EFFECTS OF CHRONIC IMMOBILIZATION STRESS ON GH AND TSH SECRETION IN THE RAT - RESPONSE TO HYPOTHALAMIC REGULATORY FACTORS

The effect of chronic immobilization (2 h/day) for 13 days on basal an d stress levels of GH and TSH, and their response to various hypothala mic regulatory factors was studied in male Sprague-Dawley rats. Chroni c immobilization (IMO) resulted in reduced serum TSH levels in stress situations but not in resting conditions. GH secretion was inhibited b oth in resting and stress situations. Chronic IMO impaired both GH and TSH responses to GRH and TRH, respectively, but also to another pepti de (VIP) stimulatory for the two hormones. Whereas somatostatin admini stration inhibited GH secretion in control but not in chronic IMO rats , its inhibitory effect on TSH was slight and similar in the two exper imental groups. The present results suggest that chronic exposure to a severe stressor such as IMO alters GH and TSH secretion, at least in part by changes in the response of the pituitary to the hypothalamic r egulatory factors. The actual influence of chronic IMO on the release of these peptides into the median eminence remains to be studied.