Effect of maternal sodium Fluoride administration during gestation and lactation on the thyroid gland development of albino rat offspring

ABSTRACT

The study was carried to follow up the postnatal developmental sequences of the rat thyroid gland in addition to investigate the effect of gestational and lactational administration of sodium fluoride on the offspring thyroid gland and its reversibility after fluoride withdrawal. Thirty mature female albino rats were used and allowed for mating. Then the known pregnant rats were divided into two groups group [A] [control group] received daily distilled water and group [B] [experimental group] received daily oral dose of sodium fluoride dissolved in distilled wafer via gastric tube [40mg/kgm body weight]. Drug administration started from the gestational day 14 up to the weaning on the postnatal day 21. The offspring of the control and experimental [fluoride treated] groups were used at the age of one, five, ten fifteen days.three weeks, one and six months [eight pups from each age]. The thyroid glands were dissected out and then the thyroid specimens were processed for histological study using Hemtoxylin and Eosin and Van Gieson 's staining methods. Histomorphometric technique was done to estimate the volume proportion of the thyroid follicles and interstitial tissues as well as the thickness of follicular epithelium of the rats of the experimental [fluoride treated] group compared to that of the control group at the age of three weeks, one and six months using the point counting technique. The obtained results were statistically analyzed using student t test. The histological results highlighted the normal postnatal developmental events of rat thyroid gland. The thyroid gland showed a primitive and immature microfollicular pattern at birth to attain the macrofollicular pattern by the second postnatal week. Further functional maturation was observed by the third postnatal week till they reached full maturity by the first postnatal month. These observations demonstrated well defined mature macrofollicles that contain abundant colloid material with visible absorptive vesicles. The histological findings of the current study demonstrated the effect of sodium fluoride on thyroid follicular pattern, follicular colloid content and the interfollicular connective tissue. These observations included predominance of microfollicular pattern, presence of disturbed follicular pattern reduction of colloid content [glycoprotein], widening of the interfollicular spaces, increased vascularity as well as obvious fibroplastic and monocytic infiltration. The histomorphometric measurements revealed statistically significant changes behween rats of the control and experimental groups at the age of three weeks and one month. The histological and histomorphometric results of the rats of the experimental group at the age of six months remained more or less similar to that of the control apart from widening of the interfollicular space. This partial recovery of thyroid histopathological and histomorphometric indices after cessation of sodium fluoride administration could indicate reversibility of its adverse effect