Diurnal Variation in the Acute Effects of Estradiol and Progesterone on Beta-Endorphin and Met-Enkephalin Levels in Specific Brain Regions of Ovariectomized Rats

Abstract

The present investigation was conducted to evaluate the effects of estradiol and progesterone on β-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 µg/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 β-endorphin and Met-enkephalin levels were determined by radioimmunoassay. Estradiol administration at 8.00 h resulted in a significant decline in β-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 β-endorphin levels in the cerebral cortex (34.7% increase) and in the mid-brain (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 β-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. However, estradiol and progesterone administered in combination produced a significant change in β-endorphin levels in the hypothalamus (25% increase) and in the cerebral cortex (30% increase). Moreover, the Met-enkephalin levels in the cerebral cortex significantly increased with all treatments whereas these levels in the mid-brain increased only when estradiol and progesterone were administered in combination. These findings indicate that estradiol and progesterone affect β-endorphin as well as Met-enkephalin levels in specific brain regions and that these effects are diurnally controlled. In addition, the alteration in hippocampal endogenous opioid levels induced by estrogen and progesterone may in part explain their behavioral effects.

Estradiol Alters Ethanol-lnduced Effects on β-Endorphin and Met-Enkephalin Levels in Specific Brain Regions of Ovariectomized Rats

“…Hence, just as opioid peptides modulate activity of the sex hormones, ste roid hormones can affect endogenous opioid function in the brain. In fact, findings from our laboratory indicate that estrogen and pro gesterone affect P-EN as well as ME levels in specific brain regions of ovariectomized rats and that these effects are diurnally controlled [18]. These findings are in agreement with previous findings which found that hypotha lamic P-EN contents fluctuate with a diurnal rhythm and that estradiol treatment alters the circadian changes in hypothalamic p-EN con tents in ovariectomized rats [19].…”

Contribution of endogenous opioids to gonadal hormones-induced temporomandibular joint antinociception.

“…Gonadectomy was performed in 45-day-old rats, as previously described (Fischer et al, 2008; Gordon & Soliman, 1994) under anesthesia induced by an intramuscular injection of a mixture of ketamine (55 mg/kg) and xylazine (5.5 mg/kg). A subcutaneous injection of ketoprofen (5 mg/kg) was used for postoperative analgesia (Roughan & Flecknell, 2000).…”

“…Hormone administration was performed by daily subcutaneous injection of 17 β-estradiol (50 μg/kg; Gordon & Soliman, 1994) or progesterone (8 mg/kg; He, Evans, Hoffman, Oyesiku, & Stein, 2004) in females and of testosterone propionate (1 mg; Campos, Morais Pde & Pupo, 2003) in males, during 7 days, as previously described (Fischer et al, 2008; Gordon & Soliman, 1994). At the seventh day, hormone injection was performed 1 hr prior to the TMJ injection of formalin (Fischer et al, 2008; Gordon & Soliman, 1994). Hormones were purchased from Sigma Chemical (St. Louis, MO) and dissolved in propylene glycol.…”

Mecanismos opióides centrais envolvidos no efeito protetor da testosterona no desenvolvimento da dor da ATM em ratos

“…The procedure was performed in 45-day-old male rats through a single scrotal incision, as previously described (Fischer et al, 2008;Gordon & Soliman, 1994). The testicular bundles were ligated and removed and the skin was sutured.…”