Prolactin physiologic effects

Anterior Lobe. The anterior pituitary, or adenohypophysis, secretes six important peptide hormones. The anterior pituitary releases growth hormone (GH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), and prolactin (Pr). The physiologic effects of these hormones are listed in Table 28-1. 

The source of the ergot strongly influences the type of alkaloids present, as well as the clinical picture of ergotism [171]. The ergot alkaloids have three types of physiological effects they cause contraction of smooth muscle, they block the action of serotonin and adrenaline, and they act on the hypothalamic-pituitary system to inhibit the secretion of prolactin. These properties have led to their being used to induce uterine contractions, to relieve migraine headaches, and to treat prolactin-dependent disorders. 

Prolactin plays an important role in inducing growth and differentiation of the ductal and lobu-loalveolar epithelium, which is essential for lactation. Prolactin receptors are present in many other sites however, the physiological effects of prolactin at these sites remain poorly characterized. 

Table II represents the author s estimate of the physiological significance of the in vitro findings with hormones reported in the literature, as based upon the above criteria. It will be seen that a sizable number of hormones exert in vitro effects which are comparable in their essentials to the physiological effects observed in vivo. Among these are seen all chemical classes of hormones with the exception of the steroids protein— insulin polypeptides—ACTH, antidiuretic hormone (ADH), oxytocin, and glucagon or hyperglycemic factor (HGF) and amino acid derivatives —epinephrine and nor-epinephrine. The remaining hormones listed, in which physiologically meaningful in vitro results have not been as yet achieved, may be subdivided into two groups one, wherein little work has been attempted (as with parathormone, prolactin, etc.) the other, wherein extensive in vitro studies have been carried out.

Studies identifying endocrine effects in animals do not clearly identify a dose-response relationship. In addition, it has been suggested that nickel has a physiological role in endocrine gland function, affecting prolactin levels (Kenney and McCoy 1992). Therefore, further research is required to differentiate levels of nickel required by humans for normal endocrine function, compared to levels that may impair endocrine function leading to adverse effects. It is unlikely that environmental exposure or exposure to nickel at hazardous waste sites will result in endoerine effects. 

Lee, C.G. and Ip, Y.K. (1987). Environmental effect on plasma thyroxine (T4), 3,5,3 -triiodo-L-thyronine (T3), prolactin and cyclic adenosine 3 -5 -monophosphate (cAMP) content in the mudskippers Periophthalmus chrysospilos and Boleophthalmus boddaerti. Comparative Biochemistry and Physiology 87A, 1009-1014. 

MacKeown, B.A., Leatherland, J.F. and John, T.M. (1975). The effect of growth hormone and prolactin on the mobilisation of free fatty acids and glucose in the kokanee salmon, Oncorhynchus nerka. Comparative Biochemistry and Physiology 50B, 425-430. 

Ogawa, M. (1975). The effects of prolactin, cortisol and calcium-free environment of water influx in isolated gills of Japanese eel, Anguilla japonica. Comparative Biochemistry and Physiology 52A, 539-543. 

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