Submitted to: Molecular Brain Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/1996
Publication Date: N/A
Interpretive Summary: Gonadotropin releasing hormone (GnRH), is a chemical produced in the brain. This compound is important for regulating the reproductive system of females. Ultimately, GnRH controls ovulation and some reproductive behaviors. The biological actions of GnRH are mediated through GnRH receptors located in the pituitary - a gland just beneath the brain. Altering the number of GnRH receptors in the pituitary would likely influence the entire reproductive process. By increasing our knowledge of how these receptors are regulated, we may be better able to manage reproductive problems in food-producing animals. In the present study, we examined the effect of estrogen, a female hormone, on the pituitary gland's ability to make GnRH receptors. When compared to animals without estrogen, we found that 48 hours of estrogen treatment increased the ability of the pituitary gland to make GnRH receptors. Further analysis revealed that this enhancement was due to a) more GnRH receptors being made per pituitar cell; and b) an increase in the number of pituitary cells making GnRH receptors. These effects were not observed after just twelve hours of estrogen treatment. The results of this study demonstrate that the ability of the pituitary gland to make GnRH receptors can be regulated by hormone treatment. We can now examine how other influences, like nutrition and stress, impact this important part of the reproductive process in females.
Technical Abstract: Gonadotropin releasing hormone (GnRH) is crucial in regulating the reproductive system of female vertebrates. In the present study, we have analyzed the estrogen regulation of the GnRH receptor mRNA. By quantitative IN SITU hybridization and Northern blot analysis techniques, we have found a significant increase in GnRH receptor mRNA levels after estrogen replacement in pituitary tissues of ovariectomized (OVX) Sprague-Dawley female rats. Northern blot analysis detected 3 species (5.0, 4.5 and 1.4 kb) of GnRH receptor mRNA in pituitary tissues. The GnRH receptor mRNA levels of these 3 species were increased by estrogen. By IN SITU hybridization we observed a 3.5 fold increase in GnRH receptor mRNA levels after 48 hours of estrogen treatment when compared to OVX rats. Twelve hours of estrogen treatment did not change the GnRH mRNA levels. IN SITU hybridization analysis identified clusters of anterior pituitary cells sthat expressed the GnRH receptor gene. The estradiol effect depends on increased mRNA in these clusters. Moreover, a significant increase in the number of pituitary cells that expressed GnRH receptor was observed after 48 hr of estrogen treatments. Similar increases in GnRH receptor mRNA levels by estrogen were also found in Wistar-Imamichi female rat pituitary tissue. These findings suggest that the mechanisms for estrogen regulation of GnRH receptor include changing levels of GnRH receptor mRNA in the rat pituitary.