血漿遊離脂肪酸代謝の交感神経性調節機構に関する研究

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Free fatty acid in plasma, despite its low concentration, is regarded as an important energy source for various organs and tissues. The metabolic turnover of free fatty acid (FFA) in plasma is rapid and the plasma content of FFA is regulated by both mechanisms of mobilization from adipose tissues and utilization in various organs and tissues. Of these mechanisms, the former is considered to be more predominant than the latter. The present studies were undertaken to elucidate the physiological role of sympathoadrenergic regulation in mobilization of FFA from adipose tissues. Observations were made of the effects of adrenergic blocking agents (BL) on plasma content of FFA in normal subjects under several conditions such as rest, physical exercise and intravenous administration of glucose. In addition, an in vitro study was carried out to investigate the effect of BL on the catecholamine-induced release of FFA from rat's adipose tissue. Results obtained are as follows : (1) In young, male normal subjects at rest, both changes in plasma content of FFA after the intravenous injection of 10 mg of propranolol (in 5 subjects) and after that of 5 mg of phentolamine (in 6 subjects) were observed. Plasma content of FFA determined by the method of Dole indicated a marked decrease after the injection of propranolol, while no significant alteration was found after the injection of phentolamine. (2) In each of 7 young, male normal subjects, duplicate exercise tests consisting of the first and the second exercise test with the same work load (300 kpm/min for 10 minutes) were carried out using bicycle ergometer at the 60 minutes interval. The second exercise test was performed after the intravenous injection of 10 mg of propranolol, whereas the first exercise test was not preceded by any treatment. The change of plasma content of FFA in the first exercise test was compared with that in the second exercise test. In the former, plasma content of FFA indicated a pronounced elevation preceded by a slight drop. The elevation of plasma FFA in the latter was markedly suppressed compared with that in the former. (3) In 42 young normal subjects, 40 ml of 50% glucose was intravenously injected and the changes of plasma content of FFA were observed. The biphasic change in plasma FFA which consisted of a descending phase and a subsequent ascending phase was demonstrated. (4) In five young, male normal subjects, both effects of the pretreatment with phentolamine (5 mg) and that with propranolol (10 mg) on the pattern of plasma content of FFA after the injection of glucose were observed. Namely, three kinds of investigation were carried out in each subject at intervals of one week. It was revealed that by either pretreatment with phentolamine or with propranolol, the ascending phase of plasma FFA which was found after the injection of glucose was markedly suppressed. (5) In five subjects, the same as those mentioned in (4), further observation was made of the effect of pretreatment with phentolamine (5 mg) on the response of immune reactive insulin (IRI) following the intravenous injection of glucose. The values of serum IRI were determined by the method of Morgan and Lazarow. It was demonstrated that the maximum value of serum IRI which was seen 5 minutes after the injection of glucose was significantly increased by the pretreatment with phentolamine. The result apparently incdiates that the glucose-induced early secretion of insulin is suppressed by the activation of alpha-adrenergic receptors. (6) An in vitro study was made of the effect of BL on the catecholamine-induced release of FFA from rat's adipose tissue. A marked suppressive effect of propranolol on either isoproterenol-or norepinephrine-induce release of FFA was demonstrated. It was of interest that FFA release from adipose tissue either by norepinephrine or by isoproterenol was suppressed by a large dose of phentolamine.
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血漿遊離脂肪酸代謝の交感神経性調節機構に関する研究

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