Impairment of renal function precedes establishment of hypertension in spontaneously hypertensive rats.

To determine renal function throughout development of hypertension in the spontaneously hypertensive rat (SHR) and its normotensive counterpart, the Wistar-Kyoto rat (WKY), renal clearance studies were performed at 2-wk intervals from 4 to 12 wk and again at 16 wk of age in conscious chronically instrumented rats after recovery (4-6 days) from surgery. The data indicate that the critical period for the development of hypertension in SHR was between 4 and 6 wk of age. Mean arterial pressure sharply increased from 107 +/- 5 (n = 6) to 145 +/- 6 mmHg (n = 6) between 4 and 6 wk of age, did not change between 6 and 10 wk of age, and gradually rose between 10 and 16 wk of age to 183 +/- 3 mmHg. In WKYs, blood pressure increased only slightly from 97 +/- 3 mmHg at 4 wk of age (n = 8) to 110 +/- 3 mmHg at 8 wk of age (n = 8), where it remained through adulthood. Glomerular filtration rate (GFR) in the 4-wk-old SHR was significantly decreased compared with WKY (0.94 +/- 0.03 vs. 1.11 +/- 0.04 ml.min-1 x g wet kidney wt-1), and it recovered to normal level and stabilized by 6 wk of age (1.14 +/- 0.04 ml.min-1 x g wet kidney wt-1). Renal blood flow was lower in the SHR only at 4 and 16 wk; it increased with age in both groups. Renal vascular resistance was higher in the SHR at 4 wk and remained elevated throughout the observation period.(ABSTRACT TRUNCATED AT 250 WORDS)