Unctions HPRL (human PRL) causes initiation of milk formation and its maintenance

spill into the peripheral blood These (big and big big prolactin) molecules are prohormones. when present in blood, they being RIA +ve, impart falsely high values (because They have only very weak PRL like action). Unctions HPRL (human PRL) causes initiation of milk formation and its maintenance in The female breast In human females, probably there is no other major function of PRL, but in the animals, it has some other important functions. For example, in the fats, PRL is required for The maintenance of corpus lutieum in early days of pregnancy In some other animals this hormone is required for the appearance of rnataral instincts. In birds, this hormone is necessary for the development of instincts of nest building (a behavior which is allied to the maternal behavior). HPRL is present in males and its concentration in blood rises in puberty it is now known that PRL potentates the LH action on Leydig cells and in some unknown way high PRLin our body causes im-rpotence. Incidentally, PRL receptors, in human beings, are found only in the breast and the gonads. Regulation From hypothalamus, a substance called pralactin inhibitory factor (PIF) is released and discharged in to the blood vessels. In the adenohypophysis, PLF inhibits the secretion of PRL Dopamine, a catechol amine, is a well known neurotransmitter in the hypothalamus and enters The portal system of blood vessels From vanous evidences, it appears, that dopamine is the PIF. 2. Hypothalamus also produces a PPL releasing factor (PRLPF), details are not clearly known (indeed its very existence is still debated) TRH of the hypothalamus has some PRLRF like activity. Vasoactive intestinal polypeptide (chap B. sec III) also acts as PRLRF Estrogen stimulates the growth of the lacrotroph. During pregnancy . the adenohypophysis grows in size, principally due to the growth of the laclotrophs which is mainly due to the excess estrogen derived from placenta. As a result, the HFPI. values rise greatly during pregnancy (normal, in non pregnant women 10 to 20 ng/ml normally lower values are found in male, during pregnancy 100 to 300 ng/ml values are common PRL is determined by RIA). However, the PRL cannot start acting so long the estrogen concentration of blood is high. Therefore, milk formation starts after parturition (when blood estrogen level abruptly falls) Mechanical stimulation of the female nipple, notably suckling increases the HPRL secretion Drugs which behave as dopamine (dopamine agonists) inhibit the HPRL secretion. Conversely, drugs which opose dopamine (dopamine antagonists} increase HPRL secretion Bromocriptine is one notable agonist of dopamine. Applied physiology. Reserpine and methyldopa, drugs which are used against hypertension, remove dopamine from the neurons and cause rise of PRL Prolonged usage of reserpine is known to produce clinical symptoms like breast enlargement (even breast cancer) even in male breasts.