494 EFFECT OF HYPERTHYROIDISM UPON HUMAN PANCREATIC GROWTH HORMONE RELEASING HORMONE (HPGRH)-INDUCED SECRETION OF GROWTH HORMONE (GH) IN THE ADULT MALE RAT

Abstract

Four groups (n=8) of 300 g male rats received daily s.c. injections of saline, thyroxine (T4) 20 ug, T4 40 ug, or T4 80 ug for 14 days. 24 hrs following the last injection rats were anesthetized with pentobarbital (IP 50 mg/kg) at -30 min. 10 ug HPGRH 1–44 was administered I.V. at 0 min. Blood for GH determination was obtained via cardiac puncture at 0, 5 and 10 min. Rats were decapitated at 15 min; trunk blood was collected for measurement of GH, T4RIA, and T3RIA. GH(ng/ml) *X±SD

Average daily food intake was significantly greater in groups C and D than in group A (P<.05). Final mean body wgt varied inversely with the T4 treatment dosage (Groups C,D <A;p<.01). T4RIA and T3RIA concentrations were significantly greater in rats treated with T4 then in control rats (p <.001). There were no statistical differences between mean basal or peak GH responses to HPGRH among any of the groups.

Hyperthyroidism of brief duration does not alter the GH secretory response to a pharmacologic dose of HPGRH in the adult male rat.