Cardiovascular and respiratory effects of carotid body stimulation in the monkey.

1. The carotid bodies were stimulated in the anaesthetized pig-tailed macaque monkey (M. nemestrina) using (i) brief injections of cyanide or CO2-equilibrated bicarbonate solution into a common carotid artery, and (ii) longer perfusion with hypoxic hypercapnic blood in vascularly isolated chemoreceptor preparations. 2. In spontaneously breathing animals brief stimuli (thirty-one tests, seven monkeys) consistently increased pulmonary ventilation (by 97 +/- 10% of control), slowed the heart rate (the pulse interval increasing by 36 +/- 7.5%), and increased femoral vascular resistance (by 44 +/- 7%). 3. More sustained chemoreceptor stimulation with asphyxial blood (nineteen tests, five monkeys) increased ventilation by 187 +/- 23%, but transient bradycardia occurred in only eight of nineteen tests and was followed by tachycardia; in the remaining tests, only tachycardia occurred. After 20--40s, the pulse interval was 5.8 +/- 0.9% below the control level. Femoral vascular resistance either increased (five tests, two animals) or decreased (six tests, two animals). 4. Evidence is presented that in the monkey the autonomic effects of chemoreceptor stimulation are influenced by the level of respiratory activity with bradycardia and vasoconstriction occurring when the level is low, and tachycardia and vasodilatation when it is high. 5. The interaction of autonomic responses resulting from carotid body stimulation and from mechanisms initiated by the concomitant hyperventilation are qualitatively similar in the monkey and in subprimate species, although there may be quantitative differences such as would account for the species differences to distrubances produced, for instance, by arterial hypoxia.