Puberty Results from a Continuous Process of Endocrine Changes ThatAre Initiated Shortly After Birth
The pituitary gland, gonads, and steroid-dependent target tissues are capable of responding to stimulatory hormones before puberty; therefore the hypothalamus is considered to playa pivotal role in the initiation of puberty.
Pubertyappears to be the end result of a continuous process of endocrine changes that are initiated shortly after birth. Some investigators theorize that puberty occurs when the animals hypothalamic-pituitary complex becomes desensitized to the feedback inhibition of gonadal steroids. This desensitization would apparently allow increased discharge of GnRH from the hypothalamus and a greater response of the pituitary to GnRH. Although numerous factors can influence the modulation by the central nervous system of the endocrine system, the major factors that affect age at puberty in domestic animals are breed, energy intake, and season of birth.The hypothalamic-pituitary-gonadal system in humans differentiates and functions during fetal life and briefly during infancy; it then is suppressed during childhood and is reactivated during puberty after almost a decade of low activity. Inhibition of the hypothalamic-pituitary-gonadal system in prepubertal children is mediated through the suppression of GnRH synthesis and pulsatile secretion. Progressive pulsatile stimulation of the pituitary by GnRH and the gonads by LH and FSH is required for the initiation and progression of puberty. Prepubertal children secrete small amounts of FSH and LH from the pituitary, indicating that the hypothalamic- pituitary-gonadal axis is functional, but at a low level. This low level of gonadotropin secretion rapidly decreases when sex steroids are administered. Therefore, a highly sensitive negative-feedback mechanism appears to exist in young prepubertal children, and a similar mechanism is likely to exist in prepubertal domestic animals.