Rhythmic activity of cat pial vessels in vivo

Rhythmic activity was observed in over 100 pial vessels in 58 cats with a photometric technique through a cranial window. Diameter oscillations with a frequency of mostly 5/min were present at normal mean arterial pressure (MAP) in about half of the animals. When spontaneous activity was absent the same type of oscillations could be provoked by varying MAP, mostly by lowering it to a level of around 60 mm Hg. If a rhythmic activity was present, it could be abolished by increasing and decreasing MAP. Likewise, rhythmic activity ceased during strong vasodilatation caused by hypercapnia, hypoxia, Ca antagonists or other vasoactive drugs. Rhythmic activity also decreased in amplitude or disappeared with vasoconstriction accompanied by a stable MAP. Rhythmic activity of pial vessels thus seemed to occur within an as yet unspecified range of vessel wall tensions mediated via intraluminal pressure and a state of constriction or dilatation. This rhythmic activity was not primarily influenced by sympathetic stimulation, alpha-sympathetic blockade, hyper- or hypocapnia, hypo- or hyperoxygenation. Moreover, the vascular activity fits well with the description of rhythmic smooth muscle activity in other vascular beds and organs in vitro and in vivo, ascribed to myogenic regulatory processes. Therefore, it is suggested that the rhythmic activity of pial vessels might be an expression of myogenic blood flow regulatory activity in the brain.