The total length of myocytes and capillaries, and total number of myocyte nuclei in the rat heart are time-dependently increased by growth hormone.

Growth hormone (GH) can increase size and dimensions of rat hearts. The aim was to study how GH administration influences the growth of cardiac myocytes and capillaries in relation to time. Three-month-old female rats were divided into 10 groups (n=3), and injected with either GH (5mg/kg/day) or vehicle for 5, 10, 20, 40, or 80 days. From the left ventricle (LV) histological sections were made and stereological methods applied. Linear regression showed that GH time-dependently increased: LV volume (r=0.96, P<0.001), total volume of myocytes (r=0.96, P<0.001) and capillaries (r=0.64, P<0.05), total length of myocytes (r=0.90, P<0.001) and capillaries (r=0.78, P<0.001), and total number of myocyte nuclei (r=0.85, P<0.001). In conclusion, during 80 days of GH treatment the total volume and length of myocytes and capillaries, and total number of myocyte nuclei increased in a linear way. The results indicate that GH is a potent mediator of myocardial growth.