Regulation of brain prostaglandins by sexual steroids

Hypothalamic PGF2 alpha content was determined by radioimmunoassay in rats. The male animals had significantly higher PGF/2 alpha level than the females. The hypothalamic PGF2alpha content increased following orchidectomy (GDX), while ovariectomy alone or combined with oestrone (100 microgram/kg or 1mg/kg i.m.) resulted in a significant i.m.) alone was ineffective. Testosterone (1 or 5 mg/kg i.m.) in GDX animals restored the hypothalamic PGF2 alpha content to the control level. The synthesis and breakdown of prostaglandins were also studied in the microsomal and cytosol fraction of brain homogenate. The PGD2 was the main product of the arachidonate cascade in rat brain microsomes. OVX increased the formation of PGD2 and diminished the biosynthesis of PGF2 alpha. Oestrone administration to OVX rats enhanced the formation of PGF2 alpha. Progesterone injection decreased the biosynthesis of PGF2 alpha and PGD2 alpha and PGD2 in OVX animals. Combined administration of progesterone and oestrone to OVX rats failed to restore the PGF2 alpha synthesis. In orchidectomized animals the arachidonate cascade was found to be depressed, further the synthesis of prostaglandins was normalized after testosterone substitution. The inactivation of 3H-PGF2 alpha by rat brain cytosol fraction was negligible.