Differentiated hemodynamic changes controlled by splanchnic nerve

The splanchnic (SPL) nerve is a postganglionic sympathetic nerve involved in the tonic regulation of the cardiovascular system. Electrical stimulation of this nerve produces mesenteric vasoconstriction and it has been assumed that vasodilatory responses are dependent on inhibition of the vasoconstrictor tone. Several different central stimuli have been shown to dilate the hindquarter vascular bed and constrict the mesenteric vascular bed. To determine whether vasodilatory and vasoconstrictor effects in different vascular beds are elicited by activation of different sympathetic nerves, we investigated the hemodynamic changes in hindquarter, mesenteric and renal vascular beds evoked by electrical stimulation of the SPL nerve. Stimulation of the intact or sectioned SPL nerve in chloralose-anesthetized, artificially ventilated rats evoked increases in the hindquarter vascular conductance and simultaneously decreased the mesenteric and renal vascular conductance. Intravenous (i.v.) administration of l-NAME prior to stimulation of the proximal end of the sectioned SPL nerve abolished the increase in hindquarter conductance, suggesting the involvement of nitric oxide in this response. In assessing the hemodynamic effects of tonic activity on the SPL nerves, no significant changes were observed after unilateral section of the SPL nerve, but bilateral section of the SPL nerves decreased hindquarter conductance and did not significantly change the mesenteric conductance simultaneously. No consistent response was observed in the renal vascular bed after unilateral and subsequent contralateral section of the SPL nerves. These findings demonstrate that electrical stimulation of the SPL nerve produces mesenteric vasoconstriction and simultaneous hindquarter vasodilatation, which is mediated by nitric oxide. Moreover, the present data suggest that SPL nerves may provide a tonic vasodilatory tone in the hindquarter vascular bed and simultaneously a vasoconstrictor tone in another, undetermined vascular bed.