The dynamic interaction between steroids and gonadotropins in the XXXX ovulatory cycle.

@entity1 @entity172 @entity4396 @entity1420 @entity53 @entity134
The interrelationship between @entity134 hormone secretion and gonadotropin secretion during the @entity1 menstrual cycle is a set of complex interactions. The temporal relationship between @entity53 and @entity1420 secretion, the preovulatory surge of gonadotropins and the time of ovulation, has been studied extensively. The median time interval between the first rise of @entity53 , @entity1420 , LH and FSH, and ovulation has been estimated to be 82.5 hr, 7.8 hr, 32 hr and 21.1 hr, respectively. The median time interval between peak blood concentrations of @entity53 , LH and FSH, and the time of ovulation is estimated to be 24, 16.5 and 15.3 hr. There is considerable individual variation in the above mentioned estimates. The rising levels of blood @entity53 that are secreted by the maturing ovarian follicles appear to be the primary trigger for the surge of gonadotropins leading to ovulation. In the experimental animal, the @entity172 effect takes place at the level of the hypothalamus in the release of @entity4396 and at the level of the pituitary in increasing its sensitivity to @entity4396 . There appears to be a good correlation between the nuclear translocation of occupied @entity172 receptors in the hypothalamus and the pituitary and the manifestation of @entity172 effects. In the @entity1 , a rise in @entity1420 begins to take place after the first rise in LH has occurred. @entity1420 appears to have both a stimulatory and inhibitory effect on gonadotropin secretion in the experimental animal and the @entity1 . Thus it exerts a fine-tune modulatory influence of @entity172 effects which include enhancement of the @entity53 induced gonadotropin surge, and perhaps the initiation of the midcycle FSH surge in the @entity1 . The abrupt termination of the preovulatory gonadotropin surge is difficult to explain because the pituitary gland is not depleted of its gonadotropin content or its capacity to secrete gonadotropins. Preliminary results suggests that @entity1420 by exerting its inhibitory influence may be responsible for the termination of the gonadotropin surge. This hypothesis, however, needs careful confirmation. The effects of @entity1420 may be manifested at higher brain centers, the hypothalamus and the pituitary, and may involve not only the release of @entity4396 but also an alteration of the pulsatile pattern of release of @entity4396 . The recognition of these components, along with the presence and control of @entity4396 degrading enzymes in the hypothalamus and the pituitary, emphasize the complexity of the system and the need for further work to gain a better understanding of the steroidal regulation of gonadotropin secretion.
