Carotid sinus baroreceptor modulation of fluid transport and blood flow in the feline jejunum.

Carotid sinus baroreceptor control of jejunal fluid transport and vascular resistance was studied in chloralose-anesthetized cats. The carotid sinuses were isolated and perfused with blood from the femoral arteries. The aortic nerves were divided. In an isolated jejunal segment we measured net fluid transport rate, transmural potential difference (PD), and blood flow at a constant perfusion pressure of 75 mmHg. Carotid sinus pressure (CSP) was increased to 200-250 mmHg and was then lowered, in steps of approximately 25 mmHg, down to 50 mmHg. In the pressure interval from 90 to 200 mmHg, decreases in CSP increased jejunal vascular resistance and fluid absorption rate and decreased PD. In the interval from 50 to 90 mmHg, decreases in CSP increased vascular resistance and decreased PD but did not affect net fluid absorption rate. The results indicate that changes in baroreceptor activity may reflexly influence both vascular resistance and fluid transport rate in the feline jejunum, possibly via separate sympathetic mechanisms.