Changes in serum concentrations of ACTH, corticosterone and in growth following morning or evening injection of female rats with porcine growth hormone.

The present study was designed to examine the effects of stress, associated with daily handling and placebo injection, on growth and adrenal activity in female rats. A second objective was to examine the effects of porcine GH (pGH) on growth and on serum concentrations of ACTH and corticosterone. Treatments were administered in the morning (08.00 h) in semi-darkness, or in the evening (20.00 h) towards the end of the light period and were timed to coincide with reported periods of high and low adrenal sensitivity to ACTH. Handling of and s.c. injection of saline into female rats (initial body weight 220 g) each morning for 21 days did not affect growth, food intake or organ weights. In contrast, daily handling and saline injection each evening caused a marked reduction in weight gain (25%), food intake (12%) and liver weight (8%), accompanied by a trend towards an increase in adrenal weight (11%), but no change in serum corticosterone concentrations. In a second experiment, treatment of female rats (initial body weight 180 g) with pGH (5.6 mg/kg) daily at 08.00 h caused a significant improvement in weight gain (17%), but food intake and organ weights were unaltered. Daily injection of rats with pGH at 20.00 h caused a greater relative improvement in weight gain (45%) than did treatment at 08.00 h as the growth impairment caused by the stress of handling was counteracted. The adverse effect of evening injections of saline on food intake was also counteracted by pGH. Changes in liver and adrenal weights, however, were not attenuated by pGH treatment.(ABSTRACT TRUNCATED AT 250 WORDS)