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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

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

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

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

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