Regional vasomotor responses to the somatopressor reflex from muscle.

The present study was performed to determine whether qualitative and quantitative differences are present in the regional vasomotor responses to the somatopressor reflex evoked by stimulation of muscle afferents. Studies were performed in vagotomized, chloralose-anesthetized dogs with the carotid baroreceptor reflex intact. Regional vasomotor responses were determined in the isolated, innervated, constant flow-perfused vascular beds of hindlimb muscle, hindpaw, kidney, gut (superior mesenteric), and heart (circumflex coronary). Somatic afferent fiber stimulation evoked a significant systemic pressor response (+ 42%) and increased heart rate (+ 30%). An initial vasoconstrictor response occurred in all vascular beds studied, with peak reflex responses as follows: muscle +41%, paw +6%, kidney + 17%, gut + 17%, and coronary + 8%. A late, reflex vasodilator effect occurred in the hindpaw and was caused by secondary carotid baroreflex inhibition of vasomotor tone. A late vasodilator component in the coronary bed appeared to be secondary to the inotropic and chronotropic effects of the somatopressor reflex, since coronary vasodilation was eliminated by constant rate pacing and beta-adrenergic blockade, and was unaffected by vagotomy. Primary venodilation occurred in the perfused lateral saphenous venous system. Additional experiments demonstrated that spontaneous blood flow to muscle and kidney were significantly increased during the somatopressor reflex despite the generalized vasoconstrictor response.