Origin of anti-Müllerian hormone in bovine freemartin fetuses.

The origin of AMH responsible for Müllerian duct regression in bovine freemartins has been reinvestigated, using a sensitive RIA for this hormone. Between 50 and 80 days, Müllerian duct regression occurs simultaneously in males and freemartins. Both twins exhibited high and positively correlated serum AMH concentrations, whereas gonadal in-vitro production of AMH and biological anti-Müllerian activity were detectable at a low level only in 2 out of 13 freemartins. In the gonads of approximately half the freemartins after 80 days, seminiferous tubules differentiated and the gonads produced AMH, but the output was very low compared to that of the male twin. These data suggest that regression of Müllerian duct in freemartins is essentially mediated by AMH produced by the testes of the male twin.