Altered state of primordial follicles in neonatal and early infantile rats due to maternal hypothyroidism: Light and electron microscopy approach

Abstract

tThyroid hormones (TH) are one of the key factors for normal prenatal development in mammals. Previ-ously, we showed that subclinical maternal hypothyroidism leads to premature atresia of ovarian folliclesin female rat offspring in the pre-pubertal and pubertal periods. The influence of decreased concentra-tion of TH on primordial follicles pool formation during neonatal and early infantile period of rat pupswas not investigated previously. Maternal hypothyroidism during pregnancy has irreversible negativeinfluence on primordial follicles pool formation and population of resting oocytes in female rat offspring.The study was done on neonatal and early infantile control (n-10) and hypothyroid (n-10) female ratpups derived from control (n-6) and propylthiouracil (PTU) treated pregnant dams (n-6), respectively.Ovaries of all pups were removed and processed for light and transmission electron microscopy (TEM).Number of nests, oogonia and oocytes per nest, primordial, primary, secondary and preantral follicleswere determined. Screening for overall calcium presence in ovarian tissue was done using Alizarin redstaining. Morphology and volume density of nucleus, mitochondria and smooth endoplasmic reticulum(sER) in the oocytes in primordial follicles was also assessed. Caspase-3 and terminal deoxynucleotidyltransferase dUTP nick end labelling (TUNEL), both markers for apoptosis, and proliferating cell nuclearantigen (PCNA) for proliferation were determined in oocytes and granulosa cells in different type of fol-licles. In neonatal period, ovaries of hypothyroid pups had a decreased number of oogonia, oocytes andnests, an increased number of primordial follicles and a decreased number of primary and secondary fol-licles, while in early infantile period, increased number of primary, secondary and preantral follicles werefound. Alizarin red staining was intense in hypothyroid neonatal rats that also had the highest content ofdilated sER. Number of mitochondria with altered morphology in both groups of hypothyroid pups wasincreased. Apoptosis markers have not shown significant difference between groups but PCNA had anincreased expression in the oocytes and granulosa cells in primordial follicles of hypothyroid rats. Lightand electron microscopy analysis indicate that previously detected premature ovarian follicular atresia inpre-pubertal and pubertal hypothyroid rats is preceded with premature formation of primordial folliclesfollowed by slight changes on sER and mitochondria in examined oocytes, and increased expression of PCNA.