Endocrine Abstracts

At present, the blue fox is extensively studied in connection with the process of domestication and there is a need for a better understanding of endocrine processes associated with reproductive and stress-response development in this species. Plasma concentrations of testosterone, oestradiol, ACTH and cortisol, gonadal in vitro production of testosterone and oestradiol and adrenal in vitro production of cortisol were measured by RIA in foetal (47-48 days of pregnancy, n=69), neonatal (10 days of age, n=34) and prepubertal (6-7 months of age, n=56) animals of both sexes. Body, gonadal and adrenal weights were also determined in the same foxes. Plasma ACTH and cortisol concentrations, and the adrenal cortisol production increased significantly between the prenatal and prepubertal period and sex differences were not found in these parameters in any of the ages studied. Significant decrease in ACTH (20% of foetal values) and cortisol (40% of foetal values) concentrations and a failure of the adrenal responsiveness to ACTH occurred in neonatal animals in comparison with foetal foxes of both sexes suggesting the existence of a transient stress hyporesponsive period during the early postnatal development. Plasma testosterone was detectable only in foetal and prepubertal males, while plasma oestradiol was detectable in foetal and prepubertal animals of both sexes. The testicular testosterone in vitro production was increased significantly by hCG supplementation (30-200% of pre-treatment values) at all ages studied, while the ovarian oestradiol production was never stimulated by hCG. The high testosterone production by the testes during the early development may be involved in sexual differentiation of the masculine phenotype in blue foxes.