Action of depressor-I, a hypotensive phospholipid from bovine brain, on systemic and arterial blood pressures of various species.

Effects of "Depressor-I" (D-I), a new hypotensive phospholipid obtained from bovine brain lipid fraction, on systemic arterial blood pressure were investigated. The hypotensive activity of D-I in urethane anaesthetized rats was dose dependent and tachyphylaxis and/or sensitization were not observed. Increments of the respiration and the heart rate were observed with sharp falls in blood pressures following intravenous administration of D-I, in simultaneous recordings in anaesthetized rats. D-I elicited hypotension in all species of animals examined, and the sensitivities to D-I were much the same, however, there were two types in patterns of duration on responses and the durations were also dose dependent. D-I exhibited depressor-responses even in conscious rats, though responses were much smaller compared with those seen in anaesthetized rats. In a comparison of anaesthetic agents in rats, the highest hypotensive activity of D-I was observed with pentobarbital anaesthesia, a moderate response was seen with alpha-chloralose and the least response was seen with urethane. In spinal rats or those pretreated with reserpine or antagonists, such as atropine, diphenhydramine, propranolol and hexamethonium, D-I also elicited hypotension. These results suggest that "Depressor-I" does not elicit the depressor action via the stimulation of the central and the autonomic nervous systems but rather by a direct action on peripheral blood vessels.