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

Abstract

We investigated the effect of hyperthyroidism on the responsiveness of the rabbit corpus cavernosum smooth muscle. In male albino rabbits, hyperthyroidism was established by oral feeding of l-thyroxine at increasing dosages (150–450 μg/kg) over an 8-week period. This treatment produced a stable hyperthyroid state as indicated by the increased serum T 4 levels. The reactivity of corpus cavernosum tissue from hyperthyroid animals and euthyroid control animals was studied in organ chambers. Hyperthyroidism caused impaired neurogenic and endothelium-dependent relaxant responses with decreased E max and p D 2 values. However, hyperthyroidism had no effect on both phenylephrine- and KCl-induced contractile responses and sodium nitroprusside- and papaverine-induced endothelium-independent relaxant responses, and there was no change in agonist potency. These data indicate that hyperthyroidism may impair both neurogenic and endothelium-dependent relaxation of corporal smooth muscle, and may contribute to the etiology of impotence.