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Summary.
The total gonadotrophic activities of the anterior pituitary glands and blood plasma of hens, Gallus domesticus, during the moulting period were estimated using the assay method based on the weight increase of chick testis. The activities in both the pituitary and the blood of hens in the four groups classified according to the progress of moult were significantly higher than those of laying hens. Nevertheless, no detectable level of serum vitellin and a completely regressed ovary were found in moulting hens.
Anterior pituitary glands of moulting and laying hens were assayed for their fsh and lh activities by the use of the hcg augmentation method or the ovarian ascorbic acid depletion test. The fsh activity of the moulting hen was about twofold higher than that of the laying hen, whereas lh activity was about equal during the moulting and the laying periods.
The serum vitellin of moulting hens increased steeply with the injection of oestrogen over 3 days. When chicken anterior pituitary homogenate was injected once daily for 6 days to hens in the moulting period, a satisfactory follicular growth as in the laying hen was induced in all of the treated hens. Injection of pmsg into moulting hens for 6 days resulted in an increase of serum vitellin in all the hens and the formation of yellow follicles in 40% of the treated hens.
These results suggested that the failure of follicular growth in the moulting hen, despite high levels of total gonadotrophic activity in both pituitary and blood, might be due to an unbalanced secretion of endogenous gonadotrophins.
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Summary. A system was developed for the in-vitro perfusion of the fowl ovary. The ovaries were isolated 16–18 h before expected ovulation of the first follicle of a clutch sequence and perfused at 41°C with Eagle's culture medium containing L-thyroxine and insulin. The efferent perfusion pressure was maintained at 30–40 mmHg. This model was used to investigate the mechanism of ovulation.
Addition of LH (1 U) to the perfusate induced ovulation (46%) but LH (1 U) + FSH (1 U) was more effective (88%; P < 0·05). Progesterone at 100 γg alone also induced ovulation (80%). Clomiphene prevented gonadotrophin-induced ovulation. These results suggest that progesterone may act directly on the ovary as a final hormone to induce ovulation in the domestic fowl.
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The effects of progesterone and RU486, a synthetic anti-progesterone, on ovarian 3β-hydroxysteroid dehydrogenase (3β-HSD) activity, a key enzyme of progesterone production, were studied during ovulation in immature 22-day-old rats primed with pregnant mares' serum gonadotrophin (PMSG) and human chorionic gonadotrophin (hCG). Ovarian 3β-HSD activities had increased significantly 4 h after hCG injection. These increases were inhibited at 4 and 6 h after hCG when 20 mg RU486 kg−1 was administered 2 h before hCG. However, RU486 had no influence on the activity of 3β-HSD when administered at the same time as hCG injection. A histochemical study revealed that 3β-HSD activities in the granulosa cell layer, but not in the theca cell layer, were inhibited when RU486 was given 2 h before hCG. Serum progesterone concentrations, but not oestradiol concentrations, were significantly suppressed by RU486 treatment 4 and 6 h after hCG. The effect of progesterone on ovarian 3β-HSD activity was tested by administering graded doses of progesterone exogenously to rats 2 h before hCG injection. Ovarian 3β-HSD activity was increased in a dose-dependent manner, and more than 20 mg progesterone kg−1 significantly stimulated the activity. Although 10 mg progesterone kg−1 did not stimulate ovarian 3β-HSD activities, the RU486-inhibited activities were recovered by the concomitant administration of 10 mg progesterone kg−1 with RU486. These results indicate that ovarian 3β-HSD activity depends on progesterone concentrations, and suggest an autocrine regulation of progesterone production during ovulation in immature rat ovaries stimulated with PMSG and hCG.
Search for other papers by Y Tanaka in
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Search for other papers by K Nakada in
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Search for other papers by Y Sawamukai in
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The aim of this study was to determine the relationships between early follicular development, the time at which follicles appear in early stages of follicular development, and changes in the serum concentrations of FSH in the female bovine fetus. Thirty-five female bovine fetuses aged between 59 and 285 days, as estimated from the crown-rump length, were obtained from dams at an abattoir. Serum samples were separated from fetal blood obtained from the heart. Fetal ovaries were removed and weighed. The content of oestradiol in one of the fetal ovaries and the serum concentrations of FSH and oestradiol were determined using radioimmunoassay. Sections of the other ovary were examined histologically for the appearance and number of follicles. The follicles were divided into four stages: primordial, primary, secondary and early antral. The appearance of primordial, primary, secondary and early antral follicles was observed at day 74, day 91, day 120 and day 150, respectively. Serum concentrations of FSH in female bovine fetuses increased between day 120 and day 150 of gestation. Fetal serum concentrations of oestradiol increased from day 120. The number of early antral follicles increased from day 180 together with an increase in the fetal ovarian content of oestradiol. These findings indicate that, in the female bovine fetus as well as in adult cows, the number of follicles and stages of follicular development are associated with changes in the concentration of FSH.
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The molecular mass of the arginine vasotocin receptor in membrane fractions of the uterus (shell gland) of hens was estimated by autoradiography of [125I]-labelled arginine vasotocin binding protein after SDS-PAGE. A band of approximately 67 kDa was found in all of the samples taken from laying hens before and after oviposition and from nonlaying hens. In addition to this band, another band of approximately 95 kDa was found in samples from laying hens taken immediately before and after oviposition. Both bands were reduced by the presence of unlabelled arginine vasotocin or mesotocin, but the reduction was greater by arginine vasotocin than by mesotocin. These two bands were not reduced by chicken luteinizing hormone-releasing hormone-I (Gln8-GnRH), chicken luteinizing hormone-releasing hormone-II (His5,Trp7,Tyr8-GnRH)and chicken angiotensin-II (Val5-angiotensin-II). The appearance of the arginine vasotocin receptor of the larger molecular size may be related to oviposition in hens.
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Search for other papers by S. Kawakami in
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Adenylyl cyclase activity was studied in human decidua and myometrium in early pregnancy and at term before and after the onset of labour. Decidual basal, prostaglandin-, catecholamine- and forskolin-stimulated adenylyl cyclase activities at term before the onset of labour were significantly lower than those in early pregnancy. After the onset of labour at term, decidual basal, prostaglandin-, catecholamine-, NaF- and forskolin-stimulated adenylyl cyclase activities significantly increased compared with those at term before the onset of labour. Myometrial prostaglandin- and catecholamine-stimulated activities did not alter during pregnancy, except for basal and forskolin-stimulated activity. Myometrial basal, prostaglandin-, catecholamine-, NaF- and forskolin-stimulated activities at term showed no change after the onset of labour. At term, before the onset of labour, myometrial basal, prostaglandin, catecholamine-, NaF- and forskolin-stimulated activities were the same as those in the decidua. However, after the onset of labour at term, decidual basal and the stimulated activities were significantly higher than those in the myometrium. These results suggest that decidual prostaglandin- and catecholamine-stimulated adenylyl cyclase may play an important role in the initiation or maintenance of human labour or in both processes.
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Search for other papers by M. Tanaka in
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Summary. Ovariectomized Shiba goats carrying an oestradiol implant (4–10 pg/ml) were kept under a short-day light regimen (10L:14D; Group 1, N = 4) or a long-day regimen (16L:8D; Group 2, N = 4). Plasma LH concentrations were lower (P < 0·05) in Group 2 than in Group 1 between Days 40 and 200, suggesting an enhanced negative feedback effect of oestradiol on LH secretion under a long-day regimen.
On Days 30, 60, 100, 149 and 279, an LH surge was induced by i.v. infusion of oestradiol for 48 h; the infusion rate was gradually increased from 0·5 (0 h) to 4·1 (48 h) μg/h, thereby mimicking the preovulatory increase of oestradiol secretion. The duration and magnitude of the induced LH surge were indistinguishable between the groups. The latency from the onset of oestradiol infusion to the LH surge was relatively constant in Group 1, 41·1 ± 0·9 h (mean ± s.e.m., n = 17) but was shorter in Group 2 (19·7 ± 3·7h, P < 0·05) on Day 149; less oestradiol was therefore required for induction of the LH surge (27·4 vs 89·7 μg, P < 0·01), suggesting an increased sensitivity to the oestradiol positive feedback under a long-day regimen.
These results might be interpreted to indicate that the hypothalamic–pituitary axis of the goat becomes hypersensitive to the positive as well as the negative feedback effect of oestradiol under long-day conditions.
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Summary. LH-releasing activity of the hypothalamus in non-laying hens following the injection of progesterone was increased in hens that had been treated with oestradiol 4 h earlier. Short-term priming with oestradiol may be effective in increasing the responsiveness of the hen hypothalamus to progesterone.
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Changes in intracellular calcium concentration ([Ca2+]i) in fertilized mouse oocytes were measured using the calcium-sensitive dye, fura-2. After fertilization, an initial long-lasting [Ca2+]i increase was followed by a periodic [Ca2+]i increase. The periodic increase in [Ca2+]i persisted for 1 to 3 h and all fertilized oocytes extruded the second polar body within 4 h. The mean interval of periodic [Ca2+]i increase was 470 ± 180 s (mean ± sd). The frequency of the periodic [Ca2+]i increase depended on the extracellular calcium concentration. Verapamil and nifedipine inhibited the periodic [Ca2+]i increase. Sixty-five per cent of tested cells extruded the second polar body within 90 min of exposure to 7% ethanol. In these activated oocytes, the long-lasting [Ca2+]i increase was observed. However, no cells showed a repetitive increase in [Ca2+]i Both release of calcium from intracellular stores and influx of extracellular calcium contribute to the increase in [Ca2+]i induced by ethanol. We conclude that the extrusion of the second polar body requires an increase in [Ca2+]i above a certain threshold level and the mobilization of calcium of both the intracellular and extracellular space in mouse oocytes.
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Search for other papers by T Miyazaki in
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Prostaglandin F(2alpha) (PGF(2alpha)) is implicated in the process of luteal regression in many species. Treatment of rat luteal tissue with PGF(2alpha) increases the generation of reactive oxygen species. Since reactive oxygen species have been implicated in apoptosis, the present study was undertaken to determine whether reactive oxygen species play a role in the PGF(2alpha)-induced apoptosis of rat luteal cells. Rat luteal cells were loaded with 6-carboxy-2, 7'-dichlorodihydro-fluorescein (CDCFH) diacetate, di (acetomethyl ester), which can be oxidized by reactive oxygen species to yield CDCF, a fluorescent molecule, and the cells were treated with different doses of PGF(2alpha). Incubation with 100 micromol PGF(2alpha) l(-1) induced an increase in CDCF fluorescence (P < 0. 05). Treatment of cells with PGF(2alpha) for 48 h in serum-free medium induced a dose-dependent increase in cell death, and these cells exhibited the morphological characteristics typical of apoptosis, including condensed or fragmented nuclei and fragmentation of internucleosomal DNA. Pretreatment of these cells with ascorbic acid, N,N'-dimethylthiourea, or superoxide dismutase, which acts as an antioxidant or a radical scavenger, prevented the PGF(2alpha)-induced apoptosis. These results demonstrate that PGF(2alpha) produces reactive oxygen species and induces apoptosis in rat luteal cells, indicating that the reactive oxygen species may induce apoptotic cell death during luteolysis.
