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Adenylate cyclase in lean and obese (ob/ob) mouse epididymal white adipocytes
Abstract:
The results presented in this study indicate that the defect in catecholamine-stimulated adenylate-cyclase which is characteristic of the ob/ob mouse is associated with a decrease in the sensitivity of the system to guanine nucleotides (guanosine 5'-[beta gamma-imido]triphosphate and guanosine 5'-triphosphate). No difference in the beta-adrenergic receptor activity was found between the lean and obese mice on the basis of their capacity to bind the beta-adrenergic antagonist [3H]dihydroalprenolol. The data suggest that a defect in the activation of the adenylate cyclase by beta-adrenergic agents may reside in the guanyl nucleotide binding site(s).
Insights
Obese mice show impaired adenylate cyclase activity due to reduced sensitivity to guanine nucleotides. Beta-adrenergic receptor binding remains unchanged, suggesting a defect in guanyl nucleotide binding sites.
Area of Science:
- Biochemistry
- Molecular Biology
- Physiology
Background:
- Obesity is linked to metabolic dysregulation.
- Catecholamine-stimulated adenylate cyclase activity is crucial for cellular energy balance.
- The ob/ob mouse model exhibits genetic obesity and associated metabolic alterations.
Purpose of the Study:
- To investigate the molecular mechanisms underlying adenylate cyclase dysfunction in ob/ob mice.
- To determine if beta-adrenergic receptor sensitivity is altered in obese mice.
- To identify potential defects in the guanine nucleotide regulatory pathway of adenylate cyclase.
Main Methods:
- Assessing catecholamine-stimulated adenylate cyclase activity in lean and obese mice.
- Measuring the binding affinity of beta-adrenergic antagonists ([3H]dihydroalprenolol) to receptors.
- Evaluating the response of adenylate cyclase to guanine nucleotides (GTPγS and GTP).
Main Results:
- Ob/ob mice displayed a significant decrease in catecholamine-stimulated adenylate cyclase activity.
- The obese mice showed reduced sensitivity of the adenylate cyclase system to guanine nucleotides.
- No significant differences in beta-adrenergic receptor binding capacity were observed between lean and obese mice.
Conclusions:
- The defect in obese mice is not at the beta-adrenergic receptor level.
- A defect in the guanyl nucleotide binding site(s) of adenylate cyclase is implicated.
- This suggests impaired signal transduction downstream of the beta-adrenergic receptor in obesity.