possible role of nitric oxide [NO] in ovarian steroidogenesis, ovulation and implantation in the rat

ABSTRACT

Evaluation of the effects of nitric oxide [NO] on the ovarian functions including ovulation and steriodogensis [serum 17-beta estradiol and progesterone concentrations] and to verify if nitric oxide is an essential mediator in embryonic implantation in the rat. Fifty female albino rats devided into 2 major groups, group [1] and group [2] group [I] consisted of thirty prepubertal female rats injected with 5IU pregnant mare's serum gonadotropin [PMSG] intraperitoneal [I.P.], followed after 48h by I.P. injection of 5IU human chorionic gonadotropin [hCG], this group was further subdivided into 3 subgroups each of ten rats Group IA saline treated group served as control, group IB [L-NAME treated group], group IC [L-NAME + sodium nitroprusside [SNP] treated group] both groups injected I.P. in a single dose. Twenty four hour later, blood samples were collected to measure levels of serum total nitrite, progesterone and 17 beta estradiol concentration then both ovaries removed and weighted, the ratio of ovarian weight / total body weight was obtained, number of ovarian and graafian follicles rupture sites were assessed as well. Group II consists of 20 mature pregnant rats divided into 2 sub groups [IIA, IIB] on the third day of pregnancy both uterine horns were exposed and [L-NAME] was injected [Group IIA] and [L-NAME+SNP] in the second [group IIB] into one of the uterine horns, animals allowed to recover on the eighth day of pregnancy, gravid uteri were dissected out and inspected for implantation sites. In group I [hCG] administration after [PMSG] in prepubertal rats produce superovulation. Injection of [L-NAME] [I.P.] after [PMSG] and [hCG] administration, showed a significant reduction in serum total nitrite concentration, serum progesterone and estradiol were elevated, also there was a decrease in ovarian and graafian follicles rupture sites. Ovarian weight was decreased although body weight was not changed indicating the specific effect of NO on ovarian tissue. NO generator [SNP], reverse the inhibitory action of L-NAME on the serum total nitrite levels, ovulatory process and the stimulatory action on steriodogensis as no significant difference was detected in ovarian and graafian follicles rupture sites, ovarian weight, serum progesterone and estradiol concentration compared to control group. In group II administration of L-NAME on the third day of pregnancy significantly reduced the implantation sites. Coadministration of [SNP] with [L-NAME] showed that SNP reversed the anti-implantation effect of L-NAME. [1] Nitric oxide plays an important role in the regulation of steriodogensis and ovulation. This is evident as after injection of [NOS] inhibitor [L-NAME] there was reduction in the number of both ovarian and graafian follicles rupture sites. Also decrease in ovarian weight and ovarian/body weight ratio was observed. Level of serum 17 beta estradiol and progesterone were elevated, the reversal of these effects by coadministration of a [NO] donor SNP plus L-NAME was present. [2] Nitric oxide is involved in embryonic implantation as inhibition of NOS by L-NAME led to and implantation failure where as co-treatment with [SNP] abolished this inhibitory effect