Date Published: June 12, 2006
Publisher: BioMed Central
Author(s): Elize van Lier, Ana Meikle, Håkan Eriksson, Lena Sahlin.
Insulin-like growth factor-I (IGF-I) and thioredoxin are regulated by gonadal steroids in the female reproductive tract of many species. Oestradiol regulates IGF-I and thioredoxin mRNA levels in the reproductive tract of prepubertal lambs. The physiological status (different endocrine environment) may affect the sensitivity of the reproductive tract to oestradiol and progesterone. We studied the effects of different endocrine milieus (late-follicular and luteal phases of the oestrous cycle, and ovariectomy before or after puberty) on the expression of IGF-I, thioredoxin, oestrogen receptor α (ERα) and progesterone receptor (PR) in sheep. The mRNA levels were determined by a solution hybridisation technique. In the uterus the levels of ERα, PR and thioredoxin mRNA were higher in the late-follicular phase group than in the other three groups, and IGF-I mRNA was high during both the late-follicular and the luteal phases. In the cervix only PR mRNA was significantly higher in the ewes in the late-follicular phase than in the other groups. In the oviducts the levels of thioredoxin and ERα mRNA were highest in the ovariectomised adult ewes, and thioredoxin mRNA was higher than the levels found in the ewes in the late-follicular phase. The IGF-I mRNA levels in the oviduct did not differ between any of the groups. The transcripts of IGF-I, thioredoxin, ERα and PR, varied according to the physiological status and also along the female reproductive tract, suggesting that the regulation of the mRNA levels of these factors by the steroid environment is tissue specific.
Oestrogens and progestins secreted by the ovaries are the major modulators of the female reproductive tract functions. Their actions are primarily mediated via binding to specific intracellular receptors in the target cells, and subsequent stimulation of gene transcription . The tissue response is determined by both the concentration of the sex steroids in the circulation and the concentration of their high affinity receptors in the tissues . Furthermore, the steroids regulate the sex steroid receptor content along the reproductive tract in a specific manner .
This is the first report on IGF-I and thioredoxin expression, studied together with transcripts of the main regulators of uterine function (ERα and PR), under different endocrine environments in the reproductive tract of sheep. The virtue of this study is that no exogenous hormones were used, and therefore, the differences observed reflect the physiological status of the animals. The regulation of the transcripts of IGF-I, thioredoxin, ERα and PR, was most likely dependent on the endogenous endocrine status of the ewes, and for each transcript this regulation varied in the different regions of the reproductive tract.