Cardiovascular Effects Elicited by Milonine, a New 8,14‐Dihydromorphinandienone Alkaloid

: The mechanisms underlying the cardiovascular responses evoked by milonine (i.v.), an alkaloid, were investigated in rats. In normotensive rats, milonine injections produced hypotension and tachycardia, which were attenuated after Nw‐nitro‐l‐arginine methyl esther (l‐NAME; 20 mg/kg, i.v.). In phenylephrine (10 μM), pre‐contracted mesenteric artery rings, milonine (10−10 M to 3 × 10−4 M) caused a concentration‐dependent relaxation (EC50 = 1.1 × 10−6 M, Emax = 100 ± 0.0%) and this effect was rightward shifted after either removal of the vascular endothelium (EC50 = 1.6 × 10−5, p