DIGESTION, ABSORPTION, AND DIGESTIBILITY 427 



after thiouracil was given; this supports suggested mechanisms 1 and 3 

 Usted above. For a further discussion of the effect of the thyroid upon 

 carotene utihzation, see the section on transformation of carotene into 

 vitamin A (pages 443 to 447) . 



Chanda and co-workers*^ observed a similar improved digestion of caro- 

 tene in cows and goats after the injection of thyroxine, as well as a decreased 

 utilization when thiouracil was given. It was later found*^ that normal 

 goats absorb carotene more efficiently than do normal cows ; this fact may 

 be related to the observation of Schultze and Turner*^ that the goat thyroid 

 is more active than the cow thyroid. Another indication of the improved 

 absorption of carotene produced by a hyperthyroid condition is the fact 

 that the proportion of the provitamin A excreted in milk is increased by the 

 administration of the thyroid hormone to lactating cows.'*" Cadman'*^ 

 reported that the thyroid exerts a control over carotene absorption in man 

 similar to that observed in lower animals. Thus, in a case of myxedema 

 (hypothyroidism) , the fecal loss was decreased by thyroid therapy, whereas, 

 in the case of patients with thyrotoxicosis (hyperthyroidism), the excretion 

 of carotene was increased by the administration of thiouracil. 



The absorption of /3-carotene is sensitive to substances fed concomitantly. 

 Thus, in contradistinction to the beneficial effects of food fats on the absorp- 

 tion of the provitamin, mineral oil has repeatedly been found to depress 

 the utilization of /3-carotene. ^^•^•^"''^ Burns and co-workers** noted that the 

 presence of as little as 0.08% of mineral oil, which was sufficient to prevent 

 dustiness of lucerne leaf meal, had a deleterious effect on the utilization of 

 carotene. On the other hand, Mahle and Patton^^ reported that certain 



37 R. Chanda, H. M. Clapham, M. L. McNaught, and E. C. Owen, Biochem. J., 60, 

 95-99(1951). 



38 R. Chanda, H. M. Clapham, M. L. MeNaiight, and E. C. Owen, J. Agr. Sci., 4I, 

 179-180(1951). 



38 A. B. Schultze and C. W. Turner, Univ. Missouri Coll. Agr., Agr. Expt. Sta., 

 Research Bull. No. 393, 1-89 (Aug., 1945). 



« R. Chanda and E. C. Owen, Biochem. J., 51, 404-417 (1952). 



*i E. F. B. Cadman, Personal communication, 1954; cited by T. W. Goodwin, The 

 Chemical Pathology of Carotenoids, in R. T. Williams, The Chemical Pathology of Animal 

 Pigments, Biochem. Soc. Symposia, No. 12, Cambridge Univ. Press, 71-84 (1954), p. 75. 



^2 J. I. Rowntree, /. Nutrition, 3, 345-351 (1931). 



*^ R. A. Dutcher, P. L. Harris, E. L. Hartzler, and N. B. Guerrant, /. Nutrition, 8, 

 269-283 (1934). 



" R. W. Jackson, /. Nutrition, 7, 607-616 (1934). 



« M. T. Burrows and W. K. Farr, Proc. Soc. Exptl. Biol. Med., 24, 719-723 (1927). 



« R. A. Dutcher, J. O. Ely, and H. E. Honeywell, Proc. Soc. Exptl. Biol. Med., 24, 

 953-955 (1927). 



« H. S. Mitchell, Proc. Soc. Exptl. Biol. Med., 31, 231-233 (1933). 



« A. E. Mahle and H. M. Patton, Gastroenterology, 9, 44-53 (1947). 



