Changes in concentration of serum LH and FSH associated with estrogen-advanced ovulation in 4-day cyclic rats

Changes in concentration of serum luteinizing hormone (LH) and follicle stimulating hormone (FSH) associated with estrogen-advanced ovulation in 4-day cyclic rats were determined. 50 mcg of estradiol benzoate was administered sc on the 1st day of diestrus and LH and FSH were determined by radioimmunoassay 24, 29, and 47 hours postinjection. 48 hours postinjection, ovulation was determined by the presence of ova in the oviduct. Estradiol benzoate caused a significant (p less than .01) increase in serum LH after 24 and 29 hours and a drastic decrease after 47 hours postinjection. FSH increased (p less than .05) after 29 hours postinjection. These results suggest that an ovulatory gonadotropin surge occurs 24 hours ahead of schedule in estradiol-benzoate-treated rats.     

Olfactory environment and coitus-induced ovulation and/or luteinization in the cyclic female rat

The role of pheromones in the process of ovulation and/or luteinization induced by coitus was studied in female rats primed with estradiol benzoate (EB) and early mated during 4-day cycles. The effects of coitus were evaluated by using 1) the proportion of females displaying postovulatory corpora lutea (POCL) and/or luteinized unruptured follicles (LUF), and 2) the ovulation coefficient (OC) computed in each female by dividing the number of POCL by the total number of POCL and LUF. A greater proportion of females displayed ovulation and/or luteinization following coitus than those given EB only. This proportion was slightly but significantly increased when females were exposed to bedding soiled with 5 ml of male urine prior to mating, an effect prevented by complete olfactory bulbectomy. However, in the females given EB only, the pheromonal stimulus remained inefficient. Weak ovulatory effects of coitus, as assessed by low OC values, were noted whether the females were exposed or not to male urine. An increase in the frequency of lordosis occurred after olfactory bulbectomy, but no significant changes in OC values were observed in this experimental group. It was concluded that pheromones, act as a primer on the neuroendocrine mechanisms governing ovulation in the cyclic female rat, as in other species of rodents.     

Induction of ovulation and cyclic activity in anestrous ewes with testosterone treated wethers and ewes

An experiment was conducted to evaluate the effectiveness of wethers and ewes treated with testosterone preparations to induce ovulation and breeding activity in anestrous ewes. The testosterone was administered three times at weekly intervals. Wethers and ewes treated with 105 mg testosterone propionate and wethers treated with 100 mg testosterone from testosterone cyclopentyl propionate were as successful as vasectomised rams in inducing ovulation and cyclic activity in ewes. Seven days after the last injection the concentrations of testosterone in peripheral bloods were not significantly different from that in the vasectomised rams. By day 28 the concentrations were significantly lower than in the rams. The testosterone preparations tested are suitable for the induction of male sexual behavior and are rapidly excreted by sheep.     

New data on serotoninergic mechanisms in ovulation in the cyclic female rat]

Injection of parachlorophenylalanine on dioestrus II at 18:00 was shown to decrease ovulation frequency in 4-day cyclic female rats. This effect was overcome by either HTP, or oestradiol benzoate, when administered on dioestrus II, at 18:00 and 10:00 - 11:00 respectively. No antiovulatory action of PCPA was observed on prooestrus at 13:00. These results provide support to the specificity of action of serotonin in the control of ovulation in the cyclic rat. They also suggest an interaction of serotonin and oestrogens in this control.     

Rapid modulation of rat hepatocyte HMG-CoA reductase activity by cyclic AMP or cyclic GMP

Rat hepatocytes were used to demonstrate rapid, transient effects on the modulation state (defined as the fraction of the enzyme present in the catalytically active form) of 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase, E.C. 1.1.1.34). Insulin elevated, while glucagon, cAMP or cGMP lowered HMG-CoA reductase modulation state within 10 to 15 min. These changes were accompanied by a parallel change in sterol synthesis. Total HMG-CoA reductase activity was not altered. Rapid modulation of HMG-CoA reductase activity therefore constitutes a viable in vivo control mechanism. By contrast to the hormones and second messengers, mevalonolactone lowered both HMG-CoA reductase modulation state and total reductase quantity.     

Demonstration of a critical period of ovarian activity in the control of early receptivity induced by estrogen in the female rat with 4-day cycles]

A significant decrease in early receptivity during the night from dioestrus II to prooestrus was observed in estrogen-treated 4-day cyclic rats following bilateral ovariectomy on dioestrus II at 4-5 p.m. Early receptivity appeared then to be dependent on the presence of ovary at this stage of the cycle. The mechanism whereby the adrenals may compensate for the ovaries when removed on dioestrus I, at 10-11 a. m. (Roos et al. 1973), was not observed in the present experimental conditions.     

Vaginal smear cycle in 4-day cyclic Chinese hamsters, Cricetulus griseus]

The contents of vaginal smear of 4-day cyclic Chinese hamster (Cricetulus griseus) was investigated every 3 hours for 5 days. A light-dark cycle of 14--10 hr was used with the lights turned on at 6 : 00 a.m. Estrous cycle of the Chinese hamster determined by vaginal smears can be divided into 6 periods. The proestrous phase started at about 0 : 00 of day 1, the day of the proestrous phase was designated as day 1 of the estrous cycle. In the afternoon of the same day 1, nucleated epithelial cells gradually increased in number (proestrus : I), and the vaginal contents became to consist solely of nucleated epithelial cells at about 18 : 00 to 21 : 00 (estrus : II). At about 0 : 00 of day 2, however, nucleated epithelial cells were superseded suddenly by cornified epithelial cells, and this phase lasted for 9 to 12 hr (metestrus I : III). Towards the end of the cornified stage, nucleated cells appeared in short duration (metestrus II : IV). And then, in the evening of day 2, leucocytes gradually increased in number with degeneration of nucleated cells (diestrus I : V-1). On day 3, vaginal smear contained a large amount of mucus as well as degenerated nucleated cells and leucocytes (diestrus II : V-2). At about 21 : 000 of day 4, some cornified epithelial cells were seen and then proestrous stage was returned. The females were mated with 3 to 5 males in the evening of day 1, copulation was confirmed in 83.7% females in the next morning,thus the copulation in the Chinese hamster may be thought to occur during the vaginal smear stage of nucleated epithelial cells (estrous phase), i.e. about 18 : 00 to 24 : 00 of day 1.     

Time course of the luteolytic action of LH in 4-day estrous cyclic rats

In 4-day estrous cyclic rats the neutralization of postovulatory biological activity of LH (by means of a single 0.5 ml sc injection of an anti-LH serum) (LHAS) at any time between 12.00 h on estrus and 12.00 h on metestrus prolongs the estrous cycle corpus luteum (CL) progesterone secretion for almost 24 hours. Injection of LHAS later on during the estrous cycle has no effect on CL progesterone secretion. It is concluded that postovulatory LH secreted up to time of CL maximum capacity to produce progesterone (metestrus afternoon) accelerates the intrinsic luteolytic mechanism, and that once the intrinsic luteolytic process has been switched on (shortly after noon of metestrus), it will lead to the CL functional demise regardless of the luteolytic action of LH.