significantly in any of the treatment groups with the exception of the OVX group in which there was a transient small decrease at 80 min post-GnRH infusion. There were no significant differences between treatment groups in GnRH-BC at any time after infusion of GnRH. These results demonstrate that the acute and augmented phases of GnRH-stimulated LH release and the enhancement of this biphasic response by E2 occurs independent of any increase in GnRH-BC and suggest that these events are mediated by postreceptor mechanisms.
Increased muscle glucose uptake during contractions: no need for insulin
Authors: Ploug T. , Galbo H. , Richter E. A.
Published: December 2017

We reinvestigated the prevailing concept that muscle contractions only elicit increased muscle glucose uptake in the presence of a so-called “permissive” concentration of insulin (Berger et al., Biochem. J. 146: 231–238, 1975; Vranic and Berger, Diabetes 28: 147–163, 1979). Hindquarters from rats in severe ketoacidosis were perfused with a perfusate containing insulin antiserum. After 60 min perfusion, electrical stimulation increased glucose uptake of the contracting muscles fivefold. Also, subsequent contractions increased glucose uptake in hindquarters from nondiabetic rats perfused for 1.5 h in the presence of antiserum. 3-O-methylglucose uptake was increased markedly by contractions in fast-twitch red and white fibers that were severely glycogen depleted but not in slow-twitch red fibers that were not glycogen depleted. In hindquarters from ketoacidotic rats perfused exactly as by Berger et al., 3-O-methylglucose uptake increased during contractions and glucose uptake was negative at rest and zero during contractions. An increase in muscle transport and uptake of glucose during contractions does not require the presence of insulin. Furthermore, glucose transport in contracting muscle may only increase if glycogen is depleted.
Circulating free fatty acids, insulin, and glucose during chemical stimulation of hypothalamus in rats
Authors: Steffens A. B. , Damsma G. , van der Gugten J. , Luiten P. G.
Published: December 2017

The aim of this study was to investigate plasma free fatty acids (FFA), insulin, and blood glucose during chemical stimulation of the lateral and ventromedial hypothalamic areas (LHA and VMH) in rats. Therefore male Wistar rats were implanted with bilateral cannulas in the LHA or the VMH and into the left and right jugular veins. Freely moving rats were then infused into the LHA and VMH with norepinephrine (NE), epinephrine (E), or acetylcholine or intravenously with NE or E. Before, during, and after the infusions, simultaneous blood samples were taken without disturbing the animals. Infusion of NE into the LHA resulted in a decrease of plasma FFA and a simultaneous increase of insulin. NE infusion in the VMH elicited an increase of plasma FFA, plasma insulin, and blood glucose. E infusion into the LHA did not lead to a change of plasma FFA, whereas insulin and glucose showed an increase. E infusion into the VMH evoked increases of plasma FFA and insulin. Peripheral administration of NE led to a sharp increase of FFA, whereas plasma insulin and blood glucose did not change. E in the periphery elicited an augmentation of plasma FFA and blood glucose and a suppression of insulin during infusion. After termination of E infusion, plasma FFA and glucose levels decreased, whereas plasma insulin showed a sharp increase.(ABSTRACT TRUNCATED AT 250 WORDS)
Age-related decrement in hormone-stimulated lipolysis
Authors: Hoffman B. B. , Chang H. , Farahbakhsh Z. T. , Reaven G. M.
Published: December 2017

The ability of hormones to activate responses in a variety of tissues decreases with age. The mechanism(s) responsible for these alterations are unclear. We have confirmed that the ability of a beta-adrenergic receptor agonist to activate lipolysis in isolated rat adipocytes decreases with age. Maximum response to isoproterenol was greater in 2-mo-old rats (600 +/- 30 nmol of glycerol released/10(5) cells per h) than 12-mo-old rats (250 +/- 25 nmol/10(5) cells per h), P less than 0.001. Similarly, ACTH is less effective in activating lipolysis in the adipocytes from the older rats. However, the cAMP analogue 8-(4-chlorophenothio)adenosine 3',5'-monophosphate cyclic activated lipolysis equally in the two groups, suggesting that the deficit in adipocytes from the older rats was proximal to cAMP-dependent protein kinase activation. Both isoproterenol and ACTH were significantly less effective in promoting cAMP accumulation in adipocytes isolated from 12-mo-old rats. There was no difference in phosphodiesterase activity of the adipocytes between the two groups. beta-Adrenergic receptors were measured using the antagonist radioligand [125I]cyanopindolol. The number of beta-adrenergic receptors was actually increased in the adipocytes from 12-mo-old rats (26,000 +/- 2,600 receptors/cell) compared with cells from 2-mo-old rats (7,200 +/- 1,300 receptors/cell). The results suggest that diminished cAMP production is responsible for the diminished lipolytic response in the adipocytes of older rats. The mechanism responsible for this change is uncertain but cannot be explained by a loss in beta-adrenergic receptors.
A role for vagus nerve in regulation of protein and carbohydrate intake
Authors: Li E. T. , Anderson G. H.
Published: December 2017

The effects of vagotomy on long-term protein and carbohydrate selection or on short-term food selection following cholecystokinin octapeptide (CCK-8) injections, protein, or carbohydrate premeals and on brain 5-hydroxytryptamine (5HT) and catecholamine metabolism were examined in adult rats. Vagotomy was followed by a reduction in daily protein intake that by 3 wk had fallen to 50% of preoperative levels. A corresponding increase in carbohydrate intake occurred so that total food intake was maintained at approximately 93% of that consumed by the sham-operated controls. These changes in day-to-day macronutrient selection from a choice of high- and low-protein diets were associated with a vagotomy-induced decreased turnover of 5HT in the hypothalamus. In meal consumption studies vagotomy prevented a further reduction in meal size by CCK-8 but did not block decreased consumption of total food or of protein preference of the rats in meals taken subsequent to a protein meal. It was concluded that the vagus nerve plays a role in regulating long-term protein and carbohydrate preferences but not in the relationships among meal-to-meal composition and intake.
Reduction of pituitary GnRH receptors in immature rats treated with monosodium glutamate
Authors: Dalkin A. C. , Duncan J. A. , Regiani S. , Marshall J. C.
Published: December 2017

The number of pituitary gonadotropin-releasing hormone (GnRH) receptors increases during sexual maturation in the rat and probably reflects changes in hypothalamic GnRH secretion. As GnRH is synthesized in various hypothalamic nuclei, including the arcuate nucleas (ARC), we investigated the effects of monosodium glutamate (MSG)-induced lesions of the ARC in the rat. In males and females treated with MSG during the first 10 days of life, GnRH receptor content (GnRH-RC) was unchanged from controls at 10 days but was decreased at 20 and 30 days of age (P less than 0.01). Serum concentrations of luteinizing hormone (LH) were similar in MSG-treated and control males but were significantly lower in 10-day-old females (P less than 0.01). Injections of GnRH (3 micrograms every 8 h on days 18 and 19) restored GnRH-RC to control values in MSG-treated rats. Both MSG and untreated control rats showed similar LH responses to acute injections of GnRH, but responses were attenuated (P less than 0.05) after 2 days pretreatment with GnRH in rats that had received MSG. Ovarian GnRH-RC was similar in both MSG-treated and untreated controls. These data indicate that MSG-induced lesions of the ARC reduce pituitary GnRH-RC in immature rats, and the more marked effects in females suggest a more significant role in the ARC in the control of GnRH secretion during maturation in females. The lack of MSG-induced changes in ovarian GnRH-RC indicates that GnRH from the arcuate nucleus is not responsible for the increase in ovarian GnRH receptors seen during sexual maturation.
Effects of ANG II and K+ on Ca efflux and aldosterone production in adrenal glomerulosa cells
Authors: Kojima I. , Kojima K. , Rasmussen H.
Published: December 2017

A comparison was made of the effects of angiotensin II (ANG II) and K+ on aldosterone secretion and calcium efflux from porcine adrenal glomerulosa cells. In the presence of 1.25 mM Ca2+ in the perifusion medium, both 1 x 10(-9) M ANG II and 12 mM K+ caused a 3-fold increase in rate of aldosterone secretion. ANG II caused a 3.5-fold increase in the fractional efflux ratios of radiocalcium from cells prelabeled with 45Ca, but K+ caused only a 1.5-fold increase. When the perifusate contained no Ca2+ or the Ca2+ was replaced by 0.6 mM Sr2+, the effects of K+ on both 45Ca efflux and aldosterone production were abolished. On the other hand, ANG II still caused approximately the same increase in the fractional efflux ratio of radiocalcium and 25-50% of the normal increase in aldosterone production rate. When the perifusate contained 1.25 mM calcium and 25 microM dantrolene, K+ produced the same 1.5-fold increase in calcium efflux and the same maximal rate of aldosterone production as seen in the absence of dantrolene. In contrast, dantrolene greatly inhibited ANG II-induced increase in the fractional efflux ratio of calcium, 1.5-fold compared with 3.5-fold in the absence of dantrolene. Likewise, dantrolene delayed the onset of the ANG II-induced increase in aldosterone secretion and reduced the maximal rate of secretion to 50%. Cells incubated with both dantrolene and media containing no Ca2+ or containing Sr2+ in place of Ca2+ showed no response to ANG II either in terms of calcium efflux or aldosterone production.(ABSTRACT TRUNCATED AT 250 WORDS)
TRH-induced membrane hyperpolarization in rat clonal anterior pituitary cells
Authors: Ozawa S.
Published: December 2017

Thyrotropin-releasing hormone (TRH) induces biphasic membrane potential changes, a transient hyperpolarization followed by a prolonged enhancement of the generation of action potentials in the clonal GH3 pituitary cell. The nature of the TRH-induced hyperpolarization was studied in Cl--free solutions. Among various test substances, only TRH and its analogue, which stimulates the release of prolactin from the GH3 cells, were capable of inducing the transient membrane hyperpolarization. The Ca2+ ionophore A23187 also caused a transient hyperpolarization accompanied by an increase in the membrane conductance, although it failed to mimic the late facilitation of spike generation. The reversal potential of the TRH-induced hyperpolarization was identical with that induced by A23187. Reduction of the K+ concentration of the bathing medium caused a similar shift of both these reversal potentials toward a more hyperpolarized level. Injection of the Ca2+-chelator EGTA into the cell suppressed both TRH and Ca2+ ionophore-induced hyperpolarizations. These results suggest that TRH mobilizes the cellular-bound Ca, which in turn activates Ca2+-mediated K+ channels, thus causing the transient membrane hyperpolarization. The relationship between the membrane hyperpolarization and the TRH-stimulated hormone release is discussed.
Glucose and FFA kinetics in sepsis: role of glucagon and sympathetic nervous system activity
Authors: Wolfe R. R. , Shaw J. H.
Published: December 2017

We have assessed the role of glucagon and sympathetic nervous system (SNS) activity on glucose and palmitate kinetics and oxidation in the conscious dog infused with live Escherichia coli bacteria by means of the simultaneous primed constant infusion of [1,2–13C]palmitate and [U-14C]-glucose. The basal rate of glucose production in septic dogs and controls was similar. However, when the glucagon concentration was selectively decreased in the septic animals by the appropriate infusion of somatostatin (S), insulin (I), and glucagon (G), the rate of glucose production decreased significantly, whereas in control animals S + I + G infusion had no effect on glucose kinetics. When alpha- and beta-adrenergic blockade was added to the infusion, the rate of glucose production decreased further and hypoglycemia developed in the septic dogs, whereas in the controls both glucose production and concentration increased. The basal rate of appearance of palmitate was increased in the septic dogs (P less than 0.01). S + I + G had no effect on palmitate appearance in either group, and sympathetic blockade caused a significant decrease in palmitate appearance in both groups of dogs. The rates of oxidation of both glucose and palmitate was related directly to their availability in plasma. Thus, in sepsis, glucagon and SNS activity play important roles in the mobilization of glucose and palmitate into the plasma and therefore in the overall state of energy metabolism.
Processing of cell-bound insulin by capillary and macrovascular endothelial cells in culture
Authors: Dernovsek K. D. , Bar R. S.
Published: December 2017

The processing of cell-bound insulin was determined in endothelial cells cultured from three large blood vessels (human umbilical vein, bovine pulmonary artery, and bovine aorta) and one microvascular source (bovine fat capillaries). Cells were exposed to monoiodinated TyrA14-insulin, the rates of dissociation of cell-bound TyrA14-insulin determined, and cell alteration of insulin assessed by gel filtration and high-performance liquid chromatography analysis. We found that 1) overall degradation rates of insulin are low for all cultured endothelial cells, 2) cell-bound insulin is rapidly processed to a nonreceptor compartment and then rapidly dissociated from all cells, primarily as biologically intact insulin, and 3) degradation of cell-bound insulin, although relatively low, does occur in endothelial cells with the least degradation by capillary cells. The presence of specific surface receptors for insulin on endothelial cells coupled with rapid cellular processing of intact insulin is consistent with a potential role for endothelial cells in either the transport of intact insulin out of the bloodstream or as a regional storage site for intact hormone.
Effect of conceptus number, hysterectomy, and progesterone on prolactin surges in rats
Authors: Tonkowicz P. A. , Voogt J. L.
Published: December 2017

Mating induces two daily surges of prolactin (PRL) secretion in the rat. Termination of the diurnal and nocturnal surges coincides with the development of the placenta and the secretion of rat placental lactogen (RPL). The number of conceptuses present was altered to induce changes in RPL levels in the blood. The presence of one intact viable conceptus is sufficient to cause termination of the diurnal PRL surge. The presence of one or zero conceptuses allowed resumption of the nocturnal surge after day 14, whereas presence of two or more conceptuses prevented the surge. Hysterectomy on day 14 allowed the resumption of the nocturnal PRL surges for 2 days and diurnal PRL surges for 3 days. Progesterone treatment stimulated an additional third nocturnal PRL surge and blunted the magnitude of the resuming diurnal surges. It is concluded that secretions from the conceptus and progesterone contribute to the regulation of prolactin during pregnancy.
Relationship between degree of obesity and in vivo insulin action in man
Authors: Bogardus C. , Lillioja S. , Mott D. M. , Hollenbeck C. , Reaven G.
Published: December 2017

Previous studies have demonstrated reduced in vivo insulin action in obese subjects compared with lean controls. However, little data is available on the relationship between degree of obesity and insulin action, and this relationship has not been shown to be independent of individual differences in maximal aerobic capacity. We studied 55 male Pima Indians and 35 male Caucasians with normal glucose tolerance. In vivo insulin action was measured using the hyperinsulinemic, euglycemic clamp technique at a plasma insulin concentration of approximately 100 microU/ml. Body composition was determined by densitometry, and maximal aerobic capacity was estimated using a graded exercise test. The results showed that degree of obesity was nonlinearly related to in vivo insulin action. In both Indians and Caucasians there was a significant decline in insulin action with increasing obesity up to a percent body fat of approximately 28-30%. Further increases in obesity in the Indians were not associated with significant changes in insulin action. Maximal aerobic capacity was positively linearly correlated with insulin action over the entire range of insulin action in both racial groups. Degree of obesity and maximal aerobic capacity were each independently associated with insulin action although these independent relationships were of marginal significance in the Caucasians. Surprisingly, individual differences in obesity and maximal aerobic capacity accounted for only half the variability observed in insulin action in these glucose tolerant subjects.
Role of palatability on meal-induced thermogenesis in human subjects
Authors: LeBlanc J. , Brondel L.
Published: December 2017

To study the possible participation of food-induced sensory stimulation on meal thermogenesis an experiment was performed with eight female subjects. On alternate days subjects were fed either a highly palatable meal (HPM), containing 710 calories, or a nonpalatable meal (NPM). The NPM was prepared by mixing all the ingredients of the HPM and was presented to the subjects as a desiccated biscuit. The subjects were not informed about the composition of the NPM, which they rated as tasteless and unappetizing. The increase in O2 consumption was approximately 20% during the 90 min following the HPM compared with 12% with the NPM (P less than 0.01). With comparable increases in plasma glucose, plasma insulin level was significantly (P less than 0.01) lower following NPM ingestion than with ingestion of the HPM. At that time a significant increase in plasma norepinephrine was also observed but only following ingestion of the HPM. It would appear that both central sensory stimulation or plasma insulin level, as affected by food palatability, could be considered at this time as possible activators of the increased sympathetic activity observed following ingestion of the HPM. It is suggested that a part of meal thermogenesis is due to food palatability and that the concomitant activation of the sympathetic system may be related to this action.
Effects of glucocorticoid treatment on excitation-contraction coupling
Authors: Laszewski B. , Ruff R. L.
Published: December 2017

We studied the myofibrillar calcium affinity and mechanical threshold of single muscle fibers from the extensor digitorum longus (EDL) and soleus muscles of male Sprague-Dawley rats treated with daily intramuscular injections of dexamethasone, 1.5 mg/kg, for 14 days. The strength-duration and pCa-tension relationships of EDL fibers were not altered by glucocorticoid treatment. However, in soleus fibers the mechanical threshold was increased and the myofibrillar calcium sensitivity was reduced by dexamethasone treatment. Glucocorticoid treatment did not change the maximum tension per cross-sectional area of single-skinned EDL or soleus fibers. The glucocorticoid-induced atrophy and impaired force-generating capacity of fast-twitch muscle are probably not caused by impaired excitation-contraction coupling.
Beta-adrenoreceptors in rat brown adipose tissue: proportions of beta 1- and beta 2-subtypes
Authors: Rothwell N. J. , Stock M. J. , Sudera D. K.
Published: December 2017

Binding of (-)-[3H]dihydroalprenolol [( 3H]DHA) to isolated brown adipose tissue (BAT) microsomal membranes was used to estimate beta-adrenoreceptor density, and this was found to be saturable, reversible, and stereospecific. Scatchard analysis indicated a single class of binding sites of equilibrium dissociation constant 2.2 nM, with a maximum number of binding sites of 160-170 fmol/mg protein. These values were unaffected by the age or sex of the animals, and similar Kd values were obtained for binding to heart and lung membranes. The kinetically derived Kd from forward and reverse reactions was 1.4 nM for BAT. Hofstee analysis of displacement of [3H]DHA produced linear plots for propranolol but curvilinear plots for atenolol and ICI 118,551. Atenolol showed 50-fold selectivity for beta 1-receptors and ICI 118,551 50-fold selectivity for beta 2-receptors in heart, lung, and BAT membranes. These plots indicated beta 1:beta 2-receptor ratios of 59:41 for BAT and heart and 25:75 for lung. It is possible that both beta-adrenoreceptor subtypes in BAT may be involved in the activation of thermogenesis in the tissue.
Endotoxin increases vasopressin release independently of known physiological stimuli
Authors: Kasting N. W. , Mazurek M. F. , Martin J. B.
Published: December 2017

Plasma vasopressin (AVP) increases after endotoxin administration in freely behaving unanesthetized rats. The present experiments sought to determine the factors that mediate this vasopressin response. Endotoxin (150 micrograms/kg iv) elicited a significant increase in plasma AVP concentration. This response was accompanied by unchanged plasma osmolality, hypotension, increased hematocrit (reflecting decreased plasma volume), hypothermia, and hyperglycemia. Pretreatment with the prostaglandin synthesis inhibitor, indomethacin (5 mg/kg sc), had no effect on the vasopressin response to endotoxin but abolished or significantly attenuated the changes in blood pressure, hematocrit, temperature, and plasma glucose while leaving plasma osmolality unaltered. These investigations indicate that endotoxin stimulates vasopressin secretion into plasma independently of changes in plasma osmolality, systemic blood pressure, plasma volume, body temperature, or plasma glucose. The results also suggest that vasopressin responses to endotoxin are not mediated by prostaglandins, whereas prostaglandins do play a role in endotoxin's effects on blood pressure, plasma volume, temperature, and plasma glucose.
Minimizing false-positive errors in hormonal pulse detection
Authors: Veldhuis J. D. , Rogol A. D. , Johnson M. L.
Published: December 2017

To explore the problem of type I (false-positive) statistical errors associated with enumerating endocrine pulses, we used the analysis of immunoactive luteinizing hormone (LH) pulses as a paradigm. In this system, the distribution of measurement error was found to approximate a Gaussian pattern. Moreover, the choice of a fixed threshold criterion to identify a hormone pulse (as generally undertaken to date) was shown to yield significantly different false-positive error rates under different experimental conditions. Therefore, we developed a technique to minimize the detection of false-positive signals and to maintain an essentially uniform error rate among different experimental groups. This simple technique requires that the pulse-detection threshold be adjusted in relation to the degree of intra-assay measurement error present. Our method should facilitate the valid comparison of endocrine pulse frequencies in normal physiological states vs. those associated with hormonal deficiency when measurement error is typically greater. In addition, this approach will aid in a more meaningful assessment of pulse concordance between two or more different hormonal species (i.e., in different assays) and will assist in comparisons of pulse properties quantitated in different laboratories. In summary, rates of false-positive pulse detection using conventional fixed-threshold criteria are materially influenced by even small differences in within-assay variance. We present a technique to minimize this type I statistical error and to maintain an essentially uniform error rate among different experimental groups.
Food restriction increases torpor and improves brown adipose tissue thermogenesis in ob/ob mice
Authors: Himms-Hagen J.
Published: December 2017

Restricting the food intake of the genetically obese (ob/ob) mouse is known to ameliorate its cold intolerance. Cold intolerance of the ob/ob mouse is associated with defective thermogenesis in its brown adipose tissue. The objective of the experiments was to find out whether food restriction could increase the thermogenic function of brown adipose tissue of the ob/ob mouse. Obese and lean mice were fed a restricted amount of chow in one meal per day for 3-7 mo. Both lean and ob/ob mice were torpid (rectal temperature of approximately 32 degrees C) in the early morning and aroused spontaneously to a normal body temperature before the anticipated meal time. Obese mice were also torpid during the dark phase, whereas lean mice were active and had a normal body temperature at this time. Brown adipose tissue was in a thermogenically inactive state (low level of mitochondrial GDP binding) in torpid lean and ob/ob mice but became thermogenically active (increase in mitochondrial GDP binding) during stimulated arousal when body temperature increased by 6-7 degrees C in 15-30 min. Ad libitum-fed ob/ob mice had a normal diurnal rhythm in a rectal temperature that was at a lower level than in lean ad libitum-fed mice. They did not raise their rectal temperatures when stimulated and no activation of brown adipose tissue thermogenesis occurred under these conditions. Food restriction increased the capacity of both lean and ob/ob mice to raise their metabolic rate in response to injection of noradrenaline, indicating an increased capacity for thermogenesis in their brown adipose tissue.(ABSTRACT TRUNCATED AT 250 WORDS)
Specific interaction of fatty acyl-CoA esters with brown adipose tissue mitochondria
Authors: Strieleman P. J. , Shrago E.
Published: December 2017

The ability of low concentrations of long-chain fatty acyl coenzyme A (CoA) esters to act as inhibitors of purine nucleotide action in hamster brown adipose tissue mitochondria was observed to result from a specific interaction. Palmitoyl-CoA was found to be a competitive inhibitor of nucleotide binding with an apparent Ki of 2.46 +/- 1.09 microM for GDP and 2.98 +/- 0.538 microM for ATP and was able to counteract GDP-inhibited mitochondrial swelling. A minimum acyl-CoA carbon chain length of 12 was necessary for any significant inhibition of GDP binding or induction of swelling to be observed. The effect of palmitoyl-CoA on reversing GDP-inhibited chloride permeability of brown adipose tissue mitochondria was found to be the result of a specific interaction with the brown adipose tissue mitochondrial uncoupling protein. Mitochondria pretreated with N,N'-dicyclohexylcarbodiimide, which binds covalently to the uncoupling protein and partially inhibits brown adipose tissue mitochondrial swelling, underwent a nonspecific increase in swelling in the presence of phenylmercuric acetate. However, with palmitoyl-CoA no further increase in permeability could be mediated. In addition, under certain experimental conditions, palmitoyl-CoA was found to partially inhibit the high halide permeability of brown adipose tissue mitochondria but to a lesser extent than that observed with GDP, suggesting it may be acting as a partial agonist.
Corticotropin-releasing factor inhibits insulin release from perfused rat pancreas
Authors: Moltz J. H. , Fawcett C. P.
Published: December 2017

The ability of synthetic corticotropin-releasing factor (CRF) (rat) to influence hormone release from the endocrine pancreas of rats has been evaluated by means of perfusion in situ. Release of insulin and glucagon into the perfusate was measured in the presence and absence of CRF (0.1, 1, and 10 ng/ml) under conditions of normal and high glucose concentration (5.5 and 11 mM). Under both conditions, CRF (0.1, 1, and 10 ng/ml) induced a rapid, dose-dependent inhibition of insulin release followed by a remarkable postinhibitory rebound when exposure to CRF was discontinued. CRF had no significant effect on glucagon release when tested under these conditions. These results are reminiscent of noradrenergic inhibition of insulin release and together with evidence for the presence of CRF in the pancreas suggest that this peptide could function as a neuromodulatory transducer in addition to its role as a hypophysiotropic hormone perhaps contributing to the coordination of the overall endocrine response to stress.
Energy dependence of lung phosphatidylcholine biosynthesis studied with CO hypoxia
Authors: Fisher A. B. , Dodia C. , Chander A.
Published: December 2017

The energy dependence of lung phosphatidylcholine (PC) biosynthesis was evaluated by measuring incorporation of radiolabeled precursor substrates by the isolated perfused lung during carbon monoxide (CO)-induced hypoxia. Ventilation with gases containing 75 or 90% CO (plus 5% O2 and 5% CO2) resulted in a mean decrease of lung ATP content by 29 and 53%, respectively, and a significant decrease of [U-14C]glucose incorporation into free fatty acids and the fatty acyl moiety of lung PC. [9,10-3H]palmitate incorporation into lung PC was also decreased by hypoxia but [methyl-14C] choline incorporation was unaffected. For disaturated PC, incorporation of all three substrates was significantly depressed during CO ventilation. These results indicate that lung synthesis of PC is inhibited by alterations of lung energy state. The reactions in lung PC metabolism that are inhibited by this degree of energy limitation are the de novo synthesis of fatty acids from glucose, the acylation of exogenous palmitate, and the remodeling of PC into disaturated PC by the deacylation-reacylation pathway.
Hypertension during chronic peripheral and central infusion of angiotensin III
Authors: Fink G. D. , Bruner C. A.
Published: December 2017

Recent studies have suggested that the angiotensin II (ANG II) metabolite [Des-Asp]ANG II (ANG III) may be nearly equipotent with the parent compound in causing several acute neural responses known to be stimulated by angiotensin peptides (i.e., drinking, augmentation of sympathetic neurotransmission, and centrally mediated pressor responses). Because neural actions of ANG II are thought to contribute importantly to the ability of this hormone to cause chronic hypertension, the purpose of the present experiments was to explore the cardiovascular effects of chronic administration of ANG III either into the bloodstream or directly into the brain via the cerebral ventricles. The neurogenic component of the pressor response to acute infusion of ANG III also was reinvestigated. In anesthetized pithed rats (n = 6) ANG III had only 10% of the pressor potency of ANG II when given by acute (5-10 min) intravenous infusion. In conscious rats (n = 5) ANG III had 25% of the pressor potency of ANG II when tested using acute intravenous administration. The acute intravenous pressor potency ratio in conscious versus pithed rats was 4.8 for ANG III and 1.1 for ANG II, suggesting that, compared with ANG II, the pressor response to ANG III shows a greater dependence on neurogenic mechanisms at the doses tested. Chronic (5-day) intravenous infusion of ANG III (at 10, 20, and 100 ng/min) caused sustained hypertension without changes in fluid/electrolyte balance, but only at a dose (100 ng/min) estimated to produce blood levels of ANG III well beyond the "physiological" range.(ABSTRACT TRUNCATED AT 250 WORDS)
Diurnal-stimulated and stress-induced ACTH release in rats is mediated by ventral noradrenergic bundle
Authors: Szafarczyk A. , Alonso G. , Ixart G. , Malaval F. , Assenmacher I.
Published: December 2017

Female rats were bilaterally injected with 3 micrograms of 6-hydroxydopamine (6-OHDA) dissolved in 0.2 microliter saline, via a glass micropipet stereotaxically implanted into the ventral noradrenergic-ascending bundle (VNAB). This bundle conveys most of the catecholaminergic innervation to the paraventricular nuclei and originates from the locus coeruleus and from two medullary groups of neurons (A1 and A2). Two weeks after injection, and 1 wk after the subsequent implantation of an arterial cannula, serial blood samples were taken from each rat over a 36-h period for assay of basal secretion patterns of ACTH and corticosterone (C) by radioimmunoassay and radiocompetition, respectively. Other blood samples were collected at short intervals over a 2-h period to explore the stress-ether responses of both hormones. Effects of 6-OHDA injections on catecholaminergic innervation were attested by the striking decrease in the histofluorescence of hypothalamic catecholamines and by the 86% drop in the hypothalamic noradrenaline concentrations measured by high-performance liquid chromatography at constant dopamine titers. Compared with control, sham-lesioned rats, pharmacological destruction of the VNAB by 6-OHDA led to 1) obliteration of the circadian patterns for ACTH and C and the emergence in their place of ultradian fluctuations of reduced amplitude above base-line levels and 2) 80% inhibition of the ACTH stress response which correlated with a short-lived, depressed C response. These results are discussed within the framework of the controversial literature on the mechanisms by which catecholamines may control corticotropic function.
Hydration of fat-free body in protein-depleted patients
Authors: Beddoe A. H. , Streat S. J. , Hill G. L.
Published: December 2017

It is widely believed that increased hydration of the fat-free body accompanies most major disease processes as a result of contraction of the body cell mass and expansion of the extracellular fluid. Measurements of total body water (TBW) and total body nitrogen in 68 normal volunteers and 95 surgical ward patients presenting for intravenous nutrition have been used to derive ratios of TBW to fat-free mass (TBW:FFM) and protein indices (PI), where PI is defined as the ratio of measured total body protein to predicted TBP. Mean values of PI were 1.009 +/- 0.116 (SD) and 0.783 +/- 0.152 in the normal and patient groups, respectively, corresponding to mean TBW:FFM ratios of 0.719 +/- 0.016 and 0.741 +/- 0.029. However, 48 patients had normal TBW:FFM despite having lost 15% of body protein. A theoretical model of body composition changes in catabolic illness is presented, which is in accord with the patient data, demonstrating that TBW:FFM does not necessarily increase in catabolic illness and that the ratio masks underlying shifts in body fluid compartments.
Binding, degradation, and biological activity of insulin in vascular smooth muscle cells
Authors: Kaiser N. , Tur-Sinai A. , Hasin M. , Cerasi E.
Published: December 2017

The interaction of insulin with the vascular smooth muscle was studied using cultures derived from the bovine aortic arch. The cultured cells exhibited specific binding of 125I-insulin that was reversible and dependent on pH. Both insulin and insulinlike growth factor (IGF) I competed for 125I-insulin binding; IGF I, however, was less effective than insulin by at least an order of magnitude. Insulin binding was accompanied by internalization and degradation of the hormone in a temperature- and time-dependent manner. Chloroquine and other lysosomotropic agents elevated the internalized insulin and reduced its degradation. Pre-exposure of cell cultures to insulin resulted in downregulation of cell surface receptors. Insulin stimulated alpha-aminoisobutyric acid transport in confluent smooth muscle cells. The maximal response was observed at 100 ng/ml insulin with a half-maximal effect at 10 ng/ml. Sparse, serum-starved smooth muscle cells responded to insulin with a dose-dependent increase in [3H]-thymidine incorporation into DNA. Although the effect was already apparent at 1 ng/ml insulin, it reached near maximal level only at 10,000 ng/ml. IGF I also stimulated DNA synthesis in smooth muscle cells; however, at low concentrations insulin was more efficient in this respect. Human growth hormone was inactive. The data indicate the presence of specific receptors for insulin in bovine aortic smooth muscle cells. These receptors appear to mediate the metabolic activity as well as part of the mitogenic effect of insulin in these cells.
Insulin binding and glucose transport in rat skeletal muscle sarcolemmal vesicles
Authors: Grimditch G. K. , Barnard R. J. , Kaplan S. A. , Sternlicht E.
Published: December 2017

A new method is described for isolation of sarcolemma (SL) from skeletal muscle of rats that produces vesicles of high purity and yield. There was a mean 59-fold purification (n = 22) of the SL marker enzyme K+-p-nitrophenylphosphatase. Specific activities of marker enzymes for sarcoplasmic reticulum and mitochondria were low, indicating minimal contamination. Despite the high purity and low contamination, a relatively high protein yield was achieved (0.43 +/- 0.03 mg/g wet wt, n = 25). Electron microscopy showed that the membranes were primarily vesicles. Specific 125I-insulin binding association constants derived from the high- and low-affinity portion of the Scatchard plots were 0.764 +/- 0.154 and 0.0096 +/- 0.0012 X 10(9) M-1, whereas the apparent number of receptors were 15.0 +/- 4.1 and 925 +/- 80 X 10(9) per mg of SL protein. Equilibrium exchange glucose transport studies at 37 degrees C indicated that the SL vesicles exhibited specific D-glucose transport which was responsive to in vivo insulin stimulation. We conclude that this isolation procedure, especially in light of the high purity and yield, provides a good and practical experimental model for studying insulin binding and glucose transport in skeletal muscle.
Use of residence time moments in compartmental analysis
Authors: Matis J. H. , Wehrly T. E. , Gerald K. B.
Published: December 2017

Residence time moments, particularly mean residence times, can be very useful in the modeling and kinetic analysis of physiological systems. They are defined and illustrated, and their practical utility is then explored by comparing the model formulation based on these moments with three alternative formulations: component half-lives, compartmental model rate coefficients, and multiexponential model coefficients and exponents. The residence time moment formulation is shown to have several advantages: a smaller number of parameters are usually needed to describe a biological system; they have a clear physical interpretation; their statistical "power" to detect certain treatment differences is greater; and they are computationally simpler in many situations.
A 24-m3 direct heat-sink calorimeter with on-line data acquisition, processing, and control
Authors: Jacobsen S. , Johansen O. , Garby L.
Published: December 2017

The construction and performance of a 24-m3 direct heat-sink calorimeter for continuous measurement of evaporative and sensible heat loss in human subjects are described. Extensive use of real-time processing for compensation of physical time constants and delays made it possible to solve response-time and stability problems associated with the large volume. The performance characteristics of the calorimeter are 1) a linear response between 0 and 320 W (471 g . h-1) for evaporative heat with a precision of 4.0-0.6% in the range 25-100 W, 2) a linear response between 0 and 280 W for sensible heat with a precision of 1.4-0.2% in the range 50-200 W, 3) a stability corresponding to a drift of less than 0.6 W (24 and 72 h) on both evaporative and sensible heat outputs and 24- and 72-h standard deviations (values every 2 min) of 0.3 and 0.4 W for evaporative heat and 0.6 and 0.7 W for sensible heat, 4) response times (95%) of 15 min for both evaporative and sensible heat, 5) independency on the position of the calibration source within the chamber, 6) no measurable "cross talk" between evaporative and sensible heat inputs, 7) negligible dependency of the external air humidity between 14 and 70%, and 8) operating temperature range from 18 to 30 degrees C. More than 40 experiments of 25-h duration with human subjects have been carried out. In no case was any discomfort recorded. An example of the 25-h continuous evaporative and sensible heat output tracing of one experiment is given.