Accumulated endogenous nitric oxide synthase inhibitors in inhibiting urethral relaxation following estrogen supplementation in ovariectomized rabbits.
OBJECTIVE
We investigated the possible role of the endogenous nitric oxide (NO) synthase (NOS) inhibitors N-monomethyl-L-arginine (L-NMMA) and asymmetrical N, N-dimethyl-L-arginine (ADMA) in inhibiting urethral relaxation following estrogen supplementation in ovariectomized rabbits.


METHODS
A total of 16 mature Japanese White female rabbits were divided into 2 groups. In the control group rabbits were sacrificed 2 weeks after bilateral ovariectomy. In the estrogen group estradiol was administered subcutaneously for 2 weeks with the aid of sustained release pellet from 2 weeks after ovariectomy until sacrifice. Isolated urethra was cut into transverse strips for functional study and processed to determine endogenous NOS inhibitors, NOS activity, dimethylarginine dimethylaminohydrolase (DDAH) activity as a metabolizing enzyme of endogenous NOS inhibitors and cyclic guanosine monophosphate production.


RESULTS
Electrical field stimulation produced NO mediated and neurogenic relaxation of the urethral strip in the presence of guanethidine and atropine under contraction with phenylephrine. Relaxation was significantly decreased in the estrogen group and accompanied by decreased cyclic guanosine monophosphate production. Sodium nitroprusside induced relaxation was not different between the 2 groups. The content of L-NMMA plus ADMA in the urethra was significantly increased in the estrogen group. Ca dependent NOS activity in the urethra remained unaffected. DDAH activity was significantly lower in the estrogen group.


CONCLUSIONS
Estrogen supplementation leads to decreased NO mediated and neurogenic urethral relaxation through the accumulation of L-NMMA and ADMA in the urethra. The accumulation of NOS inhibitors is possibly brought about by impaired DDAH activity.
Okuno
Tetsuo
T
Department of Urology and Reproductive Medicine, Institute of Biomaterials and Bioengineering, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.
Masuda
Hitoshi
H
Tsujii
Toshihiko
T
Kihara
Kazunori
K
Yamauchi
Yukinao
Y
Azuma
Hiroshi
H
D000581:Amidohydrolases / Q000378:metabolism; D000818:Animals; D001835:Body Weight; D006152:Cyclic GMP / Q000032:analysis; D003692:Delayed-Action Preparations; D004558:Electric Stimulation; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D009929:Organ Size; D010052:Ovariectomy; D011817:Rabbits; D011863:Radioimmunoassay; D040521:Subcutaneous Tissue; D014521:Urethra / Q000187:drug effects* / Q000201:enzymology; D019323:omega-N-Methylarginine / Q000502:physiology*
D003692:Delayed-Action Preparations; D019323:omega-N-Methylarginine; D004958:Estradiol; D019001:Nitric Oxide Synthase; D000581:Amidohydrolases; C059999:dimethylargininase; D006152:Cyclic GMP