Prolactin inhibiting hormone PIH

The release of prolactin from the adenohypophysis is normally inhibited by prolactin-inhibiting hormone (PIH, dopamine) from the hypothalamus. Prolactin secretion is also controlled by prolactin-releasing factor (PRF). The release of PRF from the hypothalamus is mediated by reflexes elicited by suckling and breast stimulation. 

Prolactin-inhibiting hormone (PIH), also known as dopamine, is not a peptide (Chapter 17). It functions as a neurotransmitter in the CNS and as a precursor of norepinephrine and epinephrine in the adrenal medulla. In the hypothalamus, it originates in the TIDA and is released at the median eminence. Dopamine is a potent inhibitor of PRL release by the lactotropes (and mammosomatotropes) of the anterior pituitary, and this effect is mediated by D2 receptors that are coupled to Gj inhibition of adenylate cyclase. The lactotropes are unique in that they do not require stimulation by the hypothalamus to secrete PRL in fact, blockage of the blood flow from the hypothalamus to the anterior pituitary results in elevated serum levels of PRL, due to withdrawal of dopamine. Thus, unlike somatostatin, the effectiveness of dopamine does not depend on the presence of a stimulating hormone (Chapter 34). 

F. Prolactin-Inhibiting Hormone (PIH, Dopamine) Dopamine is the physiologic inhibitor of prolactin release. Because of its peripheral effects and the need for parenteral administration, dopamine is not useful in the control of hyperprolactinemia, but bromocriptine and other orally active ergot derivatives (eg, cabergoline. pergolide) are effective in reducing prolactin secretion from the normal gland as well as from pituitary tumors. 

Definition of abbreviations ACTH, adrenocorticotropin hormone DA, dopamine FSH, follicle-stimulating hormone GH, growth hormone GnRH, gonadotropin-releasing hormone LH, luteinizing hormone PIH, prolactin-inhibiting hormone. 

Prolactin releasing factor (PRF), prolactin releasing hormone, prolactoliberin a hormone thought to be identical with thyrotropin releasing factor, llie structure of Prolactin release inhibiting hormone (PIH) (prolactostatin) is unknown. PRF promotes, whereas PIH inhibits the synthesis and secretion of prolaction by the anterior pituitary. 

Prolactostatin, prolactin release-inhibiting hormone, PRIH or PIH, prolactin release-inhibiting factor, PRIF, a hypothalamic substance of (until now) unknown structure that inhibits the release of prolactin. 

PIH acronym of prolactin release inhibiting hormone (see Releasing hormones). 

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