Vascular effects of apomorphine and related compounds in the perfused rat kidney

The renal vascular effects of aporphines and related compounds were studied on the isolated perfused rat kidney in the presence of 10(-5) M phenoxybenzamine and 10(-5) M sotalol and after contraction of the vascular bed with prostaglandin F2 alpha (10(-7) -3 X 10(-6) M). Under these conditions, (R)-(-)-apomorphine showed renal dopaminomimetic activity, i.e. renal vasodilation competitively inhibited by (+)-butaclamol (10(-8) M) but not by (-)-butaclamol (3 X 10(-8) M). It had an apparent affinity 25 times higher but a markedly lower intrinsic activity than dopamine. N-n-Propyl and trihydroxylated aporphines were less potent and the mono-10-hydroxylated aporphine was completely inactive. (S)-(+)-Bulbocapnine also showed weak dopaminomimetic activity but tetrahydropapaveroline was devoid of such an effect. (-)-N-(2-Chloroethyl)-norapomorphine (10(-5) M) irreversibly antagonised dopamine-induced renal vasodilation. At concentrations above 3 X 10(-6) M, most aporphines and tetrahydropapaveroline induced additional non-dopamine receptor related renal vasodilation.