DEVELOPMENT OF THE GUBERNACULUM AND PROCESSUS-VAGINALIS IN FREEMARTINISM - FURTHER EVIDENCE IN SUPPORT OF A SPECIFIC FETAL TESTIS HORMONE GOVERNING MALE-SPECIFIC GUBERNACULAR DEVELOPMENT

Background: Freemartinism occurs in some species of ruminants and affe cts most female bovine fetuses in heterosexual, multiple pregnancies o wing to fusion of the chorionic blood circulations soon after implanta tion. Maldevelopment of the ovaries and Mullerian ducts have been desc ribed and recognized as resulting from exposure of their respective pr imordia to an excess of anti-Mullerian hormone. The present study aime d to analyse the prenatal growth and development of the gubernaculum i n freemartins to find out its possible affliction through foetal testi s hormones derived from their male co-twin. Methods: Histological sect ions of young and drawings and photographs of further developed freema rtins and control male and female bovine foetuses were analysed. The s pecimens had been collected earlier for analysis of the time course of male and female gonadal and genital development and its impairment as sociated with freemartinism. Results: The gubernaculum of 35-40-day-ol d male and female fetuses was in the initial stage of development and of similar appearance in all specimens. Gubernacula of 60-70-day-old m ale fetuses differed from those of females of similar age in various r espects: the male gubernaculum size was larger and extension of the pr ocessus vaginalis was deeper. Freemartins showed an intermediate devel opment with some individuals resembling male and others resembling fem ale agemates. During further development, gubernacula in males develop ed into muscular cremaster sacs, whereas those in females generally di d not develop beyond the size and structural complexity of 70-day-old foetuses. Beyond day 70 of fetal life, gubernaculum development in fre emartins definitely showed male characteristics with respect to size a nd growth of a processus vaginalis with a cremaster muscular wall. The male-like pattern of the outgrowth of the processus vaginalis changed during the second half of prenatal life. Rather than its further deep ening as in males, this structure became inverted to become emerging a s a papilla-like structure from the inguinal abdomen bottom. An explan ation is proposed for this unprecedented inversion, taking into accoun t: (1) the faster and higher reaching rightsided ascent of the kidneys and gonads, (2) the femalelike outgrowth of the cranial gonadal suspe nsory ligaments, and (3) the absence of scrotum development. The ovari es and mesonephric remnants in developing freemartins, during their as cent together with the kidneys while remaining attached to the bottom of the developing processus vaginalis sacs via the gubernaculum ligame nt, are proposed to act together to pull up the bottom of the processu s vaginalis sacs. From this action, ''inverted hernia sacs'' result as the irreversible consequence. Conclusion: The data support the concep t that foetal testes act, via as an yet unidentified third hormone, to establish malelike development of gubernacula into muscular cremaster sacs. Further work is required to reveal the identity of this hormone . Furthermore, the apparent similarity of the freemartins' inverted pr ocessus vaginalis sacs and the fetal rodents' gubernacular cones sugge sts that the ruminants' and rodents' processus vaginalis are essential ly similar structures. Thus there is no longer an urgent need to disti nguish between two different types of gubernaculum development and tes tis descent in rodents and ruminants, respectively, and involving or n ot fetal gubernacular cones. The present observations may thus contrib ute to the development of a unified hypothesis for sexually dimorphic development of the gubernaculum throughout the mammalian class. (C) 19 95 Wiley-Liss, Inc.