SOME ACTIONS OF METHYLPHENIDATE ON THE VASCULAR SYSTEM, ARTERIAL TISSUE AND THE NICTITATING MEMBRANE

¹ Research Department, Ciba Pharmaceutical Products Inc., Summit, New Jersey

Methylphenidate suppresses the actions of amphetamine in the femoral bed and in the heart of the dog. Methylphenidate augments the positive inotropic action of norepinephrine on the heart. It is difficult to demonstrate an augmentation of the vasoconstrictor effect of norepinephrine in the hind limb of the dog although methylphenidate can be demonstrated to antagonize the action of phentolamine in the hind limb.

Methylphenidate, in the same concentration, suppresses tyramine activity and augments norepinephrine activity in isolated strips of rabbit aorta. The augmenting effect of methylphenidate on norepinephrine in aortic strips is not affected by catechol or by iproniazid.

The dose-response curves for epinephrine and tyramine on the nictitating membrane of the cat indicate that the curve for epinephrine fits Clark's first equation and the curve for tyramine fits Clark's second equation. Methylphenidate administration does not alter the value of the exponent of the dose in each equation but only alters the K values. In the case of epinephrine the K value is increased and in the case of tyramine the K value is decreased.

The theoretical implications of these findings are discussed.