Endocrine studies in anencephaly.

Endocrine function has been investigated in four anencephalic neonates to determine the influence of absence of cortical and hypothalamic tissue and of hypoplasia of the pituitary. Intravenous glucose administration resulted in higher peak values for blood sugar and more rapid glucose disposal rates than reported in normals. Intravenous insulin tolerance tests on two of the infants failed to evoke elevations in plasma growth hormone, and the infants showed a remarkable resistance to the hypoglycemic effect of insulin. Administration of lysine-vasopressin caused an active growth hormone release. Similarly, there was a large increase in serum thyrotropin after administration of synthetic thyrotropin-releasing hormone. Basal levels of both thyrotropin and growth hormone were low as compared with values reported for normal newborns. Prolactin values obtained on three of the infants were in the normal range. The results strongly suggest that anterior pituitary function mediated by the hypothalamus and its releasing factors is deficient in anencephaly. However, the anterior pituitary can release growth hormone and thyrotropin when stimulated directly and, in the case of thyrotropin release, may function autonomously. The normal prolactin values presumably reflect the absence of the hypothalamic prolactin inhibitory factor.