Secretion of free and conjugated steroids by the horse testis into lymph and venous blood.

In 3 testes of 2 adult Pony stallions under halothane anaesthesia, catheters were inserted into a vein and a lymphatic vessel in the spermatic cord and into a vein on the surface of the testis. Lymph and venous blood were collected from the catheters in the cord and p-aminohippurate (2% w/v, 0 . 1 ml/min) was infused into the vein on the testis to determine blood flow by dilution. After 1 h, 6000 i.u. hCG was injected i.v. and collections continued for 45 min. The testes weighed 126-176 g. Lymph flow was 20-150 microliter/min before hCG and 100-270 microliter/min after hCG; the range of blood flow, with a haematocrit of about 22%, was unchanged (27-47 ml/min) after hCG. The concentration of testosterone in spermatic venous blood rose from 6-20 ng/ml to 160-270 ng/ml within about 30 min after hCG. Peripheral levels rose from about 2 to 6 ng/ml and lymph levels increased from 9-20 to 34-150 ng/ml after hCG. In contrast, the concentrations of oestrone sulphate in spermatic venous blood were about 400 ng/ml, compared with about 250 ng/ml in peripheral blood, while lymph values ranged from 600 to 1500 ng/ml; hCG had no consistent effect. DHA and its sulphate were present in spermatic venous blood at concentrations (about 3 and 5 ng/ml respectively) slightly higher than in peripheral blood (1 . 7 and 2 . 5 ng/ml), but the sulphate was at a very much higher concentration in lymph (about 5 and 200 ng/ml respectively). These results indicate that testicular lymph is an important route for the secretion of conjugated steroids by the horse testis.