IX. METABOLISM 47 



PABA. rrinary excretion of PABA \va« found to he of the order of loO 7 

 per day. This vahie for "free" PAliA is much higher tlian that rei)()i'ted 

 by Lewis'-' or by Landy and Dicken.'-- Feeal excretion of PABA, also (h'ter- 

 mined without prior hydrolysis of the samples, was found by Denko el al. 

 to average about 250 7 i)er day. 



PABA excretion by normal adults has been studied by l^loomberg," 

 using the microbiological assay of MacLeod'^ that measures PABA in 

 terms of sulfonamide-reversing activity. Like others, Bloomberg found 

 PABA to occur in the urine both in the "free" and in the "combined" 

 state. Less than 0.002 7 of "free" PABA per milliliter was found, while 

 the "combined" PABA, determined after acid hydrolysis, was found to 

 be about 0.02 7 per milliliter. From a study of the behavior of pure solu- 

 tions of derivatives of PABA to acid hydrolysis, Bloomberg concluded 

 that the "combined" form of PABA present in urine is mainly p-acetyl- 

 aminobenzoic acid. Li the opinion of the reviewers, the approach of Bloom- 

 berg is subject to criticism in that the presence of other derivatives of 

 PABA of the same acid lability is not precluded. When the results reported 

 by Bloomberg are recalculated in terms of probably daily output, less than 

 2 7 of "free" and about 20 7 of "combined" PABA appear to be excreted. 

 These values are considerably lower than those found by Lewis,-' Landy 

 and Dicken," Thompson et alP and Denko et ai}'^ 



The investigations of Bray et alP (see Excretion in Lower Animals) on 

 the nature of the metabolic forms of PABA found in the urine of rabbits 

 have been extended by Tabor et al.,- who made a similar study in normal 

 human beings. Li^sing the countercurrent distribution technique. Tabor 

 and her collaborators concluded that very little of the administered PABA 

 (single 6.2-g. dose) is eliminated as such, and only a small fraction is ex- 

 creted as acetylated PABA. The bulk of the PABA is excreted either as 

 the glj'-cine conjugate or as the glucuronide. Additional evidence for the 

 excretion of PABA in the form of the glucuronide is to be found in the 

 work of Zarafonetis and Chandler," who suggested that this was the re- 

 ducing substance-^' -^ found in the urine of patients receiving PABA, rather 

 than glucose as had been earlier presumed.^" 



Ger.shberg and KuhF' report that 9'> % of a small dose (100 mg.) of PABA 



" B. M. IJloomberg, S. African J. Med. Sci. 11, 51 (1946). 



26 C. U. McLeod, J. Exptl. Med. 72, 217 (1940). 



2' C. J. D. Zarafonetis and J. P. Chandler, ./. Lab. Clin. Med. 37, 425 (1951). 



28 R. H. Grekin and C. J. D. Zarafonetis, /. Invest. Dermatol. 12, 319 (1949). 



" C. J. D. Zarafonetis, R. H. Grekin, and X. C. Curtis. ./. Invest. Dermatol. 11, 



359 (1948). 

 '« C. J. D. Zarafonetis, G. A. .\ndre\vs, M. C. Meyers, and F. IL Bethel!, Blood 3, 



780 (1948). 

 '' 11. Gershl^erg and W. .J. Kulil, Jr., ./. Clin. Invest. 29, 1625 (1950). 



