The influence of thyroxine on the differentiation of adipose tissue and skin during fetal development

Abstract

Preobese fetuses have elevated thyroid hor­mone levels and depressed growth hormone levels relative to lean fetuses. Therefore, we are studying various exper­imental fetal pig models to explore the relationship be­tween endocrine status and onset of obesity. In the present study, intact and hypophysectomized (d 70) fetuses were implanted with thyroxine (T4) pellets on d 70 of gestation, and blood, adipose tissue, and skin samples were obtained upon removal of d 90 of gestation. Body weights were similar for all groups and T4 treatment reversed myxedema in hypophysectomized fetuses. Serum T4 levels were ele­vated (p < 0.05) and skin and hair development were enhanced (p < 0.05) to a similar degree by T4 treatment in intact and hypophysectomized fetuses. However, T4 did not influence adipose tissue development in intact fetuses, but markedly enhanced development in hypophysectom­ized fetuses. For instance, fat cell size and lipogenic enzyme activities in hypophysectomized fetuses were increased (p < 0.05) by 5-mg and 15-mg T4 treatments, with a marked increase (p < 0.05) in apparent fat cell number with the 15-mg T4 treatment. In contrast, there was no effect of T4 (15 mg) on these parameters in intact fetuses. Therefore, fetal obesity may be directly associated with elevated thy­roid hormone levels and suppressed growth hormone levels, but not with elevated T4 levels alone. © 1992 International Pediatric Research Foundation, Inc.