Facilitation of baroreceptor reflex response by endogenous somatostatin in the rat

We evaluated the potential participation of endogenous brain somatostatin-14 (SOM) in central cardiovascular regulation, using adult male Sprague-Dawley rats anesthetized with pentobarbital sodium (40 mg/kg, i.p.). Intracerebroventricular (i.c.v.) application of SOM (2 or 4 nmol) promoted a significant elevation in baroreceptor reflex (BRR) response, induced by phenylephrine (5 μg/kg, i.v.). Blocking the endogenous SOM activity with its specific receptor antagonist, cyclo-[7-aminoheptanoyl-Phe-d-Trp-Lys-Thr(Bzl)] (2 or 4 nmol, i.c.v.) or antiserum against SOM (1 : 20, i.c.v.), on the other hand, appreciably attenuated the same response. These modulatory effects on the BRR response were essentially duplicated upon bilateral microinjections of SOM (320 pmol), SOM antagonist (320 pmol) or anti-SOM (1 : 20) into the caudal portion of the nucleus of tractus solitarius (NTS), the terminal site for baroreceptor afferents. These results suggest that neurons that contain SOM may participate in cardiovascular control by tonically facilitating the BRR, possibly by exerting an influence on the neurons at the NTS.