Variations of pre-prosomatostatin MRNA levels in the hypothalamic periventricular nucleus during the rat estrous cycle.

Cellular levels of pre-prosomatostatin (pre-proSS) mRNA were measured by quantitative in situ hybridization in sections through the hypothalamic periventricular nucleus in female rats examined at different times of the estrous cycle. Pre-proSS mRNA levels were lowest on the afternoon of diestrus. They increased progressively and were nearly twofold in the afternoon of the proestrus. They remained high during the day of the estrus and declined in metestrus. These data suggest that somatostatin synthesis in the periventricular nucleus is modulated by variations in the circulating levels of ovarian steroids in the female rat.