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Acute Pressor and Hormonal Effects of ß-Endorphin at High Doses in Healthy and Hypertensive Subjects: Role of Opioid Receptor Agonism

Cardiovascular Research Center, II University of Naples, 80131 Naples, Italy

Address all correspondence and requests for reprints to: Dr. Domenico Cozzolino, M.D., via Pansini, 5, 80131 Napoli, Italy. E-mail: cozzolino_domenico{at}libero.it.

Context: The opioid system is involved in blood pressure regulation in both normal humans and patients with essential hypertension.

Objective: The objective of the study was to investigate the effects of a high-dose infusion of ß-endorphin, an opioid peptide, on blood pressure and on the hormonal profile in healthy subjects and in hypertensive patients and the mediation played by opioid receptor agonism.

Design, Setting, and Participants: According to a randomized double-blind design, 11 healthy subjects (controls) and 12 hypertensive inpatients (mean age, 38.9 and 40.4 yr, respectively) received 1-h iv infusion of ß-endorphin (250 µg/h) and, on another occasion, the same infusion protocol preceded by the opioid antagonist naloxone (8 mg).

Main Outcome Measures: Hemodynamic and hormonal measurements were performed at established times during the infusion protocols.

Results: At baseline, circulating ß-endorphin, norepinephrine, and endothelin-1 in hypertensive patients were significantly (P < 0.05) higher than in controls. In controls, ß-endorphin reduced blood pressure (P < 0.01) and circulating norepinephrine (P < 0.02) and increased plasma atrial natriuretic factor (P < 0.003) and GH (P < 0.0001). In hypertensive patients, ß-endorphin decreased systemic vascular resistance (P < 0.0001), blood pressure (P < 0.0001), and plasma norepinephrine (P < 0.0001) and endothelin-1 (P < 0.0001) and raised circulating atrial natriuretic factor (P < 0.0001), GH (P < 0.0001), and IGF-I (P < 0.0001). These hemodynamic and hormonal responses to ß-endorphin in hypertensive patients were significantly (P < 0.0001) greater than in controls but were annulled in all individuals when naloxone preceded ß-endorphin infusion.

Conclusions: High doses of ß-endorphin induce hypotensive and beneficial hormonal effects in humans, which are enhanced in essential hypertension and are mediated by opioid receptors.

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