Pharmacological evidence that 5-HT(1B/1D) receptors mediate hypotension in anesthetized rats.

5-Carboxamidotryptamine (5-CT; 0.003-310 microg/kg, i.v.) produced dose-dependent hypotensive responses which were blocked in a complex manner by the 5-HT(7) receptor antagonist, (R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl) ethyl] pyrrolidine (SB-269970; 1 mg/kg, i.v.), in anesthetized vagosympathectomized rats. Interestingly, the 5-HT(1B/1D) receptor antagonist, N-[4-methoxy-3-(4-methyl-1-piperazinyl) phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl) [1,1-biphenyl]-4-carboxamide hydrochloride monohydrate GR-127935 (1 mg/kg, i.v.), also inhibited 5-CT-induced hypotension but the effect was clearly noncompetitive. Finally, the combination of GR-127935+SB-269970 (1 mg/kg, i.v., each) produced a further decreased of 5-CT-induced responses as compared to the effect of individual treatments. These data suggest that, in addition to 5-HT(7) receptors, 5-HT(1B/1D) receptors may also mediate hypotension in rats.