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Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0 and Department of Biological Sciences, University of Idaho, Moscow, Idaho 83843, U.S.A.
Oestrogen has been shown to be necessary to precipitate implantation in the rat and mouse (see review by Nalbandov, 1971). Progesterone alone can initiate implantation in most other mammals studied to date, and oestrogen either facilitates or has no effect on the nidatory process (Nalbandov, 1971; McLaren, 1971). Recent studies on hormonal control of implantation in ferrets (Wu & Chang, 1972, 1973) indicate that progesterone alone will support implantation (as indicated by uterine swellings) on Day 13 in ferrets ovariectomized on Days 8 or 10. However, implantation was usually delayed in ferrets ovariectomized on Days 6 or 7 and treated with progesterone or progesterone + oestrogen.
This study was designed to investigate further the role of oestrogen in inducing implantation in ferrets by administration of specific antiserum to
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Peripubertal male mink (Mustela vison) were treated with prolactin, melatonin or antibodies against melatonin to determine the effects of altered circulating concentrations of prolactin and melatonin throughout one season of testicular development. Treatment began on 1 October and continued until 4 March. Administration of 0.5 mg ovine prolactin day−1 by minipump increased the circulating concentration of prolactin for the duration of the study and increased serum concentrations of LH. This treatment had no effect on the testosterone concentration or on testis size. Neither chronic treatment with melatonin throughout the period of crudescence nor passive immunization against melatonin for 79 days affected the circulating concentrations of prolactin, LH, testosterone or testis size. These results show clearly that, unlike in other seasonally breeding species, prolactin does not play a significant role in testis growth in the mink. Administration of melatonin to male mink in October did not affect testis growth, presumably because the melatonin signal that cues photoperiodic events had already been received. Administration of antibodies against melatonin did not affect any of the features measured, suggesting that melatonin may have neural but not peripheral effects. Further support for this view can be found in the absence of an influence of melatonin on testis growth or on the plasma concentration of testosterone.
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Ovarian follicular dynamics were studied during the breeding season, before and after ovulation in mink. Nulliparous female mink were stimulated to ovulate with an injection of 4 μg GnRH. Ovaries from three animals were collected on days 0, 2, 3, 4, 5, 6 and 7 after hormone treatment. A second dose of GnRH was administered on day 8 and ovaries were collected from three animals on day 9. Corpora lutea and follicles were identified in histological sections and follicles were classified by stage of development, healthy versus atretic, and by diameter. Preovulatory follicles (diameter 0.7–1.0 mm) were present in the ovaries of all animals on day 0 and these responded to GnRH treatment by ovulating. A synchronized wave of follicular development occurred following ovulation. Changes in follicle populations indicated that follicles are recruited from the small antral follicle class (0.2–0.4 mm) into the 0.4–0.6 mm class, with the first defined changes occurring between days 2 and 4. From the recruited group, a smaller cohort of follicles is selected to become the dominant follicles between days 4 and 6, and these acquire the ability to respond to a stimulus which induces ovulation at diameters of > 0.7 mm. The ovaries of unmated mink also contained substantial numbers of large, degenerating, luteinized, unruptured follicles. These degenerating, luteinized follicles are considered to represent the demise of large follicles that failed to receive an ovulatory stimulus.
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Summary. Immature female mink, 8 weeks of age in July, were treated with implants releasing melatonin. Mating, which induced ovulation, took place during the normal breeding season in the following March. Circulating prolactin and progesterone concentrations did not undergo the expected gestational increases, and no embryos implanted. A similar absence of gestational changes in prolactin and progesterone values ensued in primiparous mink treated with the melatonin implant 2–3 days after the second of 2 matings. Administration of exogenous sheep prolactin (0·5 mg/day) by minipump induced precocious elevation of progesterone concentrations in mated mink. Prolactin administration overcame the effects of melatonin, in that the corpora lutea were activated and embryos implanted, but exogenous prolactin resulted in degeneration of implanted embryos both in the presence and absence of chronic melatonin. The results suggest that melatonin has a single effect in alteration of gestation in mink; i.e. the prevention of prolactin secretion. Hyperprolactinaemia may inhibit embryo development in this species.
Keywords: melatonin; prolactin; mink; delayed implantation
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Experiments were designed to test the hypotheses that (1) follistatin gene expression in granulosa cells is regulated during follicular growth, and (2) that alteration of follistatin mRNA concentration can be hormonally induced in primary cultures of porcine granulosa cells. RNA isolated from granulosa cells from small (1–3 mm diameter), medium (3–5 mm) and large (> 5 mm) follicles of prepubertal and postpubertal sows was analysed by hybridization to a porcine follistatin cDNA probe. Amounts of follistatin mRNA increased with follicular diameter, but no differences in follicular follistatin mRNA were detected between prepubertal and postpubertal sows. Treatment of cultured porcine granulosa cells with FSH or LH for 20 h stimulated follistatin mRNA concentration by a factor of two (100 ng FSH ml−1) and a factor of 1.5 (10 ng LH ml−1), respectively, over untreated controls. Treatment of cultured granulosa cells with 200 ng FSH ml−1, 200 ng LH ml−1, 10 μmol dibutyryl cAMP l−1, 30 μmol forskolin l−1 and 100 ng cholera toxin ml−1 stimulated follistatin mRNA accumulation in granulosa cells by factors of 4.9, 3.7, 1.6, 13.7 and 3.5, respectively, compared with control cultures. Stimulation of follistatin mRNA accumulation in cultured granulosa cells by dibutyryl cAMP (30, 100 and 300 μmol l−1) and forskolin (3, 10 and 100 μmol l−1) was dose dependent. FSH and forskolin induced time-dependent increases in follistatin mRNA concentration in cultured granulosa cells, with maximal induction occurring 72 h after treatment (a factor of 4.5 for FSH and 15.5 for forskolin). These results demonstrate that (1) increased follistatin mRNA in granulosa cells is associated with increased follicular diameter, (2) increased follistatin mRNA in cultured porcine granulosa cells can be induced by gonadotrophins, and (3) the gonadotrophin-induced increase in follistatin mRNA accumulation in cultured granulosa cells can be mimicked by agents that increase intracellular cAMP concentrations.
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Summary. A highly localized increase in permeability of uterine blood vessels in the immediate vicinity of implanting blastocysts was first detected on the morning of the 12th day of pregnancy (290 h post coitum). The amount of extravasated dye which accumulated at implantation sites continued to increase through the evening of Day 13 (321 h p.c.). Blastocyst expansion, as indicated by small uterine swellings, preceded a detectable change in vascular permeability by about 10 h, suggesting that the timing of increased permeability is closely associated with initial blastocyst attachment to the uterine epithelium.
The results do not support the hypothesis that prostaglandins are required for increased uterine vascular permeability as two doses of indomethacin (4 and 8 mg/kg body wt) administered 5 times/day failed to decrease endometrial vascular permeability. However, the 8 mg dose did cause a significant reduction in size and number of uterine swellings and delayed or inhibited attachment of the trophoblast to the uterine epithelium in 2 of 5 ferrets. These findings suggest that prostaglandins play an important role in the process of implantation that is unrelated to decidual formation as the ferret is an adeciduate species.
Keywords: ferret, implantation, uterine vascular permeability, indomethacin
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Summary. Mink ovariectomized 14 days after the first of two matings received injections of 2 mg MPA, the same MPA treatment + an oestradiol-17β implant or no replacement therapy. Some mink were ovariectomized after implantation and given a single dose of 2 mg MPA or no replacement therapy. MPA persisted in the serum at detectable levels for 13 or more days in all mink treated. MPA and MPA + oestradiol induced uterine growth but neither treatment was capable of inducing embryo implantation. More embryos were retained in mink treated with MPA alone and these appeared to be viable. Implanted embryos persisted for a longer period in animals that were ovariectomized and treated with MPA. MPA neither supported pregnancy nor permitted parturition. Serum LH was elevated by 1 week after ovariectomy and elevations persisted for a further 20 or more days. While MPA alone had no apparent negative feedback effects on LH, animals that received MPA + oestradiol did not display any elevation of LH, suggesting that oestradiol or a combination of MPA and oestradiol has a potent negative feedback in mink.
