Answer to Question #102767 in Human Anatomy and Physiology for Nibedita Rudra

Question

Describe the estrous cycle of rat.

Answer 1

Rats have a short cycle with a duration of 4-5 days, demonstrating spontaneous ovulation. However, rat females develop a typical corpus luteum if the coital stimulation is present. Pregnancy is associated with fertile mating, whereas infertile mating causes a pseudopregnancy. The development of several follicles is activated at the end of proestrus. The rate of their growth is similar until the next estrus associated with the rapid activation of the growth and ovulation of the follicle that is observed approximately 4.5 days after the beginning of follicle growth.

The events of the cycle depend on circadian rhythm. In particular, a maximum concentration of estrogen is observed on the day of proestrus (commonly first half of a day). Following the gradual decrease in estrogen level, the concentration of progesterone, LH and FSH rapidly increase causing the ovulation that occurs at 4 AM the next day. During the following day, the corpora lutea grow extensively achieving maximum size within the next 24 hours. These structures halve before the next metestrus and shrink before the following estrus.