Role of alpha-adrenoceptors in the cutaneous postocclusive reactive hyperaemia

Laser-Doppler (LD) flow measurements reveal typical flow oscillations in the descending part of the cutaneous postocclusive reactive hyperaemia (PRH). The origin of these oscillations is still poorly understood. We tested the hypothesis that the high frequency (HF) components within the frequency band 0.06-0.2 Hz are due to the local myogenic mechanism, whereas the low frequency (LF) components within frequency band 0.01-0.05 Hz reflect sympathetic vasomotor activity. LD flow was monitored on fingertips of 11 healthy volunteers before and after an 8-minute occlusion of digital arteries. We studied the effect of intradermal microinjection (1 μl) of α-antagonists (prazosine, yohimbine) and α-agonists (phenilephrine, clonidine) on PRH oscillations. We analysed the magnitude of peak flow and its duration and performed spectral power analysis to obtain fundamental HF and LF frequencies (defined as components with the highest amplitude in the part of the respective frequency band). The results (mean ± SE) for each substance were compared to the control values obtained after microinjection (1 μl) of 0.9% NaCl. The fundamental HF significantly decreased from 0.11 ± 0.008 Hz after an injection of saline solution to 0.08 ± 0.006 Hz after an application of antagonists (p<0.05). The local application of α-antagonists did not abolished HF oscillations what suggests that activity of local sympathetic nervous system is not essential in generation of these oscillations. However, the significant decrease of fundamental frequency in HF band after application of α-antagonists supports the hypothesis of their local origin and could be explained by the effect on pacemaker myogenic mechanism.