Naloxone [0.4 mg iv.] increased blood pressure and heart rate of 13 clonidine-treated [0.3 mg per os for 3 days] patients with essential hypertension [reacting group] while it has no such effect in 11 clonidine-treated patients [non-reacting gr.] Clonidine increased plasma β-endorphin concentration of the reacting patients by 17.53 ± 1.68 pM/l and in the non-reacting ones by 5.91 ±0.88 pM/l. Significant linear correlation was found between the clonidine-induced increase in plasma β-endorphin level and the naloxone-induced change in mean blood pressure [r=0.9572,n:24, p<0.001]. In another group of 8 patients clonidine [0.15 mg iv.] decreased mean blood pressure but naloxone, 30 min after the clonidine injection, did not reverse the clonidine hypotension. We suggest that β-endorphin, released by chr.clonidine therapy, contributes to the antihypertensive effect only in the reacting group.
ASJC Scopus subject areas
- Endocrine and Autonomic Systems
- Cellular and Molecular Neuroscience