1,25-Dihydroxyvitamin D3 regulation of myocardial growth and c-myc levels in the rat heart.

In this report we demonstrate that rats maintained on a calcium supplemented vitamin D3-deficient diet for nine weeks showed an increase in heart to body weight ratio. Morphometric analysis indicated that vitamin D3 deficiency produced cardiac myocytes that were smaller yet more numerous, indicating hyperplasia. Western blot analysis showed that vitamin D3 deficiency also resulted in increased c-myc protein levels in the hearts of vitamin D3-deficient rats. Furthermore, 1,25-dihydroxyvitamin D3 reduced c-myc protein levels in primary cultures of ventricular myocytes from neonatal rat hearts. Our data suggest a possible relationship between myocyte hyperplasia and increased c-myc levels in the vitamin D3-deficient rat heart.