Mitotic response to high protein intake in different renal cell types in weanling rats

We examined the effect of high protein intake on the mitotic response (3H-thymidine incorporation) in the glomerulus, proximal tubule (PT), thick ascending limb of Henle (TAL), distal tubule (DT) and collecting duct (CD) in kidneys from 16- to 24-day-old rats that received an isocaloric diet containing 21% (NP) and 50% (HP) protein from 16 days of age. Nephron filtration rate was also determined. After two days of HP diet, thymidine incorporation (TI) was significantly increased in PT and TAL. After two days on HP diet TI was most pronounced in TAL. After eight days on HP diet TI remained elevated in PT, but not in TAL. HP did not increase TI in DT or CD. The glomerular TI was the same in HP as in NP rats after two and four days on the diet, but was significantly elevated after eight days on HP diet. The nephron filtration rate was increased after two days and remained significantly elevated after eight days on HP diet. The proximal tubule fractional reabsorption was the same in 24-day-old NP and HP rats. We conclude that the results are compatible with the hypothesis that the Na load is a major factor triggering tubular growth after HP intake. Glomerular growth is secondary to increase in nephron filtration rate.