Screening for opioids in dog heart.

Area of Science:

• Cardiovascular Physiology
• Neuroendocrinology
• Pharmacology

Background:

• Opioid peptides are present in the heart, but their precise role and distribution remain incompletely understood.
• Cardiac catecholamines are well-studied neurotransmitters involved in cardiovascular regulation.
• Investigating cardiac opioids alongside catecholamines provides insight into myocardial neurochemical signaling.

Purpose of the Study:

• To quantify total and specific opioid peptides in canine cardiac tissue.
• To determine the distribution of opioids and catecholamines within the canine heart.
• To evaluate the effects of anesthesia, hemorrhage, and ganglionic blockade on cardiac opioid and catecholamine levels.

Main Methods:

• Homogenization of canine heart tissue (atria, ventricles, septum) for acid extraction.
• Quantification of total opioids (radioreceptor assay) and specific peptides like methionine-enkephalin (radioimmunoassay).
• High-performance liquid chromatography (HPLC) with amperometric detection for catecholamine analysis.

Main Results:

• Opioids and epinephrine were uniformly distributed; norepinephrine concentrated in atria.
• Methionine-enkephalin constituted a small fraction (1-2%) of total cardiac opioids.
• Hemorrhage reduced methionine-enkephalin; ganglionic blockade increased total opioids and certain peptides/catecholamines, but not methionine-enkephalin.

Conclusions:

• Canine myocardium possesses significant opioid concentrations responsive to physiological and pharmacological stimuli.
• Cardiac opioid responses differ from catecholamine responses under similar experimental conditions.
• These findings suggest a distinct role for cardiac opioids in myocardial function.