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ABSTRACT
The frequency of pup sucking behaviour was related to serum concentrations of prolactin and LH in rats during various phases of lactation. Sucking frequency and prolactin levels decreased and LH levels increased as lactation progressed. There was no clear relationship between sucking frequency and either prolactin or LH levels. Serum prolactin concentrations were highest when the rats spent most of their time away from their pups and lowest when the rats spent most of their time with the pups attached to their nipples. Prolactin was secreted episodically during prolonged continuous nipple stimulation. Removal of the pups in late lactation and replacement with a newborn litter increased sucking frequency but did not affect serum LH levels and only marginally increased serum prolactin levels. Injection of the dopamine receptor antagonist domperidone produced a far more pronounced release of prolactin from the pituitary gland in early than in late lactation. A circadian control mechanism and an episodic pattern of release may contribute to the great variation in serum prolactin concentrations seen in early lactation; decreased pituitary sensitivity to dopamine receptor blockade may be related to the low concentration of serum prolactin found in late lactation.
J. Endocr. (1984) 102, 251–256
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SUMMARY
Treatment of intact adult male rats with 10 mg. perphenazine (Trilafon)/kg. resulted in a decrease in the prolactin content of the pituitary within 1 hr. This decrease was probably due to suppression of the hypothalamic prolactin-inhibiting factor (PIF). Subsequent intracarotid infusion of neutralized acid extracts of rat hypothalamus restored the pituitary prolactin content. This effect was dose-dependent within a range of ½-2 hypothalami. Infusion of extracts of cerebral cortex failed to increase pituitary prolactin. The response to the hypothalamic extracts is considered to be specific for PIF and is proposed as an assay method for PIF.
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Hypophysectomized mice were treated daily for 28 days with 12 i.u. prolactin, 10 μg luteinizing hormone (LH), 10 μg LH plus 12 i.u. prolactin, 50 μg testosterone propionate (TP), or 50 μg TP plus 12 i.u. prolactin. The yield of spermatogenesis was studied quantitatively from the counts of spermatogonia, preleptotene and pachytene spermatocytes and spermatids in the seminiferous tubules at stage VII of spermatogenesis. Prolactin administered alone caused a small, but significant, increase in the yield of spermatogenesis. Treatment with a mixture of LH, follicle-stimulating hormone and growth hormone in amounts 1·5 times higher than those reported as contaminants of prolactin had similar effects. Injections of LH or TP caused partial restoration of spermatogenesis. The yield of spermatogenesis was significantly higher in animals given LH plus prolactin than in the animals given LH alone. Prolactin, however, did not augment the effects of TP on spermatogenesis. It is concluded that prolactin acts on the Leydig cells of the testis to increase their responsiveness to LH. More androgen appears to be produced under the influence of LH when prolactin is also present.
Oncology Research Institute, Department of Biological Sciences, Greenville Hospital System, 900 West Faris Road, Greenville, South Carolina 29605-4255, USA
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Oncology Research Institute, Department of Biological Sciences, Greenville Hospital System, 900 West Faris Road, Greenville, South Carolina 29605-4255, USA
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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
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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
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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.
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SUMMARY
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.
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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
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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.
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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
