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The development of tolerance to antilipolytic agents by isolated rat adipocytes
Abstract:
Using an isolated rat epididymal adipocyte system we have studied the development of tolerance to and cross-tolerance between nicotinic acid, 5-methylpyrazole-3-carboxylic acid and pyridyl-3-tetrazole. Preincubating isolated adipocytes with any one of these compounds results in a reduction of the antilipolytic activity of that compound when the cells are exposed to a subsequent challenge dose. Furthermore, preincubation with nicotinic acid, 5-methylpyrazole-3-carboxylic acid or pyridyl-3-tetrazole results in a reduction of the antilipolytic response to challenge with either of the other two compounds. Preincubation of isolated adipocytes with nicotinic acid does not affect the subsequent antilipolytic activity of the PGE2 analogue, sulprostone. Preincubation with sulprostone does not lead to the development of tolerance to its own antilipolytic actions. The results obtained from these studies suggest that nicotinic acid, 5-methylpyrazole-3-carboxylic acid and pyridyl-3-tetrazole exert their antilipolytic activity via a common biochemical pathway which is distinct from that mediating the antilipolytic activity of prostaglandins. These findings also indicate that the development of tolerance occurs prior to the involvement of adenylate cyclase in lipolysis.
Insights
This study shows that nicotinic acid, 5-methylpyrazole-3-carboxylic acid, and pyridyl-3-tetrazole develop tolerance and cross-tolerance in rat adipocytes. Their antilipolytic effects share a common pathway distinct from prostaglandins.
Area of Science:
- Biochemistry
- Pharmacology
- Cell Biology
Background:
- Lipolysis regulation is crucial for metabolic homeostasis.
- Nicotinic acid and related compounds are known antilipolytic agents.
- Understanding drug tolerance mechanisms is vital for therapeutic development.
Purpose of the Study:
- To investigate the development of tolerance and cross-tolerance to nicotinic acid, 5-methylpyrazole-3-carboxylic acid, and pyridyl-3-tetrazole in isolated rat adipocytes.
- To elucidate the biochemical pathway(s) involved in the antilipolytic action of these compounds.
- To determine the stage at which tolerance develops in relation to adenylate cyclase activity.
Main Methods:
- Isolated rat epididymal adipocyte system.
- Preincubation with test compounds (nicotinic acid, 5-methylpyrazole-3-carboxylic acid, pyridyl-3-tetrazole, sulprostone).
- Challenge dose administration to assess antilipolytic activity and tolerance development.
Main Results:
- Preincubation with nicotinic acid, 5-methylpyrazole-3-carboxylic acid, or pyridyl-3-tetrazole led to reduced antilipolytic activity upon subsequent challenge.
- Cross-tolerance was observed between nicotinic acid, 5-methylpyrazole-3-carboxylic acid, and pyridyl-3-tetrazole.
- No tolerance or cross-tolerance was observed with the prostaglandin E2 analogue, sulprostone, indicating a distinct pathway.
Conclusions:
- Nicotinic acid, 5-methylpyrazole-3-carboxylic acid, and pyridyl-3-tetrazole share a common antilipolytic mechanism distinct from prostaglandins.
- Tolerance development to these compounds precedes the involvement of adenylate cyclase in lipolysis.
- These findings provide insights into the molecular mechanisms of antilipolytic drug action and tolerance.