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SHAO-YAO YING and ROLAND K. MEYER

Summary.

Female rats treated with 3 i.u. pmsg at 22 days of age yielded an average of five ova with approximately 80% ovulation. Treatment with progesterone at 22 or 23 days of age resulted in postponement or advancement of ovulation respectively. Time of progesterone injection and concentration and dosage of progesterone were investigated. One to four successive injections of progesterone produced 1 to 2 days' postponement of ovulation. The importance of the optimal oestrogen-progesterone ratio for ovulation is discussed.

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MARTHA N. KLAUSING and ROLAND K. MEYER

Summary.

The ovulating hormone (oh) of the pituitary gland was determined in untreated, 30-day-old immature female rats given an ovulating dose of pregnant mare's serum gonadotrophin (pmsg), and in pmsg-primed rats given sodium phenobarbital (PB) before the critical period (13.30 hours) or after the critical period (16.30 hours) on Day 32. PB given at 13.30 hours blocks ovulation for 24 hr. The adenohypophysis was removed at various times from 14.00 hours on Day 32 to 07.30 hours on Day 35 and assayed for oh in 24-day-old pmsg-PB treated test rats. The number of ova ovulated by the test rats indicated the pituitary oh. In untreated animals the pituitary oh remained high. In the pmsg-primed rats, the hormone decreased during the critical period, 14.00 to 16.00 hours on Day 32, but was minimal on the morning of Day 33 and remained low through Day 35. In pmsg-treated animals injected with PB at 13.30 hours on Day 32, the oh changes were delayed for 24 hr. When PB was administered at 16.30 hours, oh decreased during the critical period on Day 32 but minimal oh on Day 33 was not as low as in the pmsg-primed rats at the same time. Instead of remaining low the hormone increased by 16.00 hours on Day 33. In ten of twelve test situations between 14.00 and 16.00 hours each day there was an oh decrease, indicating a diurnal oh secretion.

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ROLAND K. MEYER and ROBERT L. COCHRANE

Summary.

Deciduomal reactions were obtained during the delay in ovo-nidation in ovariectomized progesterone-treated rats when the uterus was traumatized as late as the 15th day of pregnancy. Subsequent ovo-implantation was induced in many of these same animals by addition of oestrone to the progesterone. Deciduomata were also elicited in the same type of animal when the uterus was traumatized early or late during the 'implantation period' which was induced by addition of small amounts of oestrogen. The deciduomal reaction did not induce implantation of the blastocysts prior to the administration of oestrogen, nor did it hasten nidation after oestrone treatment. The presence of deciduomata during the period of retarded nidation appeared to inhibit ovo-implantation in the traumatized horn completely, while induction of deciduomata early in the 'implantation period' only partially inhibited it, and induction late in the 'implantation period' failed to have any apparent inhibitory effect.

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JANE J. YASUKAWA and ROLAND K. MEYER

Summary.

A sequential study was made of non-delayed and of experimentally delayed rat blastocysts. Alterations in shape, axis lengths and area of non-delayed blastocysts first appeared on the afternoon of Day 5 of pregnancy. Similar changes were observed in delayed blastocysts beginning 12 hr after the simultaneous administration of oestrone and progesterone. In both cases implantation occurred within the subsequent 24 hr. In contrast, delayed blastocysts maintained only with progesterone were markedly larger than normal but failed to demonstrate typical pre-implantation changes or to implant. Therefore it was concluded that changes necessary for and indicative of impending implantation are induced by the synergistic action of oestrone and progesterone on the blastocyst.

Blastocysts from non-delayed and delayed, oestrone-treated animals were consistently free of their zonae pellucidae at least 18 hr prior to implantation—6 hr after pre-implantation changes were initially noted. Progesterone, although it appeared to influence zonae-loss during the period of delayed nidation, was ineffective in accelerating and synchronizing the shedding process unless associated with oestrone.

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LESTER E. BARNES and ROLAND K. MEYER

Summary.

Intact, female Holtzman rats were treated daily with medroxyprogesterone acetate (map; Provera) in corn oil, beginning on the day of insemination. This caused delay of implantation in 14% (0·5 mg/day) to 100% (2·4 mg/day) of the animals tested. It is possible that map suppresses the synthesis or the release of luteinizing hormone (lh) from the pituitary gland and thus prevents the production of sufficient endogenous oestrogen to cause implantation.

Implantation was achieved in 'delayed' rats by simultaneous administration of 1 μg of oestrone with the dose of map they had been receiving. The viability of foetuses in such animals varied inversely with the dose of map the mothers had received.

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F. W. STRATMAN, N. L. FIRST and ROLAND K. MEYER

Summary.

Female piglets injected subcutaneously with 25 mg/day of testosterone propionate in 1 ml of oil on Days 1, 3, 5 and 7 postnatally, ovulated and formed corpora lutea, thus failing to prove that testosterone in the manner given affects ovulation and puberty.

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MUHAMMAD ARSLAN, RICHARD C. WOLF, ROLAND K. MEYER and M. R. N. PRASAD

Summary.

Twelve immature female monkeys were treated with varying amounts of pregnant mare's serum gonadotrophin (pmsg). Seven of these monkeys responded to pmsg treatment as shown by sex skin development, ovarian enlargement and withdrawal bleeding. These animals reached menarche between 23 and 26 months of age, almost 1 year earlier than untreated control monkeys. Five other animals did not show an initial response to pmsg treatment and attained puberty simultaneously with the untreated animals. It is suggested that increased production of oestrogen by the pmsg-stimulated ovaries may affect the hypothalamo-hypophysial axis in such a way that puberty is accelerated.