Implantation in Armadillos Ovariectomized During the Period of Delayed Implantation

Abstract

The effect of ovariectomy during delayed implantation on the fate of the free blastocyst has been studied in the armadillo. If bilateral ovariectomy is performed about the middle of the 4-month delay period, implantation occurs 30-34 days later and is indistinguishable from normal implantation. In animals ovariectomized toward the end of the delay period, implantation occurs at the time when normal implantation would have been expected, which is less than 30 days postoperatively. However, resorption or abortion follows shortly thereafter. Removal of the corpus luteum towards the end of the delay period for the most part results in loss of the blastocyst and non-implantation. Removing the corpus luteum in early gestation causes loss of the embryos, but no effect was observed following loss of the corpus luteum in animals past approximately the first third of gestation. A possible explanation of the findings is discussed.The effect of loss of the luteal tissue, or loss of all the ovarian tissue, on the course of pregnancy has been studied in a number of species. The invariable result of such operations in early pregnancy is abortion or résorption of the embryos. In many species (e.g. man, monkey, cat, guinea-pig) ablation of the ovaries in the latter portion of pregnancy does not lead to foetal loss, while in others (e.g. rat, rabbit) the ovaries must be present until parturition, but this is generahy conceded to be due to the placental production of steroid hormones in the former species, which renders the ovaries expendable as a source of these secretions.The effect of ovariectomy prior to implantation (but necessarily after ovulation) has scarcely been investigated. The time interval in most species is short, usually 7-10 days, and since the maintenance of early pregnancy is dependent on the presence of functional corpora lutea, it seems improbable that implantation could be initiated in the absence of the ovaries. Animals exhibiting delayed implantation offer an extended period in which such operations can be performed. Furthermore, possible interference with other events preceding implantation, such as tubai passage, can be avoided easily.A few workers have examined the results of ovariectomy in the interval between ovulation and implantation in laboratory rodents. Loeb [1923] reported that removal of the corpora lutea of the guinea-pig in the first 48 hr following ovulation caused a failure to implant, but that removal after this time did not. He examined his animals 2 weeks after the operation and found normal embryos in the latter cases ; apparently, however, he did not ahow any animals to go to term. Loeb felt that in the first 48 hr after ovulation, the corpora lutea were able to sensitize the uterus suffi¬ ciently to make it receptive to the ova.

Implantation and Early Pregnancy in Ovariectomized Guinea-Pigs

“…Apart from the few recently mated guinea-pigs, ovariectomized by Loeb with results confirmed by the present work, the only records of implantation follow¬ ing ovariectomy are those of Buchanan, Enders & Talmage ( 1956) who found that implantation could occur in the armadillo 1 month after ovariectomy if the latter were carried out during the 4-month period when the eggs were normally delayed in the uterus.…”

Some Effects of Ovariectomy and Injection of Ovarian Hormones in the Armadillo

“…Interposed between the period of blastocyst formation and implantation, there is a period of delay of implantation during which the blastocyst remains relatively quiescent in the uterus [Patterson, 1913;Hamlett, 1932;Buchanan, Enders & Talmage, 1956]. Since implantation characteristically occurs in November, the length of delay of implantation has been estimated as 14-18 weeks [Hamlett, 1932[Hamlett, , 1933Buchanan et al 1956].…”

“…Since implantation characteristically occurs in November, the length of delay of implantation has been estimated as 14-18 weeks [Hamlett, 1932[Hamlett, , 1933Buchanan et al 1956]. Parturition generally occurs in March or early April, although pregnant animals have been found as late as May.…”

Hormone involvement in the establishment of pregnancy

“…In all mammals studied progesterone is essential for the maintenance of early pregnancy and in most species it is also a pre-requisite for implantation (Davies & Ryan, 1972); the guinea-pig (Deanesly, 1960) and the armadiUo (Buchanon, Enders & Talmage, 1956) are two notable exceptions to the latter. In the rat and mouse post-ovulatory oestrogen is also required since it is necessary to achieve an endometrial status conducive both to implantation and normal blastocyst development (Surani, 1977).…”