['Many therapeutic agents stimulate histamine release from mast cells, which results in a decrease in blood pressure. The purpose of this study is to establish a method to determine if the mechanism of action, or one of the mechanisms, of hypotensive compounds is related to the release of histamine. The method was developed using a novel hypotensive compound, SC-372.', 'In Inactin anesthetized rats, after intravenous administration of SC-372 (0.3-7 mg/kg), the 2 and 7 mg/kg resulted in a dose-dependent decrease in blood pressure. Histamine (0.1 and 1 mg/kg) was injected intravenously to establish whether histamine release was the mechanism of action for the hypotension induced by SC-372. Compound 48/80 (0.1 mg/kg, promotes histamine release) and Cromolyn (1 mg/kg/min, [5 min], prevents histamine release from mast cells) were characterized and used intravenously in combination with/or compared to SC-372.', 'Histamine resulted in a decrease in blood pressure that was unaffected by Cromolyn (1 mg/kg). Administration of Compound 48/80 resulted in a rapid reduction of systemic blood pressure. Intravenous infusion of Cromolyn prior to the injection of Compound 48/80 significantly attentuated the hypotensive response and the increase in histamine levels in the plasma. Intravenous administration of SC-372 resulted in a rapid reduction in blood pressure with a profile similar to that of Compound 48/80. When the rats were treated with Cromolyn prior to the administration of SC-372, both the blood pressure and plasma histamine levels were maintained at their pretreatment control levels.'] Does a method for determining whether hypotension caused by novel compounds in preclinical development result from histamine release?