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1. In mice and guinea-pigs, the number of glomeruli was counted in kidneys during normal growth and in hypertrophy induced by unilateral nephrectomy. 2. In mice, the number of glomeruli increased sharply during the first 2 weeks in life, and more slowly afterwards. Unilateral nephrectomy, when performed during this period of natural increase, induced the formation of supplementary nephrons in the contralateral kidney. 3. In guinea-pigs, the number of glomeruli was almost complete at birth. No evidence of a supplementary increase in the number of nephrons was found in hypertrophied kidneys following unilateral nephrectomy. 4. These results, together wit previous data obtained in the rat, suggest that the ability to induce new nephrons after unilateral nephrectomy in different species would depend more on the state of kidney maturity at birth than on differences in the renal mechanisms which lead to hypertrophy.

Single-nephron glomerular filtration rate (SNGFR) of superficial (S) and juxtamedullary (JM) nephrons was measured in conscious rats with a [14C]ferrocyanide infusion technique. Experiments were carried out in nondiuretic (ND), salt-loaded (SL), and hemorrhagic hypotensive (HH) rats. Mean SNGFR values of S and JM nephrons were 48.7 +/- 4.5 SE and 61.7 +/- 4.2 in ND, 73.6 +/- 8.7 and 87.5 +/- 10.8 in SL, and 29.9 +/- 5.9 and 36.4 +/- 7.1 in HH rats. These values are higher than the values reported in anesthetized rats. The S-to-JM SNGFR ratio was not significantly different in the three experimental conditions (ND, 0.788 +/- 0.032; SL, 0.843 +/- 0.018; and HH, 0.824 +/- 0.030), and did not differ from the values reported in anesthetized rats in similar experimental conditions. It is concluded that anesthesia exerts a depressive effect on GFR, but does not modify intrarenal SNGFR distribution. Neither saline loading nor hemorrhagic hypotension induces SNGFR intrarenal redistribution in conscious rats.

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