Inhibitors of nitric oxide synthase influence oocyte maturation in rats.
OBJECTIVE
To examine the effect of inhibiting nitric oxide synthase (NOS) on the number of ovulated oocytes and on oocyte meiotic maturation.


METHODS
Female Sprague-Dawley rats (25 days old) were superovulated with a subcutaneous injection of 10 U pregnant mare's serum gonadotropin, followed 52 hours later by a subcutaneous injection of 10 U human chorionic gonadotropin (hCG). Three hours before and 3 hours after hCG injection, the rats were treated orally with the vehicle (0.5% methylcellulose) as the control or with either of two NOS inhibitors, N omega-nitro-L-arginine methyl ester (L-NAME) and L-N6-(1-iminoethyl)-lysine (L-NIL). The rats were killed 20 hours after hCG injection, and oocytes present in the oviduct were flushed, counted, and classified for stages of meiosis. In addition, ovarian oocytes (12 hours post-hCG) and ovulated oocytes were treated with an immunofluorescent stain for the presence of endothelial NOS (eNOS).


RESULTS
Strong positive staining for eNOS was observed in the cytoplasm of ovarian and ovulated oocytes. Control rats ovulated an average 43.0 +/- 4.1 oocytes each, which was lowered with either L-NAME or L-NIL (23.8 +/- 4.3 and 23.5 +/- 4.0 oocytes per rat, respectively; P < .002). We observed that significantly fewer ovulated oocytes obtained from rats treated with NOS inhibitors were at metaphase II (P < .006), the normal stage of meiosis for unfertilized oocytes, and a significantly greater percentage of oocytes displayed atypical morphology as compared with control oocytes (P < .0001).


CONCLUSIONS
Ovarian nitric oxide synthesis is required for maximal ovulation, and a lack of nitric oxide during the periovulatory period results in severe defects in oocyte maturation.
Jablonka-Shariff
A
A
Department of Obstetrics and Gynecology, Washington University, St. Louis, Missouri, USA.
Basuray
R
R
Olson
L M
LM
D000818:Animals; D002452:Cell Count; D006063:Chorionic Gonadotropin / Q000008:administration & dosage; D004727:Endothelium / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005187:Fallopian Tubes / Q000166:cytology; D005260:Female; D005455:Fluorescent Antibody Technique; D006064:Gonadotropins, Equine / Q000008:administration & dosage; D008239:Lysine / Q000031:analogs & derivatives / Q000494:pharmacology; D008540:Meiosis; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000032:analysis / Q000037:antagonists & inhibitors*; D009865:Oocytes / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D010053:Ovary / Q000166:cytology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013480:Superovulation
D006063:Chorionic Gonadotropin; D004791:Enzyme Inhibitors; D006064:Gonadotropins, Equine; C090663:N(6)-(1-iminoethyl)lysine; D019001:Nitric Oxide Synthase; D008239:Lysine; D019331:NG-Nitroarginine Methyl Ester