Effect of Hyperoxia on the Erythropoietic Response to Sodium-L-Triiodothyronine

Abstract

An interaction of thyroid function and hematopoiesis is evident from numerous clinical and experimental observations. Accelerated erythropoiesis has been documented in association with thyroid hyperactivity (1) and decreased erythropoiesis with thyroid hypoactivity (2). The anemia in hypothyroidism results from multiple factors, but a hyporegenerative component is the essential feature. Prior observations (3–4) have been the basis for the conclusion that the major effects of the thyroid on erythropoiesis are mediated through an alteration in oxygen requirement and oxygen utilization. Other investigators (5) have postulated an additional direct stimulatory effect not related to changes in metabolism. The present experiments tested the effects of hyperoxia on erythropoiesis and the erythropoietic response to L-triiodothyroine. Graded doses of LT₃ produced the expected augmentation of red blood cell mass in animals maintained in a normal environment while an atmosphere of 50% oxygen clearly attenuated this erythropoietic response to LT₃. These observations are consonant with the fact that a major stimulating influence of thyroid hormone on erythropoiesis is related to augmented oxygen requirement.

Methods. Ten-week-old female Sprague-Dawley rats weighing approximately 200 g were utilized throughout. Rodent chow and water were available at all times. The rats were divided into four groups and each animal was given either 1, 2.5, or 10 μg of sodium L-triiodothyronine 1 in saline intraperitoneally each day for 14 days; control animals were given saline alone. The four groups were further subdivided and approximately one-half of the rats of each group were maintained in plastic cages in a normal environment. The remaining animals were placed in an environment of 50% oxygen-50% nitrogen in a modified atmosphere chamber. Humidity and temperature were not selectively controlled and oxygen content was analyzed at regular intervals with a portable Beckman oxygen analyzer.