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Department of Physiology, Department of Physiology, Consortium for Calcium and Bone Research, Faculty of Medicine, Srinakharinwirot University, Sukhumvit 23, Wattana, Bangkok 10110, Thailand
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cells also exhibited Na + transport that was activated by insulin and insulin-like growth factor, and inhibited by epidermal growth factor ( Deachapunya et al . 1999 , Deachapunya & O'Grady 2001 ). Prolactin (PRL) is synthesized and secreted from the
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Introduction Among the pituitary hormones, prolactin (PRL) is the most versatile in the spectrum and number of functions it regulates. PRL modulates virtually every aspect of vertebrate physiology, including osmoregulation, growth, metabolism
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SUMMARY
Both oestradiol and perphenazine induced a significant increase in prolactin release by ovariectomized rats. Ergocornine completely inhibited the initial perphenazine-induced prolactin release which normally reaches a maximum during the first 2·5 h. However, ergocornine did not prevent a significant increase in prolactin release after daily administration of perphenazine. It inhibited oestrogen-induced prolactin release. The results support earlier suggestions that prolactin release is controlled by two mechanisms. Only one of the mechanisms can be blocked by ergocornine.
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The Endocrine Unit, Department of Medicine, Royal Postgraduate Medical School, Du Cane Road, London, W12 OHS
(Received 16 December 1977)
Radioimmunoassays for prolactin described previously require incubation periods of 3–8 days (Hwang, Guyda & Friesen, 1971; Sinha, Selby, Lewis & Vanderlaan, 1973; Aubert, Becker, Saxena & Raiti, 1974). In our studies on prolactin secretion by human pituitary adenomas (Mashiter, Adams, Beard & Holley, 1977; Trinder, Barratt, Sood, Holley, van Noorden, Joplin & Mashiter, 1977), we were anxious to obtain assay data more rapidly in order to maximize the experimental life of each preparation. This report describes a 24 h assay which retains the characteristics of our existing 7 day assay with which it is compared.
Human prolactin VLS 1 was used as standard, human prolactin VLS 3 for iodination and rabbit anti-VLS 3 as antiserum, all generously donated by the National Pituitary Agency, NIAMDD, U.S.A. Labelled Na125I (IMS 30) was
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Hayashida & Li (1958) and Hayashida (1962) reported that ox growth hormone produced antibodies against ox lactogenic hormone, a serum protein and the growth hormone itself, but Chadwick, Folley & Gemzell (1961) obtained negative results with ox growth hormone in the bioassay for lactogenic hormone. Ferguson & Wallace (1963) found that the electrophoretic bands characteristic of prolactin could be detected on starch-gel electrophoretograms of some ox growth hormone preparations.
The purpose of this communication is to show the results of assays of various ox growth hormone preparations for the presence of prolactin, as measured by the deciduoma method (Kovačić, 1963). In this method the formation of deciduomata in the damaged uterine horn of adult hypophysectomized mice is used as the endpoint. In the mouse, prolactin has luteotrophic properties; it is believed that luteal cells secrete progesterone, which causes decidual reactions.
The results of assays for prolactin on two preparations (72-GH-1
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The development of trophic hormones in foetal pituitary cells has been shown by the use of fluorescent antibodies, differential staining techniques and bioassay of pituitary homogenates. In foetal rat pituitaries, growth hormone, thyrotrophin and adrenocorticotrophin have been detected by radioimmunoassay and bioassay (Contopoulos & Simpson, 1957; Phillips & Schmidt, 1958; Milkovic & Milkovic, 1962; Birge, Peake, Mariz & Daughaday, 1967); but prolactin has not been detected by these techniques.
During experiments involving disc electrophoresis of rat pituitary homogenates the pituitaries from foetal rats were examined and a protein band appeared in the gel in a position almost identical with that of prolactin in the maternal pituitary (Plate). Rat pituitary hormones separated by disc electrophoresis according to the method of Davis (1964) have been identified by Jones, Fisher, Lewis & Vanderlaan (1965). Prolactin is the hormone that has the greatest mobility in this system; maternal prolactin had an R F value
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The capacity of the pigeon pituitary gland to release prolactin was investigated in vivo, to evaluate its hypothalamic regulation and to establish the dominant hypothalamic factor for prolactin secretion. After 3 days of systemic administration of some physiological and pharmacological agents, followed by 2 consecutive days of local intradermal injections of prolactin into their crop sacs, the crop mucosa was scraped, dried and weighed. The substances tested were: oestradiol and tamoxifen (antioestrogen), thyrotrophin-releasing hormone (TRH) and anti-TRH serum, perphenazine (releases prolactin in mammals) and bromocriptine (suppresses prolactin in mammals). Prolactin and anti-prolactin serum were tested as controls.
While prolactin markedly proliferated and anti-prolactin serum significantly inhibited the mucosal weight, oestradiol, TRH and perphenazine dramatically depressed proliferation of the mucosa, suggesting that prolactin secretion was inhibited. Tamoxifen, anti-TRH serum and bromocriptine significantly increased the proliferation of the crop mucosa, indicating an increase in the endogenous release of prolactin. Since the effect of these substances on prolactin release in the pigeon is the opposite from their well-established effects in mammals, these results suggest, in a specific and homologous model, that the dominating regulator for prolactin in the pigeon is contrary to that in the mammal, namely prolactin-releasing factor, and that TRH may play a significant role in the physiological regulation of prolactin secretion.
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ABSTRACT
The objectives of this investigation were to determine whether decidual tissue possesses specific binding sites for prolactin, and to examine whether the locally produced prolactin-like hormone binds to these receptors. Characterization of the binding of prolactin to decidual tissue from rats at day 9 of pseudopregnancy revealed specific, high-affinity sites. Binding approached saturation with increasing concentrations of either the ligand or the protein. Cytosolic extracts of day-9 decidual tissue, containing various amounts of decidual luteotrophin which possesses several of the physiological and biochemical characteristics of prolactin, displaced the binding of 125I-labelled prolactin to decidual membranes in a linear fashion. Prolactin-binding sites were detectable 72 h after induction of decidualization and 48 h after the appearance of decidual luteotrophin in the decidua. Prolactin receptor concentrations increased significantly between days 8 and 9, reached a plateau between days 9 and 12 and declined abruptly on days 14 and 15, accompanied by a similar decline in decidual luteotrophin concentration in the tissue. Thus rat decidual tissue possesses specific receptors for prolactin to which decidual luteotrophin locally produced can bind, thereby suggesting an auto/paracrine role for this substance.
J. Endocr. (1986) 110, 115–121
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neuroendocrine physiology, including the lactotrophic and reproductive axes, via the PT in adult mammals. Photoperiodic regulation of prolactin secretion In many seasonally breeding species, the lactotrophic axis exhibits robust annual cycles with increased
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ABSTRACT
We have examined the effects of dopamine on prolactin gene expression using quantitative in-situ hybridization histochemistry in different pituitary cell (sub)populations separated according to their density on a discontinuous Percoll gradient. Administration of dopamine resulted in a drastic reduction in hybridization of 35S-labelled DNA probe complementary to prolactin mRNA in total pituitary cells and in lactotrophs with low density. In contrast, dopamine significantly stimulated mRNA accumulation in prolactin-secreting cells with high density compared with other cell layers. The combined use of Percoll gradient and quantitative in-situ hybridization is a valuable and sensitive method with which to examine prolactin-secreting cell response to a given stimulation. Prolactin-secreting cells with high and low density clearly show functional heterogeneity in their response to dopamine.
Journal of Endocrinology (1992) 132, 401–409
