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Summary.

A surgical technique for the selective extirpation of corpora lutea of pregnancy is described. Numbers of corpora lutea in the pregnant rat were reduced to three or less on the 5th day post coitum. Although two corpora lutea sufficed for the decidual response of nidation, three were the minimum for successful post-nidation pregnancy in a majority of rats.

Vaginal cornification usually followed reduction of the numbers of corpora lutea. If the ova implanted, no new corpora lutea were formed at this time, but if implantation was blocked oestrus was accompanied by ovulation and a prolonged period of leucocytic vaginal smears followed, presumably a pseudopregnancy. The results suggest that, even when progesterone levels from the reduced numbers of corpora lutea were still high enough to maintain pregnancy, they did not inhibit gonadotrophin secretion.

Corpora lutea (CL) of pregnancy have been isolated from the other ovarian tissues as autografts under the renal capsule in rats. These grafts were maintained for a period corresponding to a full gestation provided that exogenous progesterone was available until placental luteotrophin was secreted (Gibori & Kraicer, 1972). Despite their excellent histological appearance, however, these grafts secreted little progesterone (G. Gibori, Y. Shaham and P. F. Kraicer, unpublished observations).

This paper describes attempts to increase the amount of progesterone secreted by the CL by increasing the amount of luteal tissue grafted and by supplying supplemental substrate.

In our technique, only the bulging domes of the CL were used and it seemed possible that the total mass of grafted CL may not have sufficed to produce adequate amounts of progesterone (Kraicer, 1969). As a test of this hypothesis, five rats were given their own CL plus the CL of five other

Summary.

A technique is described for the isolation and autotransplantation under the renal capsule of cl of pregnancy in the rat. Maintenance of exogenous progesterone, at least until placentation, ensures maintenance of normal luteal structure. The grafts do not appear to secrete oestrogen. They do secrete reduced quantities of progesterone. Early withdrawal of exogenous progesterone or later hysterectomy cause regression of the grafts. It is speculated that luteotrophic hormones act directly to maintain luteal structure and function.

Summary.

Follicular oocytes were examined at various times preceding ovulation. The timing of the preovulatory changes was established in relation to the `critical period' and to ovulation time. The earliest detectable change in the oocyte, loss of the germinal vesicle and the nucleolus, occurred about 2 hr after the presumed time of lh release, or about 9 hr before ovulation. The first polar body was extruded about 4 hr before ovulation. The morphology of the dictyate oocyte as revealed by interference contrast microscopy is described.

Summary.

One-fifth of rat blastocysts contain morphologically identifiable sperm heads or tails. In the electron microscope, the sperm remnants are seen to interpenetrate the cells as well as to lie free in the perivitelline space. On the background of these morphological findings, the possible role of sperm derivatives in nidation is discussed.

Summary.

Impregnated rats were given a subcutaneous injection of ergocornine methanesulphonate between 0·15 and 0·5 mg/rat on the 4th day of gestation. The earliest response studied was the appearance of the oestrous vaginal smear, 2 to 3 days after drug injection. Gestation was terminated in three-quarters of the rats exhibiting vaginal oestrus. The ED₅₀ for induction of oestrus and for termination of pregnancy was approximately 0·3 mg. Following the ergocornine-induced oestrus, the minority of rats exhibited normal oestrous cycles. Most rats had a spontaneous pseudopregnancy. During this pseudopregnancy, deciduomata could be elicited by `physiological' means, i.e. systemic histamine release. The weight of these deciduomata was, however, somewhat depressed. It is pointed out that a single injection of the drug elicits a complex series of endocrine sequelae.

Summary.

To study the duration of inhibition of decidual induction by intrauterine antihistamine, 163 rats were made pseudopregnant immediately after experiencing two consecutive normal oestrous cycles. Decidualization was induced by systemic injection of histamine releaser on 4th day of dioestrous state of pseudopregnancy (L⁴). Antihistamine (as inhibitor of decidual induction) was instilled unilaterally into uteri of groups of rats, on each of the 14 days (2×4 days of oestrous cycles plus pro-oestrus, oestrus and first 4 days of leucocytic phase of pseudopregnancy). Practically no decidual response was elicited when inhibition treatment was administered during pseudopregnancy; earlier administration resulted in partial inhibition of response.

Summary.

Samples were obtained from ovarian tissue excised during the second quarter of the menstrual cycle. Sodium, potassium and chloride concentrations resembled those of blood, while pO₂ was highly variable, and not correlated with follicular histology. The pCO₂ was correlated with pH, but follicular fluid had a more acid pH than blood plasma. It is concluded that culture media based on 'physiological' saline solutions are appropriate for culture of oocytes.

Summary.

A method is described for inducing decidualization of the uterus of the pseudopregnant rat, which is based on the utilization of systemically released histamine. Although per os, subcutaneous, intraperitoneal, intravenous and intracardiac routes can be used, the most generally effective is intraperitoneal. A single injection of pyrathiazine hydrochloride (Pyrrolazote, Upjohn) as 1 ml of 0·06 m aqueous solution (2% w/v), administered at 1000 hr on the 4th day of dioestrus of pseudopregnancy, was effective in inducing extensive decidualization of the endometrium.

Summary. The effect of adding LH (10 μg NIH-LH-B8/ml) to the medium in which oocytes were undergoing maturation in vitro was studied. The fertilizability of the oocytes was evaluated in the sterile oviduct of a unilaterally ovariectomized, mated recipient. Freshly ovulated oocytes, used as a control of the method, were fertilized at a rate of 72%. Only 14% of oocytes matured in culture (without LH) were penetrated by spermatozoa, and 11% were fertilized normally. Addition of LH to the medium increased these proportions to 43 and 33% respectively. Oocytes matured in the presence of LH were able to develop into apparently normal rats. It is concluded that, although oocytes can mature in vitro spontaneously, and that these matured oocytes can be fertilized, addition of LH increases the numbers 3-fold. LH therefore has a direct maturation-promoting action on the rat oocyte–cumulus complex in vitro.