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Introduction The bovine placenta produces an array of proteins structurally and functionally similar to pituitary prolactin (PRL; Soares 2004 ). Bovine placental lactogen (bPL) and ten PRL-related protein (bPRP) genes have been identified
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SUMMARY
The reaccumulation after suckling of prolactin by the pituitary of spayed lactating rats was significantly increased after a single s.c. injection of acidic extract of rat hypothalamus (stalk-median eminence region) given at the start of the reaccumulation period. Injection of ammonium acetate, an extract of ovine hypothalamus rich in luteinizing hormone-releasing factor (LH-RF), extract of rat occipital cortex or oxytocin was ineffective. An extract of ovine hypothalamus rich in prolactin-inhibiting factor (PIF) (0·15 ml./rat) blocked the fall in pituitary prolactin concentration induced by suckling, but in the same or higher (0·3 ml.) doses neither increased nor depressed the reaccumulation of prolactin after suckling. A single s.c. injection after suckling of 2–8 mg. ovine prolactin in each of four instances significantly increased the amount of prolactin reaccumulated by the pituitary. The level attained was equal to or greater than that resulting from injecting rat hypothalamic extract. These results suggest that the increased blood level of prolactin after suckling stimulates the reaccumulation of prolactin in the pituitary possibly indirectly via a factor or factors in the hypothalamus.
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Haloperidol, bromocriptine and diethylstilboestrol dipropionate were given in various régimes to male rats to determine their effects on pituitary DNA synthesis, prolactin secretion and growth hormone secretion.
Haloperidol increased serum prolactin but did not stimulate pituitary DNA synthesis or reduce pituitary prolactin concentrations. Haloperidol potentiated the effects of oestrogen on serum prolactin and on pituitary DNA synthesis; pituitary prolactin concentrations were greatly reduced, and growth hormone secretion was slightly inhibited.
The inhibitory effects of bromocriptine in oestrogen-stimulated rats were demonstrated by smaller pituitary weights and decreased DNA synthesis; serum prolactin levels were lowered and pituitary prolactin concentrations were increased. Haloperidol, given to rats treated with oestrogen and bromocriptine, reversed the inhibitory effects of bromocriptine on DNA synthesis and serum prolactin; pituitary prolactin concentrations fell to well below normal. The results suggest that the haloperidol potentiation of oestrogeninduced pituitary DNA synthesis may depend upon stimulation of prolactin secretion together with reduction of intracellular prolactin levels.
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ABSTRACT
We have investigated the role of physiological prolactin levels in the development of prepubertal male rats. Prolactin GH and testosterone levels, as well as body, ventral prostate and testicular weight, have been analysed in both control and bromocriptine-treated rats between 21 and 60 days of life. Furthermore the role of prolactin in the regulation of its own receptors has also been studied during the same period. In control rats, prolactin levels showed a prepubertal peak of secretion at 25 days of age. At this time GH and testosterone levels were low and did not show any significant variation. After this age, prolactin levels increased more gradually; determinations of GH showed great variation with low levels in most of the rats and very high values in the other animals; testosterone levels remained low until day 35 after which they increased. Simultaneously with the serum prolactin peak on day 25, a decrease in prolactin-binding capacity of ventral prostate glands, was observed and a maximum rate of body, prostate and testicular weight gain was obtained. Furthermore, in rats with pharmacologically suppressed serum prolactin levels (lower than 1 μg/l), prolactin binding to prostate glands as well as the weight of body, ventral prostate and testes were lower than in control animals. When results were expressed in mg prostate or testes/g body weight, testes from 25-day-old treated rats weighed significantly less than controls. The later stages of development, from days 25 to 60, were characterized by an initial decline in serum prolactin levels at 29 days of age which was followed by a continuous increase until adult values were reached. During this period, prostatic prolactin receptors which were at their lowest value at 33 days of age showed a gradual rise parallel with the observed increase in plasma prolactin levels. When testicular tissue was analysed, no changes in prolactin-binding sites caused by sexual maturation were observed. The present results indicate that physiological prolactin secretion has a specific effect on the normal increase in the prostate, testes and body weight and clearly is also implicated in the regulation of its prostatic receptors at the earlier stages of development.
Journal of Endocrinology (1992) 132, 449–459
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In female rats neonatal treatment with oestrogen induces persistent vaginal cornification and sterility at maturity (Takewaki, 1962). Recently, we found that the pituitary secretion of prolactin, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in such oestrogenized female rats is permanently altered (Nagasawa, Yanai, Kikuyama & Mori, 1973). No data are available, however, on the effect of pituitary hormones, administered neonatally, on the secretory activity of the pituitary in adult rats. In the present experiment the pituitary secretion of prolactin, LH and FSH was measured in adult female rats treated neonatally with prolactin.
Virgin female Sprague—Dawley rats were used. Half the females in each litter were given a daily subcutaneous injection of bovine prolactin (NIH-P-B2) dissolved in 0·25–1·0 ml 0·9% NaCl solution (pH 8) for 20 days beginning on day 0 of age. The dose of prolactin was 0·5 mg for the first 5 days, 1·0 mg for the second 5
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Department of Physiology, Charing Cross Hospital Medical School, London, W6
(Received 7 April 1977)
It has been reported (Horrobin, Burstyn, Lloyd, Durkin, Lipton & Muiruri, 1971; Buckman & Peake, 1973; Wallin & Lee, 1976) that prolactin affects salt and water metabolism. To assess any interaction of the antidiuretic hormone arginine-vasopressin (AVP) and prolactin, four experiments were performed.
The antidiuretic action of AVP was measured by the standard AVP bioassay method using the water-loaded ethanol-anaesthetized rat described by Jeffers, Livesey & Austin (1942) with the minor modifications of Forsling, Jones & Lee (1968). Male Wistar rats (150-200 g) were used with at least six preparations for each experiment. When stable antidiuretic responses to standard AVP (3rd International Standard, 1957, National Institute for Biological Standards, London) were obtained, the infusion fluid was changed to one containing the appropriate hormone for the experiment and the effect of AVP within the succeeding hour compared
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ABSTRACT
Salmon calcitonin inhibited TRH-stimulated release of prolactin in isolated pituitary cells from untreated female rats. These cells were still capable of responding to the fresh addition of TRH after the removal of calcitonin. Calcitonin gene-related peptide had only a weak effect in inhibiting prolactin release in these cells.
Pituitary cells isolated from female rats which had been treated with weekly s.c. injections of 1 mg oestradiol dipropionate for 4 weeks, exhibited a marked increase in the magnitude of the inhibition of prolactin release by salmon calcitonin. Both basal and TRH-stimulated release of prolactin were inhibited by concentrations of 0·1 nmol salmon calcitonin/l or higher. Prolactin release from these cells was also inhibited at somewhat higher concentrations by calcitonin gene-related peptide. Our results demonstrate that calcitonin can directly inhibit basal as well as TRH-stimulated prolactin release by acting directly at the pituitary. The results strongly suggest that the peptide may be involved in the regulation of prolactin release in certain physiological conditions.
J. Endocr. (1988) 116, 279–286
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ABSTRACT
Three ampouled preparations of purified human prolactin were assessed by 20 laboratories in eight countries for their suitability to serve as International Standards for the estimation of human prolactin in serum. Bioassays (pigeon crop sac assays and NB2 cell assays) were carried out in two laboratories, radioreceptor assays by one laboratory and radioimmunoassays by 17 laboratories.
By physicochemical analysis the preparations appeared similar. Each preparation contained small amounts of contaminants and/or prolactin variants. No major differences among the three preparations were detected by immunoassay although, in one radioreceptor assay system, one of the preparations was found to differ from the other two.
On the basis of all the available information, the Expert Committee on Biological Standardization of the World Health Organization (ECBS) in 1986 established the preparation in ampoules coded 83/562 as the Second International Standard for Prolactin and in October 1988 established the preparation in ampoules coded 84/500 as the Third International Standard for Prolactin. A value of 0·053 IU (53 mIU) prolactin activity/ampoule was assigned to both the Second and Third IS on the basis that this unitage would, insofar as possible, maintain continuity of the IU defined by the First International Reference Preparation of Prolactin, human, for Immunoassay (coded 75/504).
Journal of Endocrinology (1989) 121, 157–166
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Three groups of Suffolk-cross ewes were kept in (A) summer photoperiod plus melatonin feeding in such a way as to mimic the plasma levels found in winter photoperiod, (B) winter photoperiod or (C) natural light/dark from mid-June onwards. Prolactin levels remained high in group C throughout July and August but were dramatically reduced in both groups A and B. The rise in prolactin levels associated with dusk, however, was still apparent in all three groups. Appropriate administration of melatonin can thus influence prolactin secretion in the same way as an extension of the dark phase. This effect is associated with an early onset of the breeding season in the ewe.
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prolactin (PRL) producing cells (PRL cells) in the anterior pituitary can be detected by immunohistochemistry at embryonic day 18.5 ( Watanabe & Haraguchi 1994 , Stefaneanu et al . 1999 ). PRL cells are rarely observed in the fetal anterior pituitary
