Endocrinological studies were performed on the peri-estrous period in each 2 cows showing normal and feeble estrus. In 2 cows with normal estrus the ovulations occurred 21 and 26 h after the luteinizing hormone (LH) peak. In another 2 cows that showed feeble estrus had delayed ovulation at 44 and 52 h after the LH peak. However, in the latter 2 cows, the maximum level of the LH peak was not low (39.0 and 61.5 ng/ml). A gradual increase in plasma estradio1-17β (E2) was shown in all cows before the onset of estrus. The 2 cows with feeble estrus maintained the increased E2 level until 26 and 48 h after the LH peak, respectively. Progesterone (P) levels were around 4ng/ml in the 2 cows with normal estrus, but were about 2ng/ml in the 2 cows with feeble estrus, before the regression of the corpus luteum. Several plasma 13, 14-dihydro-15-keto-prostaglandin F2_α (PGFM) peaks were randomly observed in all cows around the regres-sion of the corpus luteum.

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Chimaeras were produced from highly asynchronous mouse embryos, in which single nucleus of 2-cell embryos (F1×F1;C57BL/6J×CBA) was exchanged with allogenic 2- or 8-cell nucleus (CD-1×CD-1 or BALB×BALB). The pattern of distribution of each component was examined by judging of the coat color in the pups derived from chimaeric embryos after transfer. The proportion of chimaeric embryos developed to blastocyst was 81-96%, and 56%-70% of these embryos give rise to live young after transfer. Seventy percent of the pups which derived from 2-cell F1 embryos receiving single nucleus from 2-cell CD-1 embryos was chimaeric. However the proportion of chimaeras was signifi-cantly decreased and that of colored was significantly enhanced when nucleus from 8-cell embryo was transferred. Similar results were obtained in the chimaeras produced from F1 and BALB embryos. These facts suggest that cells with nucleus from 8-cell embryos were tended to exclude from the ICM. In the male chimaeras, the cells with CD-1 nuclei were predominantly distributed to their germ line, but the cells with BALB nuclei were excluded from it.

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This study was undertaken to examine the effects of follicle stimulating hormone (FSH) and/or fetal calf serum (FCS) added to the maturation medium (TYH) on subsequent fertilization and preimplantation development of mouse follicular oocytes in vitro. Oocytes were cultured in the maturation medium for 16 hours (h). Fertilization was examined at 2 and 4h after insemination (im.) with whole mount preparations. Oocytes were transferred to modified Whitten's medium at 6 h after im. for further development at 24h interval up to 120h. Oocytes matured in TYH supplemented with 0.12IU/ml FSH showed slightly higher rate of fertilization than TYH group at 2 and 4 h after im., but pronuclear formation at 4 h was very low (3%). Addition of 5% FCS to the maturation medium resulted in a markedly increase in the fertilization rates 2 or 4h im. (63-86%) and in the pronuclear formation (34-38%) at 4 h when compared to TYH and TYH+FSH groups (p<0.01 or 0.001). Delay in the process of fertilization was observed in FCS added groups as compared to that in the oocytes matured in vivo. All oocytes with both male and female pronuclei at 6 h after im. in FCS added groups (60-64%) developed to the 2-cell stage, but approximately half of these oocytes failed to develop to blastocyst. In contrast, almost of all pronuclear oocytes matured in vivo developed to the blastocyst stage (94%). These results indicate that FCS added to the maturation medium improves the rates of fertilization and preimplantation development in vitro, however, some of these oocytes exhibited developmental delay, when compared to the oocytes matured in vivo.

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The effect of progesterone on prolactin secretion induced by DOPA decarbo-xylase inhibitor (NSD 1015) was compared between pubertal and adult female rats. In pubertal rats pretreated with pregnant mare serum gonadotropin (5 I.U. PMSG) at 28 days of age and in adult rats showing 4-day estrous cycles, a Silastic tubing (10 cm, PP or 5cm, P) was implanted at the time of ovariectomy (ovx) performed between 07:00 and 08:00 h on the day of estrus. When NSD 1015 (100mg/100 g B.W.) was administered at 11:30 h 3 days after the operation, plasma prolactin (PRL) levels increased, reached a peak 30 min after administration and declined to the level of pre-treatment at 60 min in both adult and pubertal rats. In pubertal rats, the peak value 30 min after ad-ministration was in P group two times more than in ovx group. On the other hand, in adult rats, the peak value at 30 min after administration in PP group was about twice the values observed in ovx or P groups. Plasma progesterone concentration in PP groups was about twice the levels in P groups. Therefore the progesterone treatment enhanced the responsiveness to the NSD 1015 administration in the pubertal P group of rats, though, in adult rats, this effect was seen only in the PP group. These results indicate that the circulating progesterone augments the anti-dopaminergic effect of NSD 1015 on PRL secretion more effectively in pubertal rats.

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This study was conducted to examine the effects of gonadotropins (PMSG and hCG) and estradio1-17β (E₂) on the timing of nuclear maturation and cumulus mass expansion in pig oocytes cultured in vitro. Irrespective of the addition of hormones, the progression of meiosis to metaphase II was enhanced within 30 to 36 hr after culture. On the other hand, the proportion of oocytes reaching metaphase II was significantly increased by the addition of gonadotropins with or without E₂ after 36 hr of culture (69-77%). High proportions of the oocytes with expansion of the whole cumulus mass were observed in the media containing PMSG within 30 to 36 hr after culture. However, most of cumulus mass had already formed monolayer after 24 hr of culture in the medium containing hCG alone or in the control medium without hormones. These results indi-cate that under our conditions, the progression of meiosis to metaphase II and cumulus mass expansion of pig oocytes cultured in vitro can be synchronously induced by 36 hr of culture in the media containing PMSG with or without E₂.

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Levels of three kinds of estrogens, estrone, estradiol-17β and estriol, in milk from 5 Thoroughbred mares during foal estrus were measured by radioimmunoassay. Estradiol-17β and estriol levels in milk have no relevant importance in predicting con-ceptionable estrus. Only estrone concentration in milk showed a relation to the con-ceptionable estrus cycle in thoroughbred mares. This is probably the first report that deals with estrone concentration in milk during foal estrus and the measurement of estrone could be a reliable guide to know the estrus to be capable of conception in postpartum mares.

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Chromosomal sexing was done in goat embryos preserved in liquid nitrogen. Sex determination was performed on the basis of detection of the Y chromosome, without examining the X chromosome. The incidence of embryos with one or more metaphase spreads was 54.5% and 85.7% in morulae and blastocysts, respectively. Successful sexing rate was achieved with a proportion of 50% for morulae and 58.3% for blastocysts in sexed embryos with metaphase spread.

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The activities of various kind of hydroxysteroid dehydrogenases (HSDs) were histochemically examined in the rat Sertoli cells. The cells isolated from 30-day-old Wistar rats were cultured for 8 days. The activities of 3α-HSD (androsterone as the substrate), Δ⁵-3β-HSD (pregnenolone, 17α-hydroxypregnenolone) and 17β-HSD (testoster-one) were weak, while the activities ⁵Δ-3β-HSD (dehydroepiandrosterone), 17β-HSD (estradiol-17β), 20α-HSD and 20β-HSD were strong. These results suggest that cultured Sertoli cells have enzyme systems related to the metabolism of progestin, estrogen and androgen.

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Numbers of FSH and LH receptors in granulosa cells and LH receptors in theca interna, and concentrations of steroid hormones in follicular fluid of bovine developing follicles and cystic follicles were measured, and the following results were obtained. 1. The number of FSH receptors in granulosa cells tended to increase from small (3.0-7.0 mm) to medium follicles (8.0-11.0 mm), and to decrease from medium to large follicles (12.0-19.0 mm). FSH receptors in granulosa cells of cystic follicles ( ?? 23.0 mm) did not differ in number significantly from those of large follicles. 2. The number of LH receptors in granulosa cells increased significantly from small and medium to large follicles (P<0.05), but it was significantly fewer in cystic follicles than in large follicles (P<0.05). LH receptors in theca interna of large follicles also showed the tendency to increase, but not significantly, from those of small and medium follicles. The number of LH receptors in theca interna of cystic follicles was significantly fewer than those of normal follicles (P<0.05). 3. While the concentration of testosterone in follicular fluid significantly decreased from small and medium to large follicles (P<0.05), that of estradio1-17p increased significantly in inverse relationship (P<0.05). The tes-tosterone concentrations in follicular fluid of cystic follicles tended to be lower than those of large follicles, and the concentration of estradio1-17p in follicular fluid of cystic follicles was significantly lower than that of large follicles (P<0.05). On the other hand, the progesterone level in the follicular fluid of cystic follicles was significantly higher than that of large follicles (P<0.05). These results suggest that numbers of FSH receptors increase in the early stage of bovine antral follicular development, and that the numbers of LH receptors rapidly increase concomitantly with augmentation of aromatase activity in the latter stage. The results also indicate that reduction of LH receptor numbers and inhibition of syntheses of testosterone and estradio1-17β have occurred in cystic follicles.

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Effects of age at unilateral ovariectomy (ULO) on compensatory responses of the remaining ovary were examined in rabbits. ULO was performed on 8 does for each group at 30 (group 30), 90 (group 90), 160 (group 160) and 230 days of age (group 230). Eight intact does were served as controls. Four does of each group were laparotomized and remaining ovaries were removed at first estrus (over 250 days of age). Numbers of large follicles on ovarian surface ( ?? 1.5 mm in diameter) per doe in all groups were nearly 10 and these values of ULO groups were twice as large as controls. Mean ovarian weight and volume of group 90 were the highest, and those of group 30 were second. The values in these ULO groups showed significant differences in comparison with controls. In histology of these ovaries, numbers of large, healthy follicles ( ?? 1 mm in diameter) per ovary in ULO groups were roughly double compared with those in controls. There was a tendency that the number of small, atretic antral follicles (< 1 mm in diameter) was increased in ULO animals operated at young age. The number of atretic antral follicles was closely correlated with ovarian weight and volume. To induce ovu-lation, the remaining 4 does of each group were injected with 20 IU of hCG. The num-bers of corpora lutea per doe of all groups were about 10 with no significant difference among groups. These results suggest that ULO in the immature period induces marked compensatory hypertrophy after puberty and that, regardless of age at ULO, the re-maining ovary in the ULO animal fulfills the function of both ovaries in the intact animal.

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