| Abstract: | Intracerebroventricular (ICV) injections of prostacyclin (PGI2) produced biphasic blood pressure responses consisting of an initial hypotensive phase followed by a sustained pressor phase in awake rats. Heart rate increased following such injections in either awake or anesthetized rats. PGI2, 1 microgram, produced biphasic responses and, 10 micrograms, purely vasodepressor responses in anesthetized rats, but abdominal sympathetic nerve firing recorded was consistently increased. Hypophysectomy did not affect the hypotensive phase of the responses. These results indicate that the initial hypotension can not be explained by centrally-induced changes in sympathetic nerve activity or vasopressin release, but may be due to peripheral effects of PGI2 leaking from the injection site. |
