J. srerotd Biochem. Vol. 19. No. I, pp. 979-983, 1983 Printed in Great Britain. All rights reserved 35. Steroid Rhythms and Disorders Related to Aging 0022-4731/83 $3.00+0.00 Copyright Q 1983 Pergamon Press Ltd zyxwvuts HORMONE PRODUCTION BY THE EARLY BOVINE EMBRYO MORDECHAISHEMESH and WILLIAM HANSEL Department of Hormone Research, Kimron Veterinary Institute, Beit-Dagan, P.O. Box 12, Israel and Department of Physiology, Veterinary Research Tower, Cornell University, Ithaca, NY 14853, U.S.A. SUMMARY Progesterone is the main steroid produced by bovine blastocysts collected at days 13-15 and placed in TCM-199 supplemented with 5% calf serum. PGF and PGE2 were increased (P < 0.05) in the cultured blastocysts. It is suggested that PG synthetase and enzymes capable of synthesizing progesterone and possibly estradiol are present in these early bovine blastocysts. The source of the steroids produced by the blastocyst appear to be trophoblast. At day 2&30 of fetal life, a new source of steroid production appears in the form of the fetal gonads. The undifferentiated gonad at 30-40 days, was shown to produce progesterone but not testosterone or estrogen, regardless of the sex of the fetus, and did not respond to LH. Between 95 and 110 days the amount of testosterone produced per mg declined from 1703 +- 391 to 37 k pg/mg gonad/24 h. Fetal testes from fetuses of 3.3 to 20 cm CRL were responsive to LH. Srmilar to the testes, the fetal ovary also showed a marked initial rise in steroidogenesis at the time of gonadal differentiation. However, the principal product of the ovary was 17/I-estradiol which was produced in ng amounts. The initial production of 2674 f 512 pg/mg gonad/24 h incubation at 3.3-4.5 cm dropped rapidly to 286 f 176 pg/mg gonad/24 h at 7.8-8.5 cm CRL. Furthermore, 17/I-estradiol production was undetectable in all older fetuses, while testosterone was readily detectable in testes of the same size. The mean values of 17P-estradiol secreted by the cultured ovaries from fetuses of 3.4 to 8.1 cm CRL was significantly enhanced by the presence of bovine LH. In the presence of testosterone the mean value of 17b-estradiol secreted by the incubated ovaries from fetuses of 5-8 cm and of 1@20cm CRL was significantly increased from 1.5 +_0.4 to 6.5 + 0.7ng and from ND to 2.2 +_0.4ng, respectively. In contrast, neither progesterone, 17a-hydroxyprogesterone, nor DHT affected 17/I-estradiol secretion in ovaries of the older group. 8-Br-CAMP added to the culture medium significantly stimulated both 17/&estradiol and testosterone production by the cultured ovaries from fetuses of 5-8 cm CRL. However, when the refractory ovaries from fetuses of 10-20 cm CRL were examined, only progesterone secretion was significantly enhanced. The role of estradiol secretion by the early fetal ovaries is not clear. The high levels of testosterone produced by testes and 17b-estradiol by ovaries in 45 k 3-day gonads suggest that bovine embryonic gonads are not only morphologically, but also functionally differentiated by this time. INTRODUCTION We have investigated the production of steroids by the early bovine embryo using blastocysts as well as early fetal gonads. The steroids produced by the blas- tocyst may serve to maintain pregnancy and in ad- dition may play a role in sexual differentiation. The role of steroids produced by the bovine blasto- cyst is difficult to define, as the mechanism by which the developing conceptus signals its presence to the mother is unknown. An essential requirement for the maintenance of pregnancy is that the normal ovarian cycle should be changed and the functional activity of the corpus luteum prolonged. In the cow, sheep and pig this signal is transmitted even before the embryo- nic tissue becomes intimately attached to the uterine epithelium and is therefore clearly distinct from im- plantation. This allows for the possibility that the blastocysts itself might participate in the events lead- ing to its own implantation by signaling its presence to the uterus. In the cow, the early effect of the con- ceptus on plasma progesterone level is evident on the 8th day after ovulation [l] in sheep on day 16 [2]. We have already shown that the pre-implantation blasto- cyst can produce progesterone, testosterone, and pro- staglandins by day 13 of gestation [3]. These results are illustrated in Table 1. The source of the steroids produced in the blasto- cyst appear to be trophoblast. Indeed preliminary studies in our laboratory indicate that the trophoblas- tic cells are capable of producing nanogram quantities of progesterone when maintained in cell culture (about 1 ng/300,000 cells/72 h). This could be ob- served in cells obtained as early as the third week of gestation. The role of this blastocyst progesterone is unknown. However, since it continues throughout pregnancy, it may serve to inhibit the production of prostaglandins which can cause luteolysis. These steroids may act directly or indirectly to maintain the corpus luteum. The immunosuppressive properties of progesterone are also well known [4]. At day 28-30 of fetal life, a new source of steroid production appears in the form of the fetal gonads. These steroids are presumably involved in sexual dif- 979