Selected substrate and hormonal responses to exercise were compared in two phases of the menstrual cycle. Exercise-induced changes in substrate [glucose, lactate, free fatty acids (FFA), glycerol] and hormonal patterns [luteinizing hormone (LH), follicle-stimulating hormone (FSH), insulin, progesterone (P), growth hormone (GH), cortisol] were compared in the follicular and luteal phases of the menstrual cycle in 24-h-fasted (n = 5), glucose-loaded (n = 6; 1.50 g/kg, 20% solution), and control subjects (n = 8). A treadmill walk was maintained for 60 min (30 min, 40% VO2 max; 30 min, 80% VO2 max). Blood samples were obtained 5 min before, 15, 30, 45, and 60 min during, and 30 min after exercise. In the glucose group a blood sample was also taken 20 min before exercise, and glucose was ingested 15 min before exercise. Within each nutritional group the metabolic and endocrine responses to exercise were similar in the two phases for glucose, lactate, glycerol, LH, FSH, and cortisol (P greater than 0.05). In the glucose group the FFA response was lower in the luteal phase (P less than 0.05). In the fasted subjects insulin and GH responses were elevated in the luteal phase (P less than 0.05). P responses in the control and glucose groups were markedly greater in the luteal phase (P less than 0.05). In the fasted subjects no alteration in P occurred in either phase (P less than 0.05), and the LH concentration was lower in these subjects relative to the control groups (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of hyperinsulinemia (2 wk of twice daily NPH insulin) on the kinetics of very-low-density lipoprotein (VLDL)-triglyceride (TG) was studied in rats. To avoid profound hypoglycemia the rats were allowed sucrose ad libitum. Two control groups were needed: chow only and ad libitum sucrose-supplemented (high-CHO). The insulin-treated rats had 15 times higher IRI and 50% lower plasma glucose levels than either control group. Their TG production exceeded and their TG concentrations were less than those of either control group. This indicated that their TG removal was increased even more than their TG production. This increase in TG production occurred despite lower plasma free fatty acid (FFA) levels, suggesting that a greater proportion of TG fatty acids came from a source other than FFA. Compared with chow controls, high-CHO controls had the same peripheral IRI, a slight increase in TG production, and an increase in TG concentration. The differences between the effects of CHO supplementation alone or together with injected insulin may relate to the IRI and/or the route of access of insulin (peripheral vs. portal). The present studies indicate that hyperinsulinemia, either directly or indirectly, accelerates triglyceride turnover.

Hepatocytes or hepatic plasma membranes were photoaffinity-labelled with radioiodinated N epsilon B29-monoazidobenzoyl-insulin. Analysis of the samples by SDS/polyacrylamide-gel electrophoresis and autoradiography revealed the insulin receptor as a predominant band of 450 kDa. When hepatic plasma membranes were first treated with clostridial collagenase and then photolabelled, the insulin receptor appeared as a predominant band of 360 kDa. This effect of collagenase treatment on the insulin receptor was due to Ca2+-dependent heat-labile proteinases contaminating the preparation of collagenase, and it could be mimicked by elastase. The decrease in size of the insulin receptor to 360 kDa resulted from the loss of a receptor component that was inaccessible to photolabelling. In contrast, the size of the insulin receptor of intact cells was not affected by collagenase treatment. This suggests that the site sensitive to proteolysis was located on the cytoplasmic side of the plasma membrane. In hepatic plasma membranes that were treated with collagenase or elastase, and contained the 360 kDa form of the insulin receptor, the binding affinity for insulin was increased by up to 2-fold. These findings support the concept that a component which is either a part of, or closely associated with, the insulin receptor may regulate its affinity for insulin.

HAYNES, F. J., CHEEMA-DHADLI, S . , HALPERIN, R. M., ZETTLE, R., ROBINSON, L., and WALPER~, M. L. 1988. Effect of anaesthesia on insulin-induced hypoglycemia in rabbits. Can. J . Physiol . Phamacol .66: 1 53 1 -1537.The aim of this study was to determine how anaesthetized rabbits survive much longer than awake rabbits after receiving an insulin overdose. Insulin appeared to act in both groups of rabbits because there was a prompt fall in circulating glucose, free fatty acids, and P-hydroxybutyate concentrations. Carbohydrate appeared to be the principal energy source for anaesthetized rabbits because their respiratory quotient approached unity. Although the fall in glycemia was similar in both groups of rabbits, the circulating lactate concentration rose only in the anaesthetized group. This rise in lactate in the initial 60 min after insulin was given could account for most of the fall in glycemia if the source of lactate was the glucose pool. The decline in hepatic glycogen was close to 180 prnol/g liver; this would account for about one-third of the total energy turnover and close to one-half of the measured glucose appearance in these anaesthetized rabbits, As judged from the rate of oxygen consumption, muscle glycogen seemed to supply two-thirds of the fuel to be oxidized in these rabbits. However, only one-third of the lactate released from muscle was first converted to glucose and the remainder was oxidized directly to C02. Although insulin provided the metabolic setting for a rapid rate of glucose oxidation, this rate appeared to be diminished when the overall rate of oxygen consumption was lower during anaesthesia. WAYNES, F. J . , CHEEMA-DHADLI, S . , HALPEWIN, R. M., ZETTLE, R., ROBINSON, L., et HALPEWIN. M. L. 1988. Effectof anaesthesia on insulin-induced hypoglycemia in rabbits. Can. J. Physiol. Pharmacol. 66 : 153 1 -1537. Ee but de cette dtude a Ct C de dCteminer pourquoi des lapins anesth6siCs ont survdcu plus longtemps que des lapins dveillCs aprbs avoir r e p une surdose d'insuline. L'insuline a semblC agir chez les deux groups de lapins, ayant observ6 une chute rapide des concentrations de glucose, d'acides gras libres et de p-hydroxybutyrate circulants. L'hydpate de carbone a semblt Ctre la principale source Cnergetique pour les lapins anesthksiks, du fait que leur quotient respiratoire s'est approchk de I'unitC. Bien que la chute de glycCmie ait 6tC similaire chez les deux groupes de lapins, la concentration de lactate cifculant n'a augment6 que chez le groupe anesthksid. Cette augmentation de lactate dans les premibres 60 min suivant l ' a~t m t i o n c k l'huline p W t expliqum en p d e @e la chute de glydmie si la source de lactate Ctait le p l de glucose. La diminution de glycogbne hkpatique a kt6 proche de 188 ymoYg de foie; ceci pourrait rendre compte d'environ un tiers de la consommation energetique totale et de pr&s de la moitiC de l'apparition de glucose CvaluCe chez ces lapins anesthdsits. D'aprks le taux de consommation d90xyg&ne, le glycogbne musculaire a semblC fournir Hes deux t...

Photoaffinity labelling of hepatic insulin receptors revealed specifically-labelled bands of 130, 90 and 40kDa. Endogenous protease activity in hepatic plasma membranes, as well as contaminating proteases present in preparations of clostridial collagenase, degraded some of the 130-kDa insulinbinding subunit to a 115-kDa form. However, a large proportion of the 130-kDa subunits were resistant to degradation, suggesting the presence of two classes of insulin receptor in hepatic plasma membranes. In one class the 130-kDa subunit was sensitive to proteolysis, while in the other it was not. In contrast, the 130-kDa receptor subunits of adipose tissue were all resistant to such degradation. Scatchard analysis of control and collagenase-treated plasma membranes demonstrated that conversion of the 130-kDa subunit to a ll5-kDa form did not affect the insulin-binding characteristics of the receptor. It was also apparent that insulin binds to a single class of highaffinity sites in hepatic plasma membranes.