Frequency response characteristics of sympathetic transmission to skin vascular smooth muscles in rats

Sympathetic modulation of cutaneous vasomotor waves in humans is most effec tive at frequencies up to 0.1 Hz. In contrast, sympathetic modulation of me senteric vasomotor waves in rats is strongest in the frequency band between 0.2 and 0.75 Hz. Therefore, we addressed the question as to whether these different frequency response characteristics are due to species- or organ-s pecific disparities. Eleven Sprague-Dawley rats were instrumented with cath eters in the carotid artery and in the jugular vein, together with electrod es on the centrally sectioned left lumbar sympathetic trunk (LST) and laser Doppler flow probes directed to the plantar surface of the skin of the lef t and right hind paws. In anesthetized rats, the LST was electrically stimu lated at eight different stimulation frequencies, and the responses in lase r Doppler blood flow were recorded in the skin of the ipsilateral and contr alateral paw. At stimulation frequencies <0.2 Hz, LST stimulation induced c orresponding oscillations in skin blood flow in the ipsilateral, but not in the contralateral, paw. These dynamic responses to LST stimulation in the ipsilateral paw were strongest at 0.05 and 0.075 Hz. At higher stimulation frequencies a tonic vasoconstriction was observed. It is concluded that org an-specific disparities exist in sympathetic transmission to vascular smoot h muscles, whereas no species-specific differences are apparent in sympathe tic transmission to cutaneous blood vessels of humans and rats.