Effect of hypophysectomy and growth hormone substitution on red blood cell morphology and filterability in rats

Growth factors, including insulin, are known to stimulate erythroid cell formation in vitro. This somatotrophic effect of insulin might be involved in blood abnormalities in diabetes mellitus. We therefore investigated whether growth hormone (GH) affects the morphology or filterability of circulating red blood cells (RBCs) in hypophysectomized rats. After hypophysectomy, rats became anemic with a decrease in hematocrit, hemoglobin concentration, RBC count, and reticulocytes. The RBC membrane area was enlarged, giving an increased area-to-volume ratio compared with the control RBCs. The calculated minimum cylindrical diameter (MCD) and resistance to initial folding of the RBC decreased after hypophysectomy, and was confirmed by an enhanced filtration of RBCs through 3 microns Nucleopore membranes. The number of filter clogging particles was also lower in hypophysectomized rats than in control rats. Substitution for 21 days with bovine GH (via subcutaneously implanted osmotic minipumps) normalized RBC morphology and filterability. After withdrawal of GH, all parameters returned toward the presubstitutional levels. Neither cortisone nor thyroxine had any measurable effect on RBC morphology or deformability, indicating that GH deficiency contributes to the abnormal RBC morphology and rheology seen after hypophysectomy.