Dogs of different ages without
testicular diseases were evaluated to study possible age-related changes in
hormone concentrations in serum. Dogs with testicular tumours were also investigated to study the relation between tumour type and
hormone concentrations; in this study, dogs with Sertoli cell tumours, Leydig cell tumours and
seminomas were included. We measured
testosterone,
oestradiol, LH, FSH and
inhibin-like immunoreactivity concentrations in peripheral venous and testicular venous blood of these animals. In normal dogs there appeared to be no age-related changes in the concentrations of the investigated
hormones, except for a significant age-related decrease in
oestradiol concentrations in testicular venous blood (P<0.02). Dogs with a Sertoli cell tumour had greater
oestradiol concentrations and
inhibin-like immunoreactivity in both peripheral and testicular venous blood than did dogs without a
neoplasm (P<0. 05).
Testosterone concentrations were reduced 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 dogs with a Leydig cell tumour; it was accompanied by a significantly greater
oestradiol concentration than in normal dogs 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 both peripheral venous and testicular venous blood than did dogs without a
neoplasm (P<0.05). The
testosterone concentration in testicular venous blood of these dogs was lower than that in dogs with normal testes. The concentration of LH in peripheral venous blood was also reduced (P<0. 05).
Hormone concentrations in dogs with a
seminoma were not different from those in normal dogs. It was concluded that
seminomas are not endocrinologically active. In contrast, both Sertoli cell tumours and Leydig cell tumours can cause increased oestrogen production leading to signs of feminisation. These tumours also have considerable amounts of
inhibin-like immunoreactivity, but only in Sertoli cell tumours does this result in a reduction in FSH concentrations, suggesting that Sertoli cell tumours secrete dimeric
inhibin, whereas Leydig cell tumours presumably produce loose alpha-subunits that cross-react in the
inhibin assay but are not biologically active.