Attenuation of aortic baroreflex responses by microinjections of endomorphin-2 into the rostral ventrolateral medullary pressor area of the rat

American Journal of Physiology. Regulatory, Integrative and Comparative Physiology
Ken Kasamatsu, Hreday N Sapru

Abstract

The presence of mu-opioid receptors and endomorphins has been demonstrated in the general area encompassing the rostral ventrolateral medullary pressor area (RVLM). This investigation was carried out to test the hypothesis that endomorphins in the RVLM may have a modulatory role in regulating cardiovascular function. Blood pressure and heart rate (HR) were recorded in urethane-anesthetized male Wistar rats. Unilateral microinjections of endomorphin-2 (0.0125-0.5 mmol/l) into the RVLM elicited decreases in mean arterial pressure (16-30 mmHg) and HR (12-36 beats/min), which lasted for 2-4 min. Bradycardia was not vagally mediated. The effects of endomorphin-2 were mediated via mu-opioid receptors because prior microinjections of naloxonazine (1 mmol/l) abolished these responses; the blocking effect of naloxonazine lasted for 15-20 min. Unilateral stimulations of aortic nerve for 30 s (at frequencies of 5, 10, and 25 pulses/s; each pulse 0.5 V and 1-ms duration) elicited depressor and bradycardic responses. These responses were significantly attenuated by microinjections of endomorphin-2 (0.2 and 0.4 mmol/l). The inhibitory effect of endomorphin-2 on baroreflex responses was prevented by prior microinjections of naloxonazine. Micr...Continue Reading

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Related Concepts

Naloxonazine
Ascending Aorta Structure
Diastolic Blood Pressure
Dose-Response Relationship, Drug
Electric Stimulation Technique
Pulse Rate
Medulla Oblongata
Microinjections
Naloxone, (5 beta,9 alpha,13 alpha,14 alpha)-Isomer
Oligopeptides

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