Pattern of renal growth and compensatory hypertrophy during development in rats: a mathematical approach

High protein intake accelerates glomerulosclerosis independent of effects on glomerular hemodynamics

It is unclear whether glomerular hemodynamic changes always accompany alterations in dietary protein, and whether nonhemodynamic factors associated with a high protein intake can influence glomerular injury. In the present study, uninephrectomized (UNx) male rats were fed either standard (20%) or high (40%) protein diets. Body growth was comparable in the two diet groups. At 30 weeks of age, UNx rats fed high protein had increased albuminuria (36.7 +/- 12.6 mg/24 hr), compared to UNx rats fed standard protein (10.2 +/- 6.2 mg/24 hr; P less than 0.05). The incidence of focal glomerulosclerosis (FGS) at 36 weeks was markedly increased in the high protein rats (19.0 +/- 7.7%), compared to the standard protein rats (3.2 +/- 2.0%; P less than 0.05). Moreover, FGS in the high protein rats correlated with the serum cholesterol level measured at 18, 24, and 30 weeks of age. Glomerular hemodynamics were assessed before glomerular injury developed in separate groups of UNx rats fed either standard or high protein. Single nephron GFR (SNGFR) and single nephron plasma flow (SNPF) were increased in UNx rats, compared to two-kidney rats fed standard protein. SNGFR and SNPF, however, were not different between UNx rats fed standard or high protein. Glomerular capillary pressure (PGC) was not different between UNx rats fed standard protein (51.7 +/- 1.3 mm Hg) and two-kidney controls (53.1 +/- 1.5 mm Hg). Moreover, PGC was not altered in UNx rats fed high protein (51.8 +/- 1.6 mm Hg). We conclude that high dietary protein can accelerate the development of glomerular injury independent of effects on glomerular hemodynamics.

Renal innervation is not required for compensatory renal growth in the rat

The purpose of this study was to determine whether renal innervation is required for compensatory growth of the remaining kidney following unilateral nephrectomy. In the first study, young (6-week-old) rats were divided into 4 groups and the following surgical procedures were performed. Group 1 animals had their left and right kidneys removed and weighed to provide a measure of control weight prior to compensatory growth. Group 2 and 3 animals underwent right nephrectomy, followed by left kidney denervation (Group 2) or sham denervation (Group 3). Animals from Group 4 were subjected to right sham nephrectomy and sham denervation of the left kidneys. Three weeks later, animals from Groups 2, 3 and 4 were sacrificed and left kidneys were weighed. Relative to control kidney weight (Group 1), left kidney weight increased over 3 weeks by 92% when both kidneys were present (Group 4), representing normal renal growth. Animals with prior nephrectomy but intact renal innervation (Group 3) demonstrated an additional increase in kidney weight of 74% over the same interval, representing compensatory growth. Prior denervation of the left kidney (Group 2) had no effect on the degree of compensatory growth whether expressed in absolute kidney weight or relative to body weight. A second study was performed to determine whether renal innervation influences the initial state of compensatory growth when measured at an earlier time after unilateral nephrectomy. One week after right nephrectomy, left kidney weight was similar in animals with sham left renal denervation (1.08 +/- 0.04 g) when compared to animals with left renal denervation (1.06 +/- 0.02 g). Thus, for a least young rats, renal innervation is not required for full compensatory renal growth following unilateral nephrectomy.