Pyridine nucleotides: basis for the hypotensive action of triphosphopyridine nucleotide.

Intravenous administration Gf TP produced an abrupt, transient, reproducible and dose-dependent fall in systemic blood pressure of urethane anaesthetised rats, rabbits and cats. In guinea pigs the effect was found to vary from animal to animal. Whereas in some guinea pigs, TPN provoked biphasic, pressor-depressor response; in others either of the pressor or depressor responses was obtained. Vagosympathectorny either abolished or reduced the pressor response but depressor response remained unaltered in guinea pigs. Hypotensive response persisted in pithed rats and remained unaltered in rats after {?-adrenoceptor, histaminic receptor and ganglionic blockade, Atropine antagonized the hypotensive response to TPN and physostigmine potentiated it. Antagonism by atropine was, however, more with lower doses of TPN and responses to its relatively higher doses were partially antagonised. Left vagotomy failed to alter the response to TP but right vagotomy antagonized and bilateral vagotomy further reduced it. Further reduction in depressor response to TP in bivagotomized rats by atropine indicated involvement of extravagal cholinergic component. Cumulative administration of TP reduced the pressor effect to adrenaline and depre sor effect of histamine for a short while bu t failed to alter hypotensive response to acetylcholine .