Sympatho-adrenal medullary functions in response to intracerebroventricularly injected corticotropin-releasing factor in anesthetized rats

Abstract

Effects of intracerebroventricular (i.c.v.) administration of corticotropin-releasing factor (CRF) on adrenal sympathetic efferent nerve activity, adrenal catecholamine secretion rate and cardiovascular function (i.e. blood pressure, heart rate and renal nerve activity) were investigated in halothane-anesthetized rats. Administration (i.c.v.) of CRF resulted in a dose-dependent increase (to 140% of control, for a 6.4 nmol dose) in adrenal sympathetic nerve activity which began several minutes after injection and reached maximum values approximately 30–60 min later. This increase was significant, when tested against vehicle injected controls, for doses of 6.4 nmol and 640 pmol; however, a 64 pmol dosage did not produce significant effects. Acute hypophysectomy did not influence the response of adrenal nerve activity to i.c.v. injection of CRF. Intravenous administration of CRF (6.4 nmol) did not produce any significant increases in ongoing activity of the adrenal nerve. Following i.c.v. administration of CRF (640 pmol), epinephrine and norepinephrine secretion, as measured from adrenal venous blood samples, showed a similar response pattern to that of the adrenal nerve. Significant increases (maximum increases, from 13.2 to 31.5 ng/kg/min and from 4.1 to 8.6 ng/kg/min for epinephrine and norepinephrine secretion rates, respectively) were observed over the 90 min blood sampling period. The present study demonstrates by direct recording of adrenal sympathetic nerve activity and measurement of adrenal catecholamine secretion rate, that i.c.v. administered CRF can increase adrenal sympathetic efferent nerve activity resulting in increases in catecholamine secretion. In addition, renal nerve activity also showed dose-dependent increases after CRF i.c.v. administration (to 160% of control, for a 6.4 nmol dose) as did heart rate (increases of 35 beats/min for a 6.4 nmol dose). However, blood pressure did not change with the same dose of CRF administered intracerebroventricularly, possibly as a result of direct effects of halothane upon peripheral blood vessels.