Plasma glucocorticoid and adrenocorticotropin concentrations measured serially in growth-retarded fetal lambs

We studied the fetal pituitrary-adrenal axis in 9 growth retarded fetal lambs by serially measuring plasma glucocorticoids and ACTH concentrations from 115 to 140 days of gestation and adrenal blood flow at 138 days of gestation. At each gestational age period studied, plasma glucocorticoid and ACTH concentrations were similar in both growth retarded and control fetuses (Figs. 1, 2). However, ACTH concentration tended to be higher in the last 20 days of gestation in the growth retarded fetuses. This resulted in a significantly lower glucocorticoid/ACTH ratio between 121 to 130 days of gestation in the growth retarded fetal lambs as compared to the control fetuses (212 +/- 111 vs. 1042 +/- 257). The glucocorticoid/ACTH ratio in the growth retarded fetuses became similar to the ratio of the control fetuses at 131 to 140 days (445 +/- 145 vs. 554 +/- 182). Adrenal blood flow was significantly increased at term in the the growth retarded fetuses (535 +/- 87 vs. 302 +/- 40 ml/min/100g). These data indicate that the pattern of maturation of the fetal adrenal gland in the growth retarded fetal lamb is similar to that of the normal sized fetus. Because of the increased adrenal blood flow observed at 138 days of gestation, there is a suggestion of a decreased sensitivity to ACTH in these animals.