Changes in cardiac output and total peripheral resistance during the carotid sinus baroreceptor reflex in the pregnant rabbit.

1. The reflex cardiovascular effects of changes in pressure within the isolated carotid sinus have been examined in sixteen anaesthetized pregnant rabbits. 2. Comparison of the mean results at sinus pressures of 40 and 200 mmHg showed that heart rate fell by 32.1 beats min-1 and arterial pressure was reduced by 48.2 mmHg. Cardiac output, measured by thermal dilution, fell by 25.7 ml. min-1.kg-1 and total peripheral resistance was reduced by 0-292 mmHg. ml.-1 min. kg. 3. The corresponding changes previously reported in a group of seventeen non-pregnant female rabbits were a similar fall in heart rate of 34.5 beats min-1 but significantly greater reductions in arterial pressure of 69-8 mmHg and in total peripheral resistance of 0-432 mmHg. ml.-1 min.kg. However, the fall in cardiac output of 12.6 ml.min-1.kg-1 was significantly smaller. 4. These observations show that the smaller blood pressure response of the pregnant rabbit to alterations in sinus pressure is due to a reduced change in total peripheral resistance.