title: Identification of the enzymic control point in 'de-differentiation' of oestrogen synthesis in superovulated rat ovary.
abstract: The superovulated rat model was used to investigate the enzymic focus for the decrease in oestrogen synthesis which occurs in ovary at the time of ovulation. Radioimmunoassays of progesterone, 17 alpha-hydroxyprogesterone, androstenedione, testosterone and 17 beta-oestradiol were used to measure the steroid concentrations in plasma for 6 days after the initiation of follicular development with pregnant mare's gonadotropin, and the long-term and acute effects of choriogonadotropin on these circulatory concentrations. The results showed that the cross-over point following the mid-cycle administration of gonadotropin was between 17 alpha-hydroxyprogesterone and androstenedione, and suggested that choriogonadotropin affected the 17 alpha-hydroxyprogesterone 17:20 lyase. In vitro assay of this microsomal enzyme confirmed that choriogonadotropin given in vivo at intervals before death caused 50% reduction in 17:20 lyase activity in 4 h and 93% reduction in 6 h. It was concluded that the synthesis of oestrogens declined following ovulation because the substrate (testosterone) was not available in sufficient concentration for the aromatase enzymes to use it.
mesh_terms: D000446:Aldehyde-Lyases / Q000378:metabolism; D000728:Androgens / Q000096:biosynthesis; D000818:Animals; D002784:Cholesterol / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004958:Estradiol / Q000096:biosynthesis*; D005260:Female; D006064:Gonadotropins, Equine / Q000494:pharmacology; D010053:Ovary / Q000187:drug effects / Q000502:physiology*; D010060:Ovulation; D011374:Progesterone / Q000096:biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D013254:Steroid 17-alpha-Hydroxylase; D013480:Superovulation
chemical_list: D000728:Androgens; D006064:Gonadotropins, Equine; D011374:Progesterone; D004958:Estradiol; D004247:DNA; D002784:Cholesterol; D013254:Steroid 17-alpha-Hydroxylase; D000446:Aldehyde-Lyases