THE EFFECT OF d-AND l-NOREPINEPHRINE ON RAT CARDIAC PHOSPHORYLASE ACTIVATION

¹ Department of Pharmacology, Michigan State University, East Lansing, Michigan Accepted for publication September 16, 1968

Intact, anesthetized rats were infused with various doses of d- and l-norepinephrine, and the activity of the enzyme glycogen phosphorylase was determined. The d-isomer of norepinephrine activated the enzyme to the same extent as did the l-isomer but was as potent. Simultaneous infusions of both d- and l-norepinephrine resulted in a shift to the left of the l-norepinephrine dose-response curve. Pretreatment with tripelennamine did not further shift the dose-response curves obtained when d- and l-norepinephrine were infused together or when d-norepinephrine was infused alone. Reserpine pretreatment did not affect the response to d-norepinephrine, but the response was blocked by propranolol. It was concluded that d-norepinephrine has a direct action on the cardiac beta adrenergic metabolic receptor and that d-norepinephrine utilizes the same active uptake mechanism as l-norepinephrine in the rat heart.