Calcium-independent and 1,25(OH)₂D₃-dependent regulation of the renin-angiotensin system in 1α-hydroxylase knockout mice

To determine whether the cardiovascular effect of 1,25(OH)₂D is dependent on calcium and/or phosphorus, mice with targeted deletion of the 25(OH)D 1α-hydroxylase and their wild-type littermates were fed a normal diet or a diet to rescue the ambient serum calcium and phosphorus levels. Mice on the normal diet were treated daily with vehicle or 1,25(OH)₂D₃ while mice on the rescue diet received vehicle, captopril or losartan. After four weeks the vehicle-treated knockout mice developed hypertension, cardiac hypertrophy and impaired cardiac function along with an up-regulation of the renin-angiotensin system in both renal and cardiac tissues. Although the serum calcium and phosphorus levels were normalized in knockout mice on the rescue diet, abnormalities in blood pressure, cardiac structure-function and the renin-angiotensin system remained. In contrast, 1,25(OH)₂D₃ not only normalized serum calcium and phosphorus levels but also normalized blood pressure, cardiac structure-function and the renin-angiotensin system. Treatment of the knockout mice with either captopril or losartan normalized blood pressure and cardiac structure and function although renin expression remained elevated. This study shows that 1,25(OH)2D plays a protective role in the cardiovascular system by repressing the renin-angiotensin system independent of extracellular calcium or phosphorus.