Secretion of alpha-immunoreactive inhibin by human pre-embryos cultured in vitro.

alpha-Immunoreactive inhibin was measured using an enzyme immunoassay kit in the culture medium (Ham's F-10 medium supplemented with 14% heat-inactivated human serum) from day 3 or 4 to day 14 post-fertilization of 31 surplus pre-embryos from eight women participating in an in-vitro fertilization programme. Inhibition secretion was demonstrated in all of them from the fourth day after fertilization (mean +/- SEM: 3.0 +/- 0.7 U) and was independent of the morphological development of pre-embryos (2-4 cells, n = 4; 6-8 cells, n = 4; 8-10 cells, n = 9; 10-12 cells, n = 4; morulae, n = 5 and blastocysts, n = 4). On days 7, 10, 13 and 14 post-fertilization, mean inhibin values +/- SEM for non-disintegrated pre-embryos were respectively: 6.5 +/- 0.9 U, 12.3 +/- 2.0 U, 16.8 +/- 3.2 U and 20.2 +/- 3.7 U; however, when disintegration was noted on days 10 and 13 after fertilization, inhibin mean values were 9.0 +/- 1.4 U and 8.4 +/- 1.7 U respectively. Inhibin levels were significantly correlated with human chorionic gonadotrophin levels in the same culture media only on day 13, while correlation with pregnancy specific beta 1-glycoprotein occurred on day 7 post-fertilization. In conclusion, early human pre-embryos secrete alpha-immunoreactive inhibin before the cytotrophoblast is formed. This secretion increases significantly with time when development is continued, while disintegration is followed by a net decline in the rate of inhibin release.