The enzyme-inhibitor approach to cell-selective labelling--II. In vivo studies with pIBS in small animals and man

p-Iodobenzenesulphonamide (pIBS), a potent red cell carbonic anhydrase inhibitor, was used as a carrier for radioiodine in the enzyme-inhibitor approach to cell-specific blood labelling. Radioactivity distribution was monitored in rats and man following i.v. administration of the radiolabelled carrier or of pre-labelled red cells. Rat blood activity fitted a two compartment model; the half-life for overall elimination was 69 +/- 27 h. At 24 h most activity remained associated with red cells, but there was a significant uptake in the large intestine (10 +/- 6%). In man there was no significant accretion by gut or any other organ over 93 h, and the blood clearance was mono-exponential (t1/2 = 9.8 +/- 1.5 days).