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Considerable indirect evidence exists that certain drugs, including phenothiazine derivatives, stimulate the release of prolactin from the anterior pituitary (see review by Meites, Nicoll & Talwalker, 1963). As a direct test of this hypothesis a radioimmunoassay for sheep prolactin (Bryant & Greenwood, 1968) was used to measure plasma prolactin levels after the i.m. or i.v. injection of acepromazine in eight sheep of the Clun Forest breed (Table 1). Evidence for the specificity of the plasma prolactin measurements has been adduced (Bryant & Greenwood, 1968). Nevertheless prolactin concentration in plasma has been expressed in terms of the weight of the reference standard preparation (NIH-P-S 6). If biological and immunological measurements were identical, the levels of plasma prolactin of 50–500 ng./ml. obtained here would be equivalent to 1·25–12·5 m-u./ml.

The four female sheep investigated formed part of a study relating the degree of parasitic infestation with the reproductive cycle (Connan, 1968), and

The pituitary gland of the male adult rodent contains as much prolactin as that of immature females (Jones, Fisher, Lewis & VanderLaan, 1965), but the significance of its occurrence in the male is not clear. The effect of prolactin on male fertility was therefore studied in genetically dwarf mice (dwarf = dw and Ames dwarf = df).

The adenohypophysis of dwarf mice produces little or no prolactin, even when removed from hypothalamic inhibition (Bartke, 1965b). Female dwarf mice are sterile but can reproduce normally when prolactin is provided (Bartke, 1965a, 1966). In a non-inbred stock of df dwarfs, grafting normal mouse pituitary into the renal capsule increased the proportion of fertile dwarf males. This indicates a role of prolactin in male fertility. However, pituitary grafts, in addition to secreting prolactin, have pronounced growth hormone (GH) and some thyroid-stimulating hormone (TSH) activity (Hertz, 1959) and it is known that both GH

ABSTRACT

Immunoreactive tissue kallikrein was co-localized with prolactin in all the eleven prolactin-secreting adenomas of the human anterior pituitary gland examined in this study. The intracellular distribution of immunoreactivity in the prolactin-secreting cells suggests that tissue kallikrein is located within the Golgi complex of these cells. Both the intracellular hormone-processing action and the kininogenase activity of tissue kallikrein may be of functional importance in human prolactinomas.

Journal of Endocrinology (1990) 124, 327–331

ABSTRACT

Long-term ovariectomized rabbits were given injections of progesterone and prolactin in an alternating sequence (progesterone for 5 days, prolactin for 4 days and progesterone for 5 days) to test the hypothesis that each of these hormones acts to increase the other's receptor, resulting in a positive feedback process whereby prolactin augments the progesterone-dependent increase in the mRNA for the uterine protein, uteroglobin. The results of this study support the hypothesis, in that the experimental rabbits produced exceptionally large concentrations of uteroglobin.

SUMMARY

The pattern of prolactin secretion was determined throughout the development of the male mouse. Levels of prolactin were at their lowest from birth to 20 days of age. A dramatic increase in serum prolactin occurred during pubertal maturation coincident with rapid growth of the accessory organ system. These events preceded the pubertal rise in the level of serum testosterone that is characteristic of this species.

SUMMARY

The response of rabbit mammary glands to intraductally-injected prolactin preparations has been investigated with a view to developing an assay procedure for prolactin, based on milk formation in mammals. Milk was clearly detectable in the glands by the 3rd day after injection of prolactin, and there was evidence of an increase in response with increased dose, but the variability so far encountered has been high. Intraductal injection of pituitary extracts rich in activities other than that of prolactin did not lead to milk formation.

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

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.

SUMMARY

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.