bluuebunny/crossref_metadata_2025 huggingface dataset:
Atrial natriuretic peptide stimulates submandibular gland synthesis and secretion of cGMP
Authors: Jeandel L. , Morrier E. , Heisler S.
Published: December 2017

Binding of atrial natriuretic peptide (ANP) to rat submandibular gland and its effect on guanosine 3',5'-cyclic monophosphate (cGMP) formation and salivary secretion were investigated. Membranes rapidly and specifically bound 125I-ANP. Binding was inhibited by unlabeled ANP (IC50 approximately 1.6 nM), but not by atriopeptin I, other COOH- and NH2-terminal deleted ANP fragments, or agents such as pilocarpine or substance P. Scatchard analysis revealed a single class of high-affinity sites (dissociation constant 0.74 +/- 0.25 nM; maximal binding capacity 20.5 +/- 6.3 pmol/mg protein). Intravenous infusion of ANP with pilocarpine caused a significant dose-dependent increase in the levels of cGMP detected in plasma and saliva. Because salivary cGMP may have originated in plasma, the effect of ANP on cGMP formation was evaluated in dispersed cells. ANP evoked a concentration-dependent increase in both cGMP synthesis and secretion (EC50 approximately 1.7 x 10(-8) M). The atrial peptide did affect basal or l-isoproterenol-stimulated adenosine 3',5'-cyclic monophosphate synthesis in dispersed cells. When infused by itself and/or with pilocarpine, ANP did not alter the rate of spontaneous or pilocarpine-induced salivary flow, secretion of chloride, or protein release. The data demonstrate the presence of guanylate cyclase-coupled ANP receptors in submandibular gland; the atrial peptide, however, does not exert an effect of the secretory function of the gland.
Inflation-associated increases in lung polyamine uptake: role of altered pulmonary vascular flow
Authors: Karl H. W. , Russo L. A. , Rannels D. E.
Published: December 2017

Unilateral pneumonectomy in rats leads to rapid compensatory growth of the remaining lung. Previous studies showed that postoperative increases in lung mass are preceded by enhanced uptake of exogenous polyamines and by alterations in adenosine 3',5'-cyclic monophosphate (cAMP) metabolism. These effects are both mimicked in lungs of intact animals subjected to increased inflation in vitro. Partial pneumonectomy also leads to increased flow to the contralateral lung associated with reduced pulmonary vascular resistance. This raises the possibility that the postoperative metabolic response is initiated by changes in pulmonary artery pressure (Pa) or flow, rather than altered inflation. The present studies were designed to investigate this issue. Uptake of exogenous [14C]spermidine by isolated perfused rat lungs was examined over a wide range (greater than 4-fold) of pulmonary flow and ventilation at fixed PaS. Assessment of tissue metabolism from rates of protein synthesis suggested stability of the isolated lung preparations. Apnea (0 ventilation) had no effect on spermidine uptake or flow rate, compared with lungs evaluated under normal conditions of ventilation (inspiratory pressure, 15 cmH2O; positive end expiratory pressure, 2 cmH2O; rate, 70 breaths/min). At both high and low Pa (at a flow rate of 37 +/- 1 and 11 +/- 2 ml/min, respectively, with 0 ventilation), removal of the left lung from the perfusion circuit increased specific right lung flow rate greater than 30% but had no effect on spermidine uptake. Similar alterations in flow rate to the right or both apneic lungs had no effect on the tissue content of cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)
Growth hormone directly stimulates gluconeogenesis in canine renal proximal tubule
Authors: Rogers S. A. , Karl I. E. , Hammerman M. R.
Published: December 2017

To characterize the action of growth hormone (GH) on gluconeogenesis in renal proximal tubule, glucose production was measured in suspensions of canine renal proximal tubular segments incubated with 1 mM L-alanine, 10 mM lactate, 1 mM succinate, and various concentrations (10(-11) to 10(-6) M) of recombinant bovine GH (bGH). Production of glucose increased as a function of time for 120 min. Bovine growth hormone (10(-6) M) increased glucose production at 120 min by 55 +/- 16%. Significant enhancement of glucose production occurred in suspensions of segments incubated with as little as 10(-10) M bGH. Half-maximal stimulation occurred at between 10(-9) and 10(-8) M. To ascertain whether these actions of bGH are mediated directly, we determined the effects of insulin-like growth factors (IGFs) I and II on glucose production. Addition of IGF-I to segments enhanced glucose production in a concentration-dependent manner. However, incubation with bGH did not induce measurable IGF-I production in the segments. In contrast to the action of IGF-I, IGF-II did not affect glucose production. We conclude that bGH acts directly on cells within proximal tubular segments to enhance gluconeogenesis. Stimulation of gluconeogenesis in vitro could reflect a counterregulatory action of GH exerted on renal proximal tubule in vivo.
Fiber-type composition of nine rat muscles. II. Relationship to protein turnover
Authors: Garlick P. J. , Maltin C. A. , Baillie A. G. , Delday M. I. , Grubb D. A.
Published: December 2017

Rates of protein synthesis in vivo and fiber-type composition were measured in nine limb muscles of female rats at ages ranging from weaning to 1 yr. In all muscles, there was a decline in protein synthesis with increasing age, mostly as a result of a fall in the RNA content. Rates of protein breakdown and growth were determined in six muscles and these also declined with age. Regression analysis of the data for all ages showed that protein synthesis was correlated with the content of slow oxidative fibers but not with the relative proportions of fast glycolytic to fast oxidative glycolytic fibers.
Estrogens and progestogens conserve bone in rats deficient in calcitonin and parathyroid hormone
Authors: Goulding A. , Gold E.
Published: December 2017

To examine the abilities of estrogens and progestogens to slow bone resorption and conserve bone in ovariectomized rats deficient in calcitonin (CT) or parathyroid hormone (PTH), nine groups of animals with 45Ca-labeled bones were studied for 12 wk. Rats were thyroidectomized (TX), parathyroidectomized (PTX), or given sham neck operations (Sham) and treated orally with either estrogen, 300 micrograms 17 beta-estradiol.kg body wt-1.wk-1; progestogen, 500 micrograms norethisterone acetate.kg body wt-1.wk-1; or placebo (Plac). The TX rats had parathyroid autografts and thyroxine replacement. In all surgical groups, estradiol (E2) and norethindrone (Nor) slowed urinary 45Ca excretion and conserved bone (P less than 0.001). However E2 lowered urinary hydroxyproline more than Nor. Total body Ca values (mg +/- SD) were Sham + Plac, 3,079 +/- 201; Sham + E2, 3,886 +/- 335; Sham + Nor, 3,567 +/- 459; TX + Plac, 3,123 +/- 159; TX + E2, 3,869 +/- 235; TX + Nor, 3,540 +/- 422; PTX + Sham, 3,067 +/- 249; PTX + E2, 3,775 +/- 414; PTX + Nor, 3,635 +/- 467. Importantly, E2 and Nor conserved bone as effectively in TX and PTX groups as in Sham rats, although the PTX rats had slower bone resorption and lower plasma 1,25-dihydroxyvitamin D values (P less than 0.001) than groups with intact parathyroids. We conclude that the effects of estrogens and progestogens to slow bone resorption and conserve bone are independent of CT and PTH. These findings appear relevant to the pathogenesis and treatment of postmenopausal osteoporosis.
Nonesterified fatty acids modulate steroidogenesis in mouse Leydig cells
Authors: Meikle A. W. , Benson S. J. , Liu X. H. , Boam W. D. , Stringham J. D.
Published: December 2017

The effects of nonesterified fatty acids (NEFA) in modulating testosterone synthesis stimulated by luteinizing hormone (LH, 10 ng/sample) were investigated in isolated adult mouse Leydig cells. LH-stimulated testosterone production was inhibited by triglycerides (0-500 mg/dl, 50 mg/dl, 94% of the control and 500 mg/dl, 40%) and by a mixture of NEFA (100 microM, 70% of control, 200 microM, 54%, and greater than 200 microM, less than 50%). Oleic acid was a more potent inhibitor than linoleic, stearic, or palmitic acids. 8-Bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP, 5 mM) stimulated testosterone production comparable to LH but failed to reverse the inhibition of steroidogenesis produced by the NEFA. The inhibition produced by NEFA was dependent on extracellular Ca2+; and a Ca2+ channel antagonist, verapamil (10 microM), enhanced the inhibition of chylomicrons and fatty acids. 22(R)-hydroxycholesterol (10 microM) reversed the inhibition produced by NEFA. The inhibitory effects of NEFA were reversible by removal of the fatty acids. The results indicate that NEFA are potent modulators of testosterone synthesis in Leydig cells stimulated with either LH, cAMP, or intracellular Ca2+. NEFA inhibit steroidogenesis at one of the steps preceding conversion of cholesterol to pregnenolone.
Regulation of liver angiotensinogen and kidney renin mRNA levels by angiotensin II
Authors: Nakamura A. , Iwao H. , Fukui K. , Kimura S. , Tamaki T. , Nakanishi S. , Abe Y.
Published: December 2017

The current study was designed to evaluate the role of angiotesin II (ANG II) in the regulation of renin mRNA and angiotensinogen mRNA levels. We investigated the changes in renin mRNA levels in the kidney and angiotensinogen mRNA levels in the liver induced by ANG II infusion and by inhibition of the endogenous renin-angiotensin system with enalapril or saralasin in rats. mRNAs for angiotensinogen and renin were measured by densitometric analysis of Northern blot hybridization. After a 4-h intravenous infusion of ANG II (0.2 micrograms.kg-1.min-1), angiotensinogen mRNA level in the liver increased 2.5-fold to the control level, and renin mRNA level in the kidney decreased by 45%. Four hours after treatment with a single dose of enalapril (3 mg/kg po), angiotensinogen mRNA level in the liver decreased by 50%, and renin mRNA level in the kidney increased 1.5-fold to the control level. These mRNA levels returned to control levels 8 h after treatment. After a 4-h infusion of saralasin (2.5 micrograms.kg-1.min-1) in the low-sodium state, angiotensinogen mRNA level in the liver decreased by 45%, and renin mRNA level in the kidney increased twofold to the control level. These findings suggest that ANG II is one of the factors that regulate angiotensinogen mRNA level in the liver and renin mRNA level in the kidney.
Effect of estrogen and progesterone on metabolism of apoprotein B in baboons
Authors: Kushwaha R. S. , Foster D. M. , Barrett P. H. , Carey K. D.
Published: December 2017

To determine the metabolic mechanisms by which estrogen and progesterone alter levels of apoprotein B (apo B)-containing lipoproteins, 12 ovariectomized and hysterectomized baboons, maintained on a high-cholesterol (1.7 mg/kcal) and a high-fat (40% from lard) diet and divided into four groups, were treated with estrogen, progesterone, estrogen plus progesterone, and a placebo. After 12 wk, plasma cholesterol was unchanged in the control and progesterone groups but was reduced in the estrogen- and estrogen plus progesterone-treated groups. The reduction was primarily because of decreased low-density lipoprotein (LDL) cholesterol. LDL apo B levels decreased parallel to the LDL cholesterol. Very low-density lipoprotein (VLDL) and LDL apo B metabolism were studied using a double-label turnover study. Multicompartmental modeling suggested that LDL apo B was kinetically heterogeneous and that there exists an extravascular pool, perhaps consisting of hepatic remnants, that contributes significantly to LDL apo B transport. The model was used to estimate apo B production rates and residence times. VLDL apo B production was not affected by estrogen but was increased by progesterone. LDL apo B production was increased by both estrogen and progesterone. The residence time of LDL apo B was decreased by estrogen and estrogen plus progesterone but not by progesterone. Thus estrogen and progesterone have independent effects on apo B metabolism in baboons.
Interleukin 1 stimulation of the hypothalamic-pituitary-adrenal axis
Authors: Gwosdow A. R. , Kumar M. S. , Bode H. H.
Published: December 2017

The effect of varying doses of purified human interleukin 1 (IL-1) on rectal temperature (Tr), hypothalamic corticotropin-releasing hormone (CRH), pituitary and plasma adrenocorticotropic hormone (ACTH), and plamsa corticosterone was examined in intact male rats at 24 degrees C; plasma ACTH and corticosterone responses were also studied in hypophysectomized rats. In addition, IL-1-induced changes in corticosterone concentration were investigated by means of adrenal organ cultures. Tr was measured with thermocouples. CRH and ACTH levels were determined by radioimmunoassay, and corticosterone by protein-binding assay. Intravenous administration of IL-1 (0.063-1.0 ng) resulted in hyperthermia, which began 20 min postinjection and continued for an additional 30 min. IL-1 at a dose of 0.5 ng resulted in no change in hypothalamic CRH, pituitary ACTH, or plasma ACTH levels compared with saline-treated rats. Plasma corticosterone was significantly (P less than 0.05) elevated 30 min after IL-1 administration and returned to control levels after 1 h. The higher dose of IL-1 (1.0 ng) did not affect hypothalamic CRH content, but pituitary ACTH began to rise at 15 min and was significantly (P less than 0.05) elevated 30 min after injection. Rats receiving this dose displayed elevated (P less than 0.05) plasma ACTH and corticosterone levels 30 and 60 min postinjection. No change in plasma corticosterone was observed in hypophysectomized rats administered either 1 ng of IL-1 or 1 microgram of recombinant IL-1 beta (rIL-1 beta); adrenal organ cultures treated with IL-1 (10(-11) M) responded similarly.(ABSTRACT TRUNCATED AT 250 WORDS)
Plasma amino acid kinetics during acute states of glucagon deficiency and excess in healthy adults
Authors: Couet C. , Fukagawa N. K. , Matthews D. E. , Bier D. M. , Young V. R.
Published: December 2017

The effects of glucagon deficiency and excess on plasma leucine, lysine, and alanine were examined in six healthy young adult men, with primed continuous infusions of L-[1-13C]- or L-[5,5,5-2H3]leucine, L-[alpha-15N]-lysine, and L-[3-13C]alanine for 150 min before and during 210 min of either a glucagon-deficient euglycemic state (experiment 1), a basal glucagon state (experiment 2), or a glucagon-excess state (experiment 3). Steady-state plasma hormone levels were achieved by infusion of somatostatin (250 micrograms/h) and insulin (0.07 mU.kg-1.min-1), without (experiment 1) or with an infusion of glucagon at 0.7 ng.kg-1.min-1 (experiment 2) or 2.5 ng.kg-1.min-1 (experiment 3). Plasma branched-chain amino acid (AA) concentrations did not change with altered glucagon status, whereas significant differences were observed for plasma lysine, alanine, glycine, serine, threonine, proline, tyrosine, citrulline, and ornithine levels (0.05 greater than P greater than 0.001). Plasma leucine, lysine, and alanine fluxes and the rate of de novo alanine synthesis showed no significant changes with either glucagon deficiency or excess. These findings lead to the conclusion that glucagon-induced alterations in plasma AA profiles are not due to changes in the rate of appearance of AA from peripheral tissues but rather a consequence of changes in the fate of AA within the splanchnic region.
Inhibition of renin release by 14,15-epoxyeicosatrienoic acid in renal cortical slices
Authors: Henrich W. L. , Falck J. R. , Campbell W. B.
Published: December 2017

The effects of products of the cytochrome P-450 epoxygenase pathway of arachidonate metabolism on renin have not been previously examined. Initial high-performance liquid chromatography and gas chromatography-mass spectrometry studies documented the synthesis of four epoxyeicosatrienoic acid (EET) regioisomers of epoxygenase in superficial cortical slices from male Sprague-Dawley rats. Each regioisomer was tested for effects on both isoproterenol (ISO)-stimulated and basal renin secretion from cortical slices. ISO increased renin release significantly (169%, P less than 0.01) in all incubations; 14,15-EET (10(-6) M) significantly reduced this increase in stimulated renin release to 47%. The 5,6-, 8,9-, and 11,12-EETs did not significantly affect renin release. Basal renin release was not affected by any of the four EETs. To examine the mechanism of this inhibitory action, the effects of 14,15-EET on tissue adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 5'-cyclic monophosphate (cGMP) concentrations were measured. Tissue cAMP concentrations were sharply increased (4.75-fold, P less than 0.001) by ISO; 14,15-EET did not blunt this increase significantly. ISO and 14,15-EET did not affect tissue cGMP concentrations. Incubation of [14C]EET with cortical slices resulted in only 10% conversion of the 14,15-EET to 14,15-dihydroxyeicosatrienoic acid (DHET) (diol) after 90 min; no other metabolites were observed. The 14,15 DHET did not alter either basal or stimulated renin release. These studies document the synthesis of EETs in rat kidney and demonstrate a direct effect of the 14,15-EET to inhibit stimulated renin release. This inhibitory action occurs without an effect on tissue cAMP or cGMP concentrations.
Electrophysiological response to thyrotropin-releasing hormone of rat lactotrophs in primary culture
Authors: Sartor P. , Dufy-Barbe L. , Corcuff J. B. , Taupignon A. , Dufy B.
Published: December 2017

The response of rat pituitary cells to thyrotropin-releasing hormone (TRH) in primary culture was studied in the whole-cell configuration with the patch-clamp technique. Prolactin (PRL)-containing cells were identified in the culture with a peroxidase-antiperoxidase immunocytochemical method. The cells were cultured from the pituitaries of diestrous (D) and lactating (L) female rats. Membrane electrophysiological properties (resting potential and input resistance) of pituitary cells in primary culture varied widely. Under the recording conditions reported here, the mean resting potential of lactotrophs was about -30 mV. There were spontaneous fluctuations in membrane resting potential (10-15 mV) as well as of membrane input resistance, making these parameters difficult to evaluate accurately. Most of the cells exhibited spontaneous firing activity that was shown to be mainly calcium-dependent. There was no difference between L and D cells in resting membrane electrophysiological properties. TRH (10(-7) M) induced a transient hyperpolarization of the membrane similar to that previously described in the GH3 clonal pituitary cell line. Voltage-clamp studies showed that this hyperpolarization resulted from activation of an outward current, the reversal potential of which ranged from -48 to -86.5 mV. Experimental manipulations of the ionic composition of internal and external recording media suggested that both K+ and Cl- were involved. This hyperpolarizing response was observed both in D and L cells, although L cells had larger and faster responses than D cells. This observation may be of physiological significance because lactotrophs have been reported to exist in various subtypes.
Absence of insulin-receptor downregulation in hepatocytes from hyperinsulinemic rats
Authors: Bottomley S. , Garcia-Webb P.
Published: December 2017

Insulin-induced downregulation of the insulin receptor occurs in conditions associated with high extracellular concentrations of insulin. This paper describes the effect of experimental hyperinsulinemia on insulin binding to isolated hepatocytes. In vivo experimental hyperinsulinemia was produced in rats by subcutaneous injection of long-acting insulin at low (10 mU.g-1.day-1), medium (up to 25 mU.g-1.day-1), and high (up to 50 mU.g-1.day-1) doses over 1 or 2 wk. Insulin-stimulated lipogenesis was measured to determine the efficacy of the experimentally produced hyperinsulinemia. The results showed that 1) insulin-induced downregulation, determined by insulin binding, was not present in hepatocytes from any of the hyperinsulinemic rats; 2) insulin binding was increased in hepatocytes from 1- and 2-wk high-dose hyperinsulinemic rats compared with 1-wk sucrose-control (P less than 0.05), 2-wk sucrose-control (P less than 0.01), and normal rats (P less than 0.01); 3) increased binding may have been due to an increase in the number of low-affinity receptors; 4) insulin's effect on lipogenesis (i.e., insulin-stimulated lipogenesis minus the basal value) was increased in either 1-wk (P less than 0.001) or 2-wk (P less than 0.001) high-dose insulin-treated rats compared with either normal or 2-wk sucrose-control rats; 5) insulin's effect on hepatocyte lipogenesis in sucrose-control (P less than 0.025) and in all other insulin-treated (P less than 0.008 or P less than 0.05 for 2-wk medium dose) rats was greater than insulin's effect in normal hepatocytes. The reasons for the absence of downregulation are not clear, but rapid receptor recycling, rapid degradation, and upregulation are listed as possibilities.
Elevated 1,25-dihydroxyvitamin D3 and intestinal calbindin-D9k in the toothless rat
Authors: Seifert M. F. , Gray R. W. , Bruns M. E.
Published: December 2017

The toothless (tl) rat is a nonlethal osteopetrotic mutation characterized by systemic skeletal sclerosis, growth plate morphology suggestive of rickets, and morphological evidence of reduced osteoclastic bone resorption. Vitamin D metabolites, serum calcium and phosphorus levels, and the developmental appearance of vitamin D-dependent intestinal calcium binding protein (calbindin-D9k) was studied in normal and mutant rats of tl stock from 7 to 35 days of age. 1,25-Dihydroxyvitamin D3 [1,25-(OH)2D3] was found to be significantly elevated in mutant animals by 7 days of age (71 +/- 9 pM, tl/tl vs. 24 +/- 8 pM, +/?) and continued to increase to a peak of 428 pM at the time of weaning. This was 240% higher than normals at this period. The elevated levels of 1,25-(OH)2D3 stimulated a significant and precocious appearance of intestinal calbindin-D9k in mutants, beginning by 14 days of age and reaching their peak levels at 21 days postpartum (25.6 +/- 1.7 micrograms/mg protein, tl/tl vs. 16.4 +/- 1.5 micrograms/mg protein, +/?). The cause of the elevated circulating levels of 1,25-(OH)2D3 in tl rats is unknown but may be due to the low serum phosphorus levels present in these animals.
Eicosanoid production in rabbit vascular tissues and placentas
Authors: Brown G. P. , Venuto R. C.
Published: December 2017

In pregnant rabbits, systemic levels of prostaglandin E2 (PGE2) are elevated. To evaluate the source of the rise in circulating levels of PGE2, eicosanoid production was determined in rabbit placental cotyledons and the following vascular tissues: mesenteric arteries, main renal arteries, and intrarenal preglomerular vessels (n = 6 or 7 rabbits). Comparisons were made with vascular tissues from nonpregnant rabbits (n = 6 or 7). Freshly isolated tissues were incubated for 15 min at 37 degrees C. Medium aliquots were analyzed for eicosanoids by radioimmunoassay. Maximal net production and release (pg/microgram protein) was determined by subtraction of the quantity of eicosanoids present in medium before incubation from that present at the end of incubation. Net production and release of 6-ketoprostaglandin F1 alpha (PGF1 alpha), a stable metabolite of prostacyclin, and of PGE2 was similar in vascular tissues from pregnant and nonpregnant rabbits. Thromboxane B2 (TxB2) generation in preglomerular vessels from pregnant rabbits was lower (P less than 0.05) than that of nonpregnant rabbits. This could contribute to renal vasodilation in pregnancy. The pattern of eicosanoid production in vascular tissues was 6-keto-PGF1 alpha greater than PGE2 greater than TxB2, and in cotyledons it was PGE2 greater than 6-keto-PGF1 alpha greater than TxB2. In cotyledons, PGE2 and TxB2 production was 56-219 and 2-12 times that in maternal vascular tissues, respectively. These data suggest that physiologically significant quantities of eicosanoids may be released by rabbit placental tissue.
Effects of glucose, 2-deoxyglucose, phlorizin, and insulin on food intake of lean and fatty rats
Authors: Tsujii S. , Bray G. A.
Published: December 2017

Glucose, 2-deoxyglucose, phlorizin, and insulin were injected into the third ventricle of lean and fatty rats, and food intake recorded hourly for the next 6 h. In the lean rats, there was a significant but unimpressive decrease in food intake after the intraventricular injection of glucose, but there was no effect of glucose in the fatty rat. Phlorizin in the lowest dose (10 micrograms) increased the food intake in lean animals at 1 and 2 h, and all three doses increased it significantly at 6 h after intraventricular injection. The fatty rat, in contrast, showed no response to phlorizin. 2-Deoxyglucose showed a dose-related stimulation of food intake in the lean rats at 1, 2, 3, and 6 h after injection. In the fatty rat, there was no significant effect on food intake at any dose. The intraventricular injection of insulin had no effect on food intake in either the lean or fatty rats. These studies indicate that glucose-responding systems in the region of the third ventricle are defective in the fatty rat to signals that normally increase or decrease food intake in lean animals.
Mitochondrial protein synthesis during thyroxine-induced cardiac hypertrophy
Authors: Leung A. C. , McKee E. E.
Published: December 2017

The goal of this paper was to determine the effects of 3,5,3'-triiodothyronine (T3)-thyroxine-induced cardiac hypertrophy on the rates of synthesis of mitochondrial proteins by both the cytoplasmic and mitochondrial protein synthesis systems and to compare the results with total protein synthesis and cardiac enlargement. Daily injections of T3-thyroxine in the rat resulted in a 25% increase in the growth of the ventricle compared with controls. The cytoplasmic synthesis of both mitochondrial and total proteins as measured in the isolated perfused heart was stimulated by T3-thyroxine injection to a peak of 155 and 146%, respectively, of vehicle-injected controls after 3 days of hormone treatment. This peak was followed by a gradual decline in stimulation in total protein synthesis to 132% of control by 9 days of injection, whereas the decline in stimulation of cytoplasmic synthesis of mitochondrial proteins was significantly steeper, falling to 119% of vehicle control. The rate of protein synthesis within the mitochondrial compartment was also measured during the time course of T3-thyroxine-induced hypertrophy. These rates were measured in an isolated intact heart mitochondrial protein synthesis system described and characterized in the companion papers [E. E. McKee, B. L. Grier, G. S. Thompson, and J. D. McCourt. Am. J. Physiol. 258 (Endocrinol. Metab. 21): E492-E502, 1990; and 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]. Rates of mitochondrial protein synthesis were dramatically stimulated by T3-thyroxine injection.(ABSTRACT TRUNCATED AT 250 WORDS)
Pseudoketogenesis in hepatectomized dogs
Authors: Des Rosiers C. , Montgomery J. A. , Garneau M. , David F. , Mamer O. A. , Daloze P. , Toffolo G. , Cobelli C. , Landau B. R. , Brunengraber H.
Published: December 2017

Overestimation of ketone body turnover in vivo, measured by tracer kinetics, could occur if specific activity or molar percent enrichment is diluted in extrahepatic tissues by label exchange via reversal of 3-oxoacid-CoA transferase, a process we call pseudoketogenesis. To test this hypothesis, euglycemic hepatectomized dogs were injected with a bolus of acetoacetate (0.8 mmol/kg), 32% enriched in [3,4-13C2]acetoacetate. Concentrations and labeling patterns of blood acetoacetate and R-3-hydroxybutyrate were measured by selected ion-monitoring gas chromatography-mass spectrometry. During the 60 min after bolus injection of [3,4-13C2]acetoacetate, the molar percent enrichment of blood [3,4-13C2]acetoacetate decreased to 73 +/- 3% (n = 5) in controls and to 11.5 +/- 0.8% (n = 3) during infusion of dichloroacetate, an activator of pyruvate dehydrogenase. The enrichment of R-3-hydroxy-[3,4-13C2]butyrate followed closely that of [3,4-13C2]acetoacetate. These dilutions occurred despite a net uptake of ketone bodies. Concomitantly, 10.6 +/- 2.2 (n = 5) and 6.0 +/- 2.9% (n = 3) of [13C]acetoacetate molecules were labeled on all four carbons in control and dichloroacetate-treated dogs, respectively. This uniformly labeled acetoacetate arises from partial equilibration between [3,4-13C2]acetoacetate and [1,2-13C2]acetyl-CoA via the reactions catalyzed by 3-oxoacid-CoA transferase and acetoacetyl-CoA thiolase. Our data demonstrate the reversibility of the 3-oxoacid-CoA transferase in intact extrahepatic tissues and support the concept of pseudoketogenesis. This phenomenon has been quantitated by kinetic analysis of the data.
Ischemia in normoglycemic and hyperglycemic rats: plasma energy substrates and hormones
Authors: Lundgren J. , Mans A. , Siesjo B. K.
Published: December 2017

Seizures are a documented complication to cerebral ischemia. After 10 min of forebrain ischemia in rats, preischemic hyperglycemia invariably leads to severe, most often fatal epileptic attacks. This outcome is related to the exaggerated lactic acidosis, which has been suggested as a possible contributor to severe membrane changes and widespread edema. To find out if circulating hormones or plasma energy substrates modulate this additive damage caused by the hyperglycemia, plasma concentrations of of corticosterone, epinephrine, norepinephrine, dopamine, glucagon, insulin, glucose, free fatty acids (FFA), 3-hydroxybutyrate, and acetoacetate were measured before and in the early recirculation period after 15 min of forebrain ischemia in the rat. Plasma corticosterone levels did not differ between the normo- and hyperglycemic groups. Although not significantly different from control, the catecholamine levels showed a tendency to be higher in the hyperglycemic groups. Therefore, because catecholamines have been reported to have a protective effect during ischemia the present result cannot explain why hyperglycemia aggravates the ischemic damage. Insulin levels seemed to increase during ischemia but not significantly. Levels quickly returned to normal after 30 min of recirculation. FFA concentrations were reduced after the induction of ischemia and appeared lower in all hyperglycemic groups. The level of one of the ketone bodies, 3-hydroxybutyrate, showed a significant decrease in hyperglycemic ischemia in all groups compared with normoglycemic ischemia. The same tendency was seen for acetoacetate. Results are compatible with a protective role of ketone bodies in ischemia. It is concluded that among the hormones and substrates studied only the ketone body concentrations qualify as a modulator of the exaggerated brain damage after ischemia in hyperglycemic subjects.
Role of 25-hydroxyvitamin D3 dose in determining rat 1,25-dihydroxyvitamin D3 production
Authors: Vieth R. , McCarten K. , Norwich K. H.
Published: December 2017

To understand the relationships among 1) the dose of 25-hydroxyvitamin D [25(OH)D] in vivo, 2) the activity of 1-hydroxylase in renal mitochondria, and 3) the production of 1,25-dihydroxyvitamin D [1,25(OH)2D] in vivo, we gave rats different chronic or acute doses of 25-hydroxyvitamin D3 [25(OH)D3]. We followed the metabolism of intracardially administered [25-hydroxy-26,27-methyl-3H]cholecalciferol [25(OH)[3H]D3] for 24 h before killing by measuring extracts of serum by chromatography. Specific activity of 1-hydroxylase in kidney was measured at death. In rats given 0-2,000 pmol 25(OH)D3 chronically by mouth, there was a dose-dependent decline in the percent of serum radioactivity made up of 1,25-dihydroxy-[26,27-methyl-3H]cholecalciferol [1,25(OH)2[3H]D3] as well as a decline in mitochondrial 1-hydroxylase, and these correlated significantly (r = 0.83, P less than 0.001). Serum %1,25(OH)2[3H]D3 in this experiment ranged from 0.8 to 42%. A small part of this range could be accounted for by a faster metabolic clearance rate (MCR) of 1,25(OH)2D3 from rats supplemented with 25(OH)D3 (MCR, 2.12 +/- 0.10 ml/min) compared with rats restricted in vitamin D (MCR, 0.94 +/- 0.06 ml/min, P less than 0.001). The activity of 1-hydroxylase was by far the major factor determining serum %1,25(OH)2[3H]D3. When different acute doses of 25(OH)D3 were given to rats with identical specific activities of 1-hydroxylase, the resulting 1,25(OH)2D3 concentrations in serum correlated with the 25(OH)D3 dose (r = 0.99, P less than 0.001). We conclude that the behavior of 1-hydroxylase in vivo is analogous to the classic behavior in vitro of an enzyme functioning below its Michaelis constant (Km). The amount of 1-hydroxylase present in renal mitochondria determines the fraction (not simply the quantity) of 25(OH)D metabolized to 1,25(OH)2D3 in vivo.
Age alters pulsatile prolactin release: influence of dopaminergic inhibition
Authors: Greenspan S. L. , Klibanski A. , Rowe J. W. , Elahi D.
Published: December 2017

To determine the effect of age on pulsatile prolactin secretion, we examined prolactin pulse characteristics by cluster analysis in healthy young and old male subjects during the day and night. Pulsatile prolactin secretion was identified in all subjects during the day and night, and prolactin pulse frequency remains stable with age. Younger subjects had a significantly higher prolactin pulse amplitude, area, and peak interval during the night compared with older subjects. In contrast, daytime prolactin pulse characteristics were similar in young and old subjects. Because the major neuroregulator of prolactin is dopamine and because normal aging has been reported to be associated with reductions in hypothalamic dopamine content and effect, we determined whether the mechanism of altered day-night prolactin pulsatile secretion was due to changes in dopaminergic tone. We examined endogenous prolactin secretion after administration of the dopamine antagonist metoclopramide. Metoclopramide significantly increased mean serum prolactin concentration and prolactin pulse height and amplitude in all subjects during the day and night. However, net prolactin pulse amplitude after metoclopramide stimulation at night was significantly higher in older subjects compared with younger subjects. We conclude that prolactin pulse amplitude is blunted in elderly men at night and that daytime pulsatile prolactin secretion is unaltered by age in normal men. The mechanism for this alteration of nighttime prolactin pulsatile secretion in elderly men may be due to age-associated changes in dopaminergic regulation.
Peripheral effects of insulin dominate suppression of fasting hepatic glucose production
Authors: Ader M. , Bergman R. N.
Published: December 2017

Insulin may suppress hepatic glucose production directly, or indirectly via suppression of release of gluconeogenic substrates from extrasplanchnic tissues. To compare these mechanisms, we performed insulin dose-response experiments in conscious dogs at euglycemia, during somatostatin infusion, and intraportal glucagon replacement. Insulin was sequentially infused either intraportally (0.05, 0.20, 0.40, 1.0, 1.4, and/or 3.0; protocol I) or systemically at half the intraportal rate (0.025, 0.10, 0.20, 0.50, 0.70, and/or 1.5 mU.min-1.kg-1; protocol II). Exogenous glucose infused during clamps was labeled with 3-[3H]glucose (2 microCi/g) to prevent a fall in plasma specific activity (P greater than 0.2) that may have contributed to previous underestimations of hepatic glucose output (HGO). Portal insulins were up to threefold higher during intraportal infusion, but peripheral insulin levels were not different between the intraportal and systemic protocols [7 +/- 5 vs. 9 +/- 1, 12 +/- 4 vs. 13 +/- 6, 16 +/- 3 vs. 27 +/- 5, 70 +/- 23 vs. 48 +/- 8, 83 +/- 3 vs. 86 +/- 21, and 128 vs. 120 +/- 14 microU/ml for paired insulin doses; P greater than 0.06 by analysis of variance (ANOVA)]. Despite higher portal insulin levels in protocol I, HGO suppression was equivalent in the two protocols when systemic insulin was matched, from 3.3 +/- 0.1 to near-total suppression at 0.3 mg.min-1.kg-1 at the highest insulin infusion rate (3.0 mU.min-1.kg-1; P less than 0.0001) with intraportal insulin, from 2.9 +/- 0.8 to -0.8 +/- 0.2 mg.min-1.kg-1 in protocol II (P less than 0.001). Suppression of HGO was similar at matched systemic insulin, regardless of portal insulin, suggesting the primacy of insulin's action on the periphery in its restraint of hepatic glucose production.
Interstitial glycerol concentration measured by microdialysis in two subcutaneous regions in humans
Authors: Jansson P. A. , Smith U. , Lonnroth P.
Published: December 2017

Interstitial glycerol concentrations were measured in the abdominal and femoral subcutaneous tissue in 10 lean and 6 obese subjects. In the lean subjects [waist-hip circumference ratio (WHR) 0.89 +/- 0.01] the fasting interstitial glycerol concentrations in the abdominal and femoral regions were 185 +/- 20 and 160 +/- 15 (SE) microM, respectively, whereas glycerol in venous plasma was considerably lower (66 +/- 5 microM). After an oral glucose load (100 g) the interstitial glycerol concentrations declined but remained higher than in plasma. In obese subjects (WHR 1.1 +/- 0.03) the fasting interstitial glycerol levels were higher, in both regions, than in lean individuals. Furthermore, interstitial glycerol in the abdominal site (291 +/- 32 microM) was significantly higher than in the femoral fat (210 +/- 13 microM; P less than 0.05), while plasma glycerol was similar to that in lean subjects (80 +/- 12 microM). Interstitial glycerol remained higher in the obese than in the lean subjects also after an oral glucose load, but the regional differences were less apparent. Thus interstitial glycerol is higher in the subcutaneous tissue than in venous blood. The data also suggest that lipolysis is enhanced in the abdominal subcutaneous tissue as compared with the femoral site in obese subjects and that lipolysis is exaggerated in both regions in obese as compared with lean individuals.
Activation of insulin-like growth factor gene expression during work-induced skeletal muscle growth
Authors: DeVol D. L. , Rotwein P. , Sadow J. L. , Novakofski J. , Bechtel P. J.
Published: December 2017

We have investigated the hypothesis that there is local regulation of insulin-like growth factor (IGF) gene expression during skeletal muscle growth. Compensatory hypertrophy was induced in the soleus, a predominantly slow-twitch muscle, and plantaris, a fast-twitch muscle, in 11- to 12-wk-old female Wistar rats by unilateral cutting of the distal gastrocnemius tendon. Animals were killed 2, 4, or 8 days later, and muscles of the nonoperated leg served as controls. Muscle weight increased throughout the experimental period, reaching 127% (soleus) or 122% (plantaris) of control values by day 8. In both growing muscles, IGF-I mRNA, quantitated by a solution-hybridization nuclease-protection assay, rose by nearly threefold on day 2 and remained elevated throughout the experimental period. IGF-II mRNA levels also increased over controls. A more dramatic response was seen in hypophysectomized rats, where IGF-I mRNA levels rose by 8- to 13-fold, IGF-II values by 3- to 7-fold, and muscle mass increased on day 8 to 149% (soleus) or 133% (plantaris) of the control contralateral limb. These results indicate that signals propagated during muscle hypertrophy enhance the expression of both IGF genes, that modulation of IGF-I mRNA levels can occur in the absence of growth hormone, and that locally produced IGF-I and IGF-II may play a role in skeletal muscle growth.
Diet affects the mechanisms by which TNF stimulates hepatic triglyceride production
Authors: Feingold K. R. , Adi S. , Staprans I. , Moser A. H. , Neese R. , Verdier J. A. , Doerrler W. , Grunfeld C.
Published: December 2017

Tumor necrosis factor (TNF) induces hyperlipidemia in rodents by increasing hepatic triglyceride production. We now explore the mechanism of this increase. TNF does not increase phosphatidate phosphohydrolase, glycerolphosphate acyltransferase, or diacylglycerol acyltransferase, which are enzymes of triglyceride synthesis. Rather, TNF increases triglyceride production by providing increased fatty acids (FA) as substrate. In chow-fed rats, TNF increases plasma free fatty acids (FFA). The antilipolytic drug, phenylisopropyl adenosine (PIA), prevents the TNF-induced increase in plasma FFA and, most importantly, inhibits the TNF-induced increase in plasma triglycerides. Thus increased lipolysis with delivery of FA to liver contributes to TNF-induced hyperlipidemia in chow-fed animals. In contrast, in rats fed a high-sucrose diet, TNF causes hyperlipidemia without increasing plasma FFA, and PIA has no effect on TNF-induced increases in plasma triglycerides. However, in sucrose-fed rats, TNF markedly stimulates hepatic de novo FA synthesis, which provides FA. This diet determines the mechanism by which TNF stimulates hepatic triglyceride production. The use of multiple mechanisms to increase plasma triglycerides suggests that this TNF action plays an important role in the response to infection or inflammation.
Euglycemic hyperinsulinemia augments amino acid uptake by human leg tissues during hyperaminoacidemia
Authors: Bennet W. M. , Connacher A. A. , Scrimgeour C. M. , Jung R. T. , Rennie M. J.
Published: December 2017

The effect of insulin on leg and whole body protein turnover was determined by leg exchange and plasma kinetics of [15N]phenylalanine and [1-13C]leucine during amino acid (AA) sufficiency. Eight healthy subjects were studied during AA infusion alone and during infusion of glucose and insulin (0.29 nmol.m-2.min-1) with additional AA. Insulin strongly stimulated the positive leg AA balance seen with AA (AA alone, 2.6 +/- 6.1 vs. insulin + AA, 33.1 +/- 5.8 nmol phenylalanine . 100 g leg-1.min-1; P less than 0.001). Phenylalanine uptake by leg tissues rose during insulin plus AA (47.3 +/- 11.5 vs. 73.1 +/- 7.3 nmol. 100 g-1.min-1; P = 0.022) but with only a slight reduction in leg phenylalanine release (44.7 +/- 8.1 vs. 40.0 +/- 7.9 nmol.100 g-1.min-1). Leg nonoxidative leucine plus alpha-ketoisocaproate (KIC) uptake was increased slightly with insulin (129 +/- 26 vs. 146 +/- 21 nmol.100 g-1. min-1), but leg leucine oxidation increased fourfold (P = 0.012). Leg leucine plus KIC release was reduced by insulin (120 +/- 17 vs. 84 +/- 10 nmol.100 g-1.min-1; P = 0.005); endogenous leucine appearance of leucine and phenylalanine decreased with insulin (leucine, 1.97 +/- 0.08 vs. 1.65 +/- 0.10; phenylalanine, 0.76 +/- 0.03 vs. 0.54 +/- 0.08 mumols.kg-1.min-1; P less than 0.02). The results suggest that insulin, given with sufficient amino acids, may stimulate leg and whole body protein balance by mechanisms including stimulation of protein synthesis and inhibition of protein breakdown.
Brain natriuretic peptide binding sites in rats: in vitro autoradiographic study
Authors: Konrad E. M. , Thibault G. , Pelletier S. , Genest J. , Cantin M.
Published: December 2017

Brain natriuretic peptide (BNP) is a recently discovered family of natriuretic peptides highly homologous to atrial natriuretic factor (ANF). Quantitative in vitro autoradiography with a computerized microdensitometer demonstrated that the distribution of BNP binding sites is similar to the known distribution pattern of ANF binding sites in rat tissues. Analysis of saturation and competition curves disclosed that the maximal binding capacity for BNP-(Asp-81--Tyr-106) and ANF-(Ser-99--Tyr-126) is similar within the plexiform layer of the olfactory bulb, the choroid plexus, and the adrenal zona glomerulosa. Examination of the competition curves of BNP-(Asp-81--Tyr-106), ANF-(Ser-99--Tyr-126), and des-(Gln-116--Gly-120)ANF-(Asp-102--Cys-121)NH2 (C-ANF, a ligand highly specific for ANF-R2 receptors) for 125I-labeled BNP-(Asp-81--Tyr-106) and 125I-labeled ANF-(Ser-99--Tyr-126) binding revealed that ANF fully displaced 125I-BNP binding and, conversely, BNP completely displaced 125I-ANF binding in these tissues, whereas C-ANF partially displaced 125-BNP and 125-ANF binding. Angiotensin II, insulin, glucagon, and substance P had no influence on 125I-BNP binding in the above tissues. These results support the view that BNP and ANF share the same binding sites in rats.
Effects of desipramine on norepinephrine clearance in congestive heart failure
Authors: Clemson B. , Baily R. G. , Davis D. , Zelis R.
Published: December 2017

Elevated plasma norepinephrine (NE) in congestive heart failure (CHF) is caused by increased NE spillover and decreased NE clearance. To evaluate the effects of neuronal uptake blockade on NE clearance, we studied NE kinetics during steady-state infusions of [3H]NE, before and after oral desipramine (DMI, 50 mg) in 11 patients with CHF and 8 normal volunteers. Baseline plasma NE was greater in the CHF group (637 +/- 56 vs. 271 +/- 32 pg/ml; P less than 0.001), NE clearance was lower in CHF (1.31 +/- 0.21 vs. 1.94 +/- 0.17 l.min-1.m-2; P = 0.026), and NE spillover was greater in CHF (4.71 +/- 0.78 vs. 3.04 +/- 0.35 nmol.min-1.m-2, P = 0.054). After DMI, plasma NE rose significantly in CHF (778 +/- 67; P = 0.008), and NE clearance decreased further in CHF (0.97 +/- 0.16; P = 0.024), but neither changed in normal subjects. NE spillover did not change in either group. There appears to be an enhanced effect of DMI on NE clearance in CHF patients. Two general mechanisms may be responsible for this finding, an increased concentration of drug, possibly caused by a decreased volume of distribution, and an increased sensitivity of neuronal amine pumps to DMI. Both mechanisms may reflect a more general abnormality of clearance of drugs and hormones related to abnormalities of tissue perfusion in CHF.
Effect of exercise and recovery on muscle protein synthesis in human subjects
Authors: Carraro F. , Stuart C. A. , Hartl W. H. , Rosenblatt J. , Wolfe R. R.
Published: December 2017

Previous studies using indirect means to assess the response of protein metabolism to exercise have led to conflicting conclusions. Therefore, in this study we have measured the rate of muscle protein synthesis in normal volunteers at rest, at the end of 4 h of aerobic exercise (40% maximal O2 consumption), and after 4 h of recovery by determining directly the rate of incorporation of 1,2-[13C]leucine into muscle. The rate of muscle protein breakdown was assessed by 3-methylhistidine (3-MH) excretion, and total urinary nitrogen excretion was also measured. There was an insignificant increase in 3-MH excretion in exercise of 37% and a significant increase (P less than 0.05) of 85% during 4 h of recovery from exercise (0.079 +/- 0.008 vs. 0.147 +/- 0.0338 mumol.kg-1.min-1 for rest and recovery from exercise, respectively). Nonetheless, there was no effect of exercise on total nitrogen excretion. Muscle fractional synthetic rate was not different in the exercise vs. the control group at the end of exercise (0.0417 +/- 0.004 vs. 0.0477 +/- 0.010%/h for exercise vs. control), but there was a significant increase in fractional synthetic rate in the exercise group during the recovery period (0.0821 +/- 0.006 vs. 0.0654 +/- 0.012%/h for exercise vs. control, P less than 0.05). Thus we conclude that although aerobic exercise may stimulate muscle protein breakdown, this does not result in a significant depletion of muscle mass because muscle protein synthesis is stimulated in recovery.