PRECOCIOUS PUBERTY IN TAMOXIFEN-TREATED COCKERELS - HYPOTHALAMIC GONADOTROPIN-RELEASING HORMONE-I AND PLASMA LUTEINIZING-HORMONE, PROLACTIN, GROWTH-HORMONE AND TESTOSTERONE

1. The administration of the anti-oestrogen, tamoxifen (TAM) to juveni le chicks results in precocious puberty. In the present study the effe cts of TAM administration (1 mg/kg body weight on alternate days from 12 d of age) on testicular function, hypothalamic chicken gonadotropin -releasing hormone (cGn-RH-I), plasma luteinising hormone (LH), growth hormone (GH), prolactin (PRL) and testosterone were studied in juveni le White Leghorn cockerels. 2. The increase in hypothalamic GnRH-I con tent which occurs during sexual development was advanced in TAM-treate d birds, in association with precocious testicular development, an ear ly rise of plasma testosterone content and enhanced comb growth. 3. Pl asma LH concentrations behaved similarly and were higher in the TAM-tr eated than in control birds, during most of the experimental period. P lasma PRL concentration, which is high at hatching, decreased more qui ckly in TAM-treated than in control birds; plasma GH values were not c onsistently affected by TAM treatment. 4. Both the growth and the invo lution of the bursa of Fabricius in the TAM-treated cockerels preceded that in the control chicks. 5. It is concluded that TAM treatment ind uces precocious puberty in the cockerel by blocking the negative feedb ack action of aromatised testicular androgens on the hypothalamus.