Central suppression of the arterial baroreflexes during spontaneous behaviour.

When input to the central nervous system from arterial baroreceptors was intact, or reduced to one carotid sinus, spontaneous behavioural activities in rabbits caused transient rises of systemic arterial pressure (SAP) and heart rate (HR) from low, basal levels. Complete elimination of baroreceptor input caused an immediate reversal of this pattern, so that the same activities caused abrupt falls of SAP and HR from high basal levels. This same reversal of the SAP response occurred if basal SAP was kept low by sodium nitroprusside, if cardiac nerves were blocked, or if HR was rendered invariable by propranolol and methscopolamine. It is concluded that activity-associated rises of SAP and HR can be accounted for by central suppression of baroreflex mechanisms.