Receptor regulation prolactin

The DA receptor regulating prolactin release in the pituitary is of the D2 " type [50]. This view is substantiated by the studies of Carlsson and coworkers, who reported that prolactin release response is different in male and female rats given partial DA agonists of different intrinsic efficacy [13]. In these studies, endogenous DA was depleated and prolactin levels were... 

The prolactin receptor, PER, which regulates milk production in mammals, belongs to the same receptor class as the growth hormone receptor. In addition to binding the hormone prolactin, PER also binds and is activated by growth hormone. The extracellular domain of PER forms a very stable 1 1 complex with growth hormone in solution this complex has been crystallized and its structure determined (Figure 13.21). We shall compare this structure with the 1 2 complex of the same hormone with GHR. 

Prolactin is an essential hormone for normal production of breast milk following childbirth. It also plays a pivotal role in a variety of reproductive functions. Prolactin is regulated primarily by the hypothalamus-pituitary axis and secreted solely by the lactotroph cells of the anterior pituitary gland. Under normal conditions, secretion of prolactin is predominantly under inhibitory control by dopamine and acts on the D2 receptors located on the lactotroph cells. Increase of hypothalamic thyrotropin-releasing hormone (TRH) in primary hypothyroidism can stimulate the release of prolactin. 

Other effects Blockade of a-adrenergic receptors causes orthostatic hypotension and lightheadedness. The neuroleptics also alter temperature-regulating mechanisms and can produce poik-ilothermia (body temperature varies with the environment). In the pituitary, neuroleptics block D2 receptors, leading to an increase in prolactin release. 

Prolactin appears to play a role in regulating the immune system in mammals, though the significance of this is not yet clear. Receptors for the hormone have been... 

More recently, monoclonal antibodies to the rabbit prolactin receptor have been described [49,50]. These showed strong species specificity, competed with 125I-la-belled prolactin for binding to receptors, and provided evidence for receptor heterogeneity in some tissues [49], Two of the monoclonal antibodies could block the actions of prolactin on casein synthesis in rabbit mammary gland explants, and one of them could inhibit milk production in vivo [50]. A third antibody could mimic the actions of prolactin on both casein and DNA synthesis in mammary explants. For this effect bivalency was essential, and down-regulation of receptors was much less than that produced by prolactin itself [50],... 

The interaction of factors regulating levels of prolactin receptors [26,56] in a variety of tissues is complex and not fully understood. The topic will not be considered in detail here. The actions of prolactin itself on the process will be discussed briefly, however. In the short term, prolactin often leads to down-regulation of its own receptors, presumably as a consequence of internalization following binding of... 

Sanyal S, Van Tol HH (1997) Dopamine D4 receptor-mediated inhibition of cyclic adenosine 3, 5 -monophosphate production does not affect prolactin regulation. Endocrinology 735 1871-1878. 

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