Role of alpha-adrenoceptors in the cutaneous postocclusive reactive hyperaemia

Laser-Doppler (LD) flow measurements reveal typical flow oscillations in th e 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 ba nd 0.06-0.2 Hz are due to the local myogenic mechanism, whereas the low fre quency (LF) components within frequency band 0.01-0.05 Hz reflect sympathet ic vasomotor activity. LD flow was monitored on fingertips of 11 healthy vo lunteers before and after an 8-minute occlusion of digital arteries. We stu died the effect of intradermal microinjection (1 mu l) of alpha-antagonists (prazosine, yohimbine) and alpha-agonists (phenilephrine, clonidine) on PR H oscillations. We analysed the magnitude of peak flow and Its duration and performed spectral power analysis to obtain fundamental HF and LF frequenc ies (defined as components with the highest amplitude in the part of the re spective frequency band). The results (mean +/- SE) for each substance were compared to the control values obtained after microinjection (1 mu l) 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 applic ation of antagonists (p<0.05). The local application of alpha-antagonists d id not abolished HF oscillations what suggests that activity of local sympa thetic nervous system is not essential in generation of these oscillations. However, the significant decrease of fundamental frequency in HF band afte r application of alpha-antagonists supports the hypothesis of their local o rigin and could be explained by the effect on pacemaker myogenic mechanism.