ANATOMIC AND PHYSIOLOGIC PROPERTIES OF CUTANEO-VISCERAL VASOMOTOR REFLEX ARCS

Abstract

In intact white rats under nembutal anesthesia and in unanesthetized rats with the spinal cord transected in the lower cervical region, localized warming of the skin in the caudal half of the thoracic region to approx. 45 [degree]C. consistently elicited reflex vasodilatation in the small intestine. Localized cooling of the skin in the same area consistently elicited reflex vasoconstriction in the small intestine. The sympathetic innervation of the gastro-intestinal blood vessels, through which these reflex reactions are carried out, include both vasoconstrictor and vasodilator nerve fibers. The former appear to be adrenergic; the latter cholinergic. Thermal stimulation of a cutaneous area which has been rendered hyperemic elicits no appreciable vasomotor reactions in the intestine. Somatic pain producing stimulation elicits prompt vasoconstriction throughout the gastro-intestinal tract regardless of an existing hyperemia. The receptors through which thermal sensations and reflex vasomotor reactions in viscera, elicited by thermal stimulation of the skin, are mediated appear to be closely associated with cutaneous blood vessels. Tissue deformations incident to tonic changes in the musculature of these vessels probably play an essential role in the activation of the receptors in question and, consequently, in sensory adaptation.