Arterial baroreceptor reflexes in the seal and their modification during experimental dives

Abstract

With use of single- and few-fiber preparations of the carotid sinus nerve of the anesthetized seal Phoca vitulina, relationships between impulse frequency in baroreceptor fibers and the static and dynamic pressures in the carotid sinus were established. These apparently were similar to those in terrestrial mammals. In isolated perfused carotid sinus preparations, there was an inverse relationship between mean sinus pressure and heart rate and arterial blood pressure. Baroreflex control of heart rate as a closed-loop system was studied by relating the pulse interval to the systolic and mean arterial blood pressures during pressor tests produced by i.v. phenylephrine before, during and after an experimental dive. During a dive, resetting of the baroreflex toward bradycardia occurred together with an increase in gain of the reflex control of pulse interval (.DELTA. pulse interval/.DELTA. blood pressure) at a given reference systolic pressure. The increased gain may be solely the result of a shift in the whole curve, so that the same arterial pressure now corresponds to a steeper portion of the curve. During an experimental dive, the gain of the carotid sinus baroreceptor reflex control of heart rate (.DELTA. heart rate/.DELTA. carotid sinus pressure) was increased.