184 II. DIGESTION AND ABSORPTION OF FATS 



In conformity with the hypothesis of Frazer 645 that the volatile acids are 

 transported via the portal route rather than by way of the lymphatics, 

 Kiddle et al. 83i found that the volatile acid content of lymph drawn from the 

 thoracic duct is not greater than that of the arterial blood. 



It has been reported that fatty acids are absorbed more rapidly than the 

 corresponding anions, 835 and, in fact, that no absorption at all occurs when 

 the pH. exceeds 7.0 835 When alkaline solutions of acetate, propionate, or 

 butyrate are introduced into the rumen, the reaction rapidly approaches 

 neutrality 833 ; Cl~ and C0 2 both appear in the rumen when aqueous solu- 

 tions of the short-chain fatty acids are placed in the rumen. Gray 836 re- 

 ported that the rate at which the free acid disappears from the rumen in- 

 creases with the lengthening of the hydrocarbon chain. 



The absorption of the short-chain acids differs from that of the long- 

 chain acids in that it is not controlled by the adrenocortical hormones. 

 Thus, in spite of the fact that adrenalectomy retards the absorption of fats 

 having de and Ci 8 fatty acids, Bavetta and Deuel 686 showed that no change 

 in the absorption rate of tributyrin resulted from removal of the adrenal 

 glands. In a later study, Bavetta 687 found that no significant depression in 

 absorption of tricaproin (Ce) or tricaprylin (C 8 ) resulted from adrenalec- 

 tomy. Sodium butyrate 686 and sodium caproate 687 were also absorbed at a 

 normal rate in operated rats. However, the rates of absorption of caprylic 

 (C 8 ) and capric (Ci ) acids, when fed as the free acids, were considerably 

 slower after adrenal extirpation. It was concluded that the adrenal cortex 

 is concerned only with the absorption of the longer-chain fatty acids insol- 

 uble in an aqueous medium. Frazer and associates 837 confirmed the fact 

 that adrenalectomy depresses the absorption of long-chain fats but not of 

 tributyrin. 



d. The Effect of the Melting Point of the Fat. Probably the most im- 

 portant physical property of fat which influences the rate of absorption 

 and, in fact, its digestibility also, is the melting point. Few observations 

 on the rate of absorption of fats melting above 50 °C. are available because 

 of the difficulty in administering the test material in a liquid form without 

 killing the animal. A number of tests on digestibility of higher melting 

 fats are described later (see Chap. III). However, in the absorption tests 

 listed in Table 24, some decrease in the rate of absorption was observed 

 for a blended hydrogenated fat (bland lard) melting at 48 °C, while a some- 



836 F. V. Gray, /. Exptl. Biol, 25, 135-144 (1948). 



836 F. V. Gray, J. Exptl. Biol, 24, 1-10 (1947). 



837 A. C. Frazer, J. M. French, and H. G. Sammons, Abslr. Commtm. 1st Intern. Congr. 

 Biochem., Cambridge, England, 1949, 12-13; Chcm. Abst., 1,5, 4328 (1951). 



