Growth hormone (GH) effects on
fatty acid composition and on delta5-, delta6-, delta9-desaturase and
palmitic acid elongation activities were studied in male rat hepatic microsomes.
Sham-operated and hypophysectomized animals were injected with two different dosages of GH, mimicking either the male or female GH secretion pattern. Half the hypophysectomized animals received
thyroxine and
cortisol in concentrations chosen to compensate for the lack of
thyroid hormones and
glucocorticoids. GH, administered to
sham-operated or to
cortisol/
thyroxine-treated hypophysectomized rats resulted in an increase in stearic and
arachidonic acid proportions, while
palmitic acid percentage was decreased. Total
monounsaturated fatty acids were dramatically reduced by this treatment. DeltaA-desaturase and
palmitic acid elongation activities were increased by GH treatment, while delta9-desaturase activity was decreased. These GH effects on desaturation and elongation activities could explain the modifications in microsomal
fatty acid composition.
Hypophysectomy markedly altered the
fatty acid composition by reducing arachidonic and
stearic acid proportions and increasing the
linoleic acid proportion, while delta9-, delta5-desaturase and
palmitic acid elongation activities were decreased. Restoration of most of the
fatty acid proportions to control values was realized in hypophysectomized animals with a
cortisol/
thyroxine replacement administered alone or together with the low dosage of GH mimicking the male secretion pattern. High GH dosage produces essentially a '
feminization' process of the
fatty acid composition of the hepatic microsomal membrane in male rats when compared to that of females.