THE EFFECTS OF TYRAMINE ON THE ISOLATED NICTITATING MEMBRANE OF THE CAT

¹ Department of Pharmacology, West Virginia University Medical Center, Morgantown, West Virginia

Dose-response curves to tyramine in the nictitating membrane in vitro have been studied under a variety of conditions. In control preparations, the cumulative method of obtaining the dose-response curve results in a higher maximum response than the noncumulative method. Pretreatment with reserpine or denervation shifts the curve to the right. Denervation also depresses the maximum. However, in denervated preparations the maximum response is the same regardless of whether it is determined by the cumulative or the noncumulative method. The response of the denervated nictitating membrane is markedly antagonized by phentolamine but not by atropine. It is concluded that tyramine, at higher doses, has a direct effect on the nictitating membrane which is unmasked by reducing the norepinephrine stores. This direct action seems to be mediated primarily by alpha adrenergic receptors.