Serotonin (5-HT) and serotonergic agonists stimulate the release of corticotropin-releasing factor (CRF) from hypophysiotropic neurons and thereby activate the pituitary-adrenal axis. Studies were performed to test the hypothesis that the release of CRF into central nervous system (CNS) sites where it influences cardiovascular function is likewise stimulated by serotonergic mechanisms. Experiments were thus designed to examine whether the cardiovascular effects of central administration of low doses of 5-HT and the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), are secondary to the release of CRF. Intracerebroventricular administration of 5-HT (1 nmol) and 8-OH-DPAT (3 nmol) produced cardiovascular responses similar to those evoked by CRF (0.15 nmol), i.e., simultaneous elevations of arterial pressure and heart rate, in conscious unrestrained rats. Coadministration of the CRF receptor antagonist, alpha-helical CRF-(9-41) (9 nmol), significantly attenuated the pressor and tachycardic responses to 5-HT and 8-OH-DPAT as well as those to injection of CRF. In contrast, coadministration of alpha-helical CRF-(9-41) did not alter the pressor and bradycardic responses to a high dose (100 nmol) of serotonin. It is concluded that the cardiovascular effects of low doses of 5-HT and 8-OH-DPAT are mediated in part through the release of CRF within the CNS.