The influence of growth hormone on myocardial weight and water fraction in rats.

While conducting experiments on the role of growth hormone in cardiac hypertrophy, data were also gathered on the influence of growth hormone on myocardial wet and dry weight in relation to body weight and myocardial water fraction. Male rats with either in intact hypophysis or a hypophysectomy were bilaterally adrenalectomized, and corticoids were replaced with deoxycorticosterone and hydrocortisone therapy. Hypophysectomized rats were further treated with thyroxine, testosterone, and, where appropriate, bovine growth hormone. The hormone replacement program re-established systolic blood pressure in hypophysectomized rats to levels observed in intact-hypophysis rats. The left ventricle weight (wet and dry)/body weight ratio was used as an indication of relative myocardial weight. Hypophysectomized rats without growth hormone were observed to have higher left ventricle weight/body ratios than both hypophysectomized rats with growth hormone and intact-hypophysis rats. Further, rats without growth hormone were determined to have a lower myocardial water content than rats with growth hormone. Mathematical analysis established that the relationship between myocardial water fraction and ventricular wet weight is nonlinear. This relationship shows that small changes in water fraction can produce large changes in ventricular wet weight. The reasons for the different water content in the myocardium were not further investigated.