Decreases in renal functional reserve and proximal tubular fluid output in conscious oophorectomized rats: normalization with sex hormone substitution.

Age-dependent glomerulosclerosis with reduced GFR develops earlier among men than among women. Therefore, whether female sex hormones could prevent the age-dependent decrease in GFR was investigated. The kidney function in oophorectomized rats treated with placebo (OOX group), estrogen (OOX+E(2) group), or estrogen plus progesterone (OOX+E(2)+P group) for 5 mo and in sham-operated rats (sham group) was examined. The rats were 13 mo of age at the time of the investigation. They were conscious and chronically instrumented. The results demonstrated that estrogen, alone or in combination with progesterone, was without effect on the baseline GFR and effective renal plasma flow but prevented severe decreases in the renal functional reserve and fractional proximal tubular fluid output (lithium clearance technique, fractional lithium excretion), which were observed in the OOX group. The renal functional reserve (estimated by stimulation with glycine) was -223 +/- 151, 483 +/- 129, 675 +/- 76, and 208 +/- 140 micro l/min in the OOX, OOX+E(2), OOX+E(2)+P, and sham groups, respectively. Fractional lithium excretion was 12.4 +/- 3.1, 26.8 +/- 2.0, 31.8 +/- 2.5, and 23.6 +/- 3.3% in the OOX, OOX+E(2), OOX+E(2)+P, and sham groups, respectively. In conclusion, oophorectomy at the age of 8 mo did not produce a decrease in baseline GFR in female rats within a period of 5 mo. However, oophorectomy led to severe decreases in the renal functional reserve and fractional proximal tubular fluid output. Both effects were prevented with administration of estrogen. Sham-operated rats demonstrated values for renal functional reserve and fractional lithium excretion that were between those observed for the OOX group and the groups treated with sex hormones.