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The mammary gland synthesizes little DNA during lactation in mice. The effects of daily injections of oestradiol benzoate (OB) between days 9 and 11 of lactation, and/or grafting with three isologous anterior pituitary glands on day 1, on the growth of the litter and the development and function of mammary glands were studied on day 12 of lactation in C3H/He mice.
The level of prolactin in the plasma of mice with pituitary grafts was raised, but mammary gland function was not affected. The synthesis and content of mammary gland RNA was depressed after injection of 0·5 μg OB/day; at a dose of 10 μg/day, OB also depressed litter growth and mammary DNA content, but increased the synthesis of DNA and the level of prolactin in the plasma. Pituitary grafting enhanced the effect of 10 μg OB/day on DNA synthesis. These findings suggest that one of the causes of the low level of DNA synthesis in the mammary gland during lactation in mice is a low level of oestrogen in the circulation.
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Pharmacology Division, National Cancer Center Research Institute, Tsukiji 5-1-1, Chuo-ku, Tokyo 104, Japan
(Received 1 February 1975)
Mammary tumorigenesis by a carcinogen is inhibited in rats in which mammary growth has been prestimulated by hypothalamic lesion (Clemens, Welsch & Meites, 1968) or pituitary grafting (Welsch, Clemens & Meites, 1968) before the administration of the carcinogen. [3 H] Thymidine incorporated into DNA of the mammary gland as an index of mammary DNA synthesis was markedly reduced in these rats, whereas wholemount preparations of the glands showed that much proliferation had occurred (Nagasawa & Yanai, 1974a). On the other hand, pituitary grafting is well known to promote spontaneous mammary tumorigenesis in mice and mammary DNA synthesis is associated with this tumorigenesis (Nagasawa & Yanai, 1974 a). Therefore, it is of interest to study the effect of pituitary grafting on mammary DNA synthesis in mice susceptible and insusceptible to mammary tumorigenesis and to
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There is evidence that adenosine 3′,5′-monophosphate (cyclic AMP) serves as a mediator of the secretion of several hormones (Bowers, 1971) as well as a 'second messenger' in hormone action (Sutherland, Robison & Butcher, 1968). However, information on the effect of cyclic AMP on the secretory mechanism of prolactin is scanty. Lemay & Labrie (1972) found that N 6-monobutyryl adenosine 3′,5′-monophosphate caused increased release of pituitary prolactin as measured by densitometry of acrylamide gels. We have confirmed their results by radioimmunoassay using N 6, O 2′-dibutyryl adenosine 3′,5′-monophosphate (dibutyryl cyclic AMP) and further have demonstrated that dibutyryl cyclic AMP acts primarily on the release of prolactin and not on its synthesis.
Each anterior pituitary obtained from 10-week-old Wistar—Imamichi male rats (230–250 g) was placed in 1 ml Medium 199 (Difco Labs., Detroit, Michigan). Incubation was carried out in a Dubnoff metabolic shaker under constant gassing with 95% O2
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SUMMARY
The effects of 2-hydroxyoestradiol-17β and 2-hydroxyoestriol (2OH-OE3) on levels of serum prolactin, DNA synthesis by the mammary gland and the weight of the uterus were examined in ovariectomized Sprague–Dawley rats.
2-Hydroxyoestradiol-17β had a potent oestrogenic activity in stimulating the secretion of prolactin by the pituitary gland, the synthesis of DNA by the mammary gland and in increasing the weight of the uterus. On the other hand, 2OH-OE3 increased the weight of the uterus only.
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In order to examine the effects of deficiency of adrenal corticosteroids and/or prolactin on the initiation and maintenance of lactation in mice, C3H/He female mice were adrenalectomized and/or implanted during days 13–15 of pregnancy with a pellet of 2-bromo-α-ergocryptine (EC), a potent inhibitor of pituitary prolactin secretion. Average body weights of the young and mammary contents of DNA and RNA were determined on days 0 (day of parturition) and 10 of lactation. On day 0, no differences in these parameters were found among groups, and plenty of milk was present in the stomachs of the young. Furthermore, the treatments did not affect the duration of pregnancy, the number of still-born young or the maternal behaviour at parturition. All young in the group adrenalectomized and implanted with EC died by day 2. Adrenalectomy or implantation of EC retarded the growth of young after day 2 and decreased markedly the mammary nucleic acid content on day 10. These results strongly suggest that adrenal corticosteroids and prolactin play minor roles in the initiation of lactation at parturition, while they are indispensable for the maintenance of lactation in mice.
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Recently, several investigators have reported that a peak concentration of serum prolactin occurs during the late afternoon of pro-oestrus in rats (Meites & Clemens, 1972; Meites, Lu, Wuttke, Welsch, Nagasawa & Quadri, 1972). Also Ieiri, Nobunaga & Yamamoto (1972) found that the synthesis and release of prolactin by rat anterior pituitaries in vitro increased markedly from the afternoon of pro-oestrus to the afternoon of oestrus. On the other hand, no similar information is available on the pituitary secretion of prolactin during the oestrous cycle in mice. Yanai, Nagasawa, Nobunaga & Yamamoto (1973), using mice killed between 09.30 and 10.00 h, showed that the synthesis and release of prolactin in vitro was highest on the day of dioestrus (the day before pro-oestrus) and lowest on the day of oestrus. In the present communication, we have determined the changes in pituitary and plasma prolactin levels during the oestrous cycle in mice using
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SUMMARY
Intact female rats given twice daily injections of 1 mg human placental lactogen (HPL) showed continued dioestrous vaginal smears and their ovarian corpora lutea were found to be hypertrophied and functional. The serum prolactin level was significantly lower in these rats than in the controls at dioestrus as well as at pro-oestrus. Twice-daily injections of 0·5 or 2 mg HPL to ovariectomized rats decreased serum and pituitary levels of prolactin and increased hypothalamic activity of prolactin inhibiting hormone, although the effect was less at the lower dose. Human placental lactogen had no direct effect on pituitary prolactin secretion in vitro. These findings have demonstrated that HPL, like prolactin itself, inhibits prolactin secretion by acting indirectly on the pituitary through the hypothalamus.
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The effects on reproductive function of restriction to one half of the normal food intake for 30 or 60 days and subsequent unrestricted feeding were investigated in adult female Sprague–Dawley rats.
Restricted feeding resulted in the cessation of oestrous cycles within 9 to 28 days, associated with decreased pituitary, ovarian and uterine weights. Pituitary content and concentration of FSH were increased by restricted feeding and the levels of FSH in 60 day underfed rats were about twice as high as those of the controls at dioestrus. There was little difference in pituitary LH content between the underfed groups and the controls at the end of restricted feeding. Pituitary LH concentration was significantly higher in rats underfed for 60 days than in the control rats. Pituitary prolactin content was one half and one third of that in control rats in rats underfed for 30 and 60 days respectively. Pituitary prolactin concentration was also decreased by restricted feeding. At the end of restricted feeding, no differences in serum LH and prolactin levels were found between the groups, whereas the serum FSH level in 60 day underfed rats was higher than that in the controls at dioestrus.
After re-feeding, normal oestrous cycles returned within 3–5 days in almost all rats, regardless of the length of the previous cessation of oestrous cycles. Pituitary contents of FSH and LH in underfed rats decreased after re-feeding following the return of oestrous cycles. The rate of decrease was much greater in 60 day underfed rats than that in 30 day underfed rats. On the other hand, serum levels of FSH, LH and prolactin in these underfed rats were increased by re-feeding and the levels in the evening of the first pro-oestrus were higher than those in the morning of dioestrus and pro-oestrus. Serum levels of these hormones increased more in 60 day underfed rats than in the other groups at any stage. After re-feeding, pituitary, ovarian and uterine weights increased and the uterine epithelial layer was clearly repaired in both underfed groups, although not always to the control levels by the first oestrus. The end-bud system of the mammary gland which degenerated during restricted feeding was comparable to that of the controls at the first oestrus after re-feeding in 30 day underfed rats, but not in 60 day underfed rats.
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In female rats neonatal treatment with oestrogen induces persistent vaginal cornification and sterility at maturity (Takewaki, 1962). Recently, we found that the pituitary secretion of prolactin, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in such oestrogenized female rats is permanently altered (Nagasawa, Yanai, Kikuyama & Mori, 1973). No data are available, however, on the effect of pituitary hormones, administered neonatally, on the secretory activity of the pituitary in adult rats. In the present experiment the pituitary secretion of prolactin, LH and FSH was measured in adult female rats treated neonatally with prolactin.
Virgin female Sprague—Dawley rats were used. Half the females in each litter were given a daily subcutaneous injection of bovine prolactin (NIH-P-B2) dissolved in 0·25–1·0 ml 0·9% NaCl solution (pH 8) for 20 days beginning on day 0 of age. The dose of prolactin was 0·5 mg for the first 5 days, 1·0 mg for the second 5
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SUMMARY
The serum and pituitary levels of prolactin, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were determined by radioimmunoassay in adult female rats treated neonatally with oestrogen and were compared with levels in normal cyclic rats at 90, 150 and/or 180 days of age. The serum level of prolactin was significantly higher and its pituitary content and concentration were lower in oestrogenized rats than in control rats at early prooestrus and on the 2nd day of dioestrus. The level of LH in the serum of oestrogenized rats was similar to the level in control rats at pro-oestrus and was higher than that of the controls at dioestrus. Pituitary levels of LH were lower in oestrogenized rats than in control rats at both pro-oestrus and dioestrus. The serum and pituitary levels of FSH in the oestrogenized rats were intermediate between the values found at dioestrus and at pro-oestrus in the controls. The results demonstrate that the pituitary of the neonatally oestrogenized female rat constantly secretes considerable amounts of these hormones.
