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Chlorpropamide-ethanol induced met-enkephalin secretion in dogs: release mechanisms and biochemical characterisation
Abstract:
Circulating met-enkephalin-like immunoreactivity (MLI) rises in man after chlorpropamide and ethanol although the origin and molecular forms of circulating MLI are not well defined. We have studied the response to oral ethanol in conscious and anaesthetised dogs pretreated with chlorpropamide. In conscious dogs MLI rose from a basal level of 29 +/- 7 pg/ml to a peak of 55 +/- 14 pg/ml 10 min after ethanol (P less than 0.001). In anaesthetised animals, following ethanol, plasma MLI rose in caval (35 +/- 6 pg/ml to a peak of 70 +/- 10 pg/ml), in portal (28 +/- 6 pg/ml to 51 +/- 6 pg/ml) and in adrenal blood (897 +/- 316 pg/ml to 1483 +/- 298 pg/ml; P less than 0.001). Biogel P-4 chromatography of caval and portal basal plasma showed 87% of MLI measured coeluted with the synthetic pentapeptide, while chromatography of peak plasma showed that only 65% coeluted with the pentapeptide and the remaining 35% was of larger molecular size. Sephadex G75 chromatography of adrenal vein plasma revealed three peaks of MLI of differing molecular sizes (8 k = 69.7%; 3-5 k = 12.1% and the pentapeptide = 18.2%). Treatment of the column fractions with trypsin and carboxypeptidase B resulted in the generation of new MLI with peaks of approximate molecular sizes 31 k (10.4%), and 18 k (37.1%) in addition to 8 k (40.0%), 3-5 k (5.0%) and the pentapeptide (7.5%). Acetaldehyde involvement in MLI release was investigated. Following acetaldehyde infusion, plasma MLI rose both in caval (35 +/- 9 pg/ml to 86 +/- 8 pg/ml) and adrenal vein (417 +/- 121 pg/ml to 1768 +/- 433 pg/ml) bloods. Thus we have established an animal model which enables further study of the mechanisms of MLI release and characterisation of the molecular forms. The adrenal medulla, unlike the gut, may be an important source of circulating met-enkephalin and acetaldehyde formation an essential intrinsic component of chlorpropamide-ethanol induced met-enkephalin release.
Insights
Chlorpropamide and ethanol increase circulating met-enkephalin-like immunoreactivity (MLI) in humans. This study in dogs shows the adrenal medulla releases MLI, potentially mediated by acetaldehyde, and reveals larger molecular forms of MLI.
Area of Science:
- Neuroendocrinology
- Pharmacology
- Gastroenterology
Background:
- Circulating met-enkephalin-like immunoreactivity (MLI) levels increase in humans following chlorpropamide and ethanol administration.
- The precise origin and molecular forms of circulating MLI remain incompletely understood.
- Previous studies suggest a link between chlorpropamide, ethanol, and MLI release.
Purpose of the Study:
- To investigate the origin and molecular forms of circulating MLI in response to ethanol in a canine model.
- To explore the role of acetaldehyde in MLI release.
- To establish an animal model for further research into MLI regulation.
Main Methods:
- Oral ethanol administration to conscious and anesthetized dogs pretreated with chlorpropamide.
- Measurement of MLI in peripheral, portal, and adrenal venous blood.
- Biogel P-4 and Sephadex G75 chromatography to characterize MLI molecular forms.
- Enzymatic treatment (trypsin, carboxypeptidase B) of column fractions.
- Acetaldehyde infusion to assess its effect on MLI release.
Main Results:
- Ethanol significantly increased MLI in conscious dogs and in caval, portal, and adrenal blood of anesthetized dogs.
- Chromatography revealed that a significant portion of ethanol-induced MLI consisted of larger molecular forms, not just the synthetic pentapeptide.
- Adrenal vein plasma contained multiple MLI forms, with enzymatic treatment generating larger molecular weight species.
- Acetaldehyde infusion also elevated MLI in caval and adrenal venous blood.
Conclusions:
- The adrenal medulla is identified as a potential significant source of circulating met-enkephalin.
- Acetaldehyde formation appears to be a crucial factor in the release of met-enkephalin induced by chlorpropamide and ethanol.
- This study establishes a valuable animal model for dissecting the mechanisms of MLI release and characterizing its diverse molecular forms.