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Localization of preproenkephalin mRNA in rat heart: selective gene expression in left ventricular myocardium
J Weil1, T Eschenhagen, G Fleige
1Abteilung Allgemeine Pharmakologie, Universitäts-Krankenhaus Eppendorf, D-20246 Hamburg, Germany.
Abstract:
The enkephalins are derived from a common precursor protein known as preproenkephalin (ppENK). Enkephalins appear to be one of the endogenous ligands for the opiate receptors. In the rat the ventricular myocardium contains more ppENK mRNA than any other tissue. To gain further insight into the role of cardiac enkephalins, the regional and developmental distribution of ppENK mRNA was studied by Northern blotting and in situ hybridization. In the early postnatal period, ppENK mRNA is low in atrial and ventricular myocardium. With maturation, ppENK expression increases threefold in left and right ventricular tissue, but not in the atria or cardiac conductive system. Interestingly, ppENK mRNA levels are four times higher in the left than in the right chamber. Thus, to our knowledge, ppENK is the only gene exhibiting marked differences in expression between the adult right and left ventricle. Given the left-side preference of ppENK expression, the possibility is raised that the left ventricle is an endocrine organ that supplies the body with enkephalins.
Insights
Cardiac enkephalins, derived from preproenkephalin (ppENK), show increased expression in adult rat ventricles. Left ventricular ppENK mRNA levels are significantly higher, suggesting a potential endocrine role for the left ventricle.
Area of Science:
- Cardiovascular Biology
- Neuroendocrinology
- Molecular Biology
Background:
- Enkephalins are endogenous opioid ligands derived from preproenkephalin (ppENK).
- The ventricular myocardium in rats exhibits high levels of ppENK mRNA.
- The precise role and distribution of cardiac enkephalins remain under investigation.
Purpose of the Study:
- To investigate the regional and developmental distribution of ppENK mRNA in the rat heart.
- To understand the role of cardiac enkephalins in cardiac function and development.
- To identify potential differences in gene expression between cardiac chambers.
Main Methods:
- Northern blotting was employed to analyze ppENK mRNA expression.
- In situ hybridization was used to determine the spatial distribution of ppENK mRNA.
- Quantitative analysis of mRNA levels in different cardiac regions and developmental stages.
Main Results:
- ppENK mRNA levels are low in early postnatal atrial and ventricular myocardium.
- Expression of ppENK mRNA increases significantly in both left and right ventricular tissues during maturation.
- ppENK mRNA levels are approximately fourfold higher in the left ventricle compared to the right ventricle in adult rats.
- No significant changes in ppENK mRNA were observed in the atria or cardiac conductive system.
Conclusions:
- The left ventricle exhibits a unique and marked preference for ppENK gene expression compared to the right ventricle.
- The adult left ventricle may function as an endocrine organ, producing and releasing enkephalins into circulation.
- These findings highlight a novel aspect of left ventricular function and its potential role in systemic enkephalin supply.