Aldosterone Secretagogues Increase Adrenal Blood Flow in Male Rats

Abstract

Adrenal blood flow (ABF) is closely coupled to steroid hormone release. ACTH and angiotensin (Ang) II stimulate cortisol and aldosterone secretion; however, their effects on ABF remain poorly defined. We used the laser-Doppler technique to measure rat ABF. Anesthetized male Sprague-Dawley rats were cannulated for mean arterial pressure (MAP) measurement and drug infusion. The left adrenal gland was exposed for ABF measurement. ABF and MAP changes to ACTH and Ang II were determined. Bolus injections of Ang II (0.01-1000 ng/kg) increased ABF (maximal increase = 110 ± 18 perfusion units at 1000 ng/kg) and increased MAP at doses greater than 10 ng/kg (basal, 99.2 ± 1.4 mm Hg; 1000 ng/kg Ang II, 149.7 ± 3.9 mm Hg). ACTH (0.1-1000 ng/kg) increased ABF (maximum increase = 158 ± 33 perfusion units) without increasing MAP. ABF increases induced by Ang II and ACTH were ablated by the cytochrome 450 inhibitor miconazole (2 mg/kg). Bolus injections of endothelin-1 (1-1000 ng/kg) increased ABF only at 1 ng/kg and increased MAP at 1000 ng/kg. Bolus injections of sodium nitroprusside increased ABF at 1 and 10 μg/kg and decreased MAP at 10 μg/kg. Thus, laser-Doppler flowmetry is a useful tool for understanding ABF regulation by peptides that stimulate steroid hormone release. Our results demonstrate that Ang II and ACTH increases in ABF are mediated by a cytochrome P450 metabolite.