Acute effects of ethanol on steroidogenic acute regulatory protein (StAR) in the prepubertal rat ovary.
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BACKGROUND: Steroidogenic acute regulatory protein (StAR) is a 30 kDa mitochondrial protein that plays an essential role in steroid hormone biosynthesis by facilitating delivery of cholesterol across the mitochondrial membrane, where side chain cleavage occurs to initiate ovarian steroidogenesis. Because ethanol (EtOH) suppresses estradiol secretion in prepubertal female rats, we evaluated the effects of EtOH on prepubertal ovarian StAR. METHODS: At 0700 hr, 28-day-old female rats were gavaged with saline or a 3 g/kg dose of EtOH. At 0800 hr, half of each of these two groups was treated with 15 IU of pregnant mare serum gonadotropin (PMSG). At 1000 hr, a 2 g/kg dose was administered to maintain moderately elevated blood alcohol levels. At 1600 hr, all of the animals were killed by decapitation, and blood and ovaries were collected for measurement of serum pregnenolone and estradiol and for ovarian StAR gene and protein expression. RESULTS: Northern blot analysis showed two major transcripts of 3.8 and 1.7 kb of ovarian StAR mRNA. The ovaries from EtOH-treated rats showed decreased (p < 0.01) basal expression of both 3.8 and 1.7 kb StAR transcripts. PMSG-stimulated animals showed a more than 4-fold increase (p < 0.001) in the levels of both transcripts, when compared with ovaries from animals that received saline or EtOH only. Conversely, in EtOH-treated animals, the PMSG-stimulated expression of the 1.7 kb transcript was blocked, and the increase in the 3.8 kb StAR transcript was blunted (p < 0.05 vs. PMSG). Western blot analysis revealed that EtOH exposure also depressed (p < 0.01) the basal expression of StAR protein. PMSG-stimulated animals showed an increase (p < 0.001) in levels of StAR protein, and this was blocked (p < 0.01) by EtOH. These changes observed in ovarian StAR mRNA and protein were paralleled by changes in serum pregnenolone and estradiol. Specifically, acute EtOH exposure suppressed (p < 0.05) the basal levels of both steroids. Furthermore, PMSG-stimulated animals showed an increase in the production of pregnenolone (p < 0.05) as well as estradiol (p < 0.01), and EtOH blocked this stimulatory action of PMSG on both steroids. CONCLUSION: These results demonstrate for the first time that EtOH is capable of altering ovarian StAR expression, which contributes to the detrimental effect this drug has on ovarian steroidogenesis during prepubertal development.
