EFFECTS ON THE KIDNEY 921 



(Gardier and Woodbury, 1955). Since the resorption of bicarbonate is about 

 equal in the proximal and distal segments, this indicates an exclusively 

 proximal action. Increased excretion of Ca++ and Mg++ in both man and 

 dog treated with mercurials has been reported, and it is likely that the site 

 is proximal (Wesson, 1962). The inhibition of the secretion of p-aminohip- 

 purate, tetraethylammonium ion, and phenol red has been shown not only 

 in intact animals but with low concentrations of the mercurials in isolated 

 tubules or slices (Forster and Taggart, 1950; Farah and Rennick, 1956; 

 Koishi, 1959 b). Thus 0.01 mil/ Hg++ completely blocks phenol red trans- 

 port in the flounder tubule. These and other observations all point definitely 

 to a major site of action in the proximal segment of the nephron. However, 

 there is also evidence that more distal transports can be affected. For exam- 

 ple, the secretion of K+ and the H+ and NH4+ exchanges in the distal seg- 

 ment (Dale and Sanderson, 1954), and the resorption of solute-free water 

 by the loop of Henle (Lambie and Robson, 1960) and the distal segment 

 (Goldstein et al., 1961), are depressed by the mercurials. It is difficult to 

 compare the actions on proximal and distal portions of the nephron be- 

 cause of the different magnitudes of the transport processes; i.e., effects 

 on proximal transport would be much more marked because of the major 

 role of this segment in resorption. 



(B) Disappearance of renal SH grovps. Histochemical determination of 

 the free SH groups in different regions of the kidney in normal and mer- 

 curial-treated animals might provide some information on the site of ac- 

 tion if clear-cut differences are observed. Cafruny et al. (1955 b) determined 

 the free protein SH groups in rat kidney sections by treatment with the SH 

 reagent DDD (2,2'-dihydroxy-6,6'-dinaphthyldisulfide), coupling of the 

 naphthol moiety with the azo dye Fast Blue RR, and photometric analysis. 

 Following injection of a large dose of mersalyl (20 mg/kg), reduction of SH 

 groups was observed in all portions of the nephron except the proximal and 

 distal convoluted portions (see accompanying tabulation). Even at the 

 markedly nephrotoxic dose of 40 mg/kg there is no decrease in SH groups 



