Ageing, testicular tumours and the pituitary-testis axis in dogs

Dog; of different ages without testicular diseases were evaluated to study possible age-related changes in hormone concentrations in serum. Dogs with testicular rumours were also investigated to study the relation between tum our type and hormone concentrations; in this study, dogs with Sertoli cell tumours, Leydig cell tumours and seminomas were included. We measured testo sterone, oestradiol, LH, FSH and inhibin-like immunoreactivity concentratio ns in peripheral venous and testicular venous blood of these animals. In normal dogs there appeared to be no age-related changes in the concentra tions of the investigated hormones, except for a significant age-related de crease in oestradiol concentrations in testicular venous blood (P<0.02). Do g with a Sertoli cell tumour had greater oestradiol concentrations and inhi bin-like immunoreactivity in both peripheral and testicular venous blood th an did dogs without a neoplasm (P<0.05). Testosterone concentrations were r educed in dogs with Sertoli cell tumours, as were FSH and LH. Feminisation occurred in eight of 13 dogs with a Sertoli cell tumour and in two of 14 do gs with a Leydig cell tumour; it was accompanied by a significantly greater oestradiol concentration than in normal dog; and in dogs with Sertoli cell tumours without signs of feminisation. Dogs with a Leydig cell tumour had greater concentrations of oestradiol and inhibin-like immunoreactivity in b oth peripheral venous and testicular venous blood than did dogs without a n eoplasm (P<0.05). The testosterone concentration in testicular venous blood of these dogs was lower than that in dogs with normal testes. The concentr ation of LH in peripheral venous blood was also reduced (P<0.05). Hormone c oncentrations in dogs with a seminoma were not different from those in norm al dog;. It was concluded that seminomas are not endocrinologically active. In contr ast, both Sertoli cell tumours and Leydig cell tumours can cause increased oestrogen production leading to signs of feminisation. These rumours also h ave considerable amounts of inhibin-like immunoreactivity, but only in Sert oli cell rumours does this result in a reduction in FSH concentrations, sug gesting that Sertoli cell rumours secrete dimeric inhibin, whereas Leydig c ell rumours presumably produce loose alpha-subunits that cross-react in the inhibin assay but are not biologically active.