Endocrine Abstracts

Aldosterone synthase catalyses the synthesis of the mineralocorticoid aldosterone in the adrenal zona glomerulosa and is encoded by the CYP11B2 gene. Recent studies have shown that CYP11B2 is also expressed in the cardiovascular system. CYP11B2 expression in the adrenal gland is regulated by the renin-angiotensin system and potassium. However, little is known about its expression in other tissues. In this study, we have quantitated CYP11B2 expression in the cardiovascular system following dietary manipulation of sodium.
3 groups of male WKY rats (n=6) were fed normal (0.3%), high (3%) or low (0.03%) sodium diets for 12 days. RNA was isolated from the adrenal gland, aorta, mesenteric artery and the heart. CYP11B2 expression was measured using real-time quantitative RT-PCR(LightCycler).
Low sodium increased CYP11B2 expression in the adrenal gland from 1.6x105plus/minus1.2x10⁵ to 5.9x10⁶ plus/minus 2.6x10⁶copies/micrograms RNA (mean plus/minus SEM, p<0.001). High sodium diet decreased CYP11B2 expression in the adrenal gland to 4.0x10⁴plus/minus 2.7x10⁴ copies/micrograms RNA (p=0.02). Dietary sodium manipulation had no effect on CYP11B2 expression in the aorta and mesenteric artery where basal levels were 1.3x³ plus/minus 2.8x10² and 3.9x10² plus/minus 1.9x10² copies/micrograms RNA respectively. CYP11B2 gene expression in the rat heart was never greater than 10² copies/micrograms RNA and was therefore too low to be reproducibly detected. Plasma aldosterone levels were 308 plus/minus 52, 134 plus/minus 19 and 154 plus/minus 50 pM in the low, normal and high sodium groups respectively. PRA was 2.8 plus/minus 0.3 (p=0.02), 1.6 plus/minus 0.2 and 0.07 plus/minus 0.04 ngAI/ml/h (p=0.005) in the low, normal and high sodium groups respectively.
CYP11B2 gene expression can be quantified precisely using the LightCycler. The results suggest that the peripheral renin-angiotensin system does not regulate CYP11B2 expression in the cardiovascular system. Under normal physiological conditions CYP11B2 expression in the rat heart appears to be undetectable.