In an attempt to study the relationship between litter size and mammary gland growth and mammary secretory function around parturition, we observed the relationship between litter size adjusted surgically and the gestation period and the time of delivery.
Rats of the Wistar strain, which had been bred by random mating in a closed system, were used at 3 to 4 months of age. Animals were housed in an animal room where the temperature was maintained at approximately 25°C and illuminated for 14 hours per day (lights on 6 : 00 to 20:00). After mating, the vaginal smear was taken every morning between 9:00 and 10:00 hr and the day of finding sperm was designated as day 1 of pregnancy. Each pregnant rat was kept in an individual cage thereafter. They were allowed unrestricted access to a commercial diet and water.
On day 8 of pregnancy, pregnant rats were undergone laparotomy under light ether anesthesia and the number of conceptus was reduced to various sizes less than 10 by crushing embryos with a forceps. In some rats, all conceptuses were remained intact after counting the number.
On day 20 of pregnancy, the pupping cages were transferred to another room with the same environmental conditions for the convenience of checking the delivery and inspected as frequently as possible throughout the entire 24 hrs. The dim light by a small flashlight was carefully used to determine the time of parturition during the dark period. The time of parturition was defined as the time at which the 1st pup was delivered. In one group, the mother was killed immediately after the delivery of the 1st pup and counted the number of fetuses remained in the uterus, and the sum of them was considered as the litter size at birth. In another group, the mother was killed 3 or 8 hrs after the delivery of the 1st pup and confirmed the completion of delivery of all pups by inspecting the uterus so that the length of parturition as well as litter size were recorded.
Total of 85 pregnant rats gave birth on day 22 to day 24 of gestation and an inverse relation between the gestation period and the litter size was observed. The regression line of gestation period on litter size in mothers whose litter sizes were less than 10 is Y=23.46-0.17X, where Y is the gestaion period and X is the litter size, with a correlation coefficient of -602 (P <0.01) (n=71). In most rats whose conceptus was reduced surgically, the litter size at birth was 1 or 2 less than the number of conceptuses remained on day 8 of pregnancy.
In spite of our careful inspection, we failed to confirm the time of delivery of the 1st pup in 19 rats, but could confirm that of the 2nd pup in 8, of the 3rd in 3, of the 4th in 4, of the 5th in 2, of the 6th in 1, and of the 10th pup in 2 rats. On assumption from the regression equation mentioned below, it may be safe to say that 17 rats of those also delivered during the light period. Thus, regardless of the day of parturition, more than 90% of deliveries occurred during the light phase. The distribution of the time of parturition showed similar pattern each day, i.e. the high frequency between 11:00 and 15:00 hr. These results may suggest a possibility of photoperiodic regulation of parturition.
Although interval between each pup was not always regular, the overall relationship between 44 observations of length of paturition (Y, min) and litter size (X) was presented as a strait-line regression equation, Y=53.02+4.55X, with a correlation coefficient of 0.348 (P <0.05). The results were discussed in relation to the literature.

View full abstract

The effects of prostaglandin F_2α (PGF_2α) on the estrous cycle were investigated in the ewe. The conception rate in the following estrus were also examined.
When a total amount of 10 or 15 mg of PGF_2α was injected intravenously at an interval of 24 hours on Days 7 and 8 of the estrous cycle (Day 0 refers to the first day of estrus), no significant shortning of the estrous cycle were observed in two ewes. However, when a total amount of 10 mg PGF_2α was injected intramuscularly on the same days, the estrous cycle shortened to 9.5 days and 13.5 days in two ewes. All, except one, of seven ewes, that were given a total amount of 6-27 mg PGF_2α by subcutaneous (s. c.) injections on the morning and evening of Day 7, and the morning of Day 8, came into estrus within 12 days after the treatment. Their estrous cycles shortened to 8-10 days. The luteolytic action of PGF_2α seemed to be most effective when injected s. c. at three times on successive two days.
In 12 of 16 ewes that were given a total amount of 1217 mg PGF_2α at three times by s. c. injections on successive two days between Day 3 and Day 13 of the estrous cycle, estrus occurred within 12 days after the treatment. Three out of the remaining 4 ewes showing delayed estrus were young ewes aged 7 months.
Nineteen ewes were served by natural mating at the first estrus, which occurred 12 days after the treatment, and 9 (47.4%) of them conceived.
The results indicated that PGF_2α could be applied to the synchronization of estrus in the ewe.

View full abstract

To examine the adrenocortical function in dairy cows with cystic ovaries, fluorometric determinations of serum 11-hydroxycorticosterones in oestrous cycling cows and in cows with cystic ovaries (CO-cows) were carried out during a period of 9 months.
The results obtained were summarized as follows:
1. When NH•ACTH-Z 40 IU were injected intramuscularily to 6 of cycling cows, both serum 11-OHCS values and leucocytes in blood increased remarkably after 4 to 8 hours postinjection, but the eosinophiles in blood decreased markedly after 12 to 16 hours. In CO-cows, however, these changes were not observed distinctly.
2. When 50 IU β^1-24ACTH or 40 IU β^1-24ACTH-Zinc was injected intramuscularily to each of cycling cow, serum 11-OHCS values increased in average by 5.6 μg/dl at 30 minuts later. In CO-cows, 5 cows reacted as similarly as in cycling cows, but in another 20 cows increased values of serum 11-OHCS were less than normal level. In these cows, only one half of them recovered from cystic ovaries.
3. In cases of cycling cows, average serum 11-OHCS ranged from 5.3 to 9.1 μg/dl, but in CO-cows, these values covered a wide range. In relation to recovery rate and 11-OHCS values in CO-cows, the recovery rates were 100, 77.2, 44.0% in hyper-, normal-, hypofunction groups of adrenocorticoid, respectively.
From these observations in the present experiments, the authors would like to conclued that in most cystic cows, more or less adrenocortical function seems to tend remaining in abnormal states, and in apparently hypofunctional cases, any therapy including adrenocorticoid injection may often encounter unsuccessful termination.

View full abstract

A majority of the female Holtzman rats bred in our laboratory, under controlled illumination for 14 hr daily (05:0049:00), exhibited regular 5-day estrous cycles in which 2 days of vaginal cornification (E₁ and E₂) were followed by 2 days of leucocytic smear (D₁ and D₂) and 1 day of vaginal proestrus (PE). The preovulatory excitation of hypothalamus occured around 15:0018:00 on E₁, and ovulation followed at around 02:0006:00 on E₂.
Ovarian effluent progesterone increased from 10:00 to 20:00 of E₁ (P<0.005) (preovulatory increase). Level of the hormone was low on D₁ and increased again to D2 (P<0.01) (postovulatory increase). The preovulatory increase in ovarian effluent progesterone measured in 4-day cyclic rat was comparable with that of 5-day cyclic rat. In contrast, progesterone level measured in 4-day cyclic rat declined from D₁ to D₂ (P<0.01), although the steroid level on D₁ was similar to that found in 5-day cyclic rat. 20α-Hydroxypregn-4-en-3-one (20α-OH P) levels measured in both 4-and 5-day cyclic rats were similar and did not show a significant fluctuation. Hypophysectomy performed on either E₂ or D₁ of 5-day cycle resulted in a remarkable decrease in progesterone level measured on D₂ (P<0.005) and concomitantly tended to decrease 20α-OH P secretion. This finding suggests that hypophyseal factor(s) are involved in the postovulatory increase in progesterone in 5-day cyclic rat.

View full abstract

[in Japanese]

View full abstract

The authors presented a simple, effective assay method for bovine plasma progesterone (P), estrone (E₁), estradiol (E₂), estriol (E₂), cortisol (F_k), and corticosterone (B_k), using radioimmunoassay (RIA) and competitive protein binding analysis (CPBA). The assay consisted of the two parts-the one was the RIA for P and the 3 estrogens (E_s), and another was the CPBA for Fk and Bk. About 4.0 ml of bovine peripheral plasma was usually enough for these 6 steroid assays.
I) For P and E.: At first, 3.0 ml batch of the plasma was extracted by petroleum ether, and this was kept as P fraction. The rest plasma portion was extracted again by methylene chloride (E_s fraction). Each extract was applied onto each Sephadex LH-20 microcolumn of 2.0 ml sized Tuberculin syringe. Each effluent containing P, E₂, E₂, or E₃ was applied to the RIA assay procedure. An anti-11α-OH-progesterone-11-BSA rabbit serum with ³H-P, and anti-E₁-17-BSA rabbit serum with ³H-E₃ as single tracer, was used in each assay for P and E_s. The solvent systems sellected for the microcolumn were : heptane 85 / benzene 10 / methanol 5, for separation of P, and benzene 85 / methanol 15 for E^s, suggested by CARR, et al.¹⁾ II) For F_k and B_k : A 0.5 ml plasma was applied to the CPBA for both of F_k and B_k. After an extraction of the plasma by methylene chloride, the extract was dissolved in 25% ethanol. This was partitioned by carbon tetrachloride, and then the carbon tetrachloride layer was again parti-tioned by 50% methanol reversally. These two successive partitions made satisfactory separation of F_k (in ethanol) and of B_k (in methanol) for the following CPBA procedure. Careful analysis made for the accuracy, sensitivity, and specificity of the assay method revealed that this was a satisfactory and effective laboratory method for the bovine plasma steroids concerned.

View full abstract