Growth Hormone Releasing Factor Activity in the Stalk-Median Eminence and Plasma Growth Hormone Response to the Ether-Laparotomy Stress in the Rat

Abstract

The present study was performed to aim to the development of the in vitro assay method for growth hormone releasing factor (GH-RF) activity in the rat stalk-median eminence (SME), and to reveal the relationship between GH-RF activity in SME and plasma GH levels under ether-laparotomy stress in the rat.
SME extract was incubated with a total of 8 quartered anterior pituitaries. GH released into the medium was measured by polyacrylamide gel disc electrophoresisdensitometry system, and was used as an index of GH-RF activity. Plasma GH levels were estimated by the Rat GH radioimmunoassay kit (NIAMD).
Under manual handling, no significant change occurred in the levels of GH-RF activity in SME and in plasma GH levels. The ether-laparotomy (EL) stress caused a significant rise in GH-RF activity in SME at 15min and reciprocally a significant decrease in plasma GH at 5min and 15min after starting of EL stress. Namely, there was an inverse relationship between the response of GH-RF activity in SME and that of plasma GH under EL stress. These findings may suggest that the EL stress depress the GH secretion via the hypothalamus, and diminition of GH secretion could be attributed to inhibition of GH-RF release or increased secretion of an inhibitory factor.