bluuebunny/crossref_metadata_2025 huggingface dataset:
Low oxygen selectively inhibits aldosterone secretion from bovine adrenocortical cells in vitro
Authors: Raff H. , Ball D. L. , Goodfriend T. L.
Published: December 2017

Systemic hypoxia has been reported to inhibit selectively aldosterone secretion in vivo. The mechanism of this inhibition has not been elucidated. We hypothesized that decreased tissue PO2 directly inhibited aldosteronogenesis. To test this hypothesis, we exposed dispersed adrenocortical cells (90% glomerulosa/10% fasciculata) to decreased PO2 in vitro while simultaneously stimulating aldosterone secretion with angiotensin II, N6,2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (dibutyryl cAMP) adrenocorticotropic hormone (ACTH)-(1-24), or progesterone. Decreasing buffer PO2 from approximately 150 to approximately 85 Torr significantly inhibited basal and angiotensin II, cAMP, progesterone, and ACTH-stimulated aldosterone secretion at all doses of secretagogue. Inhibition was largest for angiotensin II (55 +/- 9% inhibition at 1 microM) and cAMP (54 +/- 8% at 3 mM) and lowest for ACTH (24% at 100 nM) and basal aldosterone secretion (31 +/- 7%). This inhibition was reversed by returning the buffer PO2 to 150 Torr. Cortisol secretion was not significantly inhibited by decreased buffer PO2. We conclude that decreased buffer PO2 significantly inhibits aldosterone secretion in vitro, and this inhibition is reversible and specific. Hypoxia-induced inhibition of aldosterone secretion in vivo may be caused, at least in part, by a direct effect of low tissue PO2 within the adrenal cortex.
Vitamin D kinetics in vivo: effect of 1,25-dihydroxyvitamin D administration
Authors: Halloran B. P. , Castro M. E.
Published: December 2017

Administration of 1,25-dihydroxyvitamin D [1,25(OH)2D] can increase the metabolic clearance rate (MCR) of 25-hydroxyvitamin D [25(OH)D]. To determine whether administration of 1,25(OH)2D can also influence the metabolic clearance rates (MCR) of 1,25(OH)2D and 24,25-dihydroxyvitamin D 24,25(OH)2D, we measured metabolic clearance of 1,25(OH)2D, 24,25(OH)2D, and 25(OH)D in rats in which the serum concentration of 1,25(OH)2D was increased by continuous infusion. Infusion of 1,25(OH)2D (12 days at 75 pmol/day) increased serum 1,25(OH)2D from 128 +/- 11 to 244 +/- 14 pg/ml (P less than 0.005) and increased MCR from 169 +/- 13 to 210 +/- 9 microliters.min-1.kg-1 or 24% (P less than 0.025). Increasing serum 1,25(OH)2D to 330-360 pg/ml increased MCR 72%. Infusion of 1,25(OH)2D decreased serum 24,25(OH)2D from 3.5 +/- 0.5 to 2.4 +/- 0.3 ng/ml (P less than 0.05), increased MCR from 25 +/- 2 to 48 +/- 6 microliters.min-1.kg-1 (P less than 0.0025), and increased the production rate (PR) from 70 +/- 11 to 124 +/- 26 pg.min-1.kg-1 (P less than 0.05). Infusion of 1,25(OH)2D decreased serum 25(OH)D from 13.0 +/- 0.5 to 8.0 +/- 0.5 ng/ml (P less than 0.005) and increased MCR from 45 +/- 1 to 75 +/- 7 microliters.min-1.kg-1 (P less than 0.001) but had no effect on PR. The data indicate that increasing serum 1,25(OH)2D by chronic administration can increase the MCR of 1,25(OH)2D and suggest that 1,25(OH)2D can feedback regulate its serum concentration by regulating its MCR. The data also suggest that 1,25(OH)2D administration can increase the MCRs of 24,25(OH)2D and 25(OH)D.
Calcium dependence of osmolality-, potassium-, and angiotensin II-induced aldosterone secretion
Authors: Radke K. J. , Clendenin R. E. , Taylor R. E. , Schneider E. G.
Published: December 2017

Different calcium-dependent mechanisms may be involved in mediating stimulus-induced aldosterone secretion. Using isolated perfused canine adrenal glands, we determined the effect of reductions in extracellular [Ca2+] and of infusion of a voltage-dependent calcium channel antagonist, nifedipine, on aldosterone secretion induced by decreases in osmolality, by increases in [K+], or by infusion of angiotensin II (ANG II). Aldosterone secretion was stimulated to a similar level by reducing osmolality, by increasing [K+], or by infusing ANG II. After 50 min of stimulation, lowering [Ca2+] from 1.25 to 0.10 mM caused a marked and similar inhibition of osmolality- and [K+]-induced aldosterone secretion that was significantly greater than inhibition of ANG II-induced aldosterone secretion. Similarly, nifedipine at 3.3 X 10(-8) M caused marked and similar inhibition of osmolality- and [K+]-induced aldosterone secretion that was significantly greater than the inhibition of ANG II-induced aldosterone secretion. These data demonstrate that calcium-dependent processes are involved in osmolality-, [K+]-, and ANG II-induced aldosterone secretion. However, the calcium-dependent process(es) evoked by reductions in osmolality or increases in [K+] are considerably different from that evoked by ANG II. Osmolality and potassium appear to induce aldosterone secretion primarily by activating voltage-dependent calcium channels.
Fetal placental vascular responses to prostacyclin after angiotensin II-induced vasoconstriction
Authors: Parisi V. M. , Walsh S. W.
Published: December 2017

The vasodilator prostacyclin is produced by many fetal tissues and may serve to protect umbilical placental blood flow. We hypothesized that prostacyclin could reverse fetoplacental vasoconstriction produced by angiotensin II (ANG II). Studies were done in eight unanesthetized near-term ovine fetuses. After a control period, ANG II was infused into the fetal inferior vena cava at a rate of 0.5 microgram/min for 40 min. Twenty minutes after starting the ANG II infusion, an infusion of prostacyclin at a rate of 5 micrograms/min was added to the ANG II infusion. Blood flows were measured by the radioactive microsphere technique. Blood flow measurements were made during the control period, 20 min after starting the ANG II infusion, and 20 min after adding prostacyclin to the ANG II infusion. ANG II produced significant fetal hypertension and renal, intestinal, and placental vasoconstriction. Placental vascular resistance rose from 0.14 +/- 0.01 to 0.18 +/- 0.01 mmHg.min.kg fetal wt.ml-1 during the ANG II infusion period (P less than 0.05). The addition of prostacyclin to the ANG II infusion resulted in a return to control values for fetal blood pressure and renal and intestinal resistance. However, placental vasoconstriction was not reversed by addition of prostacyclin as placental vascular resistance remained significantly elevated over the control value (0.17 +/- 0.01 mmHg.min.kg fetal wt.ml-1). Although unchanged by ANG II infusion, fetal pH decreased significantly during the ANG II plus prostacyclin infusion period. We conclude that ANG II causes fetal hypertension and renal and intestinal vasoconstriction, which are reversed by prostacyclin.(ABSTRACT TRUNCATED AT 250 WORDS)
Plasma membrane-specific deficiency in cardiac beta-adrenergic receptor in streptozocin-diabetic rats
Authors: Kashiwagi A. , Nishio Y. , Saeki Y. , Kida Y. , Kodama M. , Shigeta Y.
Published: December 2017

Cell surface [3H]CGP 12177 binding sites in 10-wk streptozocin-diabetic rats decreased by 41% (P less than 0.01) compared with that in the control rats. In contrast, there was no difference in the total cell receptor concentration between the control and the diabetic rats, which was measured by hydrophobic antagonist [125I]-iodocyanopindolol binding. Forty-eight-hour in vivo insulin treatment significantly (P less than 0.05) increased cell surface beta-adrenergic receptor concentration by 37% above that in diabetic rats without any change in total receptor concentration in the cells. However in vitro treatment of 8 nM insulin, 33 mM glucose, or 10 mM 3-hydroxybutyrate for 2 h showed no effect on [3H]CGP 12177 binding. In contrast, 10 microM isoproterenol-dependent decrease and the recovery of cell surface receptors after the removal of the agonist were significantly (P less than 0.01) impaired in diabetic rats compared with those of control rats. These results indicate that only cell surface beta-adrenergic receptors decrease in diabetic rats, which may be associated with abnormalities in the receptor distribution. The decrease in cell surface receptor number closely associates with the diabetic state and is reversed by the short-term insulin treatment.
Hepatic glycogen in humans. II. Gluconeogenetic formation after oral and intravenous glucose
Authors: Radziuk J.
Published: December 2017

The amount of glycogen that is formed by gluconeogenetic pathways during glucose loading was quantitated in human subjects. Oral glucose loading was compared with its intravenous administration. Overnight-fasted subjects received a constant infusion or [3-3H]glucose and a marker for gluconeogenesis, [U-14C]lactate or sodium [14C]bicarbonate [14C]bicarbonate). An unlabeled glucose load was then administered. Postabsorptively, or after glucose infusion was terminated, a third tracer ([6-3H]glucose) infusion was initiated along with a three-step glucagon infusion. Without correcting for background stimulation of [14C]glucose production or for dilution of 14C with citric acid cycle carbon in the oxaloacetate pool, the amount of glycogen mobilized by the glucagon infusion that was produced by gluconeogenesis during oral glucose loading was 2.9 +/- 0.7 g calculated from [U-14C]-lactate incorporation and 7.4 +/- 1.3 g calculated using [14C]bicarbonate as a gluconeogenetic marker. During intravenous glucose administration the latter measurement also yielded 7.2 +/- 1.1 g. When the two corrections above are applied, the respective quantities became 5.3 +/- 1.7 g for [U-14C]lactate as tracer and 14.7 +/- 4.3 and 13.9 +/- 3.6 g for oral and intravenous glucose with [14C]bicarbonate as tracer (P less than 0.05, vs. [14C]-lactate as tracer). When [2-14C]acetate was infused, the same amount of label was incorporated into mobilized glycogen regardless of which route of glucose administration was used. Comparison with previous data also suggests that 14CO2 is a potentially useful marker for the gluconeogenetic process in vivo.
Volume regulation of human lymphocytes by aldosterone in isotonic media
Authors: Wehling M. , Kuhls S. , Armanini D.
Published: December 2017

In vitro binding of aldosterone to mineralocorticoid receptors on human mononuclear leukocytes (HML) and its effects on the intracellular sodium and potassium concentrations of HML have already been described. In the present paper this easily accessible human cell model was investigated with regard to the regulation of the cell volume by aldosterone, since the concordant changes of sodium and potassium were expected to be accompanied by water and volume shifts. As determined by the measurement of cell diameter and the planimetric estimation of cell area in photographs, cell volume decreased by approximately 16% when cells were incubated in RPMI-1640 medium without aldosterone added for 1 h at 37 degrees C, a decrease not seen when 1.4 nM aldosterone was added to the incubation medium; the effect was half maximal at a concentration between 0.07 and 0.14 nM. One hundred forty nanomoles canrenone antagonized the action of aldosterone, but cortisol was ineffective. The results indicate concordant changes of intracellular sodium and potassium and cell volume, if studied under the same conditions. These data are the first to demonstrate that aldosterone is a major physiological determinant of lymphocyte volume in isotonic media.
Transient reduction of metabolic rate by food restriction
Authors: McCarter R. J. , McGee J. R.
Published: December 2017

It is widely held that restriction of food intake leads to a decrease in metabolic rate, and this effect has been implicated as the mechanism by which food restriction retards aging in laboratory rodents. Data on which this belief is based were obtained mostly from studies of basal metabolic rate after acute rather than chronic food restriction. In contrast we previously reported no effect of chronic food restriction on metabolic rate measured under usual living conditions. The present study examines changes in metabolic rate immediately after restriction of food so as to include the initial response to decreased intake of food. Two groups of specific pathogen-free Fischer 344 rats were housed under barrier conditions from 6 to 24 wk of age. Restricted rats were fed 60% of food consumed by rats eating ad libitum. Metabolic rate was measured indirectly by gas analysis with rats under normal daily living conditions (24MR) and basal metabolic rate (BMR) was also measured. Both 24MR and BMR decreased after food restriction, but this decrease was transient, so that within a few weeks metabolic rate of restricted rats was the same as that of rats fed ad libitum.
Isotopic dilution of CO2 as an estimate of CO2 production during substrate oxidation studies
Authors: Kien C. L.
Published: December 2017

The rate of oxidation of a substrate is often divided by the numerical estimate of a correction factor for the proportion of labeled CO2 that is excreted during the course of the experiment. This factor, derived from tracer studies of bicarbonate kinetics, equals the product of the net rate of respiratory CO2 excretion and the ratio of the plateau isotopic enrichment of CO2 to the rate of infusion of labeled bicarbonate. The inverse of this ratio may be equated to the rate of appearance of unlabeled CO2. When one substitutes the expression for the correction factor into a typical equation for the rate of substrate oxidation, the rate of appearance of CO2 substitutes for both net CO2 excretion and the correction factor in the original oxidation equation. Thus the rate of appearance of CO2 is an index of CO2 production that takes into account both net fixation of CO2 and isotopic exchange of labeled CO2; it also may have application as an index of net CO2 production.
Atrial natriuretic factor suppresses neural stimulation of renin release in dogs
Authors: Hisa H. , Tomura Y. , Satoh S.
Published: December 2017

The effects of atrial natriuretic factor (ANF) on neural control of renin release and sodium excretion by the kidney were examined in pentobarbital-anesthetized dogs. Electrical stimulation of the renal nerves (RNS, 1 Hz) increased the renal secretion rate of renin (RSR) by 627 +/- 141 ng angiotensin I (ANG I)/min and that of norepinephrine (NESR) by 22.2 +/- 5.9 ng/min. Furthermore, urinary sodium excretion (UNaV) was decreased by 59 +/- 7%, with little change in either renal blood flow (RBF) or glomerular filtration rate (GFR). Intrarenal arterial infusion of ANF (alpha-human atrial natriuretic peptide; 10 ng.kg-1.min-1) increased basal UNaV about twofold but had no effect on basal RBF or GFR. The RNS-induced increase in RSR during ANF infusion (198 +/- 117 ng ANG I/min) was significantly lower than that before the infusion (P less than 0.05), whereas the RNS-induced changes in NESR (27.1 +/- 8.5 ng/min) and UNaV (51 +/- 11%) were unaffected. These results suggest that neural stimulation of renin release, but not of tubular sodium reabsorption, can be suppressed by exogenously administered ANF at a dose that does not affect glomerular filtration or renal neurotransmitter release.
Plasma reciprocal pool specific activity predicts that of intracellular free leucine for protein synthesis
Authors: Horber F. F. , Horber-Feyder C. M. , Krayer S. , Schwenk W. F. , Haymond M. W.
Published: December 2017

We previously proposed that, during the infusion of either labeled leucine or its alpha-ketoacid, alpha-ketoisocaproate (KIC), the plasma specific activity (SA) of the transaminated product of the infused tracer ("reciprocal pool SA") may better reflect the intracellular leucine SA than the plasma SA of either infused tracer ("primary pool SA"). To test this hypothesis, 14 dogs were simultaneously infused intravenously with [3H]leucine and [14C]KIC, and blood and tissue compartments were sampled. The ratios of [3H]-leucine to [14C]leucine [( 3H]/[14C]leucine) in mixed tissue proteins and in the intracellular space of striated muscle were the same as the ratio of the isotope infusion rates and similar, although slightly lower (P less than 0.01), than [3H]KIC/[14C]leucine SA (ratio of reciprocal pool SA) in plasma. Plasma [3H]KIC/[14C]leucine SA were essentially identical to the [3H]/[14C] of leucine in 1) mixed liver proteins, 2) intrahepatic free leucine, and 3) fibrin. The [3H]/[14C]leucine in mixed renal proteins and in the intracellular space of kidney and erythrocytes were similar to those of the venous plasma [3H]/[14C]leucine SA. The plasma [3H]KIC and [14C]leucine SA (the reciprocal pool SA) were similar to the SA of [3H]- and [14C]leucine in the intracellular space of all organs investigated with the exception of kidney. Therefore, in postabsorptive dogs, the plasma SA of the transaminated product of the infused labeled KIC or leucine is an excellent predictor of the intracellular leucine SA in all tissues investigated with the exception of kidney.
Effects of chronic metabolic alkalosis on Ca2+, PTH and 1,25(OH)2D3 in the rat
Authors: Bushinsky D. A. , Kittaka M. K. , Weisinger J. R. , Langman C. B. , Favus M. J.
Published: December 2017

The effect of chronic metabolic alkalosis on arterial blood ionized calcium concentration ([Ca2+]) and the levels of serum parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is difficult to predict. Although a fall in pH directly decreases [Ca2+], chronic alkalosis reduces urine calcium excretion, which could elevate [Ca2+]. [Ca2+] modulates the serum level of PTH and the level of 1,25(OH)2D3 directly and through PTH. To determine the effect of chronic metabolic alkalosis on [Ca2+], PTH, and 1,25(OH)2D3, rats were made alkalemic by feeding a chloride-deficient diet (LCl) or LCl with 75 mM NaHCO3 in the drinking water (LCl + HCO3-) and compared with controls fed a chloride-replete diet (NCl). Compared with NCl, after 8 days of LCl and LCl + HCO3- arterial pH and PTH rose and [Ca2+] fell. Serum 1,25(OH)2D3 tended to rise with LCl and rose with LCl + HCO3-. Serum 1,25(OH)2D3 was correlated inversely with [Ca2+] (r = -0.510, n = 54, P less than 0.001) and with pH (r = -0.291, n = 57, P less than 0.03) but not with PTH or phosphorus. Stepwise regression analysis indicated that [Ca2+] accounted for the majority of the variance of serum 1,25(OH)2D3. Chronic metabolic alkalosis induced by a low-chloride diet and HCO3- appears to increase serum PTH and 1,25(OH)2D3 through a fall in [Ca2+].
Muscle sympathetic activity and norepinephrine release during mental challenge in humans
Authors: Hjemdahl P. , Fagius J. , Freyschuss U. , Wallin B. G. , Daleskog M. , Bohlin G. , Perski A.
Published: December 2017

Muscle sympathetic nerve activity (MSA; peroneal nerve) and arterial and femoral venous plasma norepinephrine (NE) were studied in 10 volunteers at rest, during a relaxation procedure (RELAX), and during two mental challenges, a word identification test (WIT) and a color word test (CWT). [3H]NE infusions were used to assess NE spillover to and clearance from plasma. Net NE overflow from the leg was calculated. RELAX reduced MSA and femoral venous NE concentrations. CWT increased blood pressure, cardiac output (thermodilution), and calf flow and reduced systemic vascular resistance. Responses to WIT were less marked. CWT increased MSA by 25%, femoral venous NE concentrations by 25%, and NE overflow from the leg by 26% at 3 min. Fractional epinephrine and [3H]NE extractions were flow related and decreased during CWT. The arterial contribution to femoral venous NE (about half) increased by 10% during CWT. Arterial NE levels and spillover increased, but NE clearance was unchanged. Femoral venous NE concentrations and NE spillover (not based on flow measurements) and regional NE overflow correlated with MSA. Thus NE concentrations in plasma reflect spillover rather than clearance at rest and during mental challenge. Biochemical and neurophysiological indexes of sympathetic activity correlate when assessed in the same region. Mental stress increases sympathetic activity in leg muscle.
Direct evaluation of acidification by rat testis and epididymis: role of carbonic anhydrase
Authors: Caflisch C. R. , DuBose T. D.
Published: December 2017

The present experiments have employed microelectrode techniques (pH and PCO2) and microcalorimetry (total CO2 concentration) to define parameters of acidification in specific structures of the rat testis and epididymis during control conditions and after administration of the carbonic anhydrase inhibitor acetazolamide (20 or 50 mg/kg). Values for in situ pH during control conditions in seminiferous tubules (ST; 6.96 +/- 0.01), proximal caput (PCP; 6.62 +/- 0.01), middle caput (MCP; 6.59 +/- 0.01), middle corpus (MCR; 7.10 +/- 0.02), and proximal cauda epididymidis (PCD; 6.85 +/- 0.01) were significantly more acidic than in testicular artery (TA; 7.36 +/- 0.01) or systemic arterial blood (SAB; 7.40 +/- 0.01) and did not change significantly after acetazolamide. In situ partial pressure of CO2 (PCO2) in TA (52.2 +/- 0.6 mmHg), ST (52.3 +/- 0.4 mmHg), PCP (52.9 +/- 0.4 mmHg), MCP (53.0 +/- 0.7 mmHg), MCR (53.4 +/- 0.4 mmHg), and PCD (52.4 +/- 0.4 mmHg) were indistinguishable from each other, but all values were significantly higher than SAB PCO2 (39.2 +/- 0.5 mmHg). Acetazolamide increased in situ PCO2 significantly in all structures except the MCR. The total CO2 concentration in normal ST fluid (10.7 +/- 0.5 mM) was significantly higher than in "primary" fluid (6.9 +/- 0.3 mM), and both values were well below TA (26.9 +/- 1.3 mM) or SAB (24.6 +/- 0.4 mM) total CO2 concentrations. In the epididymis, total CO2 concentrations were indistinguishable and not different from the value in primary fluid.(ABSTRACT TRUNCATED AT 250 WORDS)
Single lactotroph responses to dopamine, angiotensin II, and culture duration
Authors: Anderson J. M. , Cronin M. J.
Published: December 2017

Prolactin cells were isolated from male rat pituitaries and studied individually with the reverse hemolytic plaque assay. Plaque area, linearly correlated with radioimmunoassayable prolactin in the culture medium, and percent lactotrophs were measured. A 20-h incubation period markedly enhanced the potency and efficacy of dopamine to inhibit prolactin release compared with an assay conducted on the day of enzymatic dispersion. Frequency histograms of plaque areas showed unimodal distributions after angiotensin II (ANG II)-stimulated prolactin release, with the mode shifting to the right. In contrast, the addition of dopamine to either basal or ANG II-stimulated lactotrophs shifted the mode to the left and decreased the overall range of plaque areas. No clear evidence for discrete subpopulations was generated with this approach; rather, an extensive range of secretory behavior was defined as a continuum, indicating a diverse repertoire of secretory potential in different lactotrophs. Furthermore, comparing lactotrophs from the lateral wings with the central region of the pituitary suggested that lateral cells were less inhibited by dopamine treatment. We conclude that this improved assay allows more precise assessment of the contribution that single lactotrophs make to the population response to dopamine and ANG II.
Free amino acids in muscle: effect of muscle fiber population and denervation
Authors: Turinsky J. , Long C. L.
Published: December 2017

One hindlimb of each rat was denervated by sectioning the sciatic nerve. Three days later, soleus, plantaris, and gastrocnemius muscles of the sham hindlimb and the contralateral denervated hindlimb were excised and analyzed for intracellular concentrations of 23 free amino acids and the dipeptides carnosine and anserine. Compared with the sham soleus (slow-twitch) muscle, the sham plantaris and gastrocnemius (fast-twitch) muscles showed 57-81% lower concentrations of histidine, glutamine, glutamate, aspartate, and serine and also 32-78% lower levels of taurine, citrulline, phosphoserine, and ornithine. On the other hand the fast-twitch muscles exhibited 31% higher concentrations of free glycine and alanine and 113-127% higher levels of carnosine and anserine than the soleus muscle. The denervation caused greater changes in soleus muscle than in the other two muscles. The denervation-induced changes in soleus muscle included 38-87% increases in concentrations of free valine, leucine, isoleucine, and glutamate associated with 21-56% decreases in the levels of glutamine, glycine, aspartate, serine, alanine, and citrulline. It is concluded that both muscle fiber population and muscle denervation have an independent effect on the intracellular concentrations of free amino acids in muscles.
Isolation and incubation conditions to study heart mitochondrial protein synthesis
Authors: McKee E. E. , Grier B. L. , Thompson G. S. , McCourt J. D.
Published: December 2017

Although much is now known with regard to the processes of mammalian mitochondrial gene expression, relatively little is known concerning the quantitative regulation of this pathway in response to hormones or other physiological stimuli. This has been caused, in large part, by the lack of adequate assay systems in which such processes can be meaningfully measured. The purpose of this and the companion paper [E. E. McKee, B. L. Grier, G. S. Thompson, A. C. F. Leung, and J. D. McCourt. Am. J. Physiol. 258 [Endocrinol. Metab. 21):E503-E510, 1990] is to describe a system in which the quantitative regulation of mitochondrial protein synthesis in rat heart can be investigated. In this report the conditions for mitochondrial isolation and labeling are described, and the importance of isolating intact, tightly coupled mitochondria in obtaining high and reliable rates of protein synthesis is demonstrated. The highest levels of protein synthesis are obtained in mitochondria isolated from hearts perfused and homogenized in the presence of subtilisin, conditions in which the fastest rates of state 3 respiration and the highest respiratory control ratios are also observed. Analysis of the free amino acid pools indicates that isolated heart mitochondria have a negligible level of endogenous methionine as well as other amino acids. As a result, the concentration and specific radioactivity of the [35S]methionine pool serving protein synthesis could be easily determined. Optimal translation occurred at 30 degrees C at a pH of 7.0-7.2 and required the addition of methionine (20 microM), the other 19 amino acids (0.1 mM each), K+ (60-90 mM), Cl- (30-90 mM), Mg2+ (0.5-5 mM), and bovine serum albumin (1 mg/ml). As shown in the companion paper, adenine nucleotide (0.5-4.0 mM) and oxidizable substrate (10-20 mM glutamate) are also required for isolated heart mitochondrial protein synthesis. Analysis of labeled mitochondrial translation products demonstrated that bona fide mitochondrial peptides were synthesized.
Bioactive parathyroid hormone in pregnant rats and fetuses
Authors: Bourdeau A. , Manganella G. , Thil-Trubert C. L. , Sachs C. , Cournot G.
Published: December 2017

Parathyroid function at the end of gestation (day 21) was investigated by measuring plasma calcium (PCa), immunoreactive parathyroid hormone (iPTH), bioactive parathyroid hormone (bioPTH; cytochemical bioassay), and bone histology in intact and thyroparathyroidectomized (TPTX; day 12, ether anesthesia) rats and their fetuses. In pregnant intact rats, PCa was significantly lower, and iPTH, bioPTH, and osteoclast number were higher than in nonpregnant rats. In fetuses, PCa was higher than maternal PCa and correlated with fetal bioPTH. TPTX suppressed maternal bioPTH and decreased iPTH and osteoclast number, whereas fetal iPTH and bioPTH were decreased with no change in osteoclast number. Fetal PCa was near normal and was correlated with maternal PCa but not with fetal bioPTH. The fetomaternal calcium gradient was maintained and even increased. This study shows that there is maternal physiological hyperparathyroidism and functional fetal parathyroid glands at the end of gestation in the rat. Parathyroid hormone does not seem to be responsible for maintaining the high fetomaternal calcium gradient in TPTX animals.
Adenylate cyclase blockers dissociate PTH-stimulated bone resorption from cAMP production
Authors: Reid I. R. , Lowe C. , Cornish J. , Gray D. H. , Skinner S. J.
Published: December 2017

It is uncertain whether adenosine 3',5'-cyclic monophosphate (cAMP) or the inositol-calcium pathway mediates the stimulation of bone resorption by parathyroid hormone (PTH). Incubation of bone organ cultures with cAMP analogues and forskolin has not resolved this question because of the cellular inhomogeneity of bone and the consequent presence of adenylate cyclase-linked receptors for both PTH and calcitonin, hormones with opposite effects on bone resorption. We have used two new inhibitors of adenylate cyclase, 9-(tetrahydro-2-furyl)adenine (SQ 22536) and 2',5'-dideoxyadenosine (DDA), to directly reassess the role of cAMP in PTH-stimulated osteolysis. SQ 22536 (0.01-1.0 mM) and DDA (0.01-1.0 mM) completely blocked PTH stimulation of cAMP production measured in the absence of a phosphodiesterase blocker. In the presence of 1 mM 3-isobutyl-1-methylxanthine, half-maximal inhibition of PTH-induced cAMP production occurred with 0.2 mM SQ and 0.1 mM DDA, respectively. These concentrations of SQ and DDA had no effect on PTH-stimulated 45Ca release from calvaria, although both agents inhibited bone resorption when present at concentrations of 1-2 mM. At these levels, SQ and DDA caused equivalent inhibition of 45Ca release stimulated by 1,25-dihydroxyvitamin D3 but did not affect basal 45Ca release or [3H]-phenylalanine incorporation. It is concluded that substantial blockade of PTH-induced cAMP production does not affect this hormone's stimulation of bone resorption, which is therefore likely to be mediated by another intracellular messenger system, possibly calcium. In millimolar concentrations, SQ and DDA appear to be nonspecific blockers of osteoclastic bone resorption.
Thyroidal and peripheral production of 3,5,3'-triiodothyronine in humans by multicompartmental analysis
Authors: Pilo A. , Iervasi G. , Vitek F. , Ferdeghini M. , Cazzuola F. , Bianchi R.
Published: December 2017

Multicompartmental analysis of thyroxine (T4) and 3,5,3'-triiodothyronine (T3) kinetics based on the plasma disappearance curves of the two tracer hormones (J. J. DiStefano III, M. Jang, T. K. Malone, and M. Broutman. Endocrinology 110: 198-213, 1982 and J. J. DiStefano III, T. K. Malone, and M. Jang. Endocrinology 111: 108-117, 1982) was extended to include additional experimental data, namely, the appearance curve in plasma of labeled T3 generated in vivo from precursor T4. Kinetic analysis of data obtained in 14 studies carried out in normal subjects by using a composite six-pool model made it possible to quantify the contributions of the thyroid (3.3 micrograms.day-1.m-2) and the periphery (12.7 micrograms.day-1.m-2) to T3 production. T4 monodeiodination occurred mainly in peripheral tissues rapidly exchanging with plasma (10.7 micrograms T3.day-1.m-2), whereas only 2.0 micrograms T3.day-1.m-2 arose in slowly exchanging tissues. In contrast, if plasma disappearance curves only were analyzed, a value of 10.9 micrograms T3.day-1.m-2 was calculated for peripheral conversion in slowly exchanging tissues; this underscores the need for additional data, such as the [125I]T3 plasma appearance curve for the partition of central and peripheral production of T3.
Total and net muscle protein breakdown in infection determined by amino acid effluxes
Authors: Sjolin J. , Stjernstrom H. , Friman G. , Larsson J. , Wahren J.
Published: December 2017

The present investigation was undertaken to study whether, in human infection of varying severity, peripheral 3-methylhistidine efflux and urinary excretion are associated with net protein degradation and to estimate the protein synthesis rate from the combined effluxes of 3-methylhistidine, tyrosine, and phenylalanine. Quadruplicate femoral arteriovenous differences of 3-methylhistidine, tyrosine, and phenylalanine were multiplied by leg plasma flow in 15 infected patients. Leg effluxes for 3-methylhistidine, tyrosine, and phenylalanine were -0.074 +/- 0.011, -2.57 +/- 0.43, and -3.17 +/- 0.44 mumol/min, respectively. There was a significant linear relationship (P less than 0.01) between the effluxes of tyrosine and phenylalanine and the efflux and urinary excretion of 3-methylhistidine. A significant release of tyrosine and phenylalanine was observed in patients studied at the 3-methylhistidine level seen in normal healthy subjects. It is concluded that in infection 1) there is an increased breakdown of skeletal muscle protein and a reduced rate of protein synthesis, with the latter being relatively more important in patients with mild disease; and 2) urinary 3-methylhistidine excretion is associated with net skeletal muscle protein degradation for the patient group studied.
Ketone bodies and islet function: 45Ca handling, insulin synthesis, and release
Authors: Malaisse W. J. , Lebrun P. , Yaylali B. , Camara J. , Valverde I. , Sener A.
Published: December 2017

D-(-)-beta-Hydroxybutyrate and acetoacetate cause a rapid, sustained, and rapidly reversible stimulation of insulin release from rat pancreatic islets incubated in the presence, but not absence, of D-glucose. This coincides with stimulation of both proinsulin biosynthesis and 45Ca net uptake. The ketone bodies also decrease 45Ca outflow from prelabeled islets perifused in the absence of Ca2+ and, in contrast, enhance effluent radioactivity in the presence of Ca2+. In the presence of D-glucose, the secretory response to D-(-)-beta-hydroxybutyrate is concentration related in the 2.5-20 mM range, abolished in the absence of Ca2+ or presence of KCN, and enhanced by theophylline and forskolin. It corresponds grossly to a shift to the left of the sigmoidal curve relating insulin output to the ambient concentration of D-glucose. The secretory, biosynthetic, and cationic response to acetoacetate is less marked than that evoked by an equimolar concentration of D-(-)-beta-hydroxybutyrate. These features are compatible with the view that the insulinotropic action of ketone bodies would be causally linked to their metabolism in islet cells.
Pregnancy suppresses G protein coupling to phosphoinositide hydrolysis in guinea pig myometrium
Authors: Arkinstall S. J. , Jones C. T.
Published: December 2017

The regulatory factors controlling uterine contractile activity during pregnancy remain unclear, although pathways modulating intracellular Ca2+ and prostaglandin production play an important role. Because excitatory hormones raise myometrial Ca2+ levels and prostaglandin output through increasing phosphoinositide hydrolysis, regulation of G protein coupling to phospholipase C activation could be a key site for control. To measure the functional activity of this signaling pathway, we measured formation of [3H]inositol phosphates from prelabeled guinea pig myometrial membranes in response to G protein activation by guanosine 5'-[gamma-thio]triphosphate (GTP gamma S) and fluoride. Although these agents stimulated a three- to fivefold increase in phosphoinositide phospholipase C activity in nonpregnant myometrium, at 46-47, 53-60, and 66-69 days of pregnancy (full term 67 +/- 2 days) this response fell by 43-83%. Moreover, the half-maximal effective dose (ED50) for GTP gamma S action was increased from 8.11 +/- 0.91 nM (n = 5) in the nonpregnant state to 307.4 +/- 142.3 (n = 9) and 209.7 +/- 155.1 nM (n = 8) at 53-60 and 66-69 days, respectively. Because phospholipase C levels displayed only a limited fall (28%) whether measured by direct Ca2+ activation or by immunoblotting, this study indicates a considerable suppression of G protein functional coupling to myometrial phosphoinositide hydrolysis throughout late gestation. Such a desensitization is likely to contribute to reports of diminished contractile sensitivity during pregnancy and to reflect an essential regulatory event in the processes maintaining uterine quiescence in pregnant guinea pig.
Ammonia metabolism during intense dynamic exercise and recovery in humans
Authors: Graham T. E. , Bangsbo J. , Gollnick P. D. , Juel C. , Saltin B.
Published: December 2017

This study examined the dynamics for ammonia (NH3) metabolism in human skeletal muscle during and after intense one-legged exercise. Subjects (n = 8) performed dynamic leg extensor exercise to exhaustion (3.2 min). Muscle NH3 release increased rapidly to a maximum of 314 +/- 42 mumol/min and declined immediately on cessation of exercise. Recovery was complete in approximately 20 min. Arterial [NH3] increased less rapidly and reached its maximum 2-3 min into recovery. These data demonstrate that NH3 clearance is more sensitive to the cessation of exercise than is NH3 release from skeletal muscle. Muscle [NH3] increased three to fourfold during exercise and represented 74 +/- 8% of the total net NH3 formation. Thus the change in muscle [NH3] alone underestimates the NH3 production. There was no evidence that the muscle-to-venous blood NH3 ratio shifts in accordance with the H+ data. Thus other factors must contribute to the NH3 release from active muscle. The total net NH3 formed corresponded with the intramuscular inosine 5'-monophosphate accumulation, suggesting that the NH3 was derived from AMP deamination. Changes in the known modulators of AMP deaminase (ATP, ADP, H+) were moderate, so the mechanisms initiating the deamination remain obscure.
A fluorescent analogue of hydrin 1: a new probe for vasotocin receptors
Authors: Eggena P. , Ma C. L. , Lu M. Q. , Buku A.
Published: December 2017

Hydrin 1 is the biosynthetic precursor of vasotocin in Xenopus laevis. We have synthesized deamino and fluorescein analogues of hydrin 1 and characterized their physiological action in the urinary bladder of the toad, Bufo marinus. 1-Deamino-hydrin 1 (d-hydrin) was more potent than vasotocin in stimulating osmotic water flow across intact bladders and more potent than vasotocin in displacing tritium-labeled vasopressin [( 3H]AVP) from cell membranes. 1-Deamino-[11-lysine (fluorescein)]-hydrin 1 (flu-hydrin) was found to be the most potent fluorescent vasotocin receptor probe synthesized to date. Flu-hydrin increased osmotic water flow across bladders with a half-maximal effective dose (ED50) value of 6 x 10(-10) M and displaced [3H]AVP from membranes with a half-maximal concentration (IC50) value of 3 x 10(-9) M. The hydrosmotic response to flu-hydrin was blocked by 1-deamino-[4-lysine (p-azido-benzoyl)]arginine vasotocin [d4Lys(N3)-AVT]. Epifluorescence light microscopic studies showed vesicular uptake of flu-hydrin at the basolateral membrane of toad bladder epithelial cells, and this uptake was blocked by d4Lys(N3)AVT. This study shows that d-hydrin can serve as a foundation molecule to which reporter groups, such as fluorescent residues, can be attached with better preservation of hydrosmotic activity than is possible with similar modifications of vasotocin.
Glucose homeostasis and hypothalamic-pituitary-adrenocortical axis during development in rats
Authors: Widmaier E. P.
Published: December 2017

Glucoprivation represents a model stress in which activation of different stress responses at different ages can be monitored both in vivo and in vitro. Physiological data indicate rat brain contains a liver/pancreas-type glucose sensor, yet no biochemical or immunocytochemical evidence exists for such a sensor. Young rats appear to lack normal hypothalamic glucose-sensing ability and do not show typical secretory patterns of corticotropin-releasing factor, adrenocorticotropic hormone, or corticosterone after experimentally induced glucoprivation. However, they hypersecrete catecholamines and glucagon (compared with adults) and thrive on fuel sources other than glucose that are abundant after birth. High steroid levels during the first 24 h after birth may be critical for inducing gluconeogenic enzymes and promoting differentiation of tissues like pancreas. Neonatal rats also have unique control systems to combat the damaging effects of other stresses like hypoxia; these systems may disappear in adults. Thus the definition of stress may change during development, and the compensatory mechanisms employed to combat stress change from neonatal to adult life and are intricately related to the metabolic needs of the animal.
Effect of two methods of hand heating on body temperature, forearm blood flow, and deep venous oxygen saturation
Authors: Gallen I. W. , Macdonald I. A.
Published: December 2017

Two methods of hand heating [warmed blanket 40 degrees C (WB) and warm-air box 55 degrees C (WA)] were compared with the effect of no heating (control) in six healthy females. After 30 min baseline, the left hand was either heated for 1 h or not heated. Measurements were made of skin temperature (ST), core temperature (CT), right forearm (FBF) and skin blood flow (SBF), and right forearm deep venous blood oxygen content with and without occlusion of the hand circulation. CT rose above baseline in WB (by +0.2 degrees C, P less than 0.01) but not with control or WA. Abdominal ST rose only with WB (by +0.66 degrees C above baseline, P less than 0.01). FBF increased above baseline values with both WA (by +10 ml.l forearm-1.min-1) and WB (by +12 ml.l forearm-1.min-1), but neither was significantly greater than the control. SBF increased above baseline only with WB (by +202 mV, P less than 0.01), and this was significantly greater than control SBF. With an occluded hand circulation, deep venous oxygen content rose above baseline values with WB only (+6.0%, P less than 0.01) but was not greater than control with either method of hand heating. We conclude that using a warm-air box has less effect than a heated blanket on the measured variables.
Vasoactive peptides and phenylephrine actions in isolated teleost hepatocytes
Authors: Moon T. W. , Mommsen T. P.
Published: December 2017

The metabolic actions of the vasoactive peptides vasotocin and isotocin and the alpha-agonist phenylephrine are examined in hepatocytes isolated from three teleost species: brown bullhead, rainbow trout, and American eel. These three compounds influenced hepatic gluconeogenesis and glycogenolysis with significant species differences. Vasotocin and isotocin affected only eel hepatocytes activating gluconeogenesis by 1.7-fold and glycogenolysis by 3-fold. Phenylephrine increased glycogenolysis by 7-fold in bullhead hepatocytes and gluconeogenesis by 1.4-fold in trout cells. Vasotocin and phenylephrine actions were correlated with increases in adenosine 3',5'-cyclic monophosphate (cAMP). The vasotocin effects were unaffected by beta- and alpha-antagonists supporting a V2-type receptor on eel hepatocytes. Phenylephrine effects were abolished by propranolol and reduced by prazosin and yohimbine (alpha 1- and alpha 2-antagonists, respectively). Phenylephrine, therefore, affected fish hepatocyte metabolism either by a mixed alpha/beta-receptor mechanism emphasizing beta-adrenoceptors or the classic alpha/beta agonist/antagonist scheme defined for mammals is not appropriate for these fish preparations.
Parathyroid hormone-related protein and calcium homeostasis in lactating mice
Authors: Melton M. E. , D'Anza J. J. , Wimbiscus S. A. , Grill V. , Martin T. J. , Kukreja S. C.
Published: December 2017

Parathyroid hormone (PTH)-related protein has been shown to be a factor responsible for hypercalcemia of malignancy. Recent studies have shown the presence of mRNA for PTH-related protein in lactating breast tissue, suggesting a physiological role for this peptide during lactation. In the present study, we evaluated the effect of neutralization of PTH-related protein activity in lactating mice (by passive immunization) on various parameters of maternal and neonatal calcium homeostasis. PTH-related protein bioactivity, as tested in the adenylate cyclase assay, was present in mouse milk, and this activity was completely neutralized by the antisera used in the present study. In lactating mice, the effects of injection of PTH-related protein antisera on maternal serum calcium concentrations, milk calcium and phosphorus concentration, pup growth, dam femur calcium content, and pup calcium content were similar to those of the injection of normal rabbit serum. Therefore, maternal PTH-related protein does not appear to have a role in calcium homeostasis during lactation.
Characterization of the process of sodium-calcium exchange in pancreatic islet cells
Authors: Plasman P. O. , Lebrun P. , Herchuelz A.
Published: December 2017

Na(+)-Ca2+ exchange may play a role in Ca2+ extrusion from the pancreatic B-cell. The characteristics of the process working in its reverse mode were examined in normal rat pancreatic islet cells. Isosmotical replacement of extracellular Na+ by sucrose induced a concentration-dependent increase in 45Ca uptake, displaying a pharmacological sensitivity compatible with an uptake mediated by Na(+)-Ca2+ exchange. Glucose, up to 2.8 mM, stimulated reverse Na(+)-Ca2+ exchange. Likewise, membrane depolarization activated the process but only under raised intracellular Na+ activity. In conclusion, the B-cell Na(+)-Ca2+ exchange displays properties similar to those observed in other cells: reversibility and sensitivity to membrane potential. When working in its reverse mode the exchanger displays a quite large capacity. The role played by the exchanger in the process of insulin release warrants further investigation.
Leucine kinetics from [2H3]- and [13C]leucine infused simultaneously by gut and vein
Authors: Hoerr R. A. , Matthews D. E. , Bier D. M. , Young V. R.
Published: December 2017

In amino acid tracer kinetic studies of the fed state, ingested amino acid may be taken up during its initial transit through splanchnic tissues and thus not enter the plasma compartment where tracer is infused. To investigate this possibility, adult human subjects received simultaneous intravenous (iv) and intragastric (ig) leucine tracer infusions, first during a postabsorptive (PA) 4-h primed continuous ig infusion of L-[1-13C]-leucine and L-[5,5,5-2H3]leucine iv, followed on a separate day by a fed infusion, in which an ig infusion of a liquid formula was started 2 h before the tracer infusion and continued throughout the tracer study. Subjects were accustomed to a constant experimental diet supplying 1.5 g protein.kg-1.day-1 and 41-45 kcal.kg-1.day-1 for 7 and 12 days before the PA and fed studies, respectively. For the PA study, plasma enrichment for the ig tracer was 3.34 +/- 0.27 (SE) mol + excess and for the iv tracer it was 4.18 +/- 0.10 (P less than 0.02). Enrichments of alpha-keto-isocaproic acid (KIC) were 3.24 +/- 0.16 (ig) and 3.02 +/- 0.14 (iv), respectively [not significant (NS)]. For the fed study, plasma leucine enrichment for the ig tracer was 2.15 +/- 0.14 and for the iv tracer was 2.84 +/- 0.09 (P less than 0.02). KIC enrichments were 2.02 +/- 0.08 (ig) and 2.24 +/- 0.08 (iv), respectively (NS). In the PA study, the ratio of the plasma leucine enrichments for the ig and iv tracers was 0.80 +/- 0.06 and in the fed experiment, 0.76 +/- 0.05, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)