Specificity of the effect of repeated handling on sympathetic-adrenomedullary and pituitary-adrenocortical activity in rats.

The response of the pituitary-adrenocortical and sympathetic-adrenomedullary system to single and repeated handling was studied in rats. After repeated handling (14 days, 3 x 1 min daily or 1 day, 6 x 1 min at 30 min intervals) a reduction of plasma epinephrine and ACTH level was observed, while norepinephrine levels increased to the same extent as after the first handling. When repeatedly handled rats were handled by a different person, hormonal responses were altered: The reduction in the ACTH and epinephrine response was no longer apparent, whereas the norepinephrine response was potentiated. In the case of repeated handling over a short time period (3 hr) the last handling by a different person did not alter the reduced hormonal response. Behavioral habituation to repeated handling paralleled adaptation of plasma ACTH and epinephrine levels. The observed dissociation of plasma epinephrine and norepinephrine response suggests that different pathways control the response of the adrenal medulla and the peripheral sympathetic nervous system.