Differentiation of vasodilator and sudomotor responses in the cat paw pad to preganglionic sympathetic stimulation.

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Abstract
Sweat secretion (using skin potential) and blood flow (using skin temperature) was monitored in the hind-paw skin of chloralose-anesthetized cats pre-treated with guanethidine. The responses to electrical stimulation of the ipsilateral lumbar sympathetic trunk was studied. Stimulation caused sweat secretion and an increase in skin blood flow which was almost entirely restricted to the paw pads and was completely ipsilateral. Stimulation of the tibial nerve trunk produced similar effects, except that the increase in blood flow was more prolonged. The vasodilator effect of sympathetic trunk stimulation was unaffected by chronic deafferentation of the paw. Atropine methonitrate (0.5-1 mg/kg i.v.) abolished the sudomotor response to sympathetic stimulation, but did not attentuate the blood flow response. Hexamethonium (1-2 mg/kg i.v.) abolished the vasodilator response to sympathetic stimulation, but did not affect the sudomotor response. Larger doses of hexamethonium (10-20 mg/kg) abolished both responses. The lumbar post-ganglionic neurons mediating vasodilatation in the skin of the cat paw pad are evidently distinct from those that mediate sudomotor secretion.