INFLUENCE OF METANEPHRINE ON RESPONSES OF THE NICTITATING MEMBRANE OF THE PITHED CAT TO SYMPATHOMIMETIC AMINES

¹ J. F. and C. Heymans Institute of Pharmacology, University of Ghent, Ghent, Belgium

The effects of dl-metanephrine (300 µg/kg i.v.) were determined on responses of the nictitating membrane to norepinephrine, to phenylephrine and to nerve stimulation. After the administration of metanephrine there was an increase in responses of the normal nictitating membrane to norepinephrine and to pnenylephrine in the lower part of the dose-response curve. The rest of the dose-response curve was practically superimposed on the corresponding controls. A similar pattern was observed for the denervated (2 days) nictitating membrane. Responses to pre- and to postganglionic stimulation obtained after the administration of metanephrine were increased for the range of low frequencies of stimulation. The rest of the frequency-response curve was superimposed on the control curve. The increase in responses in the lower part of the response curves was shown to be due to the additive effects of metanephrine and the injected sympathomimetic amine or the endogenously released norepinephrine. It is concluded that metanephrine does not potentiate responses to sympathomimetic amines in the normal or in the denervated nictitating membrane.