LH regulates ovarian function, promoting the maturation and ovulation of follicles. It remains unknown whether post-pubertal refinements in hypothalamic control of LH release enhance reproductive capacity in females. To address this, we monitored pulsatile LH release in female C57BL/6J mice over the estrous cycle, defining pulse patterning and the amount of LH released between the first detectable ovulatory cycle (5 weeks old) and an established adult cycle (10 weeks old) [1]. The timing of onset of the first ovulatory cycle was defined by vaginal opening, and the estrous cycle was monitored through assessment of vaginal cytology. Ovarian histology was monitored relative to estrous cycle in young (5 weeks) and mature (10 weeks) mice.
We observed a significant rise in pulse number and approximate entropy (a measure of irregularity) of LH pulsatile profile from estrus to diestrus. This coincided with a gradual rise in basal, total and pulsatile LH release. LH pulse dynamics between the first (5 weeks) and adult (10 weeks) ovulatory cycles were highly conserved and differed only by a rise in pulse number and LH pulse irregularity at diestrus. While slightly advanced, the magnitude of the first preovulatory surge was similar to that of the adult preovulatory surge. Ovarian histology demonstrates a marked rise in the number of secondary, early antral and preovulatory follicles during metestrus, diestrus and proestrus in mature adult mice. Growing and regressing corpora lutea were observed only in adult female mice. Ongoing studies are assessing functional implications of altered LH release during matured diestrus, and the potential for altered LH release to modulate enhanced reproductive capacity, and, in particular, ovarian function.
This work was supported by the University of Queensland. Y. Wan receives a postgraduate scholarship from the University of Queensland.