bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of hyperinsulinemia and hyperaminoacidemia on muscle and liver protein synthesis in lactating goats
Authors: Tauveron I. , Larbaud D. , Champredon C. , Debras E. , Tesseraud S. , Bayle G. , Bonnet Y. , Thieblot P. , Grizard J.
Published: December 2017

The experiment was carried out to clarify the roles of insulin and amino acids on protein synthesis in fed lactating goats (30 days postpartum). Protein synthesis in the liver and various skeletal muscles was assessed after an intravenous injection of a large dose of unlabeled valine containing a tracer dose of L-[2,3,4-3H]valine. The animals were divided into three groups. Group I was infused with insulin (1.7 mumol/min) for 2.5 h under glucose, potassium, and amino acid replacement. Group A was infused with an amino acid mixture to create stable hyperaminoacidemia for 2.5 h. Group C animals were controls. The fractional synthesis rates (FSR) were 31.5 +/- 2.2, 6.5 +/- 0.4, 4.3 +/- 0.8, 4.0 +/- 1.2, 3.9 +/- 1.2, and 3.6 +/- 0.4%/day (SD) in liver, masseter, diaphragm, anconeus, semitendinosus, and longissimus dorsi, respectively, for group C. Neither hyperinsulinemia in group I nor hyperaminoacidemia in group A had not affected by hyperinsulinemia but was stimulated by hyperaminoacidemia (+30%, P < 0.05). In contrast to previous experiments in which a labeled amino acid was constantly infused, this study revealed a stimulating effect of amino acids on protein synthesis in the liver but not in skeletal muscles. As previously observed in studies with the constant-infusion method, insulin had no effect on protein synthesis.
Kinetic analysis of glycogen synthase and PDC in cirrhotic rat liver and skeletal muscle
Authors: Giardina M. G. , Matarazzo M. , Sacca L.
Published: December 2017

Glycogen synthase (GS) and pyruvate dehydrogenase complex (PDC) were kinetically analyzed in the liver and skeletal muscle of fasted and refed rats with thioacetamide-induced cirrhosis of the liver. In control rats, refeeding induced a 54% decrease in the A0.5 for glucose 6-phosphate (G-6-P) of hepatic GS (P < 0.001), reflecting allosteric activation of the enzyme. In skeletal muscle the A0.5 for G-6-P did not change after refeeding, whereas the activity ratio increased by 56% (P < 0.01), indicating a greater percentage of the active G-6-P-independent form of the enzyme. In cirrhotic rats, neither the A0.5 for G-6-P of liver GS nor the activity ratio of muscle GS was influenced by refeeding. Consequently, glycogen replenishment was significantly impaired both in the liver (2.56 +/- 0.2 vs. 5.11 +/- 0.4 g/100 g; P < 0.001) and skeletal muscle (0.45 +/- 0.01 vs. 0.52 +/- 0.02 g/100 g; P < 0.01). Refeeding increased the percentage of the active form of hepatic PDC both in control (+88%; P < 0.01) and cirrhotic rats (+91%; P < 0.001). In the latter, however, the rates of total and active PDC were significantly lower than in controls [-44% and -40% in fasted (P < 0.005) and refed (P < 0.005) rats, respectively]. Muscle PDC kinetics (both maximal velocity and Michaelis constant) and the percent active form were identical in cirrhotic and control rats, regardless of the nutritional state.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of a fish oil-lard diet on rat plasma lipoproteins, liver FAS, and lipolytic enzymes
Authors: Benhizia F. , Hainault I. , Serougne C. , Lagrange D. , Hajduch E. , Guichard C. , Malewiak M. I. , Quignard-Boulange A. , Lavau M. , Griglio S.
Published: December 2017

The effects of a fish oil concentrate on blood lipids and lipoproteins were examined in relation to their effects on liver fatty acid synthase (FAS), 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, adipose tissue lipoprotein lipase (LPL), and hepatic triglyceride lipase (H-TGL). For 15 days, 2-mo-old rats were fed a control diet (10% of calories from fat, 4% fat by weight) or diets with 50% of calories (25% wt/wt) provided by lard, lard and fish oil calories (35%/15%), or lard and corn oil (35%/15%). The high-lard diet increased plasma chylomicron and liver triglycerides. The high-lard diet greatly decreased FAS, HMG-CoA reductase, and LPL activities; it also reduced H-TGL activity. Compared with the lard diet, the lard-fish oil diet decreased plasma TG by drastically lowering chylomicron (4-fold, P < 0.001) and very-low-density lipoprotein levels (P < 0.001). It also reduced high-density lipoprotein levels. The lard-fish oil diet prevented hepatic triglyceride accumulation and decreased FAS activity and mass by 3.5-fold (P < 0.001) but did not further decrease HMG-CoA reductase activity. Adipose tissue LPL activity was 2.5-fold (P < 0.001) higher with the lard-fish oil diet than with the lard diet, and H-TGL activity decreased significantly (-32%, P < 0.01), despite unaltered levels of H-TGL mRNA. These effects were significant with only 10% fish oil concentrate in the lard diet. They were not observed with the lard-corn oil diet.(ABSTRACT TRUNCATED AT 250 WORDS)
Differential short- and long-term effects of insulin on ANG II action in human adrenal glomerulosa cells
Authors: Natarajan R. , Kathuria S. , Lanting L. , Gonzales N. , Nadler J.
Published: December 2017

Insulin is known to modulate several functions in bovine adrenal cells, including steroidogenesis and growth. However, the role of insulin in regulating aldosterone synthesis in human adrenal glomerulosa cells has not been studied. In the present studies, we have examined the acute and chronic effects of insulin on angiotensin II (ANG II)-induced aldosterone synthesis in cultured normal and adenomatous human adrenal glomerulosa cells. Short-term insulin treatment (1.5 h) resulted in inhibition of ANG II-induced aldosterone synthesis. In contrast, chronic treatment (30 h) resulted in potentiation of ANG II action. The 12-lipoxygenase pathway of arachidonate metabolism has been shown to play a key role in ANG II-induced aldosterone synthesis. The acute inhibitory effects of insulin were in part mediated by inhibition of the 12-lipoxygenase pathway. The chronic stimulatory effect of insulin seemed to be due at least in part to the upregulation of cytochrome P-450 side-chain cleavage enzyme levels. These findings suggest that insulin has a differential temporal effect on ANG II action and therefore may be an important regulator of ANG II-induced aldosterone synthesis in the adrenal.
Growth responses to angiotensin II in bovine adrenal glomerulosa cells
Authors: Tian Y. , Balla T. , Baukal A. J. , Catt K. J.
Published: December 2017

The effects of angiotensin II (ANG II) on growth responses of primary cultures of bovine adrenal glomerulosa cells were studied to explore the mechanism(s) by which ANG II leads to hyperplasia and hypertrophy of the glomerulosa layer in sodium deficiency. ANG II did not increase [3H]thymidine incorporation during the first 5 days of culture, but mitogenic responses to ANG II became evident after longer periods of culture and were most prominent between 8 and 11 days after seeding. At this time, cell cycle analysis showed that ANG II increased the proportion of cells in the S phase and did not cause accumulation of cells in the G2 phase. Consistent with this finding, ANG II also stimulated proliferation of glomerulosa cells during treatment for 3 days in the presence of 1% serum. The mitogenic effect of ANG II was not inhibited by pretreatment with pertussis toxin and was mediated by AT1 receptors as indicated by its sensitivity to the subtype-selective antagonist DuP-753. Also, there was no emergence of AT2 receptors in glomerulosa cells during prolonged culture. These results indicate that intracellular mechanisms that mediate growth responses become more active during prolonged culture of glomerulosa cells. Thus, in addition to regulating the steroidogenic and secretory functions of the zona glomerulosa, ANG II exerts mitogenic actions that depend on the functional state of the glomerulosa cells.
Effect of nonworking heterotopic transplantation on rat heart glycogen metabolism
Authors: McNulty P. H. , Liu W. X. , Luba M. C. , Valenti J. A. , Letsou G. V. , Baldwin J. C.
Published: December 2017

To determine whether the contractile work history of cardiac muscle influences its responsiveness to insulin, we examined the effect of insulin infusion on glycogen metabolism in the rat heart 1 wk after transplantation into a nonworking heterotopic infrarenal position. Nonworking heterografts had higher basal glycogen concentrations than did in situ working hearts of the same animals (29.9 +/- 2.7 vs. 23.3 +/- 0.8 mumol/g; P < 0.05), and a smaller fraction of their glycogen synthase enzyme activity was in the physiologically active glycogen synthase I form (8 +/- 2 vs. 22 +/- 3%; P < 0.02). During a 25-min infusion of insulin (1 U/min) and glucose (30 mg.kg-1.min-1), the fractional glycogen synthase I activity of heterografts remained lower than that of in situ hearts (29 +/- 5 vs. 56 +/- 7%; P < 0.02) and heterografts synthesized glycogen more slowly (0.126 +/- 0.07 vs. 0.352 +/- 0.06 mumol.g-1.min-1; P < 0.02). These effects could be duplicated by a 24-h fast, which similarly increased myocardial glycogen concentration (to 32.9 +/- 5.6 mumol/g). These observations suggest that the performance of repetitive contractile work is necessary to maintain the myocardium maximally responsive to insulin. Mechanical unloading increases myocardial glycogen concentration, thereby reducing the magnitude of insulin's stimulation of glycogen synthase and consequently the rate of incorporation of circulating glucose into glycogen.
Estimation of TCA cycle flux, aminotransferase flux, and anaplerosis in heart: validation with syntactic model
Authors: Cohen D. M. , Bergman R. N.
Published: December 2017

Weiss et al. (Circ. Res. 70: 392-408, 1992) proposed a model of the citric acid cycle (CAC) in myocytes and a system of 17 differential equations that can be used to describe the changes over time in enrichment of carbons C-2 and C-4 of glutamate under conditions of metabolic steady state. They also proposed an empirical measure (KT) of flux through the CAC, which has been shown to be correlated to O2 consumption in rat hearts perfused with acetate or a mixture of glucose and acetate. We report a new method for estimation of the absolute rate of the flux through the CAC in heart (vTCA), without the numerical solution of differential equations. Unlike KT, our estimate is equal to the rate of flux catalyzed by the alpha-ketoglutarate dehydrogenase complex (vTCA), not merely correlated with it. We also estimate the rate of flux catalyzed by aspartate aminotransferase (vTA) and by NADP(+)-dependent malic enzyme (an anaplerotic reaction). The formula for vTCA during administration of [2-13C]acetate is as follows: vTCA = M[(C-2ssLC-4)/[C-4ss(LC-4-LC-2)]], where C-2ss and C-4ss represent steady-state fractional enrichment, LC-2 and LC-4 represent dominant rate constants of C-2 and C-4 of glutamate, respectively, and M is the sum of concentrations of aspartate, glutamate, and intermediates of the CAC. The assumptions underlying our formula are as follows: 1) metabolic steady state is maintained, 2) exchange of molecules between cytosolic and mitochondrial compartments is rapid, 3) 13C enters pools of the CAC only from acetyl CoA via citrate synthase, 4) [citrate]/[glutamate] < 1 + (vTCA/vTA), and 5) (m-[glutamate])/M < C-2ss/C-4ss.
Enhanced insulin sensitivity and lower waist-to-hip ratio in master athletes
Authors: Pratley R. E. , Hagberg J. M. , Rogus E. M. , Goldberg A. P.
Published: December 2017

The effect of long-term aerobic exercise training on insulin action was determined in older individuals by comparing insulin sensitivity and maximal responsiveness in 11 master athletes [63.5 +/- 1.9 (SE) yr] and 10 age- and body fat-matched sedentary individuals. Maximal aerobic power was higher and the waist-to-hip ratio (WHR) was lower in the athletes, but there were no differences in body weight, percent body fat, or fat-free mass between groups. Fasting plasma glucose levels and glucose and insulin responses during oral glucose tolerance tests were lower in the athletes. The insulin concentration producing a half-maximal increase in glucose disposal (EC50) during a three-step hyperinsulinemic-euglycemic glucose clamp was 41% lower in the athletes than in controls (483 +/- 30 vs. 822 +/- 132 pmol/l, P < 0.05), whereas maximal responsiveness was comparable (81.0 +/- 4.4 vs. 85.5 +/- 8.3 mumol.kg fat-free mass-1.min-1, P = not significant). The EC50 correlated with maximal aerobic power (r = -0.62, P < 0.01) and WHR (r = 0.52, P < 0.05), but in multiple regression analyses WHR was the only variable independently related to EC50. These results indicate that long-term aerobic exercise training is associated with enhanced insulin sensitivity and a lower WHR in older individuals. This finding suggests that regular aerobic exercise may prevent the age-associated increase in abdominal obesity and insulin resistance.
Loss of sensitivity to cholecystokinin stimulation of isolated pancreatic acini from genetically diabetic rats
Authors: Otsuki M. , Akiyama T. , Shirohara H. , Nakano S. , Furumi K. , Tachibana I.
Published: December 2017

Pancreatic exocrine function of a new inbred strain Otsuka Long-Evans Tokushima Fatty (OLETF) rat that develops spontaneous persistent hyperglycemia was evaluated in in vitro isolated pancreatic acini and compared with that in the control Long-Evans Tokushima Otsuka (LETO) rat. Serum glucose and insulin concentrations in the OLETF rats were significantly high (glucose: 270 +/- 12 vs. 208 +/- 10 mg/100 ml, P < 0.01; insulin: 12.4 +/- 1.7 vs. 4.9 +/- 0.6 ng/ml, P) < 0.01), whereas pancreatic wet weight was significantly low (803 +/- 20 vs. 1,138 +/- 17 mg, P < 0.01) compared with those in the LETO rat. Pancreatic acini isolated from the OLETF rat were totally insensitive to cholecystokinin (CCK)-8 stimulation at concentrations of up to 100 nM. However, neither the responsiveness nor the sensitivity to carbamylcholine, bombesin, and secretin of the acini from the OLETF rat was altered or even increased, probably due to the larger amylase content in the OLETF rat acini compared with those of the LETO rat acini (31.5 +/- 2.0 vs. 13.0 +/- 1.1 Somogyi units/micrograms DNA, P < 0.01). The responsiveness to fluoride, a direct activator of guanine nucleotide-binding protein, in the OLETF rat acini was similar to that in the LETO rat, suggesting that the transmembrane signaling and effectors and subsequent intracellular signal transduction molecules in the OLETF rat acini are normal. Moreover, 125I-CCK binding to the acini prepared from the OLETF rat was totally absent. These present results indicate that the OLETF rat has a selective defect in the binding of CCK to its receptors on the acinar cell surface.
Impaired postprandial clearance of triacylglycerol-rich lipoproteins in adipose tissue in obese subjects
Authors: Potts J. L. , Coppack S. W. , Fisher R. M. , Humphreys S. M. , Gibbons G. F. , Frayn K. N.
Published: December 2017

Adipose tissue is an important site of clearance of circulating triacylglycerol (TAG), especially in the postprandial period. Postprandial lipemia is usually increased in obesity. We studied the extraction of TAG from plasma and TAG-rich lipoproteins (TRLs) in subcutaneous adipose tissue in 11 control and 8 obese subjects before and after a mixed meal. Clearance of plasma TAG and very low-density lipoprotein (VLDL)-TAG was decreased in the obese subjects after an overnight fast. After the meal, chylomicron-TAG extraction increased in the control group whereas VLDL-TAG clearance decreased; these changes were not seen in the obese group, in whom the VLDL particles appeared to be better able to compete with the chylomicrons for clearance by lipoprotein lipase. In the control subjects, removal of TAG from the TRL in the postprandial period was accompanied by a shift toward addition of cholesterol to the high-density lipoprotein (HDL) fraction; this was not observed in the obese subjects. We conclude that disturbed TRL-TAG clearance in adipose tissue is related both to the elevated plasma TAG concentrations and the depressed HDL-cholesterol concentrations typical of obesity.
Effects of the normal nocturnal rise in cortisol on carbohydrate and fat metabolism in IDDM
Authors: Dinneen S. , Alzaid A. , Miles J. , Rizza R.
Published: December 2017

Plasma cortisol concentrations increase approximately three- to five-fold during sleep in healthy humans. To determine the effects of the normal nocturnal rise in cortisol on carbohydrate and fat metabolism independent of changes in endogenous insulin secretion, we studied the disposition of a mixed meal in individuals with insulin-dependent diabetes mellitus (IDDM) in whom the normal nocturnal rise in cortisol had been either prevented or mimicked by using metyrapone and a constant or variable hydrocortisone infusion. Insulin was infused intravenously on both occasions in amounts sufficient to create relative postprandial insulin deficiency. The nocturnal rise in cortisol resulted in an approximately 30 mg/dl greater (P < 0.001) peak postprandial glycemic excursion due to greater (P < 0.01) systemic glucose appearance and inappropriately low (P < 0.05) tissue glucose uptake. The latter was most evident when postprandial glucose concentrations in the presence and absence of the nocturnal rise in cortisol were matched by means of an exogenous glucose infusion to avoid the confounding effects of differences in glycemia. The nocturnal rise in cortisol also resulted in increased (P < 0.01) incorporation of 14CO2 into glucose (an index of gluconeogenesis), decreased (P < 0.05) carbohydrate oxidation, and increased (P < 0.05) rates of palmitate appearance, lipid oxidation, and beta-hydroxybutyrate concentrations. Thus the normal nocturnal rise in cortisol, independent of changes in insulin secretion, is an important regulator of postabsorptive and postprandial carbohydrate, fat, and ketone body metabolism in humans.
High-fat feeding alters the response of rat PDH complex to acute changes in glucose and insulin
Authors: Bryson J. M. , Cooney G. J. , Wensley V. R. , Phuyal J. L. , Hew M. , Denyer G. S. , Caterson I. D.
Published: December 2017

The activity of the pyruvate dehydrogenase complex (PDHC) was studied in tissues of controls and insulin-resistant fat-fed rats (FFR) both in the fed state and in overnight fasted animals after the induction of short-term changes in plasma insulin by an intravenous glucose load. Significant responses by the PDHC to the glucose challenge were seen in heart and white adipose tissue (WAT) in controls with smaller changes in brown adipose tissue (BAT) and quadriceps muscle (QM) and no change in liver. Reduced PDHC responses and lower fed values were seen in heart and BAT of FFR. The response in WAT of FFR was prolonged with no change in the PDHC response in QM. Plasma nonesterified fatty acids (NEFA) were decreased in response to the glucose load with no differences between controls and FFR. Tissue triglyceride levels were higher in liver and QM but not heart of FFR. These results show differential tissue PDHC responses to short-term changes in plasma insulin. The decreased PDHC activity in some tissues of the fat-fed animals despite the lack of change in plasma NEFA, together with the triglyceride accumulation seen in some tissues but not others, suggests that local intracellular fatty acid metabolism is important in the regulation of intracellular glucose oxidation.
Processing of pro-PTHRP by the prohormone convertase, furin: effect on biological activity
Authors: Liu B. , Goltzman D. , Rabbani S. A.
Published: December 2017

We have examined the conversion of parathyroid hormone-related peptide (PTHRP) from its NH2-terminally extended precursor pro-PTHRP. Within pro-PTHRP, an amino acid sequence exists that can serve as a substrate for the prohormone convertase, furin. To evaluate the potential role of furin in processing of this entity, we expressed pro-PTHRP in COS-7 cells, which normally produce this enzyme. Transiently transfected COS-7 cells secreted high levels of PTHRP into conditioned culture medium. Cotransfection of these cells with antisense furin cDNA resulted in marked inhibition of furin mRNA expression and secretion of an NH2-terminal fragment of pro-PTHRP, which comigrated with synthetic pro-PTHRP-(-12-->+36) on gel-permeation high-pressure liquid chromatography. In an adenylate cyclase bioassay, condition medium containing this fragment and synthetic pro-PTHRP-(-12-->+36) both exhibited lower potency than synthetic PTHRP-(1-36) and conditioned medium containing PTHRP produced by COS-7 cells in the absence of antisense furin. These results demonstrate the capacity of furin to convert pro-PTHRP to a more active product and suggest a role for this enzyme in the normal intracellular processing of this hormone.
Effects of a furan fatty acid and indoxyl sulfate on thyroid hormone uptake in cultured anterior pituitary cells
Authors: Everts M. E. , Lim C. F. , Moerings E. P. , Docter R. , Visser T. J. , De Jong M. , Krenning E. P. , Hennemann G.
Published: December 2017

A furan fatty acid, 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) and indoxyl sulfate (Indox) accumulate in serum of uremic patients and inhibit the active uptake of thyroxine (T4) into hepatocytes. We tested the effects of CMPF and Indox on the uptake of [125I]triiodothyronine (T3) and [125I]T4 and thyroid-stimulating hormone (TSH) release in anterior pituitary cells. Pituitary cells (500,000/well) were cultured for 3 days in medium with 10% fetal calf serum. Experiments were performed at 37 degrees C in the same medium with 0.5% bovine serum albumin (BSA; [125I]T3 uptake and TSH secretion) or 0.1% BSA ([125I]T4 uptake). The 15-min uptake of [125I]T3 amounted to 0.074 +/- 0.003 fmol/pM free T3 (n = 23) and that of [125I]T4 to 0.033 +/- 0.002 fmol/pM free T4 (n = 32). Preincubation (30 min) and incubation (15 min) with CMPF (20-200 microM) did not alter the uptake of [125I]T3 but reduced [125I]T4 uptake by 27% (P < 0.05) at the highest concentration tested. Indox (40-400 microM) did not affect the uptake of [125I]T3 or [125I]T4. CMPF (40 microM) and Indox (80 microM) did not directly affect the basal or thyrotropin-releasing hormone (TRH)-induced TSH release nor interfere with the effect of 10 nM T3 on TRH-induced TSH release. In conclusion, the absence of inhibitory effects of CMPF or Indox on thyroid hormone uptake by pituitary cells suggests that the transport mechanism is regulated differently compared with that in hepatocytes and underscores the significance of the thyroid hormone carriers for the intracellular availability of T3.
Sexual dimorphism in the growth response of entire and gonadectomized rats to clenbuterol
Authors: Sillence M. N. , Reich M. M. , Thomson B. C.
Published: December 2017

This study compared the anabolic effects of clenbuterol in male and female rats and determined the relative contribution of testicular and ovarian hormones to any observed gender difference. Seventy-two 12-wk-old rats were used in a 2 x 2 x 2 factorial design in which animals were either male or female, entire or gonadectomized at 3 wk of age, and fed either a control diet or a diet containing 4 mg clenbuterol/kg feed for 8 days. Compared with entire male rats, entire females gained 64% less weight, had lighter carcasses (-36%) and gastrocnemius muscles (-62%), and had higher plasma concentrations of the catabolic hormone corticosterone (P < 0.05). Castration had a negative effect on growth in male rats, and ovariectomy had a positive effect in females, but there was still a gender difference in body weight between gonadectomized males and females, which amounted to 34% of the gender difference observed in intact rats. The density of beta 2-adrenoceptors in skeletal muscle was not different between males and females, nor was it affected by gonadectomy. Clenbuterol increased both weight gain and gastrocnemius muscle weight, with the latter response in entire and castrated male rats (+ 1.31 and + 1.17 g) being more than double that seen in entire and ovariectomized females (+ 0.58 and + 0.55 g). The downregulation response of beta 2-adrenoceptors in this muscle was remarkably consistent in all treated groups (-50% to -53%).(ABSTRACT TRUNCATED AT 250 WORDS)
Cation channel activated by muscarinic agonists on porcine adrenal chromaffin cells
Authors: Forsberg E. J. , Li Q. , Xu Y.
Published: December 2017

A large portion (70%) of the secretory response to muscarinic agonists in porcine adrenal chromaffin cells has previously been shown to be dependent on extracellular Ca2+ (Xu et al., J. Neurochem. 56: 1899-1896, 1991). Results presented here show that muscarinic agonists activate a cation-selective channel which is permeable to divalent cations. The muscarinic agonist, methacholine, was found to activate the uptake of Mn2+, which paralleled the ability of methacholine to activate 45Ca2+ uptake as shown previously. Secretion induced by methacholine was not affected by nifedipine, a compound that inhibits dihydropyridine-sensitive voltage-gated Ca2+ channels. In voltage-clamped cells, methacholine activated whole cell currents, which reversed at approximately -20 mV in standard salt solutions. However, with the standard whole cell configuration, the currents were slow to activate and were often erratic. In contrast, when the perforated-patch (nystatin) technique was used to measure whole cell currents, methacholine rapidly activated sustained inward currents. Ion-substitution experiments indicated that the inward currents were carried by Na+, Ba2+, or Ca2+ but not by Cl-. Single-channel currents activated by methacholine were observed in outside-out vesicles, which were electrically accessed using the perforated-patch technique. These channels reversed at -15 mV, had a slope conductance of 20 pS, and were 14-fold more likely to be open in the presence of methacholine. These channels are probably responsible for the extracellular Ca(2+)-dependent secretory response to muscarinic receptor stimulation in porcine adrenal chromaffin cells.
Marked resistance of RAR gamma-deficient mice to the toxic effects of retinoic acid
Authors: Look J. , Landwehr J. , Bauer F. , Hoffmann A. S. , Bluethmann H. , LeMotte P.
Published: December 2017

Excessive intake of retinol or of retinoic acid causes a syndrome of characteristic toxic effects known as hypervitaminosis A. To test the role of the nuclear retinoic acid receptor (RAR gamma) in this process we produced mice with a targeted disruption of the RAR gamma gene and examined toxic effects of repeated doses of retinoic acid and two other synthetic retinoids, Ro 15-1570 and Ro 40-6055. Surprisingly, homozygous mutant mice were resistant to fourfold higher doses of retinoic acid than wild-type mice as well as to elevated doses of the synthetic retinoids, indicating that RAR gamma may have a major role in mediating retinoid toxicity, a finding that possibly has practical implications for reducing the toxicity of synthetic retinoids in clinical use.
Regulation of cholesteryl ester transfer activity in adipose tissue: comparison between hamster and rat species
Authors: Shen G. X. , Angel A.
Published: December 2017

The present study demonstrates cholesteryl ester transfer activity (CETA) in cultured hamster and rat adipose tissue. Cultured hamster and rat adipose tissue fragments released CETA into the conditioned medium, and this was associated with a reciprocal decrease in adipose tissue CETA. Regional variations in adipose CETA were observed. The levels of CETA released from cultured hamster and rat adipocytes were higher than those from adipose tissue fragments. In hamsters but not in rats, the secretion of CETA from cultured adipose tissue was increased by insulin and inhibited by EDTA in a dose-dependent fashion. Monoclonal antibodies against human cholesteryl ester transfer protein inhibited the CETA secreted from hamster adipose tissue but not that from rat adipose tissue. Fasting for 24 h and a high-cholesterol saturated fat-rich diet increased adipose CETA in hamsters and rats, and this was associated with an elevation of plasma CETA only in hamsters. This supports the view that, in hamsters, adipose CETA has in situ and intravascular functions, whereas in rats the role of adipose CETA is restricted to tissue-specific functions. Hamster cholesteryl ester transfer protein may differ from rat adipose-associated CETA in the structure of the active site and the regulatory mechanism for its secretion.
Biological activity of immunoreactive insulin-like activity extracted from rat submandibular gland
Authors: Taouis M. , Deville de Periere D. , Hillaire-Buys D. , Derouet M. , Gross R. , Simon J. , Ribes G.
Published: December 2017

Earlier studies indicate the presence of an insulin-like immunoreactivity (ILI) in rat submandibular salivary glands (SSG). Previous observations also showed that streptozotocin (STZ)-induced diabetes was accompanied by an increase in SSG ILI concentrations. In the present work we studied the effect of SSG ILI from normal and STZ diabetic rats (ILI-N and ILI-D, respectively) on insulin receptor binding and function in LMH cell line. ILI-N and ILI-D inhibited 125I-insulin binding to intact cells and wheat germ agglutinin (WGA)-purified insulin receptors with a high affinity. Furthermore, ILI-N and ILI-D activated, although weakly, the beta-subunit autophosphorylation of solubilized and WGA-purified insulin receptors. An ATP hydrolytic activity was present in ILI-N and, to a greater extent, in ILI-D extracts, which can at least in part explain their low potency for activating autophosphorylation and kinase activity of insulin receptors in vitro. However, after ILI treatment of intact cells and immunoprecipitation of insulin receptors, ILI induced a dose-dependent tyrosine phosphorylation of the insulin receptor beta-subunit. Finally, ILI-N and ILI-D stimulated amino acid uptake and lipogenesis in LMH cells. These findings suggest that SSG ILI is biologically active and can participate in metabolic regulations.
Gonadotropin-stimulated regulation of blood-follicle barrier is mediated by nitric oxide
Authors: Powers R. W. , Chen L. , Russell P. T. , Larsen W. J.
Published: December 2017

Although initially described over 30 years ago, the blood-follicle barrier has remained a biological enigma. In this study, we characterize the blood-follicle barrier with respect to its regulation of intrafollicular inter-alpha-trypsin inhibitor protein (I alpha I) influx after an ovulatory stimulus. We have found that I alpha I is localized within the ovarian vasculature but is excluded from the follicular compartment until an ovulatory stimulus is given. Within minutes after an ovulatory dose of human chorionic gonadotropin, I alpha I is localized within the follicular fluid of responding follicles where this protein becomes associated with and stabilizes the newly synthesized hyaluronic acid-rich cumulus extracellular matrix. Analysis of this process has shown that intravenous injection of sodium nitroprusside or excess substrate for nitric oxide synthase, L-arginine, mimics the effect of gonadotropic hormones on the influx of I alpha I into the follicular compartment of preovulatory follicles. Moreover, intravenous injection of specific nitric oxide synthase inhibitors, NG-nitro-L-arginine methyl ester and NG-nitro-L-arginine, inhibits gonadotropin-mediated intrafollicular influx of I alpha I and also inhibits ovulation in the mouse.
Regional differences in adipose tissue lipolysis from lean and obese women: existence of postreceptor alterations
Authors: Mauriege P. , Prud'homme D. , Lemieux S. , Tremblay A. , Despres J. P.
Published: December 2017

Lipolysis studies were performed on isolated adipose cells obtained from two subcutaneous regions (abdominal and femoral) in 26 premenopausal women (16 obese and 10 lean subjects). Because obese adipocytes from both sites were significantly larger than lean fat cells, glycerol release measured by an ultrasensitive bioluminescent method was corrected for variation in cell surface area. Epinephrine induced antilipolysis at low concentrations and a net lipolytic response at higher doses, regardless of the subjects' fatness and the anatomic location of fat. However, the catecholamine and the selective alpha 2-adrenergic agonist, UK-14304, promoted a greater maximal antilipolytic response in both femoral and subcutaneous abdominal adipose cells from obese individuals that from lean individuals. Epinephrine- and UK-14304-induced maximal antilipolysis of femoral adipocytes was also positively associated with indicators of total adiposity. On the other hand, the maximal lipolytic responses to postadrenoceptor agents such as dibutyryl adenosine 3',5'-cyclic monophosphate, forskolin, and theophylline were lower in both adipose regions in obese than in lean women. Femoral fat cell lipolysis in the presence of these agents was negatively correlated with body fatness indexes. These results suggest that, in women covering a wide range of adiposity, variations in the lipolytic response of femoral fat cells to epinephrine may involve changes in the functional balance between alpha 2- and beta-adrenoceptors and also alterations located at different postreceptor levels.
Proenkephalin gene regulation in the neuroendocrine hypothalamus: a model of gene regulation in the CNS
Authors: Borsook D. , Hyman S. E.
Published: December 2017

During the past decade, a great deal of progress has been made in studying the mechanisms by which transcription of neuropeptides is regulated by second messengers and neural activity. Such investigations, which have depended to a great extent on the use of transformed cell lines, are far from complete. Yet a major challenge for the coming decade is to understand the regulation of neuropeptide genes by physiologically and pharmacologically relevant stimuli in appropriate cell types in vivo. The proenkephalin gene, a member of the opioid gene family, has served as a model to study regulated transcription, not only in cell lines, but also in central (e.g., hypothalamic) and peripheral (e.g., adrenal) neuroendocrine tissues. Here we review regulation of proenkephalin gene expression in the hypothalamus. Several approaches, including in situ hybridization, use of transgenic mice, and the adaptation of electrophoretic mobility shift assays to complex tissues, have played critical roles in recent advances. A summary of possible future developments in this field of research is also presented.
Glucagon increases urinary oxalate excretion in the guinea pig
Authors: Holmes R. P. , Hurst C. H. , Assimos D. G. , Goodman H. O.
Published: December 2017

Factors that influence hepatic oxalate synthesis are poorly defined. Hormones are important regulators of hepatic metabolism and could potentially be involved. The effects of hyperglucagonemia were examined in guinea pigs injected with either saline or pharmacological doses of glucagon for 4 days. Glucagon treatment increased mean urinary oxalate excretion by 77% in male and 34% in female animals. The levels of hepatic peroxisomal enzymes involved in oxalate synthesis declined with glucagon treatment, but experiments with isolated peroxisomes indicated that oxalate synthesis in vitro was unaffected. Glucagon decreased hepatic alanine levels by 66%, lactate by 69%, and pyruvate by 73%, but glycolate and glyoxylate levels were unaffected. This decrease in alanine would substantially lower the activity of alanine-to-glyoxylate aminotransferase activity in vivo and make more glyoxylate available for oxalate synthesis. The decrease in lactate and pyruvate concentrations would stimulate the enzymatic conversion of glyoxylate to oxalate and may account for the increase in oxalate synthesis without an increase in glyoxylate concentration. These results demonstrate that hepatic oxalate synthesis is influenced by metabolic changes and that alterations in hepatic alanine, lactate, and pyruvate concentrations may be important elements.
Relationship between changes in body composition and insulin responsiveness in models of the aging rat
Authors: Barzilai N. , Rossetti L.
Published: December 2017

Increased body weight (BW) is one of several confounding factors that may contribute to the development of insulin resistance in human aging. Therefore aging-associated increase in BW was determined by 3H2O in Sprague-Dawley (S-D, n = 40) rats and was highly correlated with increased lean body mass (LBM), fat mass (FM), and plasma insulin and free fatty acid (FFA) levels (r2 > 0.850, P < 0.01 for all). Insulin (18 mU.kg-1.min-1) responsiveness (Rd; 270 +/- 10 mumol.kg LBM-1.min-1, P < 0.01) decreased by 17% between 2 and 4 mo but did not decline further at 14 mo. This decrease was inversely correlated with the increase in FM between 2 and 4 mo (r2 = 0.522, P < 0.05). The decline in Rd was accompanied by an approximately 20% decrease in glycolytic rate by 4 mo (P < 0.01) and in glycogen synthesis rate at 14 mo (P < 0.01) compared with 2-mo rats. Thus early impairment in intracellular glucose metabolism occurred concomitantly with an initial, rapid, and disproportionate increase in FM compared with LBM. Further increases in FM after 4 mo of age were not associated with a further decrease in insulin responsiveness in either S-D or Fischer 344 aging rats.
Ionomycin-stimulated phasic myometrial contractions
Authors: Phillippe M. , Chien E. M. , Freij M. , Saunders T.
Published: December 2017

Ionomycin, a calcium ionophore, facilitates the sustained entry of extracellular calcium; however, in myometrial tissue it stimulates phasic contractions. This study sought to define further this unanticipated effect of ionomycin and to begin to explore the possible mechanism(s) involved. Utilizing rat uterine strips, in vitro isometric contraction studies were performed to determine the effects of ionomycin with and without membrane-permeant inhibitors of cytosolic calcium oscillations. To determine the effects of ionomycin on phospholipase C, qualitative inositol phosphate production studies were performed. The in vitro contraction studies confirmed that ionomycin-stimulated phasic myometrial contractions were potentially dependent on stimulation of phospholipase C, calcium-induced calcium release, and additional calcium influx through dihydropyridine-sensitive membrane calcium channels. The inositol phosphate production studies confirmed that ionomycin stimulated phospholipase C in a dose-related fashion to levels comparable to oxytocin. In summary, these observations have confirmed the ability of ionomycin to generate dose-related phasic myometrial contractions through mechanisms potentially involving the phosphatidylinositol-signaling pathway.
Reversion of insulin resistance in the rat during late pregnancy by 72-h glucose infusion
Authors: Ramos P. , Herrera E.
Published: December 2017

To determine whether sustained exaggerated hyperinsulinemia in normoglycemic rats modifies insulin responsiveness during pregnancy, 17-day-pregnant and virgin rats were studied after receiving a continuous intravenous infusion (35 ml/day) of either 50% glucose or bidistilled water (controls) for 72 h. Plasma glucose was unchanged, whereas insulin was highly increased, and the effect was more marked in pregnant than in virgin rats. Insulin responsiveness, estimated under the hyperinsulinemic euglycemic clamp with 0.8 IU insulin.h-1.kg-1, was lower in control pregnant than in virgin rats but higher in pregnant than in virgin rats in those that had received the glucose infusion. The tissue glucose utilization metabolic index (GUI) was estimated with 2-deoxy-D-[1-3H]glucose in the clamped rats. The GUI was lower in heart, white- and red-fiber skeletal muscle, and adipose tissue in control pregnant rats than in control virgin rats, and, although the glucose infusion decreased that index in both red-fiber muscle and adipose tissue in virgin rats, glucose increased the index in red-fiber muscle in pregnant rats to the level found in virgin controls. Results therefore show that, when unaccompanied by hypoglycemia, sustained exaggerated hyperinsulinemia decreases insulin responsiveness in virgin rats but reverts insulin resistance in late-pregnant rats.
Phospholipase A2 activity is increased in guinea pig uterine cervix in late pregnancy and at parturition
Authors: Rajabi M. R. , Cybulsky A. V.
Published: December 2017

Release of arachidonic acid from phospholipids by phospholipases A2 (PLA2) is the rate-limiting step in prostaglandin (PG) synthesis. PGE2 and PGF2 alpha are essential intermediates in interstitial collagenase-mediated degradation of type I collagen, a key step in cervical dilatation at parturition. We demonstrate that PLA2 is present in cytosolic fractions of guinea pig cervix and PLA2 activity is increased during cervical dilatation at parturition. In the cervix of nonpregnant animals, PLA2 activity against phosphatidylcholine (PC) and phosphatidylethanolamine (PE) was 13 +/- 6 and 49 +/- 27 pmol.min-1.mg protein-1, respectively. Levels were similar at day 25 of pregnancy. At day 50, PLA2-PC increased to 190 +/- 54 pmol.min-1.mg-1, and PLA2-PE rose to 592 +/- 127 pmol.min-1.mg-1. At parturition (68 +/- 2 days) there were further increases of 49-67%. PLA2 activity declined toward basal levels 2 days postpartum. Almost 50% of the enhanced cytosolic PLA2 (cPLA2) activity at day 50 or at parturition was of high molecular mass and was identified as the "85-kDa cPLA2." Increases in cPLA2 activity at these time points were not, however, associated with increases in cPLA2 protein or phosphorylation of cPLA2, compared with nonpregnant animals. This study suggests that multiple PLA2 enzymes, including cPLA2, are involved in cervical dilatation at parturition.
Effect of physical exercise on glycogen turnover and net substrate utilization according to the nutritional state
Authors: Schneiter P. , Di Vetta V. , Jequier E. , Tappy L.
Published: December 2017

To determine the metabolic effects of a single bout of exercise performed after a meal or in the fasting state, nine healthy subjects were studied over two 8-h periods during which net substrate oxidation was monitored by indirect calorimetry. On one occasion, exercise was performed 90 min after ingestion of a meal labeled with [U-13C]glucose [protocol meal-exercise (M-E)]. On the second occasion, exercise was performed after an overnight fast and was followed 30 min later by ingestion of an identical meal [protocol exercise-meal (E-M)]. Energy balances were similar in both protocols, but carbohydrate balance was positive (42.2 +/- 5.1 g), and lipid balance was negative (-11.1 +/- 2.0) during E-M, whereas they were nearly even during M-E. Total glycogen synthesis was calculated as carbohydrate intake minus oxidation of exogenous 13C-labeled carbohydrate (calculated from 13CO2 production). Total glycogen synthesis was increased by 90% (from 47.6 +/- 3.8 to 90.7 +/- 5.4 g, P < 0.0001) during E-M vs. M-E. Endogenous glycogen breakdown was calculated as net carbohydrate oxidation minus oxidation of exogenous carbohydrate and was increased by 44% (from 35.8 +/- 5.6 to 51.7 +/- 6.6 g, P < 0.004) during E-M. It is concluded that exercise performed in the fasting state stimulates glycogen turnover and fat oxidation.
A model for multiple subcutaneous insulin injections developed from individual diabetic patient data
Authors: Puckett W. R. , Lightfoot E. N.
Published: December 2017

Many diabetic patients taking multiple subcutaneous insulin injections cannot adjust their dosage appropriately to maintain blood glucose within a normal range. It is hard to predict how dosage changes and physiological fluctuations affect insulin levels and subsequently glucose control. To examine these issues, we have developed a model representing the link between dosage and blood insulin levels. Our model adequately predicts insulin concentrations for individual patients and could be incorporated into an overall glucose-insulin representation. More importantly, parameter and sensitivity analysis results highlight insulin kinetic features that are difficult to isolate in a clinical setting and that may significantly influence glucose dynamics. For example, large interpatient variation, measured quantitatively by model parameters, emphasizes the need for individualized design of insulin regimens. Intrapatient variations are also large in some patients. Improved control for these patients may only be possible through more frequent sampling and control action. The sensitivity coefficient for absorption suggests a significant overlapping injection effect that is not considered in present patient management strategies.
Ouabain increases aldosterone release from bovine adrenal glomerulosa cells: role of renin-angiotensin system
Authors: Tamura M. , Piston D. W. , Tani M. , Naruse M. , Landon E. J. , Inagami T.
Published: December 2017

To evaluate the potential physiological significance of ouabain or a ouabainlike substance, we investigated the effect of nanomolar concentrations of ouabain on aldosterone release by cultured bovine adrenal glomerulosa cells. Ouabain (10 nM) increased aldosterone release from 0.35 to 0.89 ng.mg-1.4 h-1 in the serum-containing medium. Losartan prevented this increase. When angiotensinogen was added to the nonserum medium, 10 nM ouabain enhanced the aldosterone release. Losartan again blocked the increase. These findings together with a stimulation of renin release by ouabain indicate that angiotensin II generated by the adrenal cell renin-angiotensin system in the presence of exogenous serum or exogenous angiotensinogen is necessary for the ouabain-induced stimulation of aldosterone release. Ouabain (10 nM) enhanced the intracellular calcium concentration increase elicited by 0.1 nM angiotensin II severalfold. Addition of 1 nM ouabain enhanced the aldosterone secretion resulting from the addition of 1 nM angiotensin II. Nanomolar levels of ouabain, therefore, interact with both locally formed and exogenous angiotensin II to stimulate aldosterone production. A suggested mechanism is that ouabain increases calcium stores in the endoplasmic reticulum, thereby increasing the agonist response.
Mechanism of verapamil calcium channel blockade-induced hyperprolactinemia
Authors: Kelley S. R. , Kamal T. J. , Molitch M. E.
Published: December 2017

Verapamil, a phenylalkylamine calcium channel blocker, causes a doubling of serum prolactin (PRL) levels in humans. To determine whether the mechanism involved a decrease in the PRL response to dopamine (DA), we infused low doses of DA, finding that the percent inhibition of PRL was not affected by verapamil (max %decrements for 0.003, 0.01, and 0.03 microgram.kg-1.min-1 doses of DA, respectively, 86.7 +/- 19.1, 73.2 +/- 24.8, and 65.2 +/- 20.0% without verapamil and 93.4 +/- 24.6, 79.7 +/- 14.9, and 58.0 +/- 18.1% with verapamil). To determine whether the PRL elevation was due to a decrease in hypothalamic generation of DA, we measured the inhibition of PRL by L-dopa before and after inhibition of peripheral decarboxylase activity with carbidopa. Without verapamil, L-dopa alone and carbidopa-L-dopa caused similar maximum decreases in PRL levels of 83.2 +/- 2.5 and 80.3 +/- 2.0%, respectively. With verapamil, the PRL maximum decrement with L-dopa was 85.2 +/- 2.7% and with carbidopa-L-dopa was 76.3 +/- 1.9% (P < 0.01). We also found that dihydropyridine and benzothiazepine calcium channel blockers had no effect on PRL. These results suggest that verapamil acts by decreasing central DA generation, possibly through N-type calcium channels.