Stress response patterns of plasma corticosterone, prolactin, and growth hormone in the rat, following handling or exposure to novel environment.

Corticosterone, prolactin, and growth hormone responses to 5 s of handling or 3 min of novel environment were compared in rats at crest and trough of the diurnal adrenal rhythm 0, 5, 15, 30, and 60 min after stimulation. All hormones responded to stimulation, corticosterone and prolactin with a dramatic rise, and growth hormone with a precipitous fall. Resting corticosterone levels evidenced the expected diurnal variation, and prolactin but not growth hormone also showed a baseline diurnal variation of small magnitude at the times studied. Growth hormone response characteristics were unaffected by time of day or type of stimulation. Both corticosterone and prolactin response profiles differed at both times of day and following both types of stimulation. Corticosterone and prolactin levels were highly correlated and each was negatively correlated with growth hormone levels. This study confirms that hormone responses to stress are complex and depend not only on the stimulus but the context of stimulation.