Representative images of Munich Wistar Frömter glomeruli using 2-photon intravital microscopy before (panel A) and after ET-1 treatment (panel B). Although it is not possible to visually distinguish relative differences in Bowman’s space (BS) albumin content by the naked eye, the fluorescence intensity ratio between BS and capillary loop (CL) can be readily determined. Despite having been given an identical amount of Texas Red rat serum albumin initially, and imaged at the same time post injection, plasma levels of albumin following ET-1 treatment decreased more rapidly and yielded a higher fluorescence ratio, i.e., glomerular sieving coeficients (GSC). Panel C shows average GSC for individual rats taken before and after chronic ET-1 infusion. For the 6 rats, a total of 28 glomeruli were studied before and after ET-1 infusion, (Bar=15μm; CL=capillary loops).