Role of sympathetic nervous system in hypotension induced by platelet-activating factor in anesthetized dogs

This experiment was designed to investigate whether platelet-activating factor (PAF)-induced hypotension in anesthetized dogs produces changes in sympathetic activity in the heart, kidney, liver, and adrenal gland in intact animals (n = 5) and in animals with complete systemic baroreceptor denervation (n = 5). Following intravenous injection of PAF (10 micrograms/kg) in animals with intact baroreceptors, systemic blood pressure fell significantly. However, sympathetic nerve activity in the kidney, liver, and adrenal gland revealed a biphasic pattern: an initial increase (within 30 sec) followed by a progressive reduction below the preinjection level. In contrast to these nerve responses to PAF, only cardiac nerve activity showed an initial and significant increase, and it remained elevated above the preinjection level until the end of the experiment (10 min). In animals with complete systemic baroreceptor denervation, these sympathetic responses to PAF did not differ significantly from the responses in the intact animals. These results indicate that intravenous injection of PAF produces differential control of sympathetic nerve activity in different organs. The contribution of systemic baroreceptors to reflex compensations is minor in PAF-induced hypotension.