title: Dioestrous progesterone and pro-oestrous luteinizing hormone in 4- and 5-day cycles of female rats.
abstract: Female rats with showed 5-day ovarian cycles spontaneously, but 4-day cycles for periods of variable length after induction of pseudopregnancy, were examined. While the time of onset of the ovulatory LH surge at pro-oestrus was the same in both 4- and 5-day cycles, dioestrous progesterone concentrations were dissimilar. The most prominent feature was a sharp increase during the night of the first day of dioestrus of the 4-day cycle. The results are interpreted as suggesting that dioestrous steroid concentrations rather than pro-oestrous LH concentrations are important in establishing cycle duration.
mesh_terms: D000818:Animals; D004031:Diestrus; D004971:Estrus; D005260:Female; D007986:Luteinizing Hormone / Q000097:blood*; D009865:Oocytes / Q000166:cytology; D006080:Ovarian Follicle / Q000166:cytology; D010053:Ovary / Q000033:anatomy & histology; D011247:Pregnancy; D011359:Proestrus; D011374:Progesterone / Q000097:blood*; D011555:Pseudopregnancy; D051381:Rats; D013997:Time Factors; D014621:Vagina / Q000166:cytology
chemical_list: D011374:Progesterone; D007986:Luteinizing Hormone