Diurnal variation in the acute effects of estradiol and progesterone on beta-endorphin and Met-enkephalin levels in specific brain regions of ovariectomized rats.
The present investigation was conducted to evaluate the effects of estradiol and progesterone on beta-endorphin and Met-enkephalin levels in specific brain regions of ovariectomized rats. Female Sprague-Dawley rats (100-120 g) adapted to a 12-hour light, 12-hour dark illumination cycle were used in these studies. Animals were ovariectomized under pentobarbital anesthesia. After a recovery period of 10-14 days, estradiol (50 micrograms/kg in 0.2 ml olive oil) was administered subcutaneously to rats at either 8.00, 14.00 or 16.00 h, progesterone (5 mg/kg in 0.1 ml olive oil) or estradiol plus progesterone was administered subcutaneously at 16.00 h. Control rats were injected with olive oil. Animals were sacrificed 2 h later. The cerebral cortex, hypothalamus, hippocampus and midbrain were dissected, and their beta-endorphin and Met-enkephalin levels were determined by radioimmunoassay. Estradiol administration at 8.00 h resulted in a significant decline in beta-endorphin levels of the hippocampus (66% decrease) and a significant rise in Met-enkephalin levels of the hypothalamus (37.8% increase) but had no effect on other brain regions studied. When estradiol was administered at 14.00 h, it produced a significant change in beta-endorphin levels in the cerebral cortex (34.7% increase) and in the midbrain (31.3% increase), but these levels were not altered in the other brain regions. At 16.00 h estradiol and progesterone alone caused a significant increase (29 and 43%, respectively) in beta-endorphin levels of the hippocampus. Similarly, the Met-enkephalin levels in the hippocampus significantly increased following administration of estradiol (57% increase) and progesterone (54% increase) alone.(ABSTRACT TRUNCATED AT 250 WORDS)
Gordon
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FT
College of Pharmacy, Florida A&M University, Tallahassee 32307.
Soliman
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MR
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002940:Circadian Rhythm / Q000187:drug effects*; D004744:Enkephalin, Methionine / Q000378:metabolism*; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007279:Injections, Subcutaneous; D010052:Ovariectomy; D011374:Progesterone / Q000494:pharmacology*; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D001615:beta-Endorphin / Q000378:metabolism*
D011374:Progesterone; D004958:Estradiol; D004744:Enkephalin, Methionine; D001615:beta-Endorphin