Validity of iodoantipyrine clearance for measuring gastrointestinal tissue blood flow

Simultaneous determinations of 1) the clearance (mF) of 4-iodoantipyrine (IAP) and tritiated water, 2) the mF of IAP and total circulating tissue blood volume, 3) the mF of IAP and either 15- or 25-micrometers-diam-microsphere-measured flow, and 4) 15- and 25-micrometers-diam-microsphere-measured flow were made on tissues from dog gastrointestinal tracts. Results show the mF of IAP equals or exceeds that of tritiated water in all tissue layers, and tissue blood volume does not affect the measurement of the IAP mF. Perfusion of the gastrointestinal wall exhibits macroscopic heterogeneity due to differences in perfusion of the three tissue layers, but an effect of microscopic heterogeneity on tissue mF assessment was not apparent. Composite total-wall IAP mF was not significantly different from 25-micrometers-microsphere total-wall flow and was identical to this flow when colonic locations were omitted. Comparisons of 15-micrometers-microsphere flow to IAP mF and to 25-micrometers-microsphere flow both indicated shunting of 15-micrometers-microspheres. Such shunting occurred predominantly through submucosal and muscle layers. It is concluded that IAP clearance accurately measures blood flow in gastrointestinal tissue.