Impaired neurogenic and endothelium-dependent relaxant responses of corpuscavernosum smooth muscle from hyperthyroid rabbits

We investigated the effect of hyperthyroidism on the responsiveness of the rabbit corpus cavernosum smooth muscle. In male albino rabbits, hyperthyroi dism was established by oral feeding of L-thyroxine at increasing dosages ( 150-450 mug/kg) over an 8-week period. This treatment produced a stable hyp erthyroid state as indicated by the increased serum T-4 levels. The reactiv ity of corpus cavernosum tissue from hyperthyroid animals and euthyroid con trol animals was studied in organ chambers. Hyperthyroidism caused impaired neurogenic and endothelium-dependent relaxant responses with decreased E-m ax and pD(2) values. However, hyperthyroidism had no effect on both phenyle phrine- and KCl-induced contractile responses and sodium nitroprusside- and papaverine-induced endothelium-independent relaxant responses, and there w as no change in agonist potency. These data indicate that hyperthyroidism m ay impair both neurogenic and endothelium-dependent relaxation of corporal smooth muscle, and may contribute to the etiology of impotence. (C) 2001 El sevier Science B.V. All rights reserved.