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  • Title: Pituitary gonadotrophin secretion during the first weeks of pregnancy.
    Author: Jeppsson S, Rannevik G, Thorell JI.
    Journal: Acta Endocrinol (Copenh); 1977 May; 85(1):177-88. PubMed ID: 324219.
    Abstract:
    A longitudinal study of basal plasma LH and FSH and their responses to 25 microng LRH iv as well as basal levels of oestradiol, progesterone, prolatin and HCG was performed every week in 3 women, pregnant after heterologous insemination, from conception until the 6th week of gestation. A comparative study was carried out in 7 women in cycles in which no conception occurred after insemination. All hormones were assayed with radioimmunoassay. LH was measured with a specific assay for native HL, which did not cross-react with HCG. A decrease in basal levels of LH and FSH as well as decreasing responses to LRH was found during the first 2 weeks of gestation. These changes did not differ from what was observed during the luteal phase in the non-conception cycles. One week later the basal FSH levels and the FSH response in the pregnant women showed a further decrease, while in the non-pregnant women, now reaching the early follicular phase, a rise in FSH basal levels occurred. The basal levels of LH and the LH response, however, did not differ from that found in the non-pregnant woment at this time. FSH basal levels remained below the lower normal limit in eumenorrhoic women from the 3rd week of gestation. By this time the FSH response was almost completely inhibited. The LH basal levels, however, remained above the lower normal limit in eumenorrhoic women, but the LH response to LRH progressively decrease and was completely inhibited by the 5th week of gestation. In the non-conception cycles the LH response varied with the levels of oestradiol in plasma. This was not found in the pregnant women as the decrease in gonadotrophin response occurred while oestradiol remained at mid-cycle levels during the first 4 weeks of gestation. Rather it seems that the increasing and continuously elevated level of progesterone, in the presence of appropriate levels of oestradiol, might be the main go nadal steroid responsible for the diminishing pituitary secretion. The contribution of HCG to the further decrease in gonadotrophin secretion after the 2nd week of pregnancy cannot be answered by the present studies. Prolactin remained at non-pregnant levels until the 6th week of gestation, and appeared to have no influence on the secretion of gonadotrophins during early pregnancy. 10 women were studied to determine the level of pituitary gonadotropin secretion during the early weeks of pregnancy. 3 women were pregnant after heterologous insemination and 7 women were cycling and without conception. Basal plasma luteinizing hormone (LH) and follicle stimulating hormone (FSH) and their responses to 25 mcg LRH as well as basal levels of estradiol, progesterone, prolactin and human chorionic gonadotropin (HCG) were determined every week for 6 weeks in the pregnant women. During the first 2 weeks of gestation basal levels of LH and FSH and the response to LRH all decreased. These values compared with values seen in the luteal phase of the normal cycle. In the 3rd week FSH decreased again in the pregnant woman but was on the rise in the cycling woman who was entering the follicular phase of the cycle. LH at this time was at the same level in both groups of women. FSH basal levels remained low from the 3rd week of gestation and FSH response was almost completely inhibited. LH basal levels remained above the lower normal limit, but LH response decreased and was completely inhibited by the 5th week of gestation. In the nonpregnant woman LH response varied with the levels of estradiol in plasma. In the pregnant woman this association was absent. The increasing levels of progesterone in the presence of the appropriate amount of estradiol may be responsible for the diminishing pituitary secretions. The role of HCG at this early stage of pregnancy is unknown. Prolactin remained at nonpregnant levels.
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