J.P.W. Rivers

DEFECTIVE ESSENTIAL-FATTY-ACID METABOLISM IN CYSTIC FIBROSIS

Cystic fibrosis (C.F.) is characterised by low serum levels of essential fatty acids (E.F.A.). However, the fatty-acid pattern does not totally resemble that of dietary E.F.A. deficiency. The differences suggest a reduction in the desaturation of E.F.S. It is not known whether this defect is the primary lesion in C.F. or is the result of tissue damage in the disease. It is proposed that C.F. patients might have increased linoleic-acid requirements, and possibly specific requirements for its desaturation products.

The failure of the cat to desaturate linoleic acid; its nutritional implications.

In vivo administration of 1-14C-linoleic acid to domestic cats demonstrated that these animals are unable to convert this essential fatty acid to its physiologically active metabolities. This experiment confirms the absence of both the delta6 and delta8 desaturases in the cat, and suggests that this species has a dietary requirement for polyunsaturated fatty acids of animal origin.

The inability of the lion, Panthera leo L. To desaturate linoleic acid

Most studies of the metabolism of polyunsaturated fatty acids have been conducted on laboratory rodents. These animals have relatively high A6 desaturase activity and are therefore able to convert linoleic acid (18:2606) to the prostaglandin precursors dihomogamma-linolenic acid (20:3606) and arachidonic acid (20:4606). It has been assumed without much evidence that other species can desaturate polyunsaturated fatty acids equally well. However, recent work on the domestic cat, Felis catus L. [1] and the turbot, Scopthalamus maximus, L. [2] has shown that these obligate carnivores are unable to desaturate linoleic acid (18:2606) or linolenic acid (18:3603). It has been suggested that these species, have, therefore, a dietary requirement for the long-chain polyenoic acids (LCP), particularly 20:3606 and 20:4606, and hence for polyunsaturated lipid of animal origin. Because of the wider implications of the lack of desaturase activity we have begun a comparative study of fatty acid desaturation in animals of different dietary habits. We wish here to make a preliminary report of studies on the African lion, Panthera leo, which demonstrate the absence of A6 and A8 desaturase activity in this animal.