An inhibitory role of β-endorphin in central cardiovascular regulation

Abstract

The cardiovascular effects of β-endorphin after administration directly into the nucleus tractus solitarii (NTS) of urethane anaesthetised rats were investigated. Unilateral injection resulted in a dose related fall in mean arterial pressure and heart rate. No change in respiratory frequency was observed at any of the doses examined. The depressor response was prevented and the bradycardia reduced by pretreatment with locally applied naloxone (10 ng). This dose of the opiate antagonist had no effect on mean arterial pressure or heart rate when administered alone. Antiserum to β-endorphin (1:50 dilution) caused a rise in pressure and a tendency towards tachycardia on injection into the NTS, while it completely blocked the depressor response and bradycardia induced by β-endorphin. These results are consistent with the view that a β-endorphin-like peptide has a depressor role in the central nervous system. The hypotension may result from an effect within the central connections of the baroreceptor reflex arc, probably at the level of the NTS.