Changes in Cellular Levels of Messenger Ribonucleic Acid Encoding Gonadotropin-releasing Hormone in the Anterior Hypothalamus of Female Rats During the Estrous Cycle

Cellular levels of messenger RNA encoding GnRH were measured using quantitative in situ hybridization in coronal sections through the area of the organum vasculosum of the lamina terminalis of female rats examined at various times of the 4-day estrous cycle. GnRH mRNA levels were high on the morning of diestrus day 1, but declined throughout the day of diestrus day 2 to a nadir on the morning of proestrus. Although GnRH message levels were lowest on the morning of proestrus, they rose nearly two-fold by 1900h that evening and remained high during the day of estrus. These data support the hypothesis that GnRH synthesis is coupled to GnRH release, and indicate that GnRH biosynthesis is not stimulated on the morning of proestrus in preparation for the ovulatory surge release of GnRH and LH in the afternoon.