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Dexamethasone partially protects the myometrium against beta-adrenergic agonist-induced desensitization in vivo in
Z Herman-Gnjidic1, N J MacLusky, S J Lye
1Division of Perinatology, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
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.