Effect of intravenous infusion of a beta-adrenergic blocking agent on the haemodynamic changes in human masseter muscle induced by cold-pressor stimulation

Eight healthy non-smoking males (mean age: 24.1 +/- 1.1 years) without any history of chronic muscle pain and migraine participated in this study. Hae moglobin (Hb) and oxygen (O-2) saturation in the right masseter muscle were continuously recorded with a non-invasive near-infrared spectroscopic devi ce. Heart rate and blood pressure were also recorded. The experiment had th ree phases: a placebo drug (physiological saline) with cold-presser trial, a 30-sec maximal voluntary clenching (MVC) trial, and a propranolol with co ld-presser trial. The saline and drug trials each involved continuous recor ding for 1 min before, 2 min during and 5 min after the cold-presser stimul ation (4 degrees C). Physiological saline (20 ml) or propranolol hydrochlor ide (20 ml) were infused at the rate of 2 ml/min. This infusion was begun 2 0 min before the baseline recording and participants did not know which sol ution (saline or propranolol) was being infused. For the MVC trial, each pa rticipant was asked to perform a 30-sec clench of their jaw-closing muscles . There was a rest period of 15 min between each trial. The individual Hb a nd O-2 data were normalized so that the baseline at the beginning of the ex periment was equal to zero, and the Hb and O-2 data were normalized as a pe rcentage of the individual's own highest absolute Hb and O-2 after and duri ng the MVC, respectively. The results showed that the mean baseline Hb 1 mi n before cold-presser stimulation was significantly lower in the beta-block er trial than in the placebo trial (p = 0.035). The mean change in Hb from baseline during cold-presser stimulation in the beta-blocker trial was also significantly less than in the placebo trial (p = 0.035). The mean Hb rebo und change after the cold-presser stimulation in the beta-blocker trial was significantly higher than in the placebo trial, and no significant heart-r ate differences were observed in the period after cold-presser stimulation. Overall, the mean heart rate before and during that stimulation was signif icantly lower in the beta-blocker trial than the placebo trial (p < 0.001). There was no significant mean blood-pressure difference between placebo an d beta-blocker trials at any time. These results suggest that beta-adrenoce ptor blocking decreases the blood volume in the resting masseter, suppresse s the incremental blood-volume change during cold-presser stimulation. and discloses a hidden vasoconstrictive effect after that stimulation. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.