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A radioimmunoassay for canine prolactin has been used to measure prolactin in the ferret. Serial dilutions of extracts of ferret pituitary glands and of ferret plasma yielded curves that were parallel with the canine prolactin standard curve. The sensitivity, accuracy, reproducibility and precision of the assay were within acceptable limits. Plasma prolactin levels increased after the administration of thyrotrophin releasing hormone (TRH) or chlorpromazine, but not after giving luteinizing hormone releasing hormone. Female ferrets, which were anoestrous, oestrous or spayed, and male ferrets had similar basal prolactin levels when sampled under sodium pentobarbitone anaesthesia. These basal levels were higher than in conscious males and the latter also showed a lesser response to TRH. Hypophysectomy significantly reduced basal prolactin levels in female ferrets by 2 h postoperatively and abolished the response to TRH.
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SUMMARY
Preparative isotachophoresis in polyacrylamide gel using carrier ampholytes as 'spacers' has been used to purify prolactin from canine pituitary extracts. Using Ampholine pH 5–8 as spacers, a prolactin fraction was obtained which was essentially homogeneous as judged by the criteria of disc electrophoresis and isoelectric focusing. Amino acid analysis indicated a close similarity between canine and ovine prolactin. A growth hormone fraction, identified by its electrophoretic mobility, was also obtained although this was heterogeneous in disc electrophoresis at alkaline pH.
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ABSTRACT
The effect of ovine prolactin on intestinal Ca absorption and placental Ca transfer was studied in pregnant ewes. Six groups of five animals bearing a single fetus were used and injected s.c. daily between days 121 and 135. The first group was given 0·1 μg ovine prolactin/kg body wt per day, the second 0·1 μg ovine prolactin/kg body wt per day plus 0·1 μg 1α-hydroxycholecalciferol (1α-OH-D3)/kg body wt per day, the third 0 ·1 μg ovine prolactin/kg body wt per day plus 0·20 units calcitonin/kg body wt per day, the fourth 2 μg bromocriptine/kg body wt per day, the fifth 2 μg bromocriptine/kg body wt per day plus 0·1 μg ovine prolactin/kg body wt per day, and the sixth were controls injected with vehicle alone. The intestinal Ca absorption was measured on a duodenal loop tied off in vivo on day 136 and placental Ca transfer was evaluated between days 129 and 136. Ovine prolactin stimulated both intestinal Ca absorption and placental Ca transfer; these effects were further increased by 1α-OH-D3. Calcitonin had no effect on ovine prolactin-stimulated intestinal Ca absorption, but blunted the influence of ovine prolactin on Ca placental transfer. Bromocriptine decreased both intestinal Ca absorption and Ca placental transfer but these effects of bromocriptine were overcome by simultaneous injection of ovine prolactin.
J. Endocr. (1985) 107, 171–175
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SUMMARY
To determine whether human decidua and/or chorion synthesizes and secretes prolactin, explants of decidua obtained at Caesarian section and explants of chorion from the membranes separating dizygotic twins were cultured for periods of up to 6 days. The decidual explants released 366 ± 37 ng prolactin/100 mg tissue (mean ± s.d.) during each day in culture and incorporated 3H-labelled amino acids into immunoprecipitable prolactin. In the radioimmunoassay for prolactin, serial dilutions of incubation medium displaced 125I-labelled prolactin parallel to the displacement by pituitary prolactin and the prolactin in the medium eluted from Sephadex G-150 in a position identical to that of pituitary prolactin. Chorionic explants released prolactin into the incubation medium during day 1 of culture only and did not incorporate 3H-labelled amino acids into prolactin. These results demonstrate that prolactin is synthesized by the decidua and not by the chorion and suggest that the decidua is the source of prolactin in amniotic fluid.
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Hyperprolactinaemia in patients with chronic renal disease undergoing dialysis has prompted the investigation of the relative roles of liver and kidney in the degradation of prolactin. Male rabbits were acutely nephrectomized, and compared with intact animals with or without prolactin infusion. Prolactin degradation was followed after intravenous injection of 125I-labelled ovine prolactin. Measurements were made of peptide-bound 125I and 125I-labelled degradation products in plasma, liver, kidney, bile, urine and muscle and total thyroid radioactivity. A significant (P<0·01) reduction in the metabolic clearance rate of 125I-labelled prolactin was observed due to nephrectomy, with double the accumulation of 125I-labelled peptides in the livers in this group. Prolactin infusion of nephrectomized animals had a further and larger effect than nephrectomy alone on prolactin degradation. Metabolic clearance rate significantly (P<0·01) decreased from 5·5 ml/min per kg in nephrectomized rabbits to 0·8 ml/min per kg with prolactin infusion. The accumulation of 125I-labelled prolactin degradation products in the blood was significantly (P<0·01) lower in this group of animals and the amount of peptide-bound 125I in plasma at 60 min after 125I-labelled prolactin administration was significantly (P<0·01) higher. Liver degradation of prolactin in the absence of exogenous hormone appears to be sufficient to maintain an approximately normal half-life for prolactin in plasma (intact t ½ = 6·8 min; nephrectomized t ½ = 8·5 min). However, with prolactin infusion the half-life of 125I-labelled prolactin increased to 28·5 min, and the plasma prolactin concentrations measured by radioimmunoassay rose linearly with time. These data supported the view that hyperprolactinaemia associated with renal dysfunction is substantially due to hormone oversecretion.
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Formation of new capillary blood vessels, termed angiogenesis, is essential for the growth and development of tissues and underlies a variety of diseases including tumor growth. Members of the prolactin hormonal family bind to endothelial cell receptors and have direct effects on cell proliferation, migration and tube formation. Because many angiogenic and antiangiogenic factors are produced by endothelial cells, we investigated whether endothelial cells expressed the prolactin gene. Here we show that bovine brain capillary endothelial cells (BBCEC) in culture express the full-length prolactin messenger RNA, in addition to a novel prolactin transcript, lacking the third exon of the gene. In addition cultures of BBCEC synthesize and secrete prolactin-like immunoreactive proteins with apparent molecular masses of 23, 21 and 14 kDa. The prolactin-like nature of these proteins in supported by the observation that Nb2-cells, a prolactin-responsive cell line, were stimulated to proliferate when co-cultured with endothelial cells and this stimulation was neutralized with prolactin-directed antibodies. Finally, consistent with a possible autocrine effect of endothelial-derived prolactins, polyclonal and monoclonal prolactin antibodies specifically inhibited basal and basis fibroblast growth-factor-stimulated growth of endothelial cells. Taken together, the present findings support the hypothesis of the prolactin gene being expressed in endothelial cells as proteins that could act in an autocrine fashion to regulate cell proliferation.
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SUMMARY
The effect of sulpiride, a neuroleptic agent, on the secretion of prolactin by the anterior pituitary gland of the rat was studied. A significant increase in serum prolactin was observed after subcutaneous administration of the drug. Although sulpiride (0·10μmol/l or 0·14 mmol/l) had no effect on the secretion of newly synthesized or radioimmunoassayable prolactin in vitro, the drug significantly overcame the inhibitory action that dopamine (0·50 μmol/l) exerted on prolactin secretion. Rats implanted with a prolactin-secreting pituitary tumour MtTW15 showed an inhibition of prolactin biosynthesis and release. Injection of these rats with sulpiride restored prolactin biosynthesis and release of the hormone toward normal levels. These results demonstrate that sulpiride has a direct effect on the pituitary antagonizing the inhibitory effects exerted by dopaminergic mechanisms, although the drug itself does not stimulate the secretion of prolactin in vitro. Sulpiride may have a direct action on the pituitary lactotrophs in vivo, but effects at higher centres have not been excluded.
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Production of prolactin is very tissue-specific – the gene is present in all cells, but in the rat it is expressed only in the anterior pituitary gland, while in man it is also expressed at low levels in the decidualized endometrium. Much of the work on rat prolactin gene expression has been greatly facilitated by the availability of the rat pituitary tumour-derived GH cell line (including the GH1, GH3 and GH4 cell subclones) which produces both prolactin and growth hormone. In contrast, much less is so far known about the regulation of the human prolactin gene, due in part to the lack of readily available human pituitary tissue for in-vitro studies.
An increasing amount is known about hormonal and intracellular regulation of prolactin mRNA production, which has been reviewed elsewhere (Davis, Belayew & Sheppard, 1989). However, some of the most impressive and important recent advances have been
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Department of Anatomy, Duke University Medical Center, Durham, North Carolina 27710, U.S.A.
(Received 15 July 1975)
Radioimmunoassay of luteinizing hormone (LH) in sequential blood samples collected continuously over 2–12 min periods from ovariectomized (OVX) rats has shown the concentration of LH in blood to fluctuate at high levels in a pulsatile rhythm (Gay & Sheth, 1972). The present study investigates whether plasma prolactin fluctuates regularly at low levels in OVX rats.
Sprague–Dawley rats kept in a room with the lights on from 05.00 to 19.00 h were ovariectomized and used 12–16 weeks later. A cannula was inserted into the right atrium (Terkel, 1972) before 10.00 h. At this time or 3 days later rats were placed in separate buckets containing food and water. Blood (0·3 ml) was withdrawn through the cannulae and replaced with heparinized saline over a 60 s period at 10 min intervals from 17.00 to 18.00 h
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, Blackwell 1992 ) and other ( Bartke et al . 1977 , McNeilly et al . 1978 ) mammalian species. While the specific mechanisms underlying prolactin (PRL) effects on gonadotrophin release are still unresolved, it has become increasingly apparent that, in
