PRESSOR AND TACHYCARDIC RESPONSES TO INTRAVENOUS SUBSTANCE-P IN ANESTHETIZED RATS

Intravenous injection of 3-33 nmol/kg of substance P (SP) caused press er and tachycardic responses in anesthetized rats. The responses were not blocked by a ganglion nicotinic receptor antagonist or by pithing. Pretreatment with reserpine blocked both responses. beta-Adrenoceptor blockade attenuated only the tachycardic response, and alpha-adrenoce ptor blockade attenuated only the presser response. These findings ind icated that the effects of SP to increase blood pressure and heart rat e are due to sympathetic ganglion stimulation. Studies with adrenalect omized rats showed that stimulation of the adrenals by SP contributes to both responses but makes a greater contribution to the tachycardic response. These observations raise the possibility that the tachykinin innervation of sympathetic ganglia and the adrenal medulla may be inv olved in the local regulation of blood pressure and heart rate.