Ontogeny of triamcinolone-acetonide binding sites in outer cortical tissue from rat kidneys

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Abstract
The ontogeny of glucocorticoid binding sites and the glucocorticoid hormone (GC) feedback control of available glucocorticoid binding sites was studied using the cytosolic fraction of outer cortical tissue obtained from kidneys in 20- and 40-day-old intact and adrenalectomized rats. Morphometric analysis showed that this tissue contained 85.7% (20 days) and 88.7% (40 days) of proximal tubular cells. Glucocorticoid binding sites were determined by [3H]triamcinolone-acetonide (TA) binding and isoelectric focusing analysis. In intact rats, TA binding sites (fmol/mg DNA) were significantly higher at 20 (3,624) than at 40 (1,640) days. Adrenalectomy significantly increased TA binding sites (fmol/mg DNA) at 40 (to 8,445) but not at 20 days. TA binding sites related to DNA were significantly higher in 20- than in 40-day-old intact rats and significantly higher in 40- than in 20-day-old adrenalectomized rats. Serum corticosterone (nM) was not significantly different in 20- (230) and 40- (189) day-old rats. After in vivo administration of a synthetic GC, TA binding sites were replenished to the cytosol after 20-24 h. Prolonged GC treatment (1-60 micrograms X 100 g body wt-1 X day-1) depressed the replenishment of TA binding sites significantly more in 40- than in 20-day-old adrenalectomized rats. Kd was determined in both intact and adrenalectomized 20- and 40-day-old rats and ranged between 1.30 and 4.33 nM. The steroidal specificity for the TA binding sites was the same in 20- and 40-day-old rats.(ABSTRACT TRUNCATED AT 250 WORDS)