Endocrine Abstracts

Objectives: Aldosterone synthase catalyses the synthesis of aldosterone in the adrenal zona glomerulosa and is encoded by the CYP11B2 gene. Recent studies have shown that the CYP11B2 gene is also expressed in the rat central nervous system (CNS), particularly the cerebellum and hippocampus, suggesting local corticosteroid production. The renin-angiotensin system regulates the expression of the CYP11B2 gene in the adrenal cortex. However, little is known about the regulation of expression of CYP11B2 in the CNS. Using real time quantitative RT-PCR (LightCycler), the aim of this study was to determine whether dietary manipulation of sodium alters CYP11B2 gene transcription in the hippocampus of the rat as it does in adrenal cortex.

Methods: Three groups of twelve-week-old male WKY rats (n=6), were fed normal sodium (0.3%), high sodium (3%) or low sodium (0.03%) diets for 12 days. RNA was isolated from the adrenal glands, hippocampus and cerebellum. Quantification of CYP11B2 mRNA was determined by continuous SYBR green I monitoring during real time RT-PCR using an exogenous homologous mRNA standard.

Results: As expected, low sodium increased CYP11B2 gene expression from 4876 plus/minus 1788 copies/microgram RNA to 46107 plus/minus 14339 copies/microgram RNA (mean plus/minus SEM, p=0.005). High salt decreased adrenal CYP11B2 expression to 1130 plus/minus 354 copies/microgram RNA (p=0.03). The level of CYP11B2 gene expression in the hippocampus following normal sodium diet was considerably lower than in the adrenal cortex (0.00036 plus/minus 0.00014 copies/microgram RNA). High and low sodium diets had no significant effect on CYP11B2 expression.

Conclusions: We have developed an accurate method of quantifying CYP11B2 gene expression. Whilst circulating levels of angiotensin II, secondary to altered sodium, regulate CYP11B2 expression in the adrenal gland, they do not appear to regulate hippocampal expression. Other mechanisms may regulate local steroid production in the CNS.