Sgd 101/75: cardiovascular effects in various animal preparations; interactions with vascular postjunctional alpha 1- and alpha 2-adrenoceptors.

The effect of the imidazolidine Sgd 101/75 (2-[2-methylindazol-4-imino]-imidazolidine HCl) on blood pressure, as well as its alpha-adrenoceptor agonist activity and affinity for these receptors, were examined in various animal preparations. After both intravenous administration to conscious spontaneously hypertensive rats and intravenous injection or infusion via the vertebral artery in chloralose-anaesthetized cats, Sgd 101/75 (1-10 mg kg-1) elicited pressor responses. Intracisternal application of Sgd 101/75 (1 mg kg-1) to chloralose-anaesthetized cats did not affect blood pressure. In the pithed rat and pithed cat the vasopressor responses to i.v. Sgd 101/75 were effectively antagonized by prazosin (0.1-1.0 mg kg-1, i.v.) but much less by yohimbine (1 mg kg-1, i.v.). Sgd 101/75 proved a less potent and less selective displacing agent of [3H]-clonidine- and [3H]-prazosin-binding in rat brain membranes than clonidine. The results suggest that Sgd 101/75 is a selective alpha 1-adrenoceptor agonist, devoid of any centrally or peripherally mediated hypotensive activity; this is probably caused by the low capacity of Sgd 101/75 for stimulating alpha 2-adrenoceptors.