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Ontogeny of triamcinolone-acetonide binding sites in outer cortical tissue from rat kidneys
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)
Insights
Glucocorticoid (GC) binding sites in rat kidneys decrease with age. Adrenalectomy increases these sites in older rats, indicating age-related changes in GC feedback regulation.
Area of Science:
- Endocrinology
- Renal Physiology
- Developmental Biology
Background:
- Glucocorticoid hormones (GC) play crucial roles in regulating physiological processes.
- Understanding the ontogeny and regulation of GC binding sites is vital for comprehending GC action.
- Kidney proximal tubular cells are key sites for GC activity.
Purpose of the Study:
- To investigate the developmental changes in glucocorticoid binding sites in rat kidney outer cortex.
- To examine the feedback control of glucocorticoid binding sites by the glucocorticoid hormone.
- To compare these parameters in intact and adrenalectomized rats of different ages.
Main Methods:
- Cytosolic fraction of outer cortical kidney tissue from 20- and 40-day-old rats (intact and adrenalectomized).
- Morphometric analysis to identify proximal tubular cells.
- [3H]triamcinolone-acetonide (TA) binding assays to quantify GC binding sites.
- Isoelectric focusing analysis and determination of dissociation constant (Kd).
Main Results:
- TA binding sites per mg DNA were significantly higher in 20-day-old intact rats compared to 40-day-old rats.
- Adrenalectomy significantly increased TA binding sites in 40-day-old rats but not in 20-day-old rats.
- Prolonged GC treatment more severely impaired TA binding site replenishment in 40-day-old adrenalectomized rats compared to younger ones.
Conclusions:
- Glucocorticoid binding site levels in rat kidney outer cortex decrease with age.
- Age-dependent alterations in glucocorticoid feedback regulation are evident.
- Kidney glucocorticoid receptor system exhibits developmental plasticity and age-related changes in responsiveness.