Changes in Cardiac Output and Total Peripheral Resistance during Development of Renal Hypertension in the Rabbit Lack of Conformity with the Autoregulation Theory

Serial measurements of cardiac output (CO), mean arterial pressure (MAP), heart rate, and total peripheral resistance (TPR), were made on unanesthetized rabbits with previously implanted Doppler flowmeters. After 2 days of control measurements tbe rabbits were subjected alternatively to bilateral renal cellophane wrapping (wrap group) or to sham operation and additional measurements were made 1, 2, 4, 8, 16, 25, and 32 days after operation. During the 1st week after operation changes in CO were identical in tbe wrap and sham-operated groups, with an overall increase to a value of 110% of control on day 4 (P < 0.05). Thereafter CO fell gradually, reaching 75% of control by day 32 in the wrap group, but only 95% of control in the sham-operated group. When CO was expressed per unit of body weight tbe latter differences were somewhat reduced, but still were significant. In wrap animals MAP and TPR rose progressively to 155% and 194% of control by day 32. In the sham-operated group the corresponding increases to 108% and 118% of control were significantly smaller. The MAP and TPR of the renal wrap rabbits exceeded the values in sham-operated rabbits, even over the 1st week after operation, by an average for MAP of 8.6 ± 1.4% (P < 0.001), and for TPR of 8.0 ± 2.5% (/> 0.01 (.Theresuits suggest that the changes in CO during the 1st week were a nonspecific consequence of the preceding wrap or sham operation. They bore no apparent relationship to the subsequent deielopment of tbe hypertension which was "resistance-mediated" from the earliest stages. We conclude that the present findings for the rabbit differ from those reported for other species and do not conform to tbe changes predicted by the autoregulation theory of the pathogenesis of hypertension.