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Desensitization of beta 2-adrenergic receptors and adrenocorticotropin release
Abstract:
Pre-exposure of mouse anterior pituitary tumor cells (A+T-20/D16-16) to (-) isoproterenol reduces the ability of this beta-adrenergic agonist to restimulate cyclic AMP synthesis or adrenocorticotropin hormone (ACTH) release from these cells. This beta-adrenergic receptor desensitization is time and dose-dependent, recoverable and specific for beta-receptors. Longer pretreatment times are required to decrease beta-receptor density than to induce receptor desensitization. This initial beta-receptor refractoriness involves an uncoupling of the receptor from adenylate cyclase since (-) isoproterenol treatment does not alter forskolin-activated cyclic AMP formation or ACTH release. In addition to diminishing beta-receptor responsiveness, (-) isoproterenol treatment induces a prolonged elevation of basal ACTH release. This finding indicates that the intracellular events leading to ACTH secretion may also be altered during the desensitization process.
Insights
Pre-exposing mouse pituitary cells to (-) isoproterenol desensitizes beta-adrenergic receptors, impacting cyclic AMP and adrenocorticotropin hormone (ACTH) release.
Area of Science:
- Endocrinology
- Cell Biology
- Pharmacology
Background:
- Beta-adrenergic receptors regulate cyclic AMP (cAMP) synthesis and hormone release.
- Desensitization of these receptors is a key cellular response to prolonged agonist exposure.
Purpose of the Study:
- To investigate the mechanisms and consequences of beta-adrenergic receptor desensitization in mouse anterior pituitary tumor cells (A+T-20/D16-16).
- To determine the effects of (-) isoproterenol pre-exposure on cellular responsiveness and adrenocorticotropin hormone (ACTH) release.
Main Methods:
- Pre-exposure of A+T-20/D16-16 cells to varying doses and durations of (-) isoproterenol.
- Measurement of cyclic AMP synthesis and adrenocorticotropin hormone (ACTH) release.
- Assessment of beta-adrenergic receptor density and coupling to adenylate cyclase.
Main Results:
- (-) Isoproterenol pre-exposure desensitized beta-adrenergic receptors in a time- and dose-dependent manner.
- Initial desensitization involved uncoupling of the receptor from adenylate cyclase, without altering forskolin-stimulated cAMP or ACTH release.
- Prolonged exposure led to a decrease in beta-receptor density and an elevation in basal ACTH release.
Conclusions:
- Beta-adrenergic receptor desensitization in pituitary cells is a complex process involving receptor uncoupling and reduced density.
- The desensitization process affects not only cAMP synthesis but also intracellular pathways regulating ACTH secretion.
- These findings highlight the adaptive mechanisms of pituitary cells to adrenergic stimulation.