Effect of Isoproterenol on the Glucose-induced Hypothalamin Somatostatin Release / 대한내분비학회지

ABSTRACT

BACKGROUND: Acute hypoglycemia stimulates somatostatin (SRIH) release from the hypothalamus, and which in turn suppress growth hormone (GH) secretion from the anterior pituitary gland. However, the exact mechanism of glucose increases the hypothalamic SRIH secretion is not well known. Beta-adrenergic pathway is known to stimulate the hypothalamus SRIH release. We, therefore, hypothesized that the glucose-induced SRIH release may be mediated by the stimulation of the central beta-adrenergic system, and investigated to determine whether a beta-adrermgic aganist, isoproterenol, contribute the suppressive effect of glucose on the GHRH-induced GH secretian. METHODS: Ten healthy young men, aged 23 to 26 years, were studied. Four endocrinological tests were carried out. (Test 1) GHRH (Bachem, CA, U.S.A.), 100pg bolus, was given intravenously at 0 minute. (Test 2) Glucose 100 gm dissolved in water, was given orally at -30 minute and GHRH was administered as Test 1. (Test 3) Isoproterenol (Isuprel, Sanofi Winthrop, USA), 0.012 mg/kg, wasinfused continuously between 0 minute and 120 minute, and GHRH was administered as Test 1. (Test 4) Isoproterenol, 0.012 mg kg was infused continuously between 0 minute and 120 minute, and glucose and GHRH were administered as Test 2. RESULTS: Oral glucose ingestion significantly suppressed the GHRH-induced GH secretion. The acute hyperglycemia significantly suppressed GHRH-induced GH secretion. The pretreatments with isoproterenol significantly suppressed the GHRH-induced GH levels. The pretreatment with glucose and isoproterenol suppressed the GHRH-induced GH levels more compared to those induced by glucose in Test 2. The GH levels in Test 4 did not significantly differ from those in Test 3. CONCLUSION: The results of this study suggests that the hypothalamic somatostatinergic activity induced by the oral glucose administeration is not mediated by the beta-adrenergic pathway in normal men. (J Kor Soc Endocrinool 14255-264, 1999)