Differential expression and effect of 1,25-dihydroxyvitamin D3 on myosin in arterial tree of rats.

The hypothesis that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3, also known as calcitriol] modulates myosin expression in vascular smooth muscle was tested. Wistar-Kyoto or spontaneously hypertensive rats given intraperitoneal injections of 25 ng 1,25(OH)2D3/100 g body weight for varying periods of time showed a greater than twofold increase in aortic mRNA encoding the myosin regulatory light chain relative to 18S rRNA (P < 0.05). 1,25(OH)2D3 administration to Wistar rats caused a significant increase in the aortic content of total myosin regulatory light chain and total myosin heavy chain. The increase in myosin light chain was the result of a specific increase in expression of its smooth muscle isoform [control = 65.2 +/- 3.4% vs. 1,25(OH)2D3 = 78.7 +/- 3.6%, P = 0.020]. 1,25(OH)2D3 had no effect on total myosin light chain or heavy chain in the superior mesenteric artery. The hormone did, however, increase the proportion of the smooth muscle isoform of the light chain in this vessel [control = 81.4 +/- 2.6% vs. 1,25(OH)2D3 = 88.8 +/- 2.1%, P = 0.048]. In branch II and III mesenteric resistance arteries, 1,25(OH)2D3 significantly increased the active stress response to 10 mumol/l norepinephrine but was without effect on total myosin light chain or heavy chain content or on the relative expression of the myosin light chain isoforms [control = 94.0 +/- 1.4% vs. 1,25(OH)2D3 = 95.8 +/- 1.1%, P = 0.33].(ABSTRACT TRUNCATED AT 250 WORDS)