ENDOGENOUS BETA-ENDORPHINS IN HYPERTENSION - CORRELATION WITH 24-HOURAMBULATORY BLOOD-PRESSURE

Objectives. The aims of this study were to determine whether hypertens ive patients shelved increased endogenous opioid tone and to find a po ssible correlation between beta-endorphin levels and 24-h ambulatory b lood pressure. We also investigated whether circulating beta-endorphin levels were associated with pain perception at rest. Background. Expe rimental studies suggest an involvement of the endogenous opioid syste m in cardiovascular control mechanisms. Methods. We determined baselin e beta-endorphin plasma levels els by radioimmunoassay in 81 consecuti ve subjects (48 hypertensive, 33 normotensive) after a 30-min rest and before 24-h ambulatory blood pressure monitoring. In 72 of 81 subject s with a dental formula suitable for the pulpar test (graded increase of test current -0 to 0.03 mA applied to three healthy teeth), pain pe rception was also investigated. Results. Hypertensive patients showed higher beta endorphin plasma levels than normotensive subjects (p < 0. 002), Circulating endogenous opioid levels correlated with 24 h diasto lic blood pressure (p < 0.01), whereas the relation,vith systolic pres sure did not reach statistical significance, When 24-h blood pressure recordings were divided into daytime and nighttime values, and blood p ressure loads (percent of measurements greater than or equal to 140 mm Hg for systolic blood pressure and greater than or equal to 90 mm Hg for diastolic pressure) were calculated, a significant correlation was found between beta-endorphin levels and diastolic pressures and load. Similarly, presampling diastolic blood pressure was significantly cor related with beta-endorphin levels. Of the 72 subjects tested, hyperte nsive patients showed a lower pain sensitivity than normotensive subje cts. A positive correlation was found between pain threshold and circu lating beta-endorphin levels (p < 0.05). Conclusions. Sustained arteri al pressure is probably involved in the tonic activation of cardiovasc ular mechanisms linked to endogenous opioid tone. Circulating plasma e ndorphins may account, at least in part, for the pain perception patte rn relating to blood pressure levels at rest.