Carbonic anhydrase in epithelia and fenestrated juxtaepithelial capillaries of Macaca fascicularis.

Thirty-nine epithelia of the monkey Macaca fascicularis and their underlying connective tissue were stained for carbonic anhydrase (CA) and studied by light microscopy. The capillaries immediately adjacent to the epithelium, 'juxtaepithelial', were also studied by electron microscopy with special attention to presence or absence of fenestrations. Only juxtaepithelial capillaries stained. These were fenestrated under many epithelia and all fenestrated juxtaepithelial capillaries stained. Often staining and fenestration were limited to the part of their circumference facing the epithelium. There was a strong association P less than 0.002 between CA-staining and fenestration of the capillaries, a moderately strong association P less than 0.02 between CA-staining of the membrane of the epithelium and the adjacent capillaries, and no association between staining of the epithelial cytoplasm on the one hand and the epithelial membrane or the capillaries on the other. Fenestrated capillaries containing CA despite unstained epithelia were found in the thyroid, parathyroid, adrenal cortex, islets and anterior pituitary, and also, but not consistently, in the prostatic and the seminal glands. Unfenestrated capillaries containing CA were found in the stomach, colon and lung, and in the Graffian follicle and Fallopian tube. The hypothesis is advanced that capillary CA besides conventional functions plays a part in conserving the state of fenestration of the endothelium and that CA-inhibitors could exert part of their therapeutic and side actions by reducing fenestrations.