[Postnatal development of hormonal relations in the hypothalamo-hypophyseal axis in bulls]

A review of basic knowledge of endocrine events associated with the development of bovine male reproductive organs during early postnatal ontogenesis and infantile, prepuberal, puberal and adult periods is presented. Changes in the dynamics of release of GnRH, LH, FSH, testosterone and other clinically significant androgens, oestrogens and inhibin, including their interactions in the hypothalamus-hypophysis-testicle axis are described. Attention is paid to the relationships between reproductive hormones and the most relevant morphological and physiological changes in bovine male reproductive organs during the postnatal development, particularly the multiplication of Leydig cells, the differentiation and multiplication of Sertoli cells, testicular growth and initiation of spermiogenesis.