Disease relevance of PRL

• These adaptations in the beta-cell may play an important role in maintaining the basal hyperinsulinemia of pregnancy while limiting the capacity of PRL and PRG to promote glucose-stimulated insulin secretion during late gestation [1].
• These findings raise the possibility of a functional role for the glycosylated variant of PRL in the initiation and/or maintenance of events associated with pregnancy and obesity in the pig [2].
• The possibility that the two physiological opposing actions of DA on PRL secretion might be mediated by different GTP binding proteins was also examined using cholera toxin (CTX) and pertussis toxin (PTX) [3].
• Thirty minutes later, the cells were fixed and plaques (zones of hemolysis) surrounding PRL-producing cells (lactotrophs) were measured and used as an index of the amount of PRL secreted [3].
• A common pathway may contribute to other independent mechanisms controlling the release of ACTH and PRL after hemorrhage [4].

Psychiatry related information on PRL

• These results indicate that TRH-induced and not basal PRL secretion is influenced by both season and social interaction of boars [5].

High impact information on PRL

• For example, in human clinical conditions of physiological or pathological prolactin excess, ovarian function is depressed, and in isolated, human granulosa cells in vitro, prolactin seems to inhibit progesterone production [6].
• Prolactin suppresses steroid production by cultured granulosa cells isolated from small (1-2 mm), immature follicles, but stimulates progesterone secretion by granulosa cells collected from large (greater than 6 mm) mature follicles [6].
• Some cases of lactation failure in the periparturient sow may thus be due to endotoxins suppressing prolactin concentrations [7].
• An endotoxin produced by Escherichia coli caused a decrease in prolactin concentrations in the plasma of sows when given at low dosages 2 days postpartum [7].
• Insulin also reversed the suppression of prolactin (PRL) secretion induced by hydrocortisone (1 uM), and actually stimulated basal PRL secretion by over 50% [8].

Chemical compound and disease context of PRL

• To determine whether PRL increases after hemorrhage in older animals, 11 immature female swine were prepared chronically under halothane and conditioned behaviorally to lie in a sling [4].
• The administration of high levels of estrogen is a well established method for producing prolactin-secreting pituitary tumors in rodents but the mechanism of tumor induction is not clear [9].
• The interaction between hyperprolactinaemia and progesterone, without oestrogen, on components of uterine flushings were determined using gilts that received progesterone (200 mg/day) and prolactin or saline on Days 4-14 after ovariectomy on Day 4 [10].
• However, when men were compared to women, significant differences were noted in basal glucagon, cortisol, and growth hormone levels, as well as in norepinephrine, prolactin, and cortisol responses to hypoglycemia [11].
• Effect of Escherichia coli endotoxin and thyrotropin-releasing hormone on prolactin in lactating sows [12].

Biological context of PRL

• Differences were also observed during pregnancy; whereas beta-lactoglobulin gene expression was induced in early pregnancy, a time when PRL levels are low, WAP mRNA levels increased sharply around parturition [13].
• Polyadenylated RNA from PRL-stimulated pigeon (Columba livia) crop was used as template to produce a cloned cDNA library in plasmids [14].
• In Exp 3, endometrium from cyclic (n = 3), pregnant (n = 4), and EV-induced pseudopregnant (n = 4) gilts was collected on day 14 after estrus and perifused with BSA or PRL to both surfaces [15].
• Moreover, interactions among E, PRL, and P modulate UF gene expression in vivo and in vitro [16].
• Rat and bovine FSH, GH, and PRL had little or no cross-reaction [17].

Anatomical context of PRL

• Addition of the combination of FSH, LH and PRL during the period of oocyte maturation marginally improved male pronuclear formation rates (41.3 vs 55.6%; P=0.06) [18].
• These antibodies also inhibited PRL binding to microsomal fractions from rabbit liver, kidney, adrenal, ovary, and pig mammary gland, although A82 showed poor inhibition in pig mammary gland [19].
• Using double labeling experiments, we have previously shown that receptor-bound LH and PRL can be colocalized in identical endosomes of granulosa cells [20].
• As much as 40% of PRL in the pituitary gland of the pig is glycosylated [21].
• When these antisera were administered to normal cycling rats, the most pronounced effect was an increase in the number of corpora lutea, presumably due to the prevention of the luteolytic effect of PRL [22].

Associations of PRL with chemical compounds

• DEX alone or combined with PRL and PRG inhibited insulin secretion in response to 16 mM glucose-stimulating concentrations [1].
• Here, we used the glucose-responsive MIN6 beta-cell line treated with prolactin (PRL), progesterone (PRG), and dexamethasone (DEX, a synthetic glucocorticoid), all elevated during late pregnancy, to study their effects on mechanisms of insulin secretion [1].
• In parallel studies, PRL was unable to mimic the effects of GH on iIGF-I or progesterone secretion [23].
• After exposure to estrogen, galanin and PRL were colocalized within the same secretory granules of the male and OVEX pituitary cells [24].
• The reverse hemolytic plaque assay (RHPA) was used in this study to further characterize the mechanism whereby low concentrations of dopamine (DA) stimulate PRL secretion in vitro [3].

Physical interactions of PRL

• Prolactin binding analysis and immunohistochemical localization of prolactin receptor in porcine ovarian cells [25].

Regulatory relationships of PRL

• Moreover, PRL appears to activate PKC, but not PI-PLC, in these cells [26].
• Even at day 116, prolactin alone or with LH or IGF-I continued to stimulate relaxin production [27].
• Prolactin stimulates transcription of aspartate aminotransferase in prostate cells [28].
• The increasing levels of cholecystokinin after refeeding and the neural reflex triggered might be related to this increase in prolactin [29].

Other interactions of PRL

• This study provides strong evidence that relaxin has a central role in modulating PRL secretion in the pig [30].
• Throughout the study, blood samples were collected, and serum was harvested to quantitate circulating concentrations of glucose, urea nitrogen, GH, insulin, insulin-like growth factor I (IGF-I), IGF-II, and PRL [31].
• Results from this study provide strong evidence that the antagonistic effect of RU 486 on progesterone receptor results in an abrupt increase in PRL and progesterone secretion in hysterectomized gilts with aging corpora lutea [32].
• In contrast to PRL, both the glycosylated and nonglycosylated forms of GH showed a steady rate of increase throughout the observation period [33].
• Thus intracellular transduction of the PRL signal may involve activation of PKC that is not dependent on PI-PLC [26].

Analytical, diagnostic and therapeutic context of PRL

• It is concluded that: 1) hypophysectomy reduces HDL uptake in the luteinized rat ovary; and 2) PRL and LH replacement therapy maintain ovarian uptake of HDL, suggesting a direct effect of these luteotropins on lipoprotein uptake [34].
• Ovariectomized gilts were fitted with an indwelling cannula in the anterior vena cava to determine sequential serum profiles of PRL secretion before, during, and 190 h after cranial surgery [35].
• Intravenous injection of LM (3 nmol/100 g BW) also raised plasma PRL levels in these animals [36].
• Quantitative estimates of the immunoblotting results revealed marked differences with age in the secretion of the two monomeric forms of PRL [21].
• In contrast, PRL concentrations in the control group remained unchanged after injection [30].

References