Abstract The influence of nervous and local chemical factors on the pre‐capillary sphincter section of the muscle vascular bed has been studied in terms of changes in the filtration coefficient (CFC). The results suggest that the vasoconstrictor fibres, beside their powerful influence on the resistance and capacitance vessels, affect also the pre‐capillary sphincters, which determine the number of capillaries open to flow. However, the influence exerted by the centrally controlled vasoconstrictor fibres on the pre‐capillary sphincters in the skeletal muscles is rapidly overcome by ‘vasodilator metabolites’, accumulating when flow is reduced or metabolism is increased. Such local metabolic factors exert an especially powerful control of the sphincter section as compared with the neurogenic influence. Thus CFC in the skeletal muscles tends to rise at any decrease of blood flow/ tissue metabolism ratio e. g. from ‘resting’ values around 0.015 up to 0.04—0.05, during muscular exercise; an increase also occurs when flow is reduced. Flow reduction following mechanical arterial obstruction induces a relatively greater CFC increase than when flow is reduced by the constrictor fibres, which unmasks their weak but still significant influence on the pre‐capillary sphincter section.
Cobbold et al. (1963) studied this question.