Abstract
BackgroundThis study aimed to detect changes in hormone levels in the hypothalamic–pituitary–ovarian axis in Sprague-Dawley (SD) rats with hypothyroidism, and identify differences in the pregnancy and abortion rates of female adult rats. The potential role of gonadotropin releasing hormone (GnRH) as the link between the hypothalamic–pituitary–ovarian axis and reproductive function regulated by thyroid hormones was also investigated.MethodsFemale SD rats (n = 136) were causally classified into two groups: the normal-drinking-water group (n = 60) and the 0.05% propylthiouracil-drinking-water group (PTU 2 mg/kg/day, n = 76) to establish an adult rat model of hypothyroidism (6 weeks). Female and male rats at a ratio of 1:2 were used to establish a hypothyroidism pregnancy model. GnRH mRNA and GnRH receptor (GnRHR) expression in rats was detected using real time quantitative PCR(qRT-PCR) and immunohistochemistry, respectively.ResultsThe abortion rate differed significantly between the hypothyroidism pregnancy group and the normal pregnancy group (P < 0.05). No significant differences were found in the distribution of the GnRHR among the five nuclei (hypothalamic arcuate nucleus, hypothalamic ventromedial nucleus, hypothalamic anterior nucleus, paraventricular nucleus of the hypothalamus, and ventral premammillary nucleus) of the hypothalamus and ovary (P > 0.05). Hypothyroidism had no significant effect on GnRH mRNA expression in the hypothalamic–pituitary–ovarian axis in the four groups (normal control group, normal pregnancy group, hypothyroidism pregnancy group, and hypothyroidism group) (P > 0.05).ConclusionsHypothyroidism had an adverse impact on pregnancy in rats and may affect the distribution of pituitary GnRHR, whereas it did not obviously affect the distribution of GnRHR in the nuclei of the hypothalamus and ovary. Hypothyroidism had no effect on GnRH mRNA expression.
Highlights
This study aimed to detect changes in hormone levels in the hypothalamic–pituitary–ovarian axis in Sprague-Dawley (SD) rats with hypothyroidism, and identify differences in the pregnancy and abortion rates of female adult rats
The present results suggested that hypothyroidism affects the distribution of the pituitary GnRH receptor (GnRHR); we observed no evident effect on the distribution of the GnRHR of the ovary and hypothalamus
The present study showed that the GnRHR is expressed in tissues of the hypothalamic–pituitary–ovarian axis in pregnant SD rats
Summary
This study aimed to detect changes in hormone levels in the hypothalamic–pituitary–ovarian axis in Sprague-Dawley (SD) rats with hypothyroidism, and identify differences in the pregnancy and abortion rates of female adult rats. The potential role of gonadotropin releasing hormone (GnRH) as the link between the hypothalamic–pituitary–ovarian axis and reproductive function regulated by thyroid hormones was investigated. The regulation of reproductive function is mainly accomplished by the hypothalamic–pituitary–ovarian axis. At the initial stage of infancy and prior to GnRH release, circulating gonadotropin levels are elevated and, in infantile female primates, are associated with blood estradiol levels in the adult range [6]. The first switch is activated and inhibits GnRH pulsation discharge, which leads to a hypogonadotropic condition that secures gonadal silencing before puberty. At the end of adolescent growth, the second switch is invoked, which leads to the recurrence of puberty in the discharge of pulsatile GnRH and the formation of the hypothalamic–pituitary–ovarian axis (gonadarche), the major physiological process underlying primate puberty [8]
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