Topic
Prolactin
About: Prolactin is a research topic. Over the lifetime, 22356 publications have been published within this topic receiving 609537 citations. The topic is also known as: lactotropin, & PRL,.
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TL;DR: The purpose of this review is to provide an account of the recent advances in PRL, which suggests that the hormone is perhaps a prohormone, which is synthesized as a precursor molecule and then converted to different bioactive forms as it traverses the secretory pathway.
Abstract: I. Introduction PROLACTIN (PRL) is one of the most versatile hormones of the pituitary gland in terms of biological actions. More than 100 different and distinct effects of the hormone have been documented (1), ranging from mammary development and initiation of lactation in mammals to osmoregulation in fishes, nesting behavior in birds, and growth and metamorphosis in amphibians. These are far in excess of the reported actions of all other adenohypophyseal hormones combined. But how does a single molecule evoke so many different responses? Studies in the last few years have shown that the hormone exists in several molecular forms, some arising from posttranslational modifications and others from genetically determined factors. Such findings have led to the suggestion that PRL is perhaps a prohormone, which is synthesized as a precursor molecule and then converted to different bioactive forms as it traverses the secretory pathway. The purpose of this review is to provide an account of the recent advances i...
418 citations
TL;DR: Data reveal a critical role of hypothalamic dopamine in controlling pituitary growth and support a multistep mechanism for the induction and perpetuation of lactotroph hyperplasia, involving the lack of dopamine signaling, a low androgen/estrogen ratio, and a final autocrine or paracrine "feed-forward" stimulation of mitogenesis, probably by prolactin itself.
416 citations
TL;DR: Addition of thyrotropin releasing hormone to the medium of 2 clonal strains of functional rat pituitary cells stimulated the production of prolactin and inhibited growth hormone production and there was no effect on cell growth.
411 citations
TL;DR: Though lactation in certain species has sometimes been observed, these cases are probably of importance only to a further elucidation of a, species variability; b, a final preparatory stage of mammary tissue development; c, and of the mechanism by which the anterior pituitary is induced to release the principle which excites milk secretion.
Abstract: That one or another principle contained in the anterior lobe of the hypophysis is the specific stimulus of the developed mammary gland (rabbit, bitch, hog, cow) to active milk secretion was demonstrated by Stricker and Griiter, and Frei (1928, 1929a, 1929b, 1929c). This result has been confirmed or extended to other species (rat, guinea pig, goat) by Corner (1930), Nelson and Pfiffner (1931), Turner and Gardner (1931) and Turner and Frank (1932) ; also, as is now evident by Parkes (1929) ; and-since the castrate or non-castrate condition has proved unessential-by observations of Evans and Simpson (1929, 1931), Putnam, Benedict and Tee1 (1929), Grater (1930-31) and Asdell (1931, 1932). Though lactation in certain species has sometimes been observed t’o follow other procedures (e.g., castration of women, estrus hormone injections, etc.) these cases are probably of importance only to a further elucidation of a, species variability; b, a final preparatory stage of mammary tissue development; c, and of the mechanism by which the anterior pituitary is induced to release the principle which actually excites milk secretion. Thus Steinach et al. (1928) and Laqueur et al. (1928) noted lactation in guinea pigs (and this species only) following high doses of the estrus-producing hormone; but later DeJongh and Laqueur (1930) reported that here tlhe milk secretion began only after (2 to 3 days; found by us up to 6 days) discontinuance or diminution of the dosage. Further, Parkes (1930) and Turner and Frank (1930) have shown that the administration of large amounts of the estrus-producing hormone alone will not induce lactation in rabbits. Griiter and Stricker suggest that the active principle of their extracts is probably not the gonad-stimulating hormone of the pituitary; but in no case hitherto observed has it been possible to know which pituitary principle induced the lactation response. That one or another principle contained in the anterior lobe of the hypophysis is the specific stimulus for the enlargement and functioning (formation of “crop-milk,” near end of incubation cycle) of the crop-glands
401 citations
TL;DR: The results suggest that continuous exposure to medium levels of estrogens, particularly in the presence of sustained low progesterone secretion, may alter pituitary secretion of prolactin in aging rats.
Abstract: Longitudinal studies were performed in a colony of aging female rats,from 4-33 months of age,to determine the chronologicalchange inreproductive patterns and the changes in sex steroid, prolactin and gonadotropin secretionassociatedwith different reproductive states. The present study demonstrates that the incidence (65%) of irregular estrous cycles in aging rats increased abruptly from 10-12 months of age. Subsequently, female rats became chronically anovulatory with persistentvaginalcornificationsand theirovariescontained developed follicles but no corpora lutea. The highest incidence (65%) of constant estrous (CE) rats occurred at the age of about 19 months. During the anovulatory state, CE rats displayed low to medium levels of serum estradiol, estrone, testosterone and androstenedione, low levels of progesterone and minimal levels of 20nhydroxyprogesterone. Preovulatory increasesin gonadotropin and prolactin release,similar to those seen in young cycling ratson proestrus,were not observed in CE rats.Whereas serum basal LH levels remained unaltered, morning FSH levelswere increased in CE rats.The lattermay account for the persistent follicular development in aging rats during chronic anovulatory state. Serum basal prolactin levels were normal in CE rats during the early phase (11-16 months of age) of the anovulatory state, but were subsequently increased 3 to 4-fold beyond 24 months of age. Moreover, ovariectomy at a young age prevented the increased pituitary prolactin release in old female rats. These results suggest that continuous exposure to medium levels of estrogens, particularly in the presence of sustained low progesterone secretion, may alter pituitary secretion of prolactin in aging rats. With further advance of age and following many months of anovulatory function, aging female rats exhibited ovulatory activity at irregular intervals. After each ovulation, formed corpora lutea were maintained for a prolonged period, presumably due in part to the existing high prolactin levels in the circulation of older female rats. These corpora lutea in old “pseudopregnant (PSP)” rats were functional as indicated by active secretion of progestins, with 20a-hydroxyprogesterone levels greater than those of progesterone in the circulation. These results indicate that the ovaries of aging rats retain their functional capacity to develop follicles and corpora lutea and to secrete steroid hormones. Although the cause(s) responsible for cessation of normal ovulatory cycles in aging female rats is unknown, the present study demonstrates that the chronic anovulatory state in aging female rats is characterized by significantly reduced ovarian secretion and the lack of cyclic increases in pituitary gonadotropin and prolactmn release. The causal relationships between the decreased ovarian steroid production and the absence of preovulatory surges of gonadotropin release in aging CE rats remain to be determined.
396 citations