Endocrine Control of the Fetal Circulation

Abstract

The ability of circulating hormones to affect the fetal circulation was cited by Bar-croft (1946), who showed that large doses of epinephrine increased arterial pressure in the fetal lamb. Subsequently, studies were directed to assessing the ability of the circulation to respond to infusion of various hormones, with little regard to the amounts given or to plasma concentrations achieved. Only recently, with the development of techniques to measure plasma concentrations of many hormones, has the role of endocrine systems in controlling fetal circulation under resting conditions and in response to stress begun to be defined. Several issues need to be addressed. These include: whether the fetus is capable of producing the hormone, what concentrations are achieved at rest, whether secretory responses to appropriate stimulation occur, and comparison of plasma concentrations with adult values. Furthermore, the ability of the heart and blood vessels to respond to various concentrations of hormones as well as the magnitude and direction of response have to be defined. In addition, it has become apparent that hormones may be important in the maturation of vascular structures during fetal development, in a manner similar to that shown for lung maturation (Ballard et al. 1977; Mescher et al. 1975). In this review, the role of hormones in normal regulation of the circulation, their responses to stress, and their influence on circulatory responses to stress will be presented briefly, while the effects of hormones on maturation of the circulation, particularly the ductus arteriosus and the heart, will be emphasized.