Effects of thyroid hormone on Leydig cell regeneration in the adult rat following ethane dimethane sulphonate treatment

We tested the effects of thyroid hormone on Leydig cell (LC) regeneration i n the adult rat testis after ethane dimethyl sulphonate (EDS) treatment. Ni nety-day-old, thyroid-intact (n = 96) and thyroidectomized (n = 5) male Spr ague-Dawley rats were injected intraperitoneally (single injection) with ED S (75 mg/kg) to destroy LC. Thyroid-intact, EDS-treated rats were equally d ivided into three groups (n = 32 per group) and treated as follows: control (saline-injected), hypothyroid (provided 0.1% propyl thiouracil in drinkin g water), and hyperthyroid (received daily subcutaneous injections of tri-i odothyronine, 100 mu g/kg). Testing was done at Days 2, 7, 14, and 21 for t hyroid-intact rats and at Day 21 for thyroidectomized rats after the EDS tr eatment. Leydig cells were absent in control and hyperthyroid rats at Days 2, 7, and 14; in hypothyroid rats at all ages; and in thyroidectomized rats at Day 21. The LC number per testis in hyperthyroid rats was twice as thos e of controls at Day 21. 3 beta-Hydroxysteroid dehydrogenase (LC marker) im munocytochemistry results agreed with these findings. Mesenchymal cell numb er per testis was similar in the three treatment groups of thyroid-intact r ats on Days 2 and 7, but it was different on Days 14 and 21. The highest nu mber was in the hypothyroid rats, and the lowest was in the hyperthyroid ra ts. Serum testosterone levels could be measured in control rats only on Day 21, were undetectable in hypothyroid rats at all stages, and were detected in hyperthyroid rats on Days 14 and 21. These levels in hyperthyroid rats were twofold greater than those of controls on Day 21. Serum androstenedion e levels could be measured only in the hyperthyroid rats on Day 21. Testost erone and androstenedione levels in the incubation media showed similar pat terns to those in serum, but with larger values. These findings indicate th at hypothyroidism inhibits LC regeneration and hyperthyroidism results in a ccelerated differentiation of more mesenchymal cells into LC following the EDS treatment. The observations of the EDS-treated, thyroidectomized rats c onfirmed that the findings in hypothyroid rats were, indeed, due to the def iciency of thyroid hormone.