A study was done to test whether ovulatory follicles destined to form subfunctional corpora lutea differed from normal ovulatory follicles in steroidogenic function. Twenty-five ewes were treated with prostaglandin F2 alpha on d 11 of the estrous cycle, then unilaterally ovariectomized before (n = 13) or after (n = 12) the surge of luteinizing hormone (LH) at the induced estrus to collect "cont...

Gonadotrophin-releasing hormone agonists (GnRHa) are routinely used in IVF programmes to prevent an unwanted LH surge and consequent ovulation. Despite its widespread use in IVF, a convincing dose recommendation for GnRHa in IVF does not exist. In our opinion, the lowest possible dose of GnRHa should be used. Thus, we performed a prospective, randomized, double-blind, placebo-controlled study t...

The suprachiasmatic nucleus (SCN) controls the timing of the preovulatory luteinizing hormone (LH) surge in laboratory rodents. Barbiturate administration during a critical period on proestrus delays the surge and prolongs the estrous cycle 1 day. Because a nonphotic timing signal (zeitgeber) during the critical period that phase advances activity rhythms can also induce the latter effect, we h...

Neuropeptide Y (NPY) has been shown to potentiate the actions of LHRH during the generation of preovulatory LH surges. It is not yet known, however, if activation of a specific subtype of NPY receptors in the anterior pituitary gland is an obligatory event in the stimulation of spontaneous LH surges. A battery of NPY receptor agonists, as well as the specific NPY Y1 receptor antagonist BIBP3226...

A robust gonadotropin-releasing hormone (GnRH) surge is a prerequisite signal for the luteinizing hormone (LH) surge that triggers ovulation. In rodents, the GnRH surge is initiated by elevated estradiol and a diurnal switch in estrogen action from negative to positive feedback. The ability of constant estradiol treatment to induce daily LH surges was tested in adult mice that were ovariectomiz...

Two experiments were performed. The first experiment was done to study the effects of dietary energy source on plasma insulin concentration using five gilts in a Latin square design with two diets over two periods. The diets contained either 200 g/kg of cornstarch (Starch) or soybean oil (Fat) as energy sources. Results indicate that insulin response was greater in the Starch-fed than in the Fa...

BACKGROUND Current methods of hormonal emergency contraception (EC) are ineffective in preventing follicular rupture when administered in the advanced pre-ovulatory phase. This study was designed to determine the capacity of ulipristal acetate (UPA), a selective progesterone receptor modulator developed for EC, to block follicular rupture when administered with a follicle of >or=18 mm. METHOD...

The experiment was conducted on 14 postpartum mithun (Bos frontalis) cows to establish the preovulatory LH and FSH surge patterns during estrus in peripheral circulation. Blood samples from jugular vein were collected every 2 h until 72 h and on alternate days till day 22 (day 0 = day of estrus) following the day of estrus onset. Plasma progesterone (P4), LH and FSH levels were estimated. Plasm...

Concentrations of progesterone have been reported to influence GnRH-induced LH surges. At the beginning of many synchronization protocols, GnRH is used to synchronize follicular growth. Therefore, the objective of this study was to determine the effect of elevated concentrations of progesterone from a controlled internal drug-releasing device (CIDR) on the GnRH-induced LH surge and ovulatory re...

Ulipristal Acetate (UPA) One study has demonstrated that UPA can delay ovulation. In this study, 34 women were treated when the size of the leading follicle was at least 18 mm. Each woman contributed one cycle treated with placebo and another with UPA. Follicular rupture failed to occur within 5 days following UPA treatment in 20 (59%) subjects while normal ovulation was observed in all women w...