Interrelations between prolactin and the hypothalamo hypophysio thyroid axis: a review

Numerous interrelationships exist between prolactin (PRL) and thyroid hormones and their respective regulating mechanisms. PRL influences the action of thyroid hormones on peripheral tissues. Thyroid hormones permissively affect PRL actions on the development of the mammary gland and on lactation. In the adenohypophysis, thyroxine (T4) inhibits both PRL and thyrotropin (TSH) secretion. Estrogens stimulate the lactotrophs and the thyrotrophs. Several reports show that, in some patients with hypothyroidism and elevated TSH levels, galactorrhea and elevated levels of PRL occur. In several species, the neurohormone releasing TSH from the adenohypophysis (thyrotropin releasing hormone: TRH) also releases PRL. Finally, the same neurotransmitters seem involved in the complex relationships regulating hypothalamic mechanisms that promote both TSH and PRL secretion. The present paper comprehensively reviews the sophisticated interrelationships between PRL and the hypothalamo pituitary thyroid axis. Emphasis is placed on their clinical significance. Interrelations at the peripheral target organ level, the hypophysial level and the hypothalamic (central nervous system) level are considered.SCOPUS: ar.j