Effect of hypothyroidism on the NO/cGMP pathway of corpus cavernosum in rabbits.
BACKGROUND
The incidence of hormonal dysfunction as a cause of impotence remains controversial. However, several recent studies have reported evidence of hormonal abnormalities in 25-35% of impotent men. Hypothyroidism has been reported to occur in 6% of impotent men. There is some evidence suggesting that hypothyroidism may be a cause of impotence.


OBJECTIVE
We aimed to investigate the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway in hypothyroidism in an experimental rabbit model and compared hypothyroid rabbits with controls to evaluate the possible involvement of the NO/cGMP pathway.


METHODS
The study comprised 20 male New Zealand white rabbits. The rabbits were divided into two equal groups. The first group had hypothyroidism induced surgically by thyroidectomy for 6 weeks. The second group underwent a sham operation.


RESULTS
There was no significant change in the mean body weight of hypothyroid rabbits and controls. Triiodothyronine and thyroxine levels were significantly lower in hypothyroid rabbits. Plasma thyroid-stimulating hormone and prolactin levels were significantly higher in hypothyroid rabbits. Plasma total calcium and parathormone levels remained in the normal range in both groups.


METHODS
Papaverine-induced concentration-dependent relaxations were similar in both groups. Carbachol-induced relaxation responses decreased in hypothyroid rabbits. There were significant differences between control and hypothyroid rabbits in frequency-dependent relaxations induced by electrical-field stimulation (EFS). YC-1-induced relaxation responses did not change significantly in hypothyroid rabbits. Concentration-dependent relaxations induced by diethylamine (DEA)/NO were similar in both groups. Amrinone-induced relaxation responses did not change significantly in hypothyroid rabbits.


CONCLUSIONS
Reductions of relaxant responses to EFS and carbachol in hypothyroid rabbits can depend on the decrease of released or synthesized NO from nitrergic nerves and endothelium.
Kilicarslan
Hakan
H
Faculty of Medicine, Uludag University, Bursa, Turkey. Electronic address: hkilicarslan@uludag.edu.tr.
Bagcivan
Ihsan
I
Faculty of Medicine, Cumhuriyet University, Sivas, Turkey.
Yildirim
M Kemal
MK
Faculty of Medicine, Cumhuriyet University, Sivas, Turkey.
Sarac
Bulent
B
Faculty of Medicine, Cumhuriyet University, Sivas, Turkey.
Kaya
Tijen
T
Faculty of Medicine, Cumhuriyet University, Sivas, Turkey.
D000818:Animals; D002217:Carbachol / Q000008:administration & dosage; D006152:Cyclic GMP / Q000378:metabolism*; D004195:Disease Models, Animal; D004558:Electric Stimulation; D007037:Hypothyroidism / Q000150:complications* / Q000378:metabolism*; D018783:Impotence, Vasculogenic / Q000209:etiology* / Q000378:metabolism; D008297:Male; D009126:Muscle Relaxation / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism*; D009599:Nitroprusside / Q000008:administration & dosage; D010208:Papaverine / Q000008:administration & dosage; D010413:Penis / Q000378:metabolism*; D011817:Rabbits; D013965:Thyroidectomy; D014665:Vasodilator Agents / Q000008:administration & dosage
D014665:Vasodilator Agents; D009599:Nitroprusside; D009569:Nitric Oxide; D002217:Carbachol; D010208:Papaverine; D006152:Cyclic GMP