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.