Effect of essential fatty acid deficiency on membrane fatty acid content and growth hormone stimulation of rat pituitaries during postnatal development.

Fatty acid composition of anterior pituitary cell membranes of rats deprived of essential fatty acids (EFA) and of rats receiving a standard diet was determined during postnatal development and in adults. Pregnant rats were fed an EFA-deficient diet and the offspring were fed the same diet after weaning. In parallel, effects of the diet on growth and on growth hormone (GH) responsiveness to GHRH stimulation were determined in control animals. Membrane content of arachidonic acid (20:4n-6) and of its elongation product adrenic acid (22:4n-6) increased regularly from day 2 to day 12 after birth. EFA-deficiency resulted on day 2 in increased oleic acid and in substitution of arachidonic and adrenic acids by corresponding elongation-desaturation products of oleic acid: eicosatrienoic (20:3n-9) and docosatrienoic (22:3n-9) acids. At the age of 24 days, n-9 series fatty acid reached the same level as in adult animals. Two-day-old EFA-deficient rats paradoxically exhibited a higher level of 20:4n-6 as compared to control rats. EFA-deficiency also decreased growth rate and GH pituitary responses to GHRH during the prepubertal period. These results suggest that changes in the lipid structure and in pituitary secretion properties elicited by EFA-deficiency depend upon the stage of development.

Effect of an essential fatty acid deficiency on the phospholipid composition in anterior pituitary membranes.

The effects of an essential fatty acid deficient diet were investigated on the phospholipid fatty acids of several membrane fractions of the rat anterior pituitary, the secretion of which is known to be partly dependent on the membrane phospholipidic constituents. In standard dietary conditions, arachidonic acid (20:4n-6) and its elongation product, adrenic acid (22:4n-6), were the two main polyunsaturated fatty acids in all fractions studied. In rats deprived of EFA for 6 weeks after weaning, the levels of both 20:4n-6 and 22:4n-6 were not changed in microsomal + plasma membrane and nuclear fractions, whereas they were decreased in heavy mitochondrial and light mitochondrial fractions. The present data suggest a mechanism of compensation between membrane fractions which may preferentially preserve 20:4n-6 and 22:4n-6 in discrete membrane fractions.