FACTORS AFFECTING RATE OF ABSORPTION 183 



chain acid. Moreover, tripropionin exhibits a similar property. 829 In the 

 case of butyric acid, it has been repeatedly observed that an exogenous 

 ketonuria results after the administration of sodium butyrate to fasting 

 rats. This would seem to constitute proof of the ready absorption of the 

 butyrate ion. The subject of exogenous ketonuria is discussed in extenso 

 in Volume III. Probably more definite proof of the absorption of butyrate 

 can be derived from the results of Morehouse, 830 who demonstrated the 

 appearance of deuterio-/3-hydroxybutyrate in the urine of fasting rats after 

 the oral administration of sodium dideuteriobutyrate. 



Direct proof of the absorption of the volatile fatty acids from the gastro- 

 intestinal tract was produced by Barcroft and co-workers, 831 who noted 

 that the concentration of volatile fatty acids in the blood draining the large 

 intestine of the horse, pig, rabbit, and sheep, as well as that of the rumen, of 

 the reticulum, and to a lesser extent of the omasum of sheep, is higher than 

 the proportion of these acids in blood from the general circulation. On 

 the basis of these studies, it was concluded that sodium acetate is rapidly 

 absorbed, sodium propionate is utilized at a somewhat lower rate, while 

 sodium butyrate is absorbed at the slowest rate of the three volatile acids. 

 Using differences between the concentration in carotid and in portal blood 

 as the criterion for absorption, Schambye and Phillipson 832 concluded that 

 both volatile fatty acids and glucose are absorbed from the alimentary 

 tract in appreciable amounts, but that the uptake of the former is greater 

 than that of the glucose. Masson and Phillipson 833 reported that, when 

 equimolecular concentrations of the volatile acids were present in the rumen 

 of sheep, the concentration in the blood leaving the rumen was in decreasing 

 order : acetate, propionate, butyrate. While acetate was found in arterial 

 blood, propionate was not present and, in most cases, butyrate was also 

 absent from the arterial blood, even when these compounds were fed. It 

 was later reported 834 that, although the mixture of acetic and butyric acids 

 present in the portal blood contains more acetic and less butyric acid than 

 the mixture present in the rumen, when a correction is made for the acetate 

 in the arterial blood, the concentrations of acetate in the portal blood and in 

 the rumen, respectively, are similar, while less butyrate occurs in the blood 

 from the latter area. 



829 H. J. Deuel, Jr., J. S. Butts, H. Blunden, C. H. Cutler, and L. Knott, J. Biol. 

 Chem., 117, 119-129(1937). 



830 M. G. Morehouse, /. Biol. Chem., 129, 769-779 (1939). 



831 J. Barcroft, R. A. McAnally, and A. T. Phillipson, Biochem. J., 38, iii (1944). 



832 P. Schambve and A. T. Phillipson, Nature, 164, 1094-1095 (1949). 



833 M. J. Masson and A. T. Phillipson, /. Physiol, 113, 189-206 (1951). 



834 P. Kiddle, R. A. Marshall, and A. T. Phillipson, ./. Physiol, 113, 207-217 (1951). 



