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

We monitored sweat secretion (using skin potential) and blood flow (using skin temperature) in the hind-paw skin of chloralose-anaesthetized cats pre-treated with guanethidine, and studied the responses to electrical stimulation of the ipsilateral lumbar sympathetic trunk. 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 not affected 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 attenuate 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 data suggest that the lumbar post-ganglionic neurones mediating vasodilatation in the skin of the cat paw pad are distinct from those that mediate sudomotor secretion.