Original research article Effects of tamoxifen metabolites on fertility of male rat M.K. Gill-Sharma, N. Balasinor, P. Parte, M. Aleem, H.S. Juneja* Department of Neuroendocrinology, Institute for Research in Reproduction (ICMR), J.M.Street, Parel, Mumbai 400 012, India Abstract The effects of chronic oral administration of tamoxifen citrate, at a dose of 0.4 mg/kg/day, were compared to those of subcutaneous (s.c) administration of tamoxifen citrate, 4-hydroxy tamoxifen, N-desmethyl tamoxifen and intermittent oral tamoxifen administration on the fertility of the male rat and its post reversal progeny. The fertility parameters of 120 day-treated male rat sires from all groups and post reversal male F1 progeny of tamoxifen-treated sires were assessed. Chronic tamoxifen treatment via oral or s.c. routes reduced the fertility of the male rat, weights of accessory sex glands, serum luteinizing hormone, and testosterone levels without altering potency or sperm counts. However, antifertility effects of s.c. treatment were comparatively more consistent than those of oral treatment. 4-Hydroxy and N-desmethyl tamoxifen failed to produce significant antifertility effects in the male rat. The antifertility effects of intermittent oral treatment were more sustained than those of chronic oral tamoxifen treatment. It is inferred that hepatic metabolism of tamoxifen interferes with its antifertility effects via oral route and that the parameters affected by chronic oral exposure in the male sires are completely reversed in progeny ensuing after an adequate period of drug withdrawal. © 2001 Elsevier Science Inc. All rights reserved. Keywords: Antiestrogens; Routes; Fertility index; Rat sires; Progeny 1. Introduction Tamoxifen, a synthetic non-steroidal antiestrogen, has been shown to induce reversible antifertility effects in the adult male rat, after oral treatment [1]. The reported effects on fecundity, however, were observed to be variable upon chronic exposure. In order to explain the inconsistent effects on fecundity by oral route, it was proposed that tamoxifen metabolites with long half-lives and varied estrogen agonis- tic/antagonistic effects, could be responsible [2,3]. The hy- pothesis, however, could not be substantiated due to paucity of information regarding the antifertility effects of tamox- ifen metabolites. Tamoxifen is metabolized to two major metabolites in the liver depending upon the liver enzymes induced. Male and female rat liver preferentially transforms tamoxifen to N-desmethyl tamoxifen and 4-hydroxy tamoxifen, respec- tively [4]. The hydroxylated metabolites undergo cis-trans isomerism in vivo and exert agonistic to antagonistic effects [5]. Tamoxifen is a ligand for the estrogen receptor and thus perceived to produce its biologic effects through estrogen receptors [6]. Modifications of tamoxifen structure, viz., hydroxylation or alteration of the side chain, have been reported to alter affinities for the estrogen receptors [7–9]. The structurally modified hepatic metabolites have altered affinities for the estrogen receptors compared to tamoxifen [10]. The effects of metabolic activation of tamoxifen in the female rat liver have been reported to produce effects much more enhanced than those observed after s.c. administration [11]. The metabolic activation in the liver has also been observed for other inactive antiestrogens [12]. Tamoxifen has been hypothesized to produce tissue- specific estrogenic and antiestrogenic effects [13]. Alterna- tively, tamoxifen is converted to biologically active metab- olites in the liver, after oral treatment, some of which have been reported to have greater affinity for the estrogen re- ceptors in vitro, and thus have the potential to modulate the tamoxifen-induced antifertility effects in vivo by exerting synergistic or antagonistic effects on fertility [14 –16]. Met- abolic activation of tamoxifen has also been associated with hepatic carcinogenicity [17]. Tamoxifen metabolism, there- fore, has the potential to be mutagenic in spermatogonia. The present study was designed to ascertain the fertility modulating effects of major tamoxifen metabolites reported in adult male rat and fertility disorders, if any, in post reversal progeny after chronic oral tamoxifen treatment. Supported by: Indian Council of Medical Research. * Corresponding author. Tel.: +1-4132111-2-6-7; fax: +1-9122- 4139412. E-mail address: dirirr@vsnl.com (M.K. Gill-Sharma). Contraception 63 (2001) 103–109 0010-7824/01/$ – see front matter © 2001 Elsevier Science Inc. All rights reserved. PII: S0010-7824(01)00178-0