Dexamethasone partially protects the myometrium against beta-adrenergic agonist-induced desensitization in vivo in the rat.

OBJECTIVE

Our purpose was to determine the ability of dexamethasone to prevent the onset of myometrial desensitization to beta-adrenergic agonists in vivo.

STUDY

DESIGN

On day 5 post partum chronically catheterized rats were randomized to receive either dexamethasone or corn oil (vehicle), followed 12 hours later by a continuous infusion of either isoproterenol or saline solution (vehicle). Uterine contractions were monitored throughout. We measured myometrial glucocorticoid receptor levels in chronically catheterized and sham-operated rats and beta 2-adrenergic receptor densities in the experimental rats before and during the infusions.

RESULTS

Surgery did not lead to any decrease in glucocorticoid receptor number. Dexamethasone significantly increased the duration of myometrial responsiveness to isoproterenol compared with vehicle-pretreated rats, although agonist-induced down-regulation of beta-adrenergic receptor number was not prevented.

CONCLUSION

Dexamethasone partially protects the rat myometrium from desensitization induced by the continuous infusion of beta-adrenergic agonists through mechanisms independent of the beta 2-receptor.