Reprod. Fertil. Dev., 1996, 8, 373-8 Influence of Hyperthyroidism Induced at Prepuberty on the Epididymal Lipids, Number and Motility of Spermatozoa in Rats P. N. Senthil ~urnar~~, M. Michael ~ruldhas* and S. C. junejaBD *~epartment of Endocrinology, Dr A.L.M. Post Graduate Institute of Basic Medical Sciences, University of Madras, Taramani, Madras 6001I3, India. B~ll India Institute of Medical Sciences, New Delhi 110029, India. C~resent address: RN. Senthil Kumar; Department of Reproductive Biology, All India Institute of Medical Sciences, New Delhi-110029, India. D~resent address and address for correspondence: Room F-4.29, Royal Victoria Hospital, Montreal, Canada H3A IAI. Abstract. Fifteen prepubertal rats were divided into 3 groups of 5 each: (I) hyperthyroid group (TH), the rats were treated with thyroxine (T4)(25pg/100gbody weightlday) for 60 days from the age of day 31 to day 90; (2) T4-withdrawalgroup (TH-T4), the rats were given T4 for 30 days from the age of day 31 to day 63 and then the T4 treatment was withdrawn for the following 30 days from the age of day 61 to day 90 and the animals were given vehicle during this period; and (3) control group, the rats were given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 triiodothyronineincreased 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 THgroup (P<0.001). The number was not restored in the TH-T, 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. Extra keywords: Prepubertal rats, Sperm count, Sperm forward motility. Introduction Spermatozoa retrieved from the seminiferous tubules and the proximal regions of the epididymis are incapable of binding the zona pellucida during the first mandatory step towards fertilization. The mammalian epididymis provides a specific intraluminal environment for the morphological and biochemical modifications necessary to produce function- ally mature spermatozoa. The sperm plasma membrane, a vital component during the early events in fertilization, undergoes extensive biochemical changes as spermatozoa move towards the cauda epididymis (Yanagimachi, 1988). Any change in the epididymal composition might alter the intraluminal environment and affect the transportation, maturation and storage of the spermatozoa, the major functions of the epididymis; these major functions are mainly dependent on the levels of the serum androgens, testosterone and its metabolites (Robaire & Hermo, 1988). Hyperthyroidism has been reported to cause infertility in man. Patients with hyperthyroidism showed oligospermia and low sperm motility (Clyde, Walsh & English, 1976). Partial failure of Leydig cell function, impairment of spermato- genesis and loss of libido have been reported in patients with thyrotoxicosis due to Graves' disease (Kidd, Glass & Vigersky, 1979). Sperm motility was reduced in rams with hyperthyroidism induced at maturity (Chandrasekhar, Holland, D'Occhio & Setchell, 1985). Hyperthyroidism in man reduced the number of spermatozoa with normal morphology and the sperm forward motility (Buitrago & Diez, 1987); the effect of the hyperthyroidism varied with the age and severity of the disease. Thyrotoxicosis has been shown to enhance lipid synthesis or degradation depending upon the tissue and the cell-type studied in vivo or in vitro (Loeb, 1991). Hyperthyroidism decreased the cholestero1:phospholipid ratio and increased the fluidity of the plasma membrane of skeletal muscle sarcolemma (Pilarska, Wrzosek, Pikula & Famulski, 1991). Short-term hyperthyroidism (20 days' treatment with thyroxine, T4), induced in pubertal and adult rats, has shown very few or no effects on the composition of individual epididymal lipids, and any effects were generally reversed by withdrawal of T4 (Pereira, Balasubramanian & Govindarajulu, 1984). The current study was designed to determine the effect of long-term hyperthyroidism (30 days' treatment with T4) induced at the prepubertal age on the