Relaxation of smooth muscle following contraction elicited by sympathetic nerve stimulation in vivo.

1. A method for studying in vivo the process of neuroeffector transmission in the nictitating membrane and nasal blood vessels of the cat is described. 2. Administration of desmethylimipramine or cocaine caused increases in both the amplitude and duration of the nasal and membrane responses which may be explained by inhibition of neuronal uptake of noradrenaline. 3. Phenoxybenzamine depressed the responses to nerve stimulation, but had little effect on the relationship between response amplitude and rate of recovery. 4. The relationship between response amplitude and rate of recovery is discussed and related to the sigmoid shape of a log concentration-response curve.