Central corticotropin-releasing hormone activates the sympathetic nervous system and reduces immune function: increased responsivity of the aged rat.

CRH acts within the brain to activate the sympathetic nervous system and reduce cellular immune function. To determine the effects of age on CRH-induced elevations of sympathetic activity and suppression of immunity, we examined the responses of plasma catecholamines, neuropeptide-Y (NPY), corticosterone, and splenic natural killer (NK) activity after microinjection of rat CRH (200 pmol) into the lateral ventricle of aged (24-month-old) Fischer 344 (F344) rats compared to those in young (4-month-old) F344 rats. Basal concentrations of plasma norepinephrine and NPY were higher in the aged than in the young animals. In addition, CRH produced a greater elevation of plasma levels of catecholamines and NPY, which persisted for a longer period of time in the aged rats compared to responses in the young animals. Splenic NK activity showed an age-related decrement at baseline, and CRH induced a further significant (P less than 0.01) reduction of lytic activity in the aged rats, but did not alter cytotoxicity in t...