Elastin production is modulated by steroid hormones and is dependent on calcium. Because vitamin D3 is involved in the regulation of calcium metabolism and influences the expression of various extracellular matrix proteins, we investigated whether vitamin D3 influences tropoelastin expression. Three elastin-producing, bovine cell types, auricular chondroblasts, nuchal ligament fibroblasts and arterial smooth muscle cells, were treated with the principal active metabolite of vitamin D3, 1, 25-dihydroxyvitamin D3 (l, 25[OH]2 D3), and with 24, 25 dihydroxy-vitamin D3 (24, 25[OH]2 D3). Tropoelastin levels in culture media and cell layers, as measured by an enzyme-linked immunoassay, decreased in a dose and exposure dependent manner after treatment with 1, 25(OH)2 D3; 24, 25(OH)2 D3 had no effect on tropoelastin production relative to solvent-treated controls. The maximal effective dose of l, 25(OH)2 D3 was 10-7 M for 48 hr, which resulted in a severalfold reduction of tropoelastin production, and decreased tropoelastin levels were detected at 8 hr after treatment. Reduction of tropoelastin protein production was paralleled by a decrease of equal magnitude in the steady-state levels of tropoelastin mRNA. Vitamin D3metabolites had no effect on DNA or total protein synthesis. These results suggest that vitamin D3 may be an important modulator of elastin expression.