Cardiovascular responses to intravenous bolus doses of certain exogenous substances (
capsaicin,
phenyldiguanide,
cryptenamine,
veratrine sulphate) which act on chemoreceptors in the pulmonary or proximal arterial circulation were compared to the naturally occurring chemoreceptor agonist, leucineenkephalin (Leu5-ENK) in the conscious dog.
Capsaicin (40 micrograms/kg) and
phenyldiguanide (40 micrograms/kg) produced
hypotension and
bradycardia 5 to 12 sec after injection (P less than 0.05) followed by
hypertension (P less than 0.05).
Cryptenamine (5 micrograms/kg) produced only
hypotension and
bradycardia (P less than 0.05) whereas Leu5-ENK (35 micrograms/kg) produced only
hypertension and
tachycardia (P less than 0.05). The
hypotension and
bradycardia produced by
capsaicin and
phenyldiguanide occurred earlier than the pressor response to Leu5-ENK,
capsaicin, and
phenyldiguanide and the depressor response to
veratrine (P less than 0.05).
Cryptenamine (5 micrograms/kg) and Leu5-ENK (35 micrograms/kg) when given together had additive effects on heart rate but interacted significantly in influencing blood pressure (P less than 0.05). It is concluded that the early response to
capsaicin and
phenyldiguanide are compatible with stimulation of known pulmonary chemoreceptors (including J receptors) whereas the pressor effect of
phenyldiguanide and Leu5-ENK and the depressor response to
veratrum alkaloids are due to activation of receptors in the proximal arterial circulation. The influence of Leu5-ENK on the haemodynamic response to
veratrine suggest that ENK may modulate the Bezold-Jarisch reflex.