Effect of Induced Apnea on Cardiovascular Renal Functions in the Rabbit

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Abstract
Renal clearance techniques, ecg, impedence plethysmography and electromanometric procedures were used to show a reflex mechanism in rabbits which resembles the response to submergence apnea previously noted in diving mammals and birds. When respiratory movements were arrested by presentation of tobacco smoke or some other volatile irritant there was an accompanying marked reduction in urine flow, glomerular filtration rate, blood flow to the kidney, and in heart rate. Arterial blood pressure remained unaltered or increased slightly. Hemodynamic alterations in renal function indicated a vasoconstrictor activity which could be abolished by surgical or pharmacological denervation of the kidney. Alteration in volume of the hind leg indicated increased pulse volume and a slightly decreased minute pulse volume accompanying reflex cardiac slowing. Atropine, an anti-cholinergic agent, abolished all of these reflex and inhibitory cardiac and renal responses, and certain other typical manifestations of parasympathetic activity such as excessive salivation and constriction of the pupils which normally accompany apnea. The presence of parasympathetic vasoconstrictors to the kidney is suggested. These cholinergic reactions to apnea are interpreted as constituting a "conservation mechanism" which may be a more or less constant feature of the physiological architecture of vertebrates effecting the conservation of O2 during quiescent periods by shunting blood from some organs while maintaining a high rate of flow to others more dependent upon a vigorous circulation.

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