[Effect of enkephalins on central processes regulating hemodynamics]

Area of Science:

• Neuroscience
• Cardiovascular Physiology
• Pharmacology

Background:

• Enkephalins are endogenous opioid peptides involved in various physiological processes.
• Opioid receptors are present in the central nervous system and play a role in cardiovascular control.
• The precise role of enkephalins in regulating arterial pressure and heart rate via central mechanisms requires further elucidation.

Purpose of the Study:

• To investigate the cardiovascular effects of intracisternal administration of leu-enkephalin and met-enkephalin in unanesthetized cats.
• To determine the involvement of opioid receptors in these cardiovascular responses using naloxone.
• To explore the influence of enkephalins on baroreceptor reflex sensitivity and hypothalamic stimulation-evoked pressor responses.

Main Methods:

• Intracisternal administration of leu-enkephalin and met-enkephalin (100 µg) to unanesthetized cats.
• Intracerebroventricular administration of naloxone (50-100 µg) to block opioid receptors.
• Monitoring of arterial pressure and heart rate.
• Assessment of baroreceptor reflex sensitivity and pressor responses to hypothalamic stimulation.

Main Results:

• Intracisternal leu- and met-enkephalins induced transient hypertension and tachycardia, followed by hypotension and bradycardia.
• Naloxone administration into the 4th ventricle prevented these cardiovascular alterations.
• Leu-enkephalin significantly inhibited baroreceptor reflex sensitivity and enhanced hypothalamic stimulation-evoked pressor responses.
• Met-enkephalin showed weaker effects on the baroreceptor reflex and no significant impact on hypothalamic stimulation responses.

Conclusions:

• Central administration of enkephalins significantly impacts cardiovascular regulation in cats.
• Opioid receptors in the central nervous system mediate these enkephalin-induced cardiovascular effects.
• Enkephalins, particularly leu-enkephalin, modulate autonomic cardiovascular reflexes and central pressor pathways.