A-74283

A-74283, (+,-)trans-2-(4-(3a,4,4a,6a,7,7a-hexahydro-4,7-etheno-1H cyclobut [f] isoindol-1,3-dionyl)-butyl)-9-methoxy-2,2,2a,4,5,9b-hexahydro-1H-benz[e]isoindol HCl, was studied in receptor binding assays and in the spontaneously hypertensive rat (SHR). In radioligand binding to rat cortex, A-74283 had high affinity (equipotent to 8-OH-DPAT) and high selectivity for 5HT_1A receptors compared to 5HT_1B sites. In conscious SHR, A-74283 lowered mean arterial pressure (MAP) in a dose-related fashion with a prolonged effect after oral administration of higher doses, but heart rate (HR) was not changed. In anesthetized SHR, i.v. administration of A-74283 decreased MAP and total peripheral resistance, but not cardiac output. Pretreatment of conscious SHR with the selective 5TH_1A receptor antagonists spiroxatrine or BMY 7378 reduced the hypotensive effect of A-74283 significantly, but pretreatment with adrenergic antagonists phenoxybenzamine or idazoxan or the 5HT₂ receptor blocker ketanserin did not alter the effect of A-74283. Intracisternal administration of A-74283 also decreased MAP; however, A-74283 had no effect on blood pressure in pithed SHR in which blood pressure was supported with vasopressin, in contrast to nitroprusside. These data demonstrate that A-74283 exerts a potent hypotensive effect in SHR via systemic vasodilation originating from a central 5HT_1A receptor mechanism. A-74283 may be useful for studying 5HT_1A receptors and cardiovascular function.