Regional distribution of brain blood flow during maximal exertion in splenectomized ponies

It has been reported in exercising ponies that O2 supply to all regions of the brain increased primarily due to a large increment in CaO2 and it was implied that this may reflect a generalized increase in brain metabolism during strenuous exercise. Splenectomy ameliorates the rise in CaO2 observed with exercise in ponies. Thus, the objective of the present study was to examine changes in regional brain blood flow and O2 supply of splenectomized ponies with sub-maximal and maximal exercise and to compare these data with previous observations in normal ponies. It was reasoned that in the absence of a marked rise in CaO2, the brain blood flow of splenectomized ponies would have to increase markedly if brain metabolism also increased with severe exercise. Regional brain blood flow was studied using 15 micron diameter radionuclide labeled microspheres injected into the left atrium during rest (control) and sub-maximal as well as maximal exertion on a treadmill. It was observed that despite marked arterial hypocapnia and acute systemic hypertension which developed during exercise, blood flow as well as O2 supply in the cerebral cortex, caudate nuclei, cerebral white matter, cerebellar white matter, thalamus-hypothalamus, mid-brain, pons and medulla were not different from control values. In the cerebrellar cortex, however, blood flow and O2 supply increased with both work intensities. Thus, it was concluded that in exercising ponies, metabolic O2 requirement increased in the cerebellar cortex but was most likely not different from control (rest) in other regions of the brain.