Effect of baseline vascular tone on vasomotor responses in cat lip

1. Parasympathetic vasodilator and sympathetic vasoconstrictor responses were monitored using laser Doppler measurement of red cell flux in the lips of anaesthetized and artificially ventilated cats. 2. Three relationships were investigated: (i) that between the reflex parasympathetic vasodilator response induced by lingual nerve (LN) stimulation and baseline red cell flux (BRCF) levels adjusted by repetitive stimulation of the cervical sympathetic nerve (CSN) at various frequencies; (ii) that between the sympathetic vasoconstrictor response elicited by CSN stimulation and the adjusted BRCF levels; and (iii) that between the vasomotor response evoked by simultaneous stimulation of the LN and CSN and the adjusted BRCF levels. 3. The amplitude of the parasympathetic vasodilator response increased as BRCF decreased. In contrast, the amplitude of the sympathetic vasoconstrictor response increased in line with BRCF. 4. Simultaneous activation of the parasympathetic and sympathetic nerves induced a blood flow decrease at high BRCF levels but an increase at low levels. 5. The tendency for the skin of cold subjects to vasodilate and that of warm ones to vasoconstrict in response to various types of stimuli discussed in the light of the present findings.