Luteinizing hormone-releasing hormone (LH-RH) and its potent analogue, des-Gly¹⁰-LH-RH-ethylamide (EA-LH-RH), were administered subcutaneously in daily doses of 100 and 500 μg/kg body weight to pregnant rats for 14 days, from day 5 to day 18 of pregnancy. The pregnant rats were sacrificed on day 20 of pregnancy, and the mother rats and their fetuses were observed.
1. In the LH-RH and EA-LH-RH treated groups, litter parameters, as assessed by the number of implanation sites, embryonic loss, litter size, fetal body weight, sex distribution, and the incidences of external, skeletal and visceral abnormalities as well as variations, were not affected by the treat-ment with the test doses of these componnds.
2. No abnormal behavior or unusual reaction was observed in the maternal rats during the course of the study. Mean body weights in the treated females were not significantly different from that in the controls. Maternal ovaries in all treated groups and uteri in groups treated with higher dosage of the releasing hormones showed significant increase in weight when compared with controls. Adrenal weight significantly increased only in rats treated with higher dosage of EA-LH-RH. Thymus weights also significantly increased in treated groups other than the group treated with a large dose of LH-RH. No other change which might be related to the administration of these compounds was observed.

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Six experiments were conducted to examine the effects of different freezing diluents, thawing temperatures and materials of thawing containers on the survival of ram spermatozoa frozen by the pellet method. The semen diluted 1:4 (v/v) with tris (hydroxymethyl)aminomethane (300 mM)-glucose (27.75 mM)-yolk (15% v/v)-glycerol (5% v/v) showed better survival of sperma-tozoa after freezing and thawing than with both lactose-yolk-glycerol and raffinose-citrate-yolk-glycerol diluents.
The best results were obtained when semen diluted with tris-glucose-yolk-glycerol extender was thawed at 37°C in glass or aluminium containers without any thawing solutions.

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Female Wistar rats were given a diet containing 6-propyl-2-thiouracil (PTU) during late pregnancy and lactation according to the method of KIKUYAMA et al.²⁾ in order to induce hypothyroidism. The growth was retarded and the opening of vagina was delayed in female pups of PTU-treated mothers.
When the developmental change in organs was examined at 540 days in the pups, the increase in weights of ovaries and uterus was inhibited.
Thyroid glands were hypertrophied at 20 days, but, the weight recovered to the control level by day 40. The content of pituitary luteinizing hormone (LH) was significantly decreased at 30 and 40 days compared with the control.
The replacement of pups of PTU-treated mothers with thyroxine from day 0 to day 19 of age restored the growth, the day of sexual maturation and the weight of organs. The pituitary LH levels were completely returned toward the normal values.
Plasma LH levels were little different between PTU-treated and non-treated groups throughout the experimental period. This result was not accordant with the previous report³⁾ in which the plasma levels elevated in hypothyroid rats induced with neonatal treatment of ¹³¹I.
These findings suggest that the normal thyroid function in early life is necessary for the de-velopment and sexual maturation and it is apparent that the deficiency of thyroid hormone affects the sexual organs weights and pituitary LH levels.
The authors acknowledge the gift of rat LH radioimmunoassay materials from the rat pituitary hormone distribution program of NIAMDD.

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Effects of prostaglandin (PG) E₂ and PGF_2α on the activities of Δ5-3β-hydroxysteroid dehydrogenase (HSD), 17β-HSD and 20α-HSD in pronuclear hamster eggs were histochemically observed in vitro. When eggs were immersed in one of the solutions either 5μg, 50μg or 100μg of PGE₂, the activity of Δ⁵-3β-HSD with pregnenolone as the substrate was stimulated; the activity of Δ⁵-3β-HSD with DHA as the substrate and that of 17β-HSD with estradio1-17β or testosterone were not stimulated; and the activity of 20a-HSD with 20a-hydroxyprogesterone was inhibited. Immersed in a solution containing either 5μg, 50μg or 100μg of PGF_2α, the activity of Δ5-3β-HSD with DHA or pregnenolone as the substrate, and that of 20α-HSD with 20a-hydroxyprogesterone were stimulated, whereas the activity of 17β-HSD with estradio1-17β or testosterone was inhibited.

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The effect of gonadotrophins and prostaglandins on the Δ⁵-3β-hydroxysteroid dehydrogenase activities in pig blastocysts 13 days of pregnancy was histochemically observed in vitro. The results obtained were as follows: the activity of Δ⁵-3β-hydroxysteroid dehydrogenase with either dehydroepiandrosterone or pregnenolone as the substrate was stimulated after the blastocysts were immersed in one of the culture media containing either a gonadotrophin or a prostaglandin: the gonadotrophins used were: FSH (100 μg/ml), LH (100μg/ml), HCG (100 i.u./ml) and prolactin (100 i.u./ml), and the prostaglandins used were PGE₂ (100 pg/ml) and PGF_2α (100 pug/ml).

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Postpartum estrus and serum levels of progesterone and estradiol-17β were investigated in fourteen beef cows. Calves were weaned at 3 days of age. All cows were given 1 kg of concentrate daily, and they were placed on pasture in summer and were fed hay ad libitum in winter season. Observations for estrus were made twice daily. Ovaries were examined by rectal palpation at 2-day intervals beginning on 7 days postpartum. Blood was collected from a jugular vein twice a weak from one month before to three months after parturition. Serum progesterone and estradiol-17β concentration were determined by radioimmunoassay. The cows were bred at the estrus after 40 days postpartum.
The cows slightly gained body weight during three months following calving. Although first postpartum ovulation occurred at 12.4 days, it was not accompanied by estrus in 9 of 14 cows. All cows except one exhibited estrus at the second ovulation, with an average of 24.0 days of first postpartum estrus. The interval from the first to the second ovulation was shorter than the second cycle (17.6 vs. 21.6 days, P <.05), particularly in cows which did not exhibit estrous behaviour at the first postpartum ovulation. It was suggested from the rectal examination and serum progesterone concentration that some of corpora lutea formed following the first ovulation might not have full function.
Serum progesterone peak after the first ovulation was lower than the peak after the second ovulation (2.55 vs. 5.16 ng/ml, P <.01). Serum estradio1-17β concentration varied from 5 to 20 pg/ml following parturition. Twice weekly blood collection, however, failed to show whether there was a difference in serum estradio1-17β concentration between quiet ovulation and estrus. The average interval from calving to conception and number of inseminations required for conception were 71.9 days and 1.6 times.

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The present study was undertaken to examine the effect of developing stages on the viability of rabbit eggs stored in liquid nitrogen.
One cell, 2-cell, 8-16-cell, morula and blastocysts were recovered respectively at 20, 25, 45, 65 and 96 or 120 h post coitum from mature New Zealand White rabbits induced to superovulate with FSH and HCG or rabbits injected with HCG (for the recovery of blastocysts). Unfertilized eggs were recovered 18 to 20 h after the injection of HCG from superovulated rabbits. The methods for freezing and thawing of eggs were conducted with the procedures reported previously.⁷⁹⁾.The samples were cooled to-76°C at 1°C/min and transferred to liquid nitrogen vapor at-100°C for 5min. The samples were finally transferred to liquid nitrogen at -196°C and preserved for 1 to 49 days. At thawing, the samples were warmed at 3 to 4°C/min. The eggs were washed with Ringer's solution containing 20% rabbit serum and cultured for 3 to 7 days to determine the number of de-veloped eggs in vitro. In some experiments, the frozen-thawed eggs were transferred to the oviducts (for 1-cell, 2-cell, 8-16-cell and morula) or the uteri (for morula and blastocysts) of synchronous pseudopregnant does which allowed to go to term.
1. The proportion of eggs which appeared morphologically normal after thawing was significantly higher when morula was used for freezing (88.9%) than when 8-16-cell eggs were used (71.3%). When unfertilized and fertilized 1-cell, 2-cell or blastocysts were used for freezing, the proportions of normal eggs were clearly low (6.5 to 33.3%).
2. The frozen-thawed eggs of various developing stages developed in culture except Day 5-blastocyst. The proportion of 1-cell eggs developed in culture was significantly low (42.3%) compared with those obtained by using other stages of eggs (66.7 to 79.1%).
3. The live young were obtained after transfer of frozen-thawed 2-cell, 8-16-cell and morula but not after transfer of eggs at 1-cell and blastocysts. Although the proportions of pregnant and live young obtained after transfer of frozen-thawed morula were slightly high (88.3 and 33.3%) com-pared with those obtained after transfer of 2-cell (40.0 and 15.4%) and 8-16-cell (75.0 and 21.9%), these difference were not significant.

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Some properties of the protein agglutinating factors in boar semen have been reported in the previous papers. This experiment was performed to clarify the variations in the agglutinating activity of boar semen owing to the season, interval of semen collection and the split ejaculation. Besides, some seminal constituents, i.e. protein, citric acid and zinc secreted from the seminal vesicle were determined quantitatively in comparison with the activity of the protein agglutinating factors. Principal results obtained are as follows;
1. There were many variations in the activity of the protein agglutinating factors of semen between boars. From the results of averaging of 153 samples obtained through out the year, con-centrations of protein, citric acid and zinc in seminal plasma having high agglutinating activity showed a tendency to be higher than those in seminal plasma having low agglutinating activity.
2. The agglutinating activity began to rise around the end of summer and maintained high level to the end of autumn, then decreased in winter and/or spring season. These tendencies of variations with the season was observed markedly on boar A. The concentrations of protein, citric acid and zinc were varied in almost parallel with the vari-ation of the agglutinating activity.
3. The interval of semen collection applied in this experiment did not affect on the agglutinat-ing activity and some contents of boar semen.
4. When semen was collected as separate fractions at half-minute intervals, the agglutinating activity lowered in the sperm rich fractions. The concentrations of citric acid and zinc were varied in nearly parallel with the agglutinating activity.

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Sexual behavior and reproductive efficiency of beef cattle were investigated in the free-ranging condition where a Japanese Black bull (5 years old) was introduced into a group of 15 heifers of same breed in a paddock of 10m×15m for about 2 days. The heifers were injected with PGF_2α analogue (ICI, Estrumate) intramuscularly twice at 10 days interval to induce estrus. The observation was initiated 47 hours after the second injection of PGF_2α analogue, when the first estrus appeared. Mounting and mount-receiving behaviors were observed in 15 and 14 heifers, respectively. The frequencies of those behaviors within heifers were av. 48 (7115) times per head for mounting and av. 51 (3113) for mount-receiving. The duration of estrus, estimated by the mount-receving behavior, was 19.2±9.0 hours. The bull mounted to 13 heifers 176 times and ejaculated to 10 heifers 21 times in order of the occurrence of estrus during the period of observation. However, the bull was puzzled for selecting a proper heifer to serve when the heifers were almost synchronized with estrus during the first half of the observation. Seven of ten heifers conceived as the result of the trial.

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