Effects of stress and fasting on plasma growth hormone levels in the immature rainbow trout.

Abstract

Effects of stress and fasting on plasma growth hormone (GH) levels were examined in the rainbow trout. Handling stress in shallow water for 30 min caused an immediate hyperglycemia which lasted for 6h, whereas a singificant increase in plasma GH levels was observed 6 and 12h after the stress. Plasma GH levels increased by starvation of 28 days, where significant hypoglycemia was observed. Intraperitoneal injection of bovine insulin (4 IU/100g body wt.) caused a significant increase in the plasma GH level 30 min after injection, although there was no change in the plasma glucose levels. Plasma GH levels also increased 30 min after saline injection. Thus, no significant difference was seen in the plasma profiles of GH between the saline-and insulin-injected fish, suggesting that the trout responded to “injection stress” by increased plasma GH. On the other hand, injection of glucose (100mg/100g body wt.) significantly increased plasma glucose levels over 6h, whereas there was no change in plasma GH levels. These results suggest that plasma GH levels of the trout are susceptible to stress and starvation, and that high plasma glucose evels may have an inhibitory effect on stress-induced GH secretion.