Fifteen prepubertal male rats (age 30 days) were divided into three groups of five each: Group 1, hypothyroid (Tx)--rats were thyroidectomized at day 30; Group 2, T4 (L-thyroxine) replacement therapy (Tx+T4)--rats were thyroidectomized at day 30 and treated daily i.m. with T4 (6 micrograms/100 g body weight/day) for 30 days from day 31 to day 60 post-thyroidectomy (age 90 days); Group 3, control--rats were sham-operated and treated with vehicle. The rats from all groups were killed on day 61 post-thyroidectomy or post-sham operation (age 91 days). The serum levels of testosterone, T4 and T3 decreased in the Tx group (p < 0.001). In the Tx+T4 group the levels of T4 and T3 were restored to control values, whereas testosterone levels remained lower than in the control group. Hypothyroidism caused various changes in the levels of epididymal phospholipids and neutral lipids. These were restored differentially or were altered further in the Tx+T4 group. The number and forward motility of spermatozoa, recovered from the cauda epididymis, were decreased significantly (p < 0.01) in the Tx group and were not restored in the Tx+T4 group. This study shows that chronic hypothyroidism, induced at prepuberty and continued for 60 days, causes various changes in the lipid composition of the caput and cauda epididymis and lowers the quality and quantity of spermatozoa in the cauda epididymis. T4 therapy for 30 days, especially during the postpubertal period, did not restore the quality or quantity of spermatozoa and caused differential changes in the levels of epididymal lipids, depending upon the region.(ABSTRACT TRUNCATED AT 250 WORDS)

Fifteen prepubertal rats were divided into 3 groups of 5 each: (1) hyperthyroid group (TH), the rats were treated with thyroxine (T4) (25 micrograms/100g body weight/day) for 60 days from the age of day 31 to day 90; (2) T4-withdrawal group (TH-T4), the rats were given T4 for 30 days from the age of day 31 to day 60 and then the T4 treatment was withdrawn for the following 30 days from the age of day 61 to day 90 and the animals were given vehicle during this period; and (3) control group, the rats were given vehicle for 60 days from the age of day 31 to day 90. All were killed at the age of day 91. Serum levels of testosterone, T4 and triiodothyronine increased in the TH group (P < 0.001). The levels decreased to the euthyroid status in the TH-T4 group. Hyperthyroidism caused various changes in the levels of epididymal lipids. The levels changed further or were restored differentially in the TH-T4 group. The number of spermatozoa decreased, in caput epididymis (CpE) as well as in cauda epididymis (CdE), in the TH group (P < 0.001). The number was not restored in the TH-T4 group. The forward motility of the spermatozoa, determined in CdE, decreased in the TH group (P < 0.001) and was not restored in the TH-T4 group. The study showed that chronic hyperthyroidism, induced at the prepubertal age, causes various changes in epididymal lipid composition and sperm parameters. The study may be helpful in revealing the reasons for male infertility in hyperthyroid patients.