Innervation of cat iris dilator

Publisher Website
Google Scholar
Abstract
Isometric tension changes of radially oriented iris strips of the cat were investigated in vitro. Electrical stimulation, norepinephrine (NE), and tyramine elicited contraction whereas isoproterenol elicited relaxation. Phentolamine reduced electrically and NE induced contractions and, in large doses, converted them to relaxation. Dichloroisoproterenol decreased this relaxation and the relaxation induced by isoproterenol. After chronic sympathetic denervation, electrical stimuli induced mainly relaxation and tyramine had no effect. These results indicate that contractions and relaxations in normal preparations are preponderantly mediated via excitation of adrenergic nerve terminals and release of adrenergic transmitter acting upon alpha and beta adrenergic receptors, respectively. Neostigmine and atropine had little effect on the electrically induced effects of normal preparations. In chronically denervated dilator strips, neostigmine increased and atropine decreased the relaxations and occasional slight contractions produced by electrical stimuli. These observations are interpreted that cholinergic relaxation mechanisms are also involved in the control of the dilator muscle, and that cholinergic contractions are due to activation of aberrant sphincter fibers contaminating the dilator muscle.

This publication has 0 references indexed in Scilit: