Introduction The prolactin receptor (PRLr) is a member of the cytokine receptor superfamily that transduces the signals of the pituitary hormone PRL, which is implicated in numerous biological functions (including mammary gland development
Gayathri Swaminathan, Bentley Varghese, Chellappagounder Thangavel, Christopher J Carbone, Alexander Plotnikov, K G Suresh Kumar, Elizabeth M Jablonski, Charles V Clevenger, Vincent Goffin, Luqin Deng, Stuart J Frank, and Serge Y Fuchs
D. S. Janik and J. D. Buntin
The role of prolactin in the maintenance of incubation behaviour in ring doves was re-examined and the dose–response relationships for behavioural, target tissue and body weight changes induced by injections of prolactin were compared in doves tested during the incubation phase of the breeding cycle. Doves given injections of prolactin twice a day starting on day 4 of incubation, during a 10-day period of isolation from their mates and nests, showed a higher persistence of incubation behaviour than doves injected with saline vehicle. However, the prolactin treatment failed to maintain incubation behaviour to the same extent as that observed in non-isolated untreated breeding pairs. Liver and body weights were higher and testicular weights lower in birds treated with high doses of prolactin than in non-isolated birds which had been incubating for 14 days. Good dose-response relationships were established between body, liver, crop and testes weights and the dose of prolactin administered. However, only a weak dose–response relationship was observed between prolactin and the maintenance of incubation behaviour. Overall, females injected with prolactin displayed more quiet sitting behaviour, less body weight gain and more gonadal regression than males injected with prolactin. Males in untreated breeding pairs had higher liver weights and lower crop weights than females. It is concluded that prolactin plays a role in maintaining readiness to incubate in doves, but that other factors may also contribute to this response. Further, it appears that prolactin mediates several target tissue changes which are sex-specific during incubation.
J. Endocr. (1985) 105, 201–209
John F Langenheim and Wen Y Chen
Introduction Human prolactin (hPRL) and GH are pituitary hormones that regulate the survival, proliferation, and differentiation of cells in a variety of tissues and endocrine glands. The effects of hPRL are mediated via the PRL receptor (PRLR
AM Corbacho, G Martinez De La Escalera, and C Clapp
Prolactin, growth hormone and placental lactogen are members of a family of polypeptide hormones which share structural similarities and biological activities. Numerous functions have been attributed to these hormones, among which stand out their recently discovered effects on angiogenesis, the process by which new blood vessels are formed from the pre-existing microvasculature. Prolactin, growth hormone and placental lactogen, along with two non-classical members of the family, proliferin and proliferin-related protein, can act both as circulating hormones and as paracrine/autocrine factors to either stimulate or inhibit various stages of the formation and remodeling of new blood vessels, including endothelial cell proliferation, migration, protease production and apoptosis. Such opposing actions can reside in similar but independent molecules, as is the case of proliferin and proliferin-related protein, which stimulate and inhibit angiogenesis respectively. The potential to exert opposing effects on angiogenesis can also reside within the same molecule as the parent protein can promote angiogenesis (i.e. prolactin, growth hormone and placental lactogen), but after proteolytic processing the resulting peptide fragment acquires anti-angiogenic properties (i.e. 16 kDa prolactin, 16 kDa growth hormone and 16 kDa placental lactogen). The unique properties of the peptide fragments versus the full-length molecules, the regulation of the protease responsible for specific protein cleavage, the selective expression of specific receptors and their associated signal transduction pathways are issues that are being investigated to further establish the precise contribution of these hormones to angiogenesis under both physiological and pathological situations. In this review article, we summarize the known and speculative issues underlying the effects of the prolactin, growth hormone and placental lactogen family of proteins on angiogenesis, and address important remaining enigmas in this field of research.
ANNE J. EVANS
The release in vitro of β-glucuronidase from rat testicular homogenates under the influence of ovine and bovine prolactin has been investigated further.
A micro modification of the original assay method has been developed, with improved specificity, sensitivity and precision.
Assay results were reproducible over 2½ yr. and were in good agreement with bioassays for prolactin and luteotrophic activity.
M. G. Hunter
Human luteal tissue recovered from varying stages of the luteal phase was minced and incubated for 3 h and the effect of human chorionic gonadotrophin (hCG), prolactin and hCG + prolactin on progesterone and oestradiol production measured. While hCG generally enhanced both progesterone and oestradiol synthesis, prolactin alone at either 20 or 200 μg/l had no significant effect on steroidogenesis. When prolactin was added along with hCG in four of six corpora lutea, however, progesterone production significantly increased and in three of six corpora lutea oestradiol production was increased above that induced by hCG alone. It is concluded that prolactin may play some role in the control of steroidogenesis by the human corpus luteum.
J. Endocr. (1984) 103, 107–110
J. E. Merritt, S. MacNeil, S. Tomlinson, and B. L. Brown
The possible role of calmodulin in the control of prolactin secretion was examined. The effects of a wide variety of agents on inhibition of prolactin secretion from isolated rat anterior pituitary cells and inhibition of calmodulin activity in an in-vitro system (calmodulin-activated cyclic GMP phosphodiesterase) were compared. A number of phenothiazines showed a close correlation of potencies in the two systems, as did the more specific calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalene sulphonamide (W7), suggesting that calmodulin may be involved in the control of prolactin secretion. Some other drugs also inhibited both prolactin secretion and calmodulin activity in addition to their other well-characterized biochemical effects. However, many of these drugs (including two phenothiazines) were more potent inhibitors of prolactin secretion than of calmodulin activity, suggesting that other intracellular systems in addition to calmodulin may be involved in the control of the secretory process.
H. M. LLOYD, J. M. JACOBI, and J. D. MEARES
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.
C. E. GROSVENOR, F. MENA, H. MAIWEG, A. P. S. DHARIWAL, and S. M. McCANN
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.
Jacob H Hollis, Stafford L Lightman, and Christopher A Lowry
corticosterone and either increases or decreases in plasma concentrations of prolactin ( Rettori et al. 1994 , Rivest 2001 , De Laurentiis et al. 2002 ). These hormones, in turn, influence homeostatic functions and provide feedback to regulate the immune