Endocrine mechanisms responsible for different follicular development during the estrous cycle in Hatano high- and low-avoidance rats.
ABSTRACT Hatano high- and low-avoidance rats (HAA and LAA strains, respectively) were selected and bred according to the avoidance rate in a shuttle-box task. Although they have clear strain differences in ovarian function, their endocrine mechanisms still remain to be clarified. Differences in female reproductive endocrinology between the strains were investigated by means of measuring the plasma concentration of reproductive hormones during the estrous cycle. LAA rats showed approximately threefold lower basal and surge levels of LH, a more than fourfold lower level of FSH surges and higher levels of inhibin A and inhibin B during the estrous cycle compared with the levels seen in HAA rats. The concentration of estradiol-17β in the proestrous stage was significantly lower in LAA rats than in HAA rats. Additionally, LH and FSH secretions from primary cultured anterior pituitary cells with or without in vitro GnRH stimulation were lower in the cells derived from LAA rats and, in terms of FSH secretion, were unresponsive to GnRH in contrast to cells derived from HAA rats. Although an increased number of preantral follicles in diestrus were observed in LAA rats, number of hCG-induced ovulation was lower in LAA rats. LAA rats may have much more follicle growth during the early stage of folliculogenesis, but most follicles might not grow into mature follicles. These results strongly suggest that the strain difference in ovarian function of these two Hatano rats is due to the difference in the regulation of hypothalamo-hypophyseal system for gonadotropins secretion.
SourceAvailable from: Takashi Kitahashi[Show abstract] [Hide abstract]
ABSTRACT: This study aims to delineate the relationship among estrogen deficiency, neurodegeneration, and cognitive impairment of ovariectomized rats. Female Sprague-Dawley rats were ovariectomized and euthanized after 1-4month periods (M(0)-M(4) groups). Blood samples were collected for the determination of serum levels of 17β-estradiol (E(2)), luteinizing hormone (LH), and follicle stimulating hormone (FSH). Five consecutive days before the euthanization, cognitive performance of the rats was examined by Morris water maze test. After euthanization, the hippocampus was collected, and expression of the genes associated with amyloid plaques (App, Adam10 and Bace1) and neurofibrillary tangles (Tau4 and Tau3) were examined by real-time PCR. Serum E(2) levels were declined following 2weeks of ovariectomy. Conversely, serum FSH and LH levels were profoundly increased by 2weeks of ovariectomy for approximately 4 and 22 times, respectively. Cognitive impairments, indicated by the longer latency and distance, were observed only in the M(3) and M(4) groups. The Tau4 mRNA levels were significantly increased as early as 1month after ovariectomy (in the M(1) group; P<0.05), and tended to be increased further with the advancing time. Similarly, the Tau3 mRNA levels were increased by ovariectomy, but with the highest level in the M(1) group, and decreased thereafter. The mRNA levels of App, Adam10 and Bace1 were increased by ovariectomy, but significant differences were observed only in the M(4) group. These results indicate that estrogen deficiency can induce a sequence of events that results in the production of neurofibrillary tangles, amyloid deposition, and spatial memory deficit in rats.General and Comparative Endocrinology 10/2013; 181:316-323. DOI:10.1016/j.ygcen.2012.07.034 · 2.67 Impact Factor
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ABSTRACT: Melanocortin-4 receptor (MC4R) and agouti-related peptide (AgRP) are involved in energy homeostasis in rat. According to MC4R and AgRP effects on luteinizing hormone (LH) secretion, they may influence the estrous cycle of rat. Therefore, the aim of this study was to investigate the expression of MC4R and AgRP mRNAs at different stages of estrous cycle in rat’s hypothalamus. The estrous cycle stages (proestrus, estrus, metestrus and diestrus) were determined in 20 adult female rats using vaginal smears. The rats were divided into four equal groups (n = 5). Four ovariectomized rats were selected as controls two weeks after surgery. Using real-time PCR, relative expressions (compared to controls) of MC4R and AgRP mRNAs in the hypothalamus of rats were compared in four different groups of estrous cycle. The relative expression of MC4R mRNA in the hypothalamus of female rats during proestrus stage was higher than those at other stages (P= 0.001). Despite a lower mean of relative expression of AgRP mRNA at proestrus stage, the relative expression of AgRP mRNA of the four stages of estrous cycle did not differ (P> 0.05). In conclusion, changes in the relative expression of MC4R and AgRP mRNAs in four stages of rat estrous cycle indicated a stimulatory role of MC4R in the proestrus and preovulatory stages and an inhibitory role of AgRP in gonadotropin releasing hormone (GnRH) and LH secretions.