Modulation of in vitro erythropoiesis. Studies with euthyroid and hypothyroid dogs.

The interactions of adrenergic agonists and thyroid hormones on the growth of erythroid colony-forming units were studied in cultures of dog marrow before and after the establishment of hypothyroidism. Erythroid colony growth in cultures form euthyroid dogs was enhanced by isoproterenol and other adrenergic agonists having beta 2-receptor specificity. With hypothyroidism, however, this responsiveness was lost, and sensitivity to alpha-agonists, such as phenylephrine and norepinephrine, was acquired. This alteration in receptor specificity appeared to be dependent upon thyroid hormone and was rapidly reversible. Preincubation of marrow cells from hypothyroid animals with thyroid hormone resulted in the reappearance of responsiveness to beta-adrenergic agonists and the loss of sensitivity to alpha-agonists. These findings are in agreement with previous suggestions that beta-adrenergic receptor activity is modulated by thyroid hormone levels and demonstrate that the specificity of adrenergic modulations of erythropoiesis in culture may accurately reflect the thyroid status of the intact animal.