Reproduction Abstracts

Introduction: Hypothalamo–pituitary–testicular feedback is intact in the ovine fetus. Exogenous testosterone suppresses fetal LH and testicular steroidogenesis to maintain normal circulating testosterone concentrations. INSL3 is a non-steroidal hormone secreted by the fetal testis whose roles include facilitating testicular descent. We hypothesised that the homeostatic response to increased androgens would have a detrimental effect on fetal INSL3 expression.

Materials and methods: Pregnant Scottish Greyface sheep were treated twice weekly with testosterone propionate (TP: 100 mg) or vehicle control from day (d) 62 gestation and male fetuses collected at d70 (TP=5, C=8) and d90 (TP=14, C=12). In some, testis explants (d90) were cultured for 1hr then LH or control was added for 1hr. Other fetuses (d90) had direct injection of TP (20 mg) or vehicle at d62 and d82 (TP=6, C=11). INSL3 expression was analysed by quantitative RT-PCR and localised by immunohistochemistry.

Results and discussion: INSL3 was localised to Leydig cells in the fetal testis. Maternal TP administration reduced the expression of INSL3 in the fetal testis at d70 (P<0.05) and d90 gestation (P<0.05). In addition, direct injection of TP into the fetus also reduced testicular INSL3 expression (P<0.05). In vitro expression of INSL3 in cultured explants was much lower after maternal TP exposure (P<0.005) and there was a non-significant increase in explant INSL3 expression after exposure to LH (P=0.06). INSL3 expression in Leydig cells in the ovine fetus is altered by testosterone, probably though LH regulation. This is further evidence that INSL3 is a marker of endocrine disruption in the developing fetus.