Hormonal Control of the Development of the Thymus of the Fœtal Rabbit

Abstract

THAT the fœtal adrenal is physiologically active has been firmly established; for example, Jost and Jacquot have shown its importance in the development of fœtal liver glycogen^1–3. That the adrenal itself is influenced in its development by a structure or structures within the skull—generally assumed to be the hypophysis—has been demonstrated in the rabbit^4,5 and rat^6,7 by fœtal decapitation, following which there is a considerable reduction in the adrenal by full term. Since it is well recognized that in the adult animal adrenal hormones have a thymolytic action, it was considered possible that the development of the fœtal thymus might be influenced by the fœtal adrenals. To test this hypothesis rabbit fœtuses were decapitated at 20–21 days of development and the thymus glands were weighed when the fœtuses had reached almost to term. The results were clear cut, for in the operated fœtuses the thymus on average was 72 per cent heavier than in their litter mate controls⁵.