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Effect of High-Dose Liothyronine on Semen Quality and Recovery Following Withdrawal in Rabbits

From the Department of Animal Science, Cornell University, Ithaca, New York.

Correspondence to: Dr Robert H. Foote, Department of Animal Science, Cornell University, Ithaca, NY 14853-4801.

Endocrine aspects of the thyroid in the pituitary-thyroid-gonadal axis have been studied extensively, but few controlled studies have been conducted on sperm output in males with hyperthyroidism. The rabbit was used as a model to study the effects of hyperthyroidism induced with supraphysiologic doses of tri-iodothyronine (T₃). Semen was collected from 18 sexually mature Dutch rabbits for 9 weeks before the experiment to standardize semen collection procedures, and to provide semen data to equalize treatment groups. Controls were continued on the same regimen for 18 weeks, whereas the treatment group received daily T₃ doses of 10 µ/kg per body weight for 5 weeks, followed by 13 weeks of recovery. Feed consumption was reduced precipitously during T₃ treatment, but it recovered rapidly following termination of T₃ administration. Gradual weight loss and recovery accompanied changes in feed consumption. Loss of libido was not detectable with treatment. Sperm output during 9 weeks following T₃ treatment was 46% of that collected during the standardization period. During the last 4 weeks, sperm output had recovered to 88% of pretreatment values, and subsequently, treated males had normal fertility. Histologic sections showed that the thyroid was inhibited by T₃ treatment and that spermatogenesis was moderately depressed. Both recovered by the termination of the experiment. These studies indicate that effects of induced hyperthyroidism on sperm production are transient.

     Key words: Hyperthyroidism, tri-iodothyronine, rabbit semen, libido, fertility