Blood levels of nitric oxide and endothelin-1 during normal menstrual cycle

ABSTRACT

Nitric oxide [NO] is a free radical gas synthesized from L-arginine by a class of specific enzymes known as NO synthases, and inducible NO synthase isoforms. Nitric oxide synthase activity has been identified in the human uterus and has been thoroughly studied in pregnant women. All three NO synthase isoforms are thought to play an important role in the maintenance of uterine quiescence during gestation, and inducible NO synthase is involved in the induction of cervical ripening before labour. However, few studies have examined the role of NO in the normal menstrual cycle. Endonthelin-1 [ET-1] might play a role in endometrial bleeding and /or repair, as previously reported. In the present study, the serum levels of NO, estradiol [E2] and plasma levels of ET-1 were measured in menstrual follicular and luteal phases of the menstrual cycle to evaluate their role in menstrual cycle. This study included twenty unmarried females with regular menstrual cycles ranging from 27 to 30 days. The levels of serum E[2] and plasma ET-1 were measured by ELISA, and the serum NO were estimated by chemical method. Our results showed that serum levels of E[2] were significantly increased during luteal phase compared with menstrual and follicular phases, whereas plasma levels of ET-1 were significantly higher during menstrual phase compared with follicular and luteal phases of the menstrual cycle. Serum levels of NO did not show significant change during the three phases of the cycle. ET-1 levels were negatively correlated with E[2] while no significant correlation between ET-1 and NO and between NO and E[2]. It can be concluded that ET-1 may play an important role in menstruation and E2 inhibits secretion of ET-1. While NO shows no relation to ET-1 and E[2]