CARDIOVASCULAR AND RESPIRATORY CHEMOREFLEXES FROM THE HINDLIMB SENSORY RECEPTORS EVOKED BY INTRA-ARTERIAL INJECTION OF BRADYKININ AND OTHER CHEMICAL-AGENTS IN THE RABBIT

Abstract

Intra-arterial injections of bradykinin into the hindlimb of the rabbit caused 2 types of cardiovascular reflex effects displayed in succession. The 1st effects were inhibitory, represented by systemic hypotension, contralateral hindlimb vasodilation and bradycardia; the 2nd effects appearing were excitatory, consisting of hypertension, hindlimb vasoconstriction and tachycardia and occurred closely associated with behavioral manifestations typical of the reaction to pain. Both the depressor and pressor effects were accompanied by hyperventilation. Analogous biphasic reflex responses may be caused by intraarterial injections of K ions. Hypertonic solutions (NaCl, glucose) usually only produced excitatory responses. No significant cardiocirculatory reflex effects were induced by even high doses of serotonin, nicotine, adenosine, adenosine triphosphate, adrenalin [epinephrine], noradrenalin [norepinephrine], angiotensin, vasopressin and oxytocin. General anesthesia greatly inhibited the pressor reflexes and potentiated the depressor responses (to bradykinin and K ions) but did not appear to be a necessary condition for provoking depressor reflexes by chemical stimulation of somatic afferents. Both chemoreflex responses were prevented by sectioning the somatic nerves of the injected limb. Denervation of sinoaortic areas and of cardiopulmonary receptors by bilateral cervical vagotomy or complete removal of the skin from the injected limb did not prevent either type of chemoreflex response. These depressor and pressor chemoreflexes have been ascribed to activation of 2 functionally distinct types of sensory receptors in the skeletal muscle, differently sensitive to chemical substances and selectively concerned with different patterns of cardiocirculatory reflex response.