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  • Author: B. M. BINDON x
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B. M. BINDON

SUMMARY

The conditions under which implantation is delayed in mice mated at the post-partum oestrus have been investigated. The critical litter size for the effect was shown to lie between three and nine pups per female. Delay of implantation was dependent on the presence of the litter until at least day 3 and the length of the delay could be significantly shortened by temporary litter removal on days 2 and 4. A study of the effect of parity showed that delayed implantation after post-partum mating continued to occur until the 4th litter. The incidence and length of implantation delay were reduced after five or more litters.

During suckling-induced delay of implantation the increase in uterine capillary permeability which occurs on day 4 of normal pregnancy was shown to be delayed to as late as day 14. The rate of development and time of entry into the uterus of zygotes was also retarded in comparison with normal pregnancy. This pattern resembled that seen after hypophysectomy on day 1 of normal pregnancy.

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B. M. BINDON

SUMMARY

The uptake of 131I-iodinated human serum albumin ([131I]HSA) by the ovary and uterus was used as an indicator of capillary permeability in these organs from pro-oestrus through to day 5 of pregnancy. Highest levels of [131I]HSA in the ovary were found on the day of pro-oestrus. Ovarian uptake declined significantly on days 1 and 2, then rose to an abrupt and transient peak at 17.00 hr. on day 3. The two peaks of ovarian uptake coincide with the appearance of ovarian hyperaemia.

Uterine incorporation of [131I]HSA was high at pro-oestrus and declined significantly on days 1 and 2. The first significant increase occurred between 09.00 hr. and 17.00 hr. on day 3 and a further increase was observed between days 4 and 5. Only the pro-oestrous peak was associated with observable uterine hyperaemia.

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B. M. BINDON

SUMMARY

The optimum conditions for delay of implantation by hypophysectomy and neurodepressive agents are described. Hypophysectomy on day 1 without hormone replacement was followed by retarded development and subsequent degeneration of zygotes. Viability of blastocysts was maintained under these conditions by a single injection of a long-acting progestagen on day 1. Hypophysectomy at intervals beginning late on day 3 indicated that implantation is initiated by pituitary activity in the several hours around midnight of this day. In animals induced to ovulate and copulate by exogenous gonadotrophin injections, the corresponding time of pituitary activity was delayed by approximately 8 hr. This delay could not be explained solely on the basis of altered times of ovulation. It is evident that the events of early pregnancy do not follow the normal physiological pattern under these conditions, and caution should be exercised in utilizing such animals.

Of five neurodepressive agents examined, only trifluoperazine effectively delayed implantation. The effect of this substance injected at various times on day 3 of pregnancy suggests that implantation in the mouse is initiated by neurally regulated pituitary activity between 16.00 and 24.00 hr. on this day. Comparison with the mechanism of ovulation indicates that ovulation and implantation are regulated by separate hypothalamic-pituitary events, one peculiar to the oestrous cycle, the other to early pregnancy.

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B. M. BINDON

SUMMARY

Gonadotrophins were injected into mated hypophysectomized and suckling mice in an attempt to induce implantation. In these two classes of animal implantation is normally delayed by absence or suppression of pituitary gonadotrophin release. Antibodies raised against ovine gonadotrophins were injected into mice soon after mating in an attempt to inhibit implantation.

Pregnant mare serum gonadotrophin (PMSG) was effective in inducing implantation in both hypophysectomized and in suckling mice. This may mean that a gonadotrophin with the qualities of PMSG normally initiates implantation. Alternatively, PMSG may have been effective by virtue of its long half-life rather than any special hormonal attributes. Human chorionic gonadotrophin was ineffective in both types of mouse. Mixtures of ovine follicle-stimulating hormone (FSH) and luteinizing hormone (LH) (100 μg of each), injected daily for 3 days, were necessary to induce implantation in hypophysectomized mice.

Implantation was readily induced in suckling mice by a single injection of FSH (equivalent to 12·5 μg NIH-FSH-S3) prepared from rat pituitary glands.

Implantation was readily inhibited by anti-ovine LH. Anti-ovine FSH was ineffective but this did not cross-react with mouse FSH.

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B. M. BINDON

SUMMARY

The method of Lamond & Bindon (1966) was used to measure follicle-stimulating hormone (FSH) in the pituitary glands of mice and rats killed at different times on each of days 1–6 of pregnancy. The sensitivity of the method allowed detection of FSH fluctuations not previously described in these species.

A significant fall in pituitary FSH occurred in both species on day 3, although it was earlier in the mouse than in the rat. This transient decline in FSH activity, interpreted as a release of the hormone, was followed in both species by a gradual increase on days 4 and 5. Ovarian weight, measured only in the mouse, increased significantly late on day 3 and is believed to reflect changes in pituitary FSH.

The results indicate that implantation in the mouse and rat is initiated by altered activity of the pituitary gland during the first 3 days of pregnancy. It appears that this pituitary mechanism differs from that responsible for the events of the oestrous cycle.

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B. M. BINDON

SUMMARY

Delayed implantation in suckling mice was interrupted by litter removal at 08.00 hr. on day 5 of lactation pregnancy. A number of preimplantation changes were examined at intervals of 2, 8 and 32 hr. after litter removal. Control groups which retained their litters were examined at similar times. Litter removal was followed by significant reduction in pituitary folliclestimulating hormone (FSH) in the 2 and 8 hr. groups. The earliest uterine response to litter removal was the incorporation of [3H]uridine. This was significantly increased by 8 hr. and was about four times the control values by 32 hr. after litter removal. Increased uterine capillary permeability and the development of dye sites were not observed until 32 hr. after litter removal. At this time the number of zygotes flushed from the uterus was significantly lower than in controls, indicating that attachment of the blastocyst to the uterus had commenced. These results indicate that delay of implantation induced by suckling is associated with increased pituitary FSH. Litter removal causes prompt release of FSH and increased oestrogenic activity in the uterus (i.e. uridine incorporation) as early as 8 hr. later.

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B. M. BINDON

SUMMARY

The indicator fractionation technique was examined and found to be of value in the measurement of organ blood flow in the anaesthetized female mouse with [131I]iodoantipyrine as the indicator substance. Blood flow per unit weight of the brain and ovary was shown to decline rapidly after hypophysectomy. A single injection of pregnant mare serum gonadotrophin (PMS), given 4 days after hypophysectomy, restored the blood flow of these organs to normal levels. Uterine blood flow was unaffected by hypophysectomy, and was significantly increased by PMS injection.

Significant changes in brain, ovarian and uterine blood flow were observed during the oestrous cycle, early pregnancy and in mice induced to ovulate by injections of gonadotrophin. There was a tendency for brain and ovarian blood flow to decline before ovulation. By contrast, significant transient increases in blood flow to the brain and ovary were observed on day 3 of pregnancy. It is thought that these changes are related to the mechanisms which initiate implantation. Uterine blood flow was lowest in mated and unmated mice on the day of oestrus and rose to peak levels 2 days later. In pregnancy, however, peak uterine blood flow was recorded between days 3 and 4 and was higher than at any stage in the oestrous cycle. Although it tended to fall after day 3, uterine blood flow in pregnancy did not decline again to low levels as it did in the oestrous cycle.

The possible physiological significance of the results is discussed, and the limitations to their interpretation are considered.

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B. M. BINDON

SUMMARY

Antisera were raised to pregnant mare serum gonadotrophin (PMSG) and human chorionic gonadotrophin (HCG) in male rabbits. The biological potencies of the antisera, A-PMSG and A-HCG, were determined against homologous antigens PMSG and HCG, using the mouse uterus test in immature mice.

A single injection of A-PMSG was shown to inhibit the response to PMSG when injected as late as 21 days after the antiserum. The duration of inhibition was shown to depend on the dose of antiserum injected. These results were confirmed in hypophysectomized mice.

A-HCG was shown to cause similar prolonged inhibition of the response to HCG in intact mice.

The results suggest that A-PMSG and A-HCG persist in the circulation of the mouse for periods of time expected on the basis of the known half-life of rabbit γ-globulin (5 days).

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B. M. BINDON and R. TASSELL

The preparation of pituitary tissue for bioassay commonly involves fractionation and lyophilization to reduce the bulk of material. It is of practical importance to know if losses of hormonal activity are associated with such procedures.

To examine this point, pituitary glands were collected from four aged crossbred ewes and frozen within 1 hr. of slaughter. The pooled anterior lobes, average weight 0·940 g., were homogenized in 20 ml. 0·15 m-NH4HCO3 buffer, pH 7·2, containing 1% n-butanol and the homogenate was divided into four aliquots. One aliquot was frozen directly and a second was treated with acetone for 36 hr. at 2° by the method of Parlow, Anderson & Melampy (1964), the resulting powder being weighed and stored 48 hr. in a desiccator. The remaining homogenate samples were stirred for approximately 8 hr. and then centrifuged. The supernatants were made up to 5 ml. with buffer

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B. M. BINDON and G. M. H. WAITES

The indicator fractionation principle (Sapirstein, 1958) has recently been used to measure blood flow changes in the testis and epididymis of the rat (Waites & Setchell, 1966). The validity of Sapirstein's principle has now been verified in the mouse by demonstrating that the ratio of isotope content of the brain, testis and epididymis to that in the rest of the body remains constant between 10 and 20 sec. after the intravenous injection of [4-131I]iodoantipyrine.

The present study was made to examine changes in the weight and relative blood flow of the testis and epididymis of the mouse at intervals after hypophysectomy. Mice of the Quackenbush strain, aged 8 weeks, were anaesthetized and about 10 μc of [4-131I]iodoantipyrine (Radiochemical Centre, Amersham) in 0·2 ml. 0·9% NaCl solution was injected into the lateral tail vein after warming the distal half of the tail to 40–43° Precisely 15 sec.