Identification of growth hormone at the myocardial cell surface

Growth hormone immunoreactivity has been demonstrated in a variety of normal human tissues, and ectopic production has been documented in a number of malignant tumors. However, myocardium has not previously been reported to contain growth hormone. Monkey anti-rat growth hormone antiserum was used in a sensitive immunoperoxidase staining method to histologically localize growth hormone in myocardium obtained from normal rats and rats harboring growth hormone-secreting tumors. Immunoreactive growth hormone was localized to the myocardial cell surface and was not seen in vascular endothelial cells of small arteries, veins, or capillaries. No intracellular staining of myocytes was evident. Specific staining was abolished by neutralization with purified growth hormone. Specific staining was abolished by neutralization with purified growth hormone. Myocardial cells did not stain with anti-triiodothyronine or anti-thyroxine immune serum. The cell surface staining is consistent with the binding of growth hormone to the myocardial cell surface, as it is unlikely that the myocardium synthesizes growth hormone polypeptide. These findings suggest that growth hormone may have a direct growth promoting or metabolic effect on cardiac tissue.