bluuebunny/crossref_metadata_2025 huggingface dataset:
Splanchnic and renal contribution to disposal of infused epinephrine in humans
Authors: Sacca L. , Hendler R. , Picardi A. , Sherwin R. S.
Published: December 2017

To evaluate the role of splanchnic and renal tissues in epinephrine disposal, we infused epinephrine (60 ng X kg-1 X min-1) into nine human volunteers during hepatic (n = 6) and/or renal (n = 4) vein catheterization. During the infusion plasma epinephrine rose higher in the artery (1,345 +/- 126 pg/ml) than in the hepatic (218 +/- 42 pg/ml) or renal vein (528 +/- 95 pg/ml). Splanchnic plasma flow increased by 43% (P less than 0.001), whereas renal plasma flow was unchanged. Net epinephrine uptake increased to a greater extent (3-fold) in the splanchnic area as compared with the kidney, amounting to 32 +/- 3% and 10 +/- 2% of the infused epinephrine load, respectively. The splanchnic epinephrine clearance also increased by 50-60%, while fractional extraction remained stable at 80-85%. Renal epinephrine clearance and extraction was not significantly altered, however. Epinephrine infusion caused splanchnic norepinephrine uptake to increase as well, partially because of the increased plasma flow. In contrast, the kidney showed net norepinephrine production throughout. We conclude that the splanchnic area plays a much more important role than the kidney in the disposal of circulating epinephrine. The great efficiency of splanchnic epinephrine removal is further enhanced by epinephrine-induced hemodynamic changes that also promote the splanchnic uptake of norepinephrine.
Stimulation by thyroid hormone of renin mRNA in mouse submandibular gland
Authors: Karen P. , Morris B. J.
Published: December 2017

Renin in the female mouse submandibular gland (SMG) is known to increase in response to thyroid hormone. In the present study a 500 base-pair renin cDNA was used to quantify renin mRNA, the product of transcription of the Ren-2 gene, in the female mouse SMG in response to thyroid hormone to assess more directly the nature of stimulation of renin biosynthesis. After daily injection for 1 wk renin mRNA increased from control values of 36 +/- 3 SE ng/g tissue to 212 +/- 41 with triiodothyronine (T3; P less than 0.005) and to 217 +/- 33 with thyroxine (T4; P less than 0.005). Treatment of mice with propylthiouracil (PTU) decreased renin mRNA to 1.2 +/- 0.3 (P less than 0.005) and after subsequent injection of T3 for 1 wk renin mRNA increased to 289 +/- 35 ng/g tissue. The time course of the response to a single injection of thyroid hormone indicated a rapid response with significant increases in renin mRNA by 1 h, reaching values 3.5 +/- 0.4 times control (P less than 0.005) by 5 h. Such rapid effects are consistent with a direct nuclear action of thyroid hormone in stimulating transcription of the Ren-2 gene in mouse submandibular gland or in stabilization of nuclear precursor renin mRNA or both.
Placental lactogen and GH receptors in sheep liver: striking differences in ontogeny and function
Authors: Freemark M. , Comer M. , Handwerger S.
Published: December 2017

To determine whether changes in the relative biological potencies of ovine placental lactogen (oPL) and ovine growth hormone (oGH) during development derive from ontogenetic changes in the binding of these hormones to hepatic receptors, we have compared the binding of 125I-oPL and 125I-oGH to hepatic membranes from fetal lambs and pregnant sheep at mid- and late gestation and from postnatal sheep at 1 day to 7 mo of age. Specific high-affinity 125I-oPL binding sites in ovine fetal liver were detected as early as day 70 of gestation (term = 145 days), and the number of fetal 125I-oPL binding sites increased progressively throughout the latter half of gestation, reaching a maximum (11.2 fmol/mg protein) at 3-7 days before parturition. The potency of oPL (Kd 0.27 nM) in competing for 125I-oPL binding sites was 90 and 1,300 times greater than that of oGH and ovine prolactin, respectively. Although the number of fetal 125I-oPL binding sites increased throughout pregnancy, there was little or no specific binding of 125I-oGH noted in the fetus. Treatment of fetal liver membranes with 4 M MgCl2 did not enhance the subsequent specific binding of 125I-oGH, suggesting that the low specific binding of oGH did not result from occupation of hepatic receptors by endogenous circulating oPL or oGH. In contrast, MgCL2 treatment markedly increased the apparent number of fetal 125I-oPL binding sites, suggesting that oPL receptors in fetal liver are partly saturated in vivo by oPL.(ABSTRACT TRUNCATED AT 250 WORDS)
Mechanism of central hyperglycemic effect of cholinergic agonists in fasted rats
Authors: Iguchi A. , Gotoh M. , Matsunaga H. , Yatomi A. , Honmura A. , Yanase M. , Sakamoto N.
Published: December 2017

The influence of cholinergic agonists on central nervous system (CNS) regulation of blood sugar homeostasis was studied in fasted rats. When carbachol, muscarine, bethanechol, methacholine, or neostigmine was injected into the third cerebral ventricle, it caused a dose-dependent increase in the hepatic venous plasma glucose concentration. However, in the case of 1,1-dimethylphenyl-4-piperazinium iodide (DMPP) or nicotine, the level of hepatic venous glucose did not differ from that of the saline-treated control rats. The increase in glucose level caused by neostigmine was dose-dependently suppressed by coadministration of atropine. These facts suggest that cholinergic activation of muscarinic receptors in the CNS plays a role in increasing hepatic glucose output. Injection of neostigmine (5 X 10(-8) mol), an inhibitor of cholinesterase, into the ventricle resulted in the increase of not only glucose, but also glucagon, epinephrine, and norepinephrine in the hepatic venous plasma. However, constant infusion of somatostatin through a femoral vein completely prevented the increase of glucagon after administration of neostigmine, although the increase of hepatic venous glucose and epinephrine levels were still observed. Neostigmine-induced increments in glucose did not occur in adrenalectomized rats. This suggests that the secreted epinephrine acts directly on the liver to increase hepatic glucose output.
Lipoprotein lipase-suppressing mediator in serum of endotoxin-treated rats
Authors: Bagby G. J. , Corll C. B. , Thompson J. J. , Wilson L. A.
Published: December 2017

The conditions under which lipoprotein lipase-suppressing mediator is present in serum of endotoxin-treated rats was determined in this study. The suppression of lipoprotein lipase activity in 3T3-L1 cells was used as a bioassay for mediator in serum. Endotoxin (0.1-10 micrograms/ml) and serum from control rats did not suppress lipoprotein lipase activity. Maximum suppression of cell lipoprotein lipase activity (70%) by serum from endotoxic rats required a cell exposure time of 5 h. At the highest dose of endotoxin used (1 mg/100 g), significant suppression was achieved when cells were incubated with 0.5% serum from endotoxic rats (P less than 0.05). Serum obtained 2-3 h after endotoxin injection possessed the maximal ability to suppress lipase activity, but suppressing activity was not present in serum collected 8 h after endotoxin. Rats rendered tolerant to endotoxin by 5 daily injections (0.1 mg/100 g) did not contain detectable levels of mediator in serum after endotoxin injection. The results demonstrate that the presence of lipoprotein lipase activity-suppressing mediator is transitory after in vivo exposure of naive rats to endotoxin, but does not appear in serum of endotoxin tolerant rats.
Autophosphorylation and kinase activity of insulin receptor in diabetic rats
Authors: Okamoto M. , White M. F. , Maron R. , Kahn C. R.
Published: December 2017

Insulin resistance is observed in insulin-deficient diabetic states in spite of an increase in insulin binding to its target cells. To characterize this type of insulin resistance, autophosphorylation and kinase activity of the insulin receptor on liver was studied with streptozotocin (STZ)-induced and BB diabetic rats. Insulin binding capacity was increased in proportion to the severity of the diabetic state in the STZ rat. In the diabetic BB rat, the insulin binding capacity was also increased, and this was partially normalized by insulin treatment. By contrast, insulin-stimulated autophosphorylation of the beta-subunit of the insulin receptor was decreased in proportion to the severity of the diabetic state in the STZ rat. Peptide mapping by reverse-phase high-performance liquid chromatography revealed a decrease in labeling at all sites of autophosphorylation. Kinase activity of the insulin receptor to exogenous substrates was also decreased in proportion to the diabetic state. In the BB rat, autophosphorylation and kinase activity of the insulin receptor were both decreased in the diabetic state and partially normalized by insulin treatment. In addition to the beta-subunit of insulin receptor, a 170 kdalton phosphotyrosine-containing protein was also identified in the glycoprotein fraction of liver. Although the phosphorylation of this protein was not insulin dependent, it was decreased markedly in the diabetic state. This protein is immunologically distinct from the insulin receptor, but is rich in phosphotyrosine. Based on its size and phosphotyrosine content, this protein may be the epidermal growth factor receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
Coordinate regulation of zinc metabolism and metallothionein gene expression in rats
Authors: Cousins R. J. , Dunn M. A. , Leinart A. S. , Yedinak K. C. , DiSilvestro R. A.
Published: December 2017

Regulation of zinc metabolism by dibutyryl cAMP, glucagon, and epinephrine was examined in rats fed adequate amounts of zinc. Dibutyryl cAMP, epinephrine, and glucagon each produced an increase in liver metallothionein levels by 10 h after they were first administered. The increase in liver metallothionein was inversely related to the serum zinc concentration. Treatment with dexamethasone, a glucocorticoid, accentuated these effects to some extent. Both metallothionein I and II were induced by dibutyryl cAMP and glucagon. Levels of metallothionein mRNA in total liver RNA extracts were measured by dot blot hybridization using a synthetic 21-base oligonucleotide complimentary to the 5' region of both the metallothionein I and II genes. Individual administration of dibutyryl cAMP, glucagon, and epinephrine increased the number of metallothionein mRNA molecules per cell by up to fourfold. The data suggest that glucagon and epinephrine are primary regulators of metallothionein gene expression acting at least in part via cAMP. In adrenalectomized rats, glucagon, dibutyryl cAMP, and epinephrine had a less potent effect in terms of metallothionein induction and depression of serum zinc concentrations. These effects were largely restored when dexamethasone was also given. Collectively these data suggest that changes in zinc metabolism associated with acute stress involve coordinate regulation mediated by many factors, including glucocorticoids and cAMP.
Glutamine metabolism in rat skeletal muscle wounded with lambda-carrageenan
Authors: Albina J. E. , Henry W. , King P. A. , Shearer J. , Mastrofrancesco B. , Goldstein L. , Caldwell M. D.
Published: December 2017

Wounding with lambda-carrageenan results in a marked decrease in the intracellular-free glutamine content of rat skeletal muscle. The potential mechanisms for this finding, including alterations in glutamine release, glutamine utilization, and glutamine synthesis, were investigated in rats under pentobarbital anesthesia. Wounding did not increase glutamine release from muscle during incubation or isolated hindlimb perfusion. Wounded muscle utilized more glutamine than nonwounded muscle, as measured both by the production of [14C]O2 and of -glutamate from labeled glutamine. Maximal glutamine synthetase activity was increased by wounding. The increase in glutamine synthetase activity in wounded muscle was prevented by adrenalectomy and restored by replacement doses of corticosterone in wounded adrenalectomized animals. The decrease in muscle free glutamine induced by wounding is therefore not mediated by an increase in the release of this amino acid, nor by a reduction in the tissue capacity for glutamine synthesis, but by an increase in glutamine utilization at the site of injury. This difference is apparently determined by the utilization of glutamine by the cellular components of the inflammatory infiltrate, which were shown to be capable of active glutaminolysis.
Plasma protein-mediated transport of steroid and thyroid hormones
Authors: Pardridge W. M.
Published: December 2017

The free hormone or free drug hypotheses have traditionally assumed that the concentration of cellular exchangeable hormone (i.e., the pool that drives cellular hormone or drug receptor occupancy) can be reliably estimated by in vitro measurements of unbound hormone concentrations. The corollary of this view is that the large reservoir of bound hormone in blood is passively transported by plasma proteins and is physiologically inactive. However, when these assumptions are subjected to direct empiric testing with either in vivo or perfused organ techniques, it is found that the large pool of bound hormone in blood is operationally available for transport across microcirculatory barriers without the plasma protein, per se, significantly exiting the plasma compartment. This process is believed to involve a mechanism of enhanced dissociation of hormone or drug from the plasma protein caused by transient conformational changes about the ligand binding site within the microcirculation: The biochemical mechanism of the interaction of the plasma protein with the surface of the microcirculation may involve receptor, charged selectivity, or local inhibitor mechanisms.
Pregnancy-induced insulin resistance in liver and skeletal muscles of the conscious rabbit
Authors: Hauguel S. , Gilbert M. , Girard J.
Published: December 2017

Insulin sensitivity of maternal nonuterine tissues (liver and skeletal muscles) has been investigated in the conscious rabbit during late gestation (24 and 30 days). The specific effect of insulin on glucose production and utilization was evaluated with the hyperinsulinemic euglycemic clamp technique. The net balance of glucose across the hindlimb muscles was studied by means of the Fick principle in basal and insulin stimulated conditions (clamp study). Our results show that an insulin-resistant state develops between days 24 and 30 of gestation in the rabbit and involves both glucose producing (liver) and utilizing (muscles) tissues. On day 30 of gestation, muscle glucose uptake was not significantly stimulated at a plasma insulin concentration of 700 microU/ml, whereas it was stimulated by 30-40% in nonpregnant and 24 day pregnant rabbits. At similar plasma insulin concentration, endogenous glucose production was suppressed by 85% in both nonpregnant and 24 day pregnant rabbits, whereas it was decreased by only 30% in 30 day pregnant rabbits. The present data suggest that hindlimb muscles of late pregnant rabbits are able to reduce their insulin-induced glucose utilization. This could contribute to meet the glucose requirements of pregnant uterus in late gestation.
First-pass hepatic extraction and metabolic effects of insulin and insulin analogues
Authors: Chap Z. , Ishida T. , Chou J. , Hartley C. J. , Entman M. L. , Brandenburg D. , Jones R. H. , Field J. B.
Published: December 2017

First-pass hepatic extraction of insulin and hepatic and peripheral contributions to hypoglycemia were compared in conscious dogs during portal infusion of insulin A1, B29 diacetyl insulin, or A1-B29 dodecoyl insulin at 7 and 14 pmol X kg-1 X min-1. The liver removed 43 +/- 2% of insulin, 12 +/- 1% of dodecoyl, and 8 +/- 1% of diacetyl insulin, in a single transhepatic circulation. The hypoglycemia induced by insulin and diacetyl insulin and the ensuing glucagon response were greater than that produced by the dodecoyl analogue. Diacetyl insulin primarily increased glucose utilization, dodecoyl insulin solely inhibited hepatic production, and insulin affected both. The lack of hepatic effect of diacetyl insulin during hypoglycemia can be ascribed to greater counterregulation, because under euglycemic clamp conditions, this analogue caused suppression of glucose production. The different patterns of hypoglycemia exhibited can be explained by the combined effects of altered distribution between the liver and peripheral tissues caused by differences in hepatic extraction, the effect of this phenomenon on the counterregulatory response, and the intrinsic biological potency of the analogues.
Insulin receptor kinase is hyperresponsive in adipocytes of young obese Zucker rats
Authors: Debant A. , Guerre-Millo M. , Le Marchand-Brustel Y. , Freychet P. , Lavau M. , Van Obberghen E.
Published: December 2017

Thirty-day-old obese Zucker rats have hyperresponsive adipose tissue, whereas their skeletal muscle normally responds to insulin in vitro. To further substantiate the role of insulin receptor tyrosine kinase in insulin action, we have studied the kinase activity of receptors obtained from adipocytes and skeletal muscle of these young obese Zucker rats. Insulin receptors, partially purified by wheat germ agglutinin agarose chromatography from plasma membranes of isolated adipocytes or from skeletal muscles, were studied in a cell-free system for auto-phosphorylation and for their ability to phosphorylate a synthetic glutamate-tyrosine copolymer. For an identical amount of receptors, the insulin stimulatory action on its beta-subunit receptor phosphorylation was markedly augmented in preparations from hyperresponsive adipocytes of obese animals compared with lean rats. Basal phosphorylation of adipocyte insulin receptors was nearly identical in lean and obese animals. Similarly the capacity of adipocyte insulin receptors to catalyze the phosphorylation of the synthetic substrate in response to insulin was increased. By contrast, the kinase activity of insulin receptors prepared from normally insulin-responsive skeletal muscle was similar in preparations of lean and obese rats. These results show that a state of hyperresponsiveness to insulin is correlated with a parallel increase of insulin receptor kinase activity suggesting an important role for this activity in insulin action.
Membrane currents of identified isolated rat corticotropes and gonadotropes
Authors: Marchetti C. , Childs G. V. , Brown A. M.
Published: December 2017

Membrane currents of identified, isolated corticotropes and gonadotropes from mammalian anterior pituitary gland have been evaluated. Pituitary gonadotropes and corticotropes were isolated enzymatically and stained in the living state using biotinylated gonadotropin-releasing hormone (Bio-GnRH) or biotinylated corticotropin-releasing hormone (Bio-CRF) followed by avidin fluorescein. Electrophysiological recordings were made with patch-clamp electrodes in the whole-cell clamp configuration. Tetrodotoxin (TTX)-sensitive sodium currents were larger in corticotropes than in gonadotropes. Corticotropes showed two components of calcium currents, a transient low-threshold component and a longer lasting high-threshold component. Small TTX-resistant inward currents were present also in gonadotropes, and both cell types had transient and steady potassium currents.
Effect of anesthesia on glucose production and utilization in rats
Authors: Penicaud L. , Ferre P. , Kande J. , Leturque A. , Issad T. , Girard J.
Published: December 2017

This study was undertaken to determine the effects of pentobarbital anesthesia (50 mg/kg ip) on glucose kinetics and individual tissue glucose utilization in vivo, in chronically catheterized rats. Glucose turnover studies were carried out using [3-3H]glucose as tracer. A transient hyperglycemia and an increased glucose production were observed 3 min after induction of anesthesia. However, 40 min after induction of anesthesia, glycemia returned to the level observed in awake animals, whereas glucose turnover was decreased by 30% as compared with unanesthetized rats. These results are discussed with regard to the variations observed in plasma insulin, glucagon, and catecholamine levels. Glucose utilization by individual tissues was studied by the 2-[1-3H]deoxyglucose technique. A four- to fivefold decrease in glucose utilization was observed in postural muscles (soleus and adductor longus), while in other nonpostural muscles (epitrochlearis, tibialis anterior, extensor digitorum longus, and diaphragm) and other tissues (white and brown adipose tissues) anesthesia did not modify the rate of glucose utilization. A decrease in glucose utilization was also observed in the brain.
Asperlicin antagonizes stimulatory effects of cholecystokinin on isolated islets
Authors: Zawalich W. S. , Diaz V. A.
Published: December 2017

Asperlicin, a product derived from the fungus Aspergillus alliaceus, antagonized the multiple stimulatory effects of cholecystokinin (CCK-8S) on isolated islets. At a level of 10 microM, asperlicin completely inhibited insulin release in response to 25 nM CCK-8S. Increasing the level of CCK-8S to 100 nM partially restored a secretory response, while an even greater insulin stimulatory effect was noted with 500 nM CCK-8S. The inhibitory effect of asperlicin on CCK-8S-induced release was reversible. Asperlicin exposure had no effect on glucose or glyceraldehyde-induced secretion. Asperlicin reduced, in parallel with secretion, the increase in 3H efflux from [3H]inositol prelabeled islets usually noted with CCK-8S addition. Asperlicin did not influence the small glucose-stimulated increase in 3H efflux. The results support the notion that asperlicin is a specific and potent antagonist of the multiple stimulatory effects of CCK-8S on islet tissue.
Role of luteinizing hormone in luteotropic complex of pregnant hamster
Authors: Tamura H. , Greenwald G. S.
Published: December 2017

Hamsters were hypophysectomized on day 4 of pregnancy (day 1 = sperm in vaginal smear) and injected subcutaneously on days 4-7 with various combinations of 200 micrograms prolactin (Prl), 10 micrograms follicle-stimulating hormone (FSH), and 20 micrograms luteinizing hormone (LH) in polyvinylpyrrolidone (PVP) to decrease its rate of absorption or in saline. End points for luteal function on day 8 were maintenance of pregnancy, serum progesterone (P4), luteal weight, and luteal binding for human chorionic gonadotropin, FSH, and Prl. After hypophysectomy, a drastic decline occurred in all parameters including an 89% decrease in luteal weight. Injection of Prl did not maintain pregnancy nor serum P4 but partially maintained luteal weight and human chorionic gonadotropin binding sites per corpus luteum. The minimal luteotropic complex of Prl and FSH was effective in maintaining pregnancy and significantly increased serum P4 and Prl and FSH receptors but not to control levels; Prl and LH (PVP) was also effective to the same extent. Antral follicles were lacking after either treatment. The effects of FSH cannot be attributed to LH contamination. All variables were restored to control levels by Prl plus FSH plus LH (PVP) and antral follicles were present; Prl plus FSH plus LH (saline), however, induced luteolysis and reduced most values to the levels found in untreated, hypophysectomized animals. Thus, the luteotropic activity of LH was only demonstrable when it was injected in a long-acting form; when delivered as a bolus, LH (saline) was luteolytic.
Ontogeny of thyroid hormone effect on tissue 5'-monodeiodinase activity in fetal sheep
Authors: Polk D. H. , Wu S. Y. , Wright C. , Reviczky A. L. , Fisher D. A.
Published: December 2017

Most of the thyroxine (T4) in fetal mammals is deiodinated to the inactive metabolite, reverse triiodothyronine (rT3), via an iodothyronine 5-monodeiodinase in fetal tissues. Maturation of the tissue 5'-monodeiodinase (MDI) enzymes required for conversion of T4 to active triiodothyronine (T3) in the rat, an altricial species, occurs in the postnatal period. To characterize fetal maturation of the enzymes for active T3 production in a precocial species, 5'-MDI activities were measured in liver, kidney, and brain tissue homogenates of ovine fetuses 13 days after total thyroidectomy (Tx) conducted at gestational ages of 99-107 or 129-132 days. Sham-operated twin fetuses served as controls. Hepatic type I 5'-MDI activity was not significantly lowered by Tx in group I but was significantly lower after Tx in group II fetuses. Renal type I 5'-MDI was not affected by Tx in either group. Type II 5'-MDI activity in cerebral cortex was significantly elevated after Tx in both groups I and II fetuses. Tissue sulfhydryl contents were similar in liver, kidney, and cerebral cortex from control and Tx fetuses in group I. These data indicate that hypothyroidism induced early in the third trimester is associated with increased brain type II 5'-MDI activity without significant change in liver or kidney type I 5'-MDI. Late third trimester hypothyroidism is associated with decreased type I 5'-MDI activity in liver homogenates as well as increased type II 5'-MDI activity in brain tissue.(ABSTRACT TRUNCATED AT 250 WORDS)
Importance of intrahepatic mechanisms to gluconeogenesis from alanine during exercise and recovery
Authors: Wasserman D. H. , Williams P. E. , Lacy D. B. , Green D. R. , Cherrington A. D.
Published: December 2017

These studies were performed to assess the importance of intrahepatic mechanisms to gluconeogenesis in the dog during 150 min of treadmill exercise and 90 min of recovery. Sampling catheters were implanted in an artery and portal and hepatic veins 16 days before experimentation. Infusions of [U-14C]alanine, [3-3H]glucose, and indocyanine green were used to assess gluconeogenesis. During exercise, a decline in arterial and portal vein plasma alanine and in hepatic blood flow led to a decrease in hepatic alanine delivery. During recovery, hepatic blood flow was restored to basal, causing an increase in hepatic alanine delivery beyond exercise rates but still below resting rates. Hepatic fractional alanine extraction increased from 0.26 +/- 0.02 at rest to 0.64 +/- 0.03 during exercise and remained elevated during recovery. Net hepatic alanine uptake was 2.5 +/- 0.2 mumol.kg-1.min-1 at rest and remained unchanged during exercise but was increased during recovery. The conversion rate of [14C]alanine to glucose had increased by 248 +/- 38% by 150 min of exercise and had increased further during recovery. The efficiency with which alanine was channeled into glucose in the liver was accelerated to a rate of 338 +/- 55% above basal by 150 min of exercise but declined slightly during recovery. In conclusion, 1) gluconeogenesis from alanine is accelerated during exercise, due to an increase in the hepatic fractional extraction of the amino acid and through intrahepatic mechanisms that more efficiently channel it into glucose.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of phosphoinositide metabolism in induction of memory in isolated perifused rat islets
Authors: Zawalich W. S. , Diaz V. A. , Zawalich K. C.
Published: December 2017

Prior exposure of isolated perifused rat islets to 20 mM glucose or 10 mM glyceraldehyde amplifies their subsequent insulin secretory response to 10 mM glucose. The involvement of phosphoinositide turnover in the induction of this "time-dependent potentiation" (TDP) was investigated. In islets in which inositol-containing phospholipids were prelabeled with myo-[2-3H]inositol, the addition of 20 mM glucose augments the efflux of 3H. This effect persists for approximately 50 min after the cessation of stimulation. Direct measurements of labeled inositol phosphate accumulation confirmed that this increase in 3H efflux is primarily the result of a persistent increase in phosphoinositide (PI) hydrolysis and not due to the slow efflux and/or degradation of performed [3H]inositol phosphates. The duration of the increase in 3H efflux parallels the duration of TDP. Mannoheptulose abolishes both the increase in 3H efflux evoked by 20 mM glucose and TDP. The omission of extracellular calcium plus 0.5 mM ethylene glycol-bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid also abolishes both of these effects of high glucose. D-Glyceraldehyde (10 mM) addition to 3H-inositol-prelabeled islets results in an acute efflux of 3H, a persistent efflux after removal of the D-glyceraldehyde from the perifusion medium, and the induction of TDP. Similar to the results obtained with high glucose, the return of 3H efflux rates to prestimulatory values is accompanied by the abolition of TDP. These results suggest that events associated with persistent stimulant-induced increases in phosphoinositide hydrolysis may participate in the induction and maintenance of TDP.
Contribution of the kidney to metabolic clearance of atrial natriuretic peptide
Authors: Woods R. L.
Published: December 2017

To quantify the role of the kidney in whole body metabolic clearance rate (MCR) from plasma of atrial natriuretic peptide (ANP), synthetic alpha-human ANP-(1-28) was infused at 200 ng/min to steady-state conditions in chronically instrumented one-kidney conscious dogs. Clearances were measured in dogs with a normally filtering kidney and they were also measured after the glomerular filtration rate (GFR) was reduced to close to zero by acutely inflating a cuff around the renal artery (RAC), which resulted in minimal urine production and renal blood flow reduction to 59% of the resting level. In normal dogs, MCR was 1,090 +/- 134 ml/min with renal clearance rate (RCR) contributing only 13.9%. After RAC, MCR fell to 864 +/- 151 ml/min, due in part to a fall in RCR (-41.5 +/- 12.9 ml/min), but mostly due to a fall in "rest of the body" (total renal) clearance of ANP. The reduced GFR accounted for virtually all the fall in RCR. Normal plasma ANP half-life was 59.6 +/- 7.9 s. In conclusion, MCR of ANP was very high, approaching the cardiac output, suggesting that most of ANP is cleared in one circulation through peripheral tissues. GFR contributed significantly to RCR (approximately 30%) but the contribution of the kidney to whole body MCR was small relative to rest of the body clearance of ANP.
Physiological attributes of endogenous bioactive luteinizing hormone secretory bursts in man
Authors: Veldhuis J. D. , Johnson M. L. , Dufau M. L.
Published: December 2017

The exact nature of glandular secretory events is difficult to discern in vivo, since underlying patterns of hormone release are confounded by metabolic clearance. Moreover, conventional immunoassay does not always agree with bioassay. Here, we have used the rat interstitial cell testosterone in vitro bioassay of luteinizing hormone (LH) to measure serial LH concentrations in the normal adult human male. The resultant bioactive LH time series were analyzed by a deconvolution model in which circulating hormone concentrations are controlled by the operation of four finite, nonzero, and determinable parameters: 1) the location(s); 2) the amplitude(s), and 3) the half-duration(s) of underlying secretory bursts, acted on by 4) endogenous exponential clearance kinetics. A macroscopic secretory burst was modeled in the algebraic form of a Gaussian distribution of instantaneous molecular secretory rates. The physiological implications of this model were examined by analyzing bioactive LH pulsatility in eight men sampled every 10 min for 6 h. Multiple-parameter deconvolution disclosed endogenous bioactive LH half-lives of 53 +/- 5.4 min (range 38-76 min), in agreement with earlier independent estimates of 65 +/- 4.9 (42-87) min in four LH-deficient men given a 35 micrograms iv bolus of human LH. Calculated endogenous production rates of bioactive LH (0.48 +/- 0.06 mIU.min-1.ml-1) were also in accord with values estimated previously from steady-state infusions of LH. Deconvolution further indicated that underlying bioactive LH secretory bursts had half-durations of only 12.2 +/- 1.5 min, occurred at intervals of 56 +/- 1.3 min, and achieved amplitudes of 2.1 +/- 0.26 mIU.min-1.ml-1.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of training and detraining on dose-response relationship between glucose and insulin secretion
Authors: Mikines K. J. , Sonne B. , Tronier B. , Galbo H.
Published: December 2017

We studied the effect of training and detraining on the dose-response relationship between plasma glucose and beta-cell secretion in seven trained young men using sequential hyperglycemic clamp technique (7, 11, and 20 mM). Experiments were performed in the habitual state 15 h after last training session (T) as well as after 5 days of detraining (DT). Results were compared to data from seven untrained subjects (UT). Glucose-stimulated insulin, proinsulin, and C-peptide levels were lower in T than in UT. They increased during detraining but not to levels seen in UT. Furthermore, in T and DT, but not in UT, increases in C-peptide and proinsulin leveled off with increasing glucose concentrations. Estimated by C-peptide-to-insulin ratios, clearance of endogenous insulin was not influenced by T. Glucose uptake in tissue was the same in T, DT, and UT during clamps, despite lower insulin levels in T and DT. Differences between groups in counterregulatory hormones, fat metabolites, alanine, or electrolytes did not account for these findings. Oxygen consumption was higher in the basal state in T and DT compared with UT but increased similarly in all groups in response to glucose. Conclusions: regular physical activity causes an adaptive decrease in glucose-mediated beta-cell secretion in humans. The training-induced decrease in glucose-stimulated insulin secretion is accurately matched to increased insulin action, keeping glucose disposal constant at any given plasma glucose concentration. Finally, training increases basal metabolic rate but does not influence glucose-induced thermogenesis or clearance of endogenous insulin.
Vasopressin is metabolized by a trypsinlike enzyme in guinea pig amniotic fluid
Authors: Uyehara C. F. , Sato A. K. , Claybaugh J. R.
Published: December 2017

We have demonstrated that arginine vasopressin (AVP) is degraded to desglycinamide AVP by a trypsinlike enzyme found in guinea pig amniotic fluid. Incubation of [3H]AVP with guinea pig amniotic fluid in vivo or in vitro produced a metabolite that comigrated on high-pressure liquid chromatography with desglycinamide AVP in three different buffer systems. Also, AVP antisera that cross-reacted with standard desglycinamide AVP could detect this amniotic fluid metabolite. Because the enzyme responsible for the cleavage of glycinamide from AVP was likely to be trypsin, experiments with aprotinin, a trypsin inhibitor, were conducted. Results demonstrated that the production of the amniotic fluid AVP metabolite could be completely blocked in the presence of the trypsin inhibitor. In addition, examination of amniotic fluid collected from fetuses in the second half of gestation (term = 68 days) showed that AVP could not be metabolized to desglycinamide AVP until after 52 days of gestation. In conclusion, AVP appears to be metabolized by a trypsinlike enzyme in amniotic fluid, and because trypsin is a general proteolytic enzyme, the amniotic compartment may also serve as a clearance site for other proteins.
Development in rats of the brain-pituitary-adrenal response to hypoglycemia in vivo and in vitro
Authors: Widmaier E. P.
Published: December 2017

To clarify the nature of the stress hyporesponsive period that occurs in neonatal rats, the development of the response of the brain-pituitary-adrenal axis to hypoglycemia stress in rats was assessed in vivo and in vitro. Hypothalami were removed from the brains of neonatal (9-35 days postnatal) or adult rats and incubated in vitro for sequential 30-min periods in Krebs buffer for determination of corticotropin-releasing factor (CRF) secretion under conditions of altered glucose concentrations. As expected from previous studies, CRF secretion from adult hypothalami was significantly increased in severely hypoglycemic conditions (0.55 mM glucose) by approximately 50% above base-line values (in 5.5 mM glucose). However, lowering glucose did not elicit an increase in CRF release from hypothalami of rats less than 35 days of age. Hypothalami obtained from rats less than or equal to 24 days old also failed to show consistent secretory responses to potassium depolarization. At 35 days postnatal the response to hypoglycemia was significant and similar to the adult response. To determine if the lack of hypothalamic response to hypoglycemia in vitro could be correlated with the in vivo responses to hypoglycemia, rats aged 4 days to adult were injected intraperitoneally with porcine insulin and killed at different times after injection. Insulin injections lowered plasma glucose levels in fasted 4-day-old rats in a dose-dependent fashion, but a nadir in glucose (approximately 40 mg/dl) was not reached until 90 min; the same treatment produced a nadir in glucose within 30 min in fasted rats 10 days old and older, suggesting that the 4-day-old rats are relatively insulin insensitive.(ABSTRACT TRUNCATED AT 250 WORDS)
Evidence for a specific role of GnRH pulse frequency in the control of the human menstrual cycle
Authors: Filicori M. , Flamigni C. , Campaniello E. , Ferrari P. , Meriggiola M. C. , Michelacci L. , Pareschi A. , Valdiserri A.
Published: December 2017

An adequate frequency of gonadotropin-releasing hormone (GnRH) pulses appears to be important for physiological gonadotropin secretion. However, limited information exists on the exact role of this parameter in the regulation of the human menstrual cycle. Thus we studied gonadotropin and gonadal steroid secretion in 32 women with primary hypogonadotropic amenorrhea who received pulsatile GnRH (60 to 120 micrograms/day) at 60- or 120-min intervals for a total of 64 ovulation induction cycles. Ovulation was achieved in 94% of 60-min and in 70% of 120-min cycles P less than 0.05). In the follicular phase of ovulatory cycles, estradiol (E2) levels did not differ among the four groups; however, mean luteinizing hormone (LH) levels were lower (P less than 0.005), and the midcycle LH surge was severely blunted in cycles of subjects receiving 120 micrograms/day (5 micrograms/bolus) GnRH every 120 min compared with subjects receiving the same dose of GnRH per day or per bolus every 60 min. Luteal progesterone (only in 60 micrograms/day GnRH cycles) and E2 levels were lower in 120-min than in 60-min cycles (P less than 0.05). The use of the higher daily GnRH dose (120 micrograms/day) reduced or abolished the frequency-associated hormone level differences. We conclude that a low frequency of pulsatile GnRH in women 1) decreases mean LH levels and blunts the midcycle gonadotropin surge, 2) does not increase follicle-stimulating hormone concentrations, and 3) is associated with a reduced rate of ovulation.
Enhancement of hepatic glycogen by gluconeogenic precursors: substrate flux or metabolic control?
Authors: Youn J. H. , Bergman R. N.
Published: December 2017

After a meal or glucose load, most carbons of hepatic glycogen are derived from gluconeogenesis. In vitro, hepatic glycogen accumulation is sluggish with glucose alone but markedly enhanced in the presence of gluconeogenic substrates. These findings conflict with the classical view that glucose is the major precursor of hepatic glycogen and have been termed the "glucose paradox." In this review, we attempt to elucidate the central mechanism underlying the glucose paradox by critically examining the in vitro data of hepatic glycogen accumulation. Our analysis is inconsistent with the current hypothesis that glucose phosphorylation is rate limiting for hepatic glycogen accumulation from glucose and that gluconeogenesis enhances glycogen accumulation primarily by increasing substrate flux to the hepatic glucose 6-phosphate pool. Instead, our analysis leads us to the conclusion that the rate-limiting step is the net incorporation of glucose 6-phosphate into glycogen, which is synergistically facilitated with glucose and gluconeogenic substrates. Thus gluconeogenic substrates are involved in the regulation of key enzyme(s) of glycogen metabolism. In addition, in the livers from fasted rats there is substantial cycling through glycogen, and that suppression of glycogen degradation may be a major mechanism in the enhancement of glycogen accumulation by gluconeogenic substrates. Thus we propose a specific hypothesis of the role of gluconeogenic substrates in glycogen metabolism (i.e., inhibition of phosphorylase), which can be tested by future studies.
Atrial natriuretic polypeptide secretion via selective activation of kappa-opioid receptor: role of dynorphin
Authors: Yamada K. , Yoshida S. , Shimada Y.
Published: December 2017

The present study was designed to investigate the direct effect of dynorphin on atrial natriuretic polypeptide (ANP) secretion in cultured rat atrial cardiocytes via a kappa-opioid receptor activation as well as the involvement of adenosine 3',5'-cyclic monophosphate (cAMP) system in the secretion of ANP from cardiocytes. Dynorphin stimulated ANP secretion dose and time dependently from 2-day cultured atrial cardiocytes. The dynorphin-induced ANP secretion was partially antagonized by MR2266, a selective kappa-opioid receptor antagonist. U-62066E, a selective kappa-opioid receptor agonist, stimulated ANP secretion. This stimulation was also antagonized by MR2266. However, no stimulation of ANP secretion was seen with [D-Ala2,D-Leu5]enkephalin, methionine (Met)-enkephalin, or [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin. Dynorphin at 10(-6) M significantly decreased the production of cAMP in the cultured cardiocytes. However, 10(-6) M Met-enkephalin had no effect on cAMP at all. The decrease in cAMP production by the addition of dynorphin was partially antagonized with a simultaneous addition of MR2266. The dynorphin-induced ANP secretion, as well as the basal secretion, were significantly decreased by the addition of 3-isobutyl-1-methylxanthine, a phosphodiesterase inhibitor, as compared with the respective controls. Dibutyryl cAMP at 10(-3) M significantly decreased the basal secretion of ANP as compared with the control. Therefore, the present studies show that dynorphin selectively stimulates ANP secretion, at least in part, via the activation of a specific kappa-opioid receptor.
Structural requirements of pancreatic polypeptide receptor binding
Authors: Gingerich R. L. , Akpan J. O. , Gilbert W. R. , Leith K. M. , Hoffmann J. A. , Chance R. E.
Published: December 2017

Pancreatic polypeptide (PP) receptors have been identified and characterized on the basolateral membranes (BLM) of canine intestinal mucosa. The present study was designed to ascertain the structural requirements of the PP molecule for binding to its receptor. A radioreceptor assay using purified BLM was employed to elucidate receptors specific to PPs of various mammalian species and to modified bovine PP (bPP) fragments. Receptor cross-reactivities (CR) to various PPs and bPP fragments were established. Results show that percent receptor CR by PPs of various species was as follows: bPP (100%) greater than human PP (68%) greater than porcine PP (50%) greater than canine PP (45%) greater than ovine PP (36%) greater than rat PP (3%). The fragments bPP-(1-15), bPP-(1-17), bPP-(1-26), bPP-(16-23), bPP-(18-30), bPP-(24-36), bPP-(27-35), and bPP-(31-36) at 500 nM did not significantly displace tracer from receptor (less than 0.1% CR). Des-COOH-terminal tyrosinamide [bPP-(1-35)] produced less than 0.1% CR. Oxidation of bPP methionine-30 residue to methionine sulfoxide decreased displacement to 67%. Modification of native amidated tyrosinamide to the free acid abolished receptor binding, whereas esterification to the methyl ester of COOH-terminal tyrosine restored binding to 60%. Additionally, percent CR decreased progressively as amino acid residues were deleted from the NH2-terminal region. We conclude that the molecular homologue of PP primary structure is necessary for full receptor binding. Both the NH2- and COOH-terminal residues are required for recognition, and the COOH-terminal tyrosinamide must be intact for PP binding to its receptor.
Application of mass isotopomer analysis for determination of pathways of glycogen synthesis
Authors: Katz J. , Lee W. N.
Published: December 2017

An elementary exposition of the application of mass spectroscopy to studies with substrates labeled uniformly with 13C is presented. A procedure to obtain mass isotopomer spectra, corrected for natural abundance, of products labeled with 13C in several positions is outlined. The calculation for enrichment, a term equivalent to specific activity with radioisotopes, is shown. Examples of mass isotopomer patterns of blood glucose and glycogen are presented, and calculations of the contribution of the direct path to hepatic glycogen synthesis and the dilution of glucose-derived pyruvate are shown. The analysis of mass isotopomer patterns recently offered by C. Des Rosiers, B. R. Landau, and H. Brunengraber [Am. J. Physiol. 259 (Endocrinol. Metab. 22): E757-E762, 1990] is critically examined.
Radiation exposure from long-lived beta emitters in clinical investigation
Authors: Landau B. R. , Shreeve W. W.
Published: December 2017

Potential hazards restrict the use of 14C in clinical investigation. Nevertheless, 14C, in readily metabolized compounds, continues to be administered and in relatively large doses. The compounds are converted to intermediates and products with longer half-lives than their half-lives. These longer biological half-lives have not always been taken into account, although calculations of radiation exposure can be markedly altered by their inclusion. The minimum dose of 14C needed to accomplish a study must also be considered, and benefits relative to risks in the administration must be assessed in terms of the kind and total number of subjects required. Similar considerations apply to the administration of 3H-labeled compounds. Furthermore, in assessing risks, the limited information available on the localization and concentration of the isotopes in the body should be taken into account. There are also concerns with regard to administrations in growth situations and to an individual on multiple occasions. Within those constraints, 14C and 3H can be given with relative safety.
Tumor necrosis factor mimics the metabolic response to acute infection in healthy humans
Authors: Van der Poll T. , Romijn J. A. , Endert E. , Borm J. J. , Buller H. R. , Sauerwein H. P.
Published: December 2017

To evaluate the role of tumor necrosis factor (TNF) in the initiation of the metabolic response to acute infection, we performed a crossover saline-controlled study in six healthy postabsorptive men, investigating the metabolic effects of a bolus intravenous injection of recombinant human TNF (50 micrograms/m2). TNF induced a transient stress hormone response, associated with an early and sustained rise in plasma glucose concentrations (percentage increase at 2 h 23 +/- 7; P less than 0.05). Glucose turnover, measured 7.5 h postinjection, was 10 +/- 3% higher after TNF administration (P less than 0.05). Plasma free fatty acids (FFA) and glycerol concentrations increased transiently after TNF injection, peaking after 4 h (percentage increase 363 +/- 83 and 67 +/- 14, respectively; both P less than 0.05). FFA turnover, determined 6.5 h postinjection, increased in five subjects to a variable extent (percentage increase 126 +/- 55; P less than 0.05). Finally, resting energy expenditure showed a transient rise after TNF injection (34 +/- 2% at 4 h; P less than 0.05). We conclude that intravenous TNF reproduces many of the metabolic changes observed in septicemia, suggesting that TNF may be an initiating factor in the development of the metabolic response to acute infection.