Abstract 041: Brain Cytochrome P450 1B1-Testosterone Generated Metabolite 6Beta-Hydroxytestosterone Contributes to Angiotensin II-Induced Increased Sympathetic Outflow and Blood Pressure

Abstract

Cytochrome P450 1B1 (CYP1B1)-generated testosterone (T) metabolite 6β-hydroxytestosterone (6β-OHT) contributes to angiotensin (Ang) II-induced hypertension in the male mice. However, the site of action of CYP1B1-testosterone metabolite 6β-OHT in Ang II-induced hypertension is unknown. The demonstration that Ang II increases blood pressure by its action in the subfornical organ and the presence of CYP1B1 in the brain led us to hypothesize that T contributes to Ang II-induced hypertension via its metabolism to 6β-OHT in the brain. To test this hypothesis, we examined the effect of intracerebroventricularly (ICV) administered T in castrated (Cas) wild-type ( Cyp1b1 +/+ ) and Cas Cyp1b1 -/- mice on the action of systemic Ang II (700 ng/kg/min) for 14 days. T (3 μg/2μL/injection/every 2nd day) or its vehicle (2-Hydroxypropyl-β-cyclodextrin dissolved in artificial CSF) was injected via a cannula implanted in the brain. Mean arterial blood pressure (MAP, mmHg) was measured by radiotelemetry (n=4-5). Ang II increased MAP in T but not its vehicle-injected Cas Cyp1b1 +/+ mice on Day 12 (159±2 vs. 98±2, P<0.05). In Cas Cyp1b1 -/- mice Ang II increased MAP in ICV injected 6β-OHT (1.5 μg/2μL/injection every 2nd day) but not T (151±3 vs. 123±5, P<0.05). Power spectral analysis of the data on day 12 showed that Ang II increased the low to high-frequency ratio of heart rate variability, index of sympathetic outflow modulation in ICV T injected Cas Cyp1b1 +/+ but not Cas Cyp1b1 -/- mice (3.8±0.0.4 vs. 1.9±0.0); whereas ICV 6β-OHT in the later mice increased this ratio (4.7±0.6). Ganglionic blocker hexamethonium (30 mg/Kg, ip) on day 14 of Ang II infusion resulted in greater reduction in MAP (P<0.05) in centrally 6β-OHT injected Cas Cyp1b1 -/- , and T-injected Cas Cyp1b1 +/+ (Δ81±11 and Δ87±10) than in T injected Cas Cyp1b1 -/- mice (Δ50±8). Furthermore, in intact Cyp1b1 -/- , but not Cas Cyp1b1 -/- mice transduction with adenovirus (Ad) of CYP1B1-DNA (ICV 2μL of 1.0 X 10 12 particles/mL) increased Ang II-induced systolic blood pressure (P<0.05, n=5/group) measured by tail-cuff on Day12 (176±11 vs. 120±2, mm Hg). These data suggest that T contributes to Ang II-induced hypertension most likely via generation by the brain CYP1B1 to 6β-OHT, which increases sympathetic outflow in male mice.