Is there a cholinergic circadian rhythm throughout the oestrous cycle related to ovulation in the rat?
Rats with a 4-day oestrous cycle were given a single dose of atropine (100, 300, 500 or 700 mg/kg body wt) at 13.00 h on the days of oestrus, dioestrus 1, dioestrus 2 or pro-oestrus and were autopsied on the next expected day of oestrus. The doses of atropine (in mg/kg body wt) necessary to block ovulation during the cycle were 300 at oestrus, 100 at dioestrus 1 or 2 and 700 at pro-oestrus. A single dose of atropine (100 mg/kg) at oestrus, dioestrus 1 or dioestrus 2 was given at 09.00, 13.00, 17.00 or 21.00 h, autopsy again being performed on the next expected day of oestrus. The ability of atropine to block ovulation appeared to have a circadian rhythm, with a maximum blockade at 13.00 h on dioestrus 1 and dioestrus 2 and a minimum at 21.00 h on the same days. Hormone replacement (human chorionic gonadotrophin at oestrus, dioestrus 1 or 2, oestradiol benzoate at dioestrus 2 or progesterone at pro-oestrus) re-established normal ovulation in rats whose ovulation was blocked with atropine (100 mg/kg) on dioestrus 1 at 13.00 h. When ovulation was blocked with atropine but no hormone replacement had been given, rats ovulated 24 h after the next expected day of oestrus. Results obtained in these experiments suggest the existence of a circadian rhythm of gonadotrophin secretion throughout the oestrous cycle and a close relationship between that rhythm and the cholinergic system.
D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D002940:Circadian Rhythm; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000494:pharmacology; D004971:Estrus / Q000187:drug effects; D005260:Female; D010060:Ovulation / Q000187:drug effects*; D011247:Pregnancy; D011374:Progesterone / Q000494:pharmacology; D051381:Rats; D013997:Time Factors; D014621:Vagina / Q000166:cytology
D006063:Chorionic Gonadotropin; D011374:Progesterone; D004958:Estradiol; D001285:Atropine