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Negative feedback regulation of the content of proenkephalin mRNA in chromaffin cell cultures
J R Naranjo1, B C Wise, B Mellstrom
1Fidia-Georgetown Institute for the Neurosciences, Georgetown University Medical School, Washington, DC 20007.
Abstract:
The content of proenkephalin messenger RNA (PEmRNA) in cultured bovine adrenal chromaffin cells was reduced in the presence of reserpine (1 nM to 0.1 microM) with a return to basal levels 3 days after removal of the drug. In these cells, the basal release of Met5-enkephalin-Arg6-Phe7 immunoreactivity (MERF-IR) into the medium was significantly decreased when the cultures were pretreated with 0.2 microM reserpine for 3 days. The addition of 0.1 microM etorphine for 3 days also decreased the basal release of MERF-IR without depleting stores of catecholamines. Neither drug modified the total (cells + medium) amount of MERF-IR. In contrast, reserpine was without effect on levels of PEmRNA or release of Met5-enkephalin immunoreactivity (ME-IR) in primary cultures of the striatum of the fetal rat. The present data establish a correlation between inhibition of the secretion of enkephalin and reduced accumulation of its specific mRNA, suggesting a negative feedback inhibition by low molecular weight enkephalins.
Insights
Reserpine and etorphine reduce enkephalin release in bovine adrenal cells by decreasing proenkephalin mRNA (PEmRNA) levels. This suggests enkephalins may inhibit their own secretion through negative feedback.
Area of Science:
- Neuroendocrinology
- Molecular Biology
- Cell Biology
Background:
- Opioid peptides, such as enkephalins, play crucial roles in regulating physiological processes.
- Understanding the regulation of enkephalin synthesis and release is vital for neuroscience research.
- Bovine adrenal chromaffin cells are a model system for studying peptide hormone regulation.
Purpose of the Study:
- To investigate the effect of reserpine and etorphine on proenkephalin messenger RNA (PEmRNA) and Met5-enkephalin-Arg6-Phe7 immunoreactivity (MERF-IR) release.
- To explore the potential for negative feedback mechanisms in enkephalin secretion.
- To compare the effects of reserpine on enkephalin regulation in different cell types.
Main Methods:
- Primary cultures of bovine adrenal chromaffin cells and fetal rat striatum were used.
- Cells were treated with varying concentrations of reserpine and etorphine.
- PEmRNA levels and MERF-IR release into the medium were quantified.
- Catecholamine stores were assessed.
Main Results:
- Reserpine significantly decreased PEmRNA content and MERF-IR release in bovine adrenal cells.
- Etorphine also reduced MERF-IR release without affecting catecholamine stores.
- Neither drug altered the total MERF-IR content (cells + medium).
- Reserpine had no effect on PEmRNA or Met5-enkephalin immunoreactivity (ME-IR) release in rat striatal cultures.
Conclusions:
- A correlation exists between reduced enkephalin secretion and decreased PEmRNA accumulation.
- Low molecular weight enkephalins may exert negative feedback on their own release.
- Cell-specific regulation of enkephalin synthesis and secretion is suggested by differential responses in bovine and rat cells.