Morphofunctional state of the thyroid gland in rats with prolonged low-dose exposure to deltamethrin

Abstract

The thyroid gland is very sensitive to various stress factors, including chemical ones. Meanwhile, the effect that many ecotoxicants have on the animal endocrine system has not been studied. The effect of cyanide-containing synthetic pyrethroids on the synthesis and secretion of thyroid hormones during prolonged low-dose exposure remains an open question. This research was aimed at assessing the morphofunctional state of the thyroid gland in laboratory rats under the specified exposure regime. The studies were conducted on 48 male Wistar rats. When modeling the effect of low doses of deltamethrin on animals, the substance was administered to rats at a dose of 1/100 LD50, and the experiment lasted for 120 days. The concentrations of thyroid-stimulating hormone, total thyroxine (T4), triiodothyronine (T3), and the ratio T4/T3 were determined in the rats' blood. The solid-phase enzyme immunoassay method was used to determine hormones. For histological examination, the thyroid gland of animals was fixed in a 4% neutral formaldehyde solution. Sections of paraffin blocks were stained with hematoxylin and eosin. Prolonged low-dose exposure to deltamethrin caused hypofunction of the thyroid gland in laboratory rats, which was accompanied by a decrease in the level of thyroid hormones in the blood serum. The stimulating effect of the pituitary gland increased compensatorily due to the additional release of thyroid-stimulating hormone. At the same time, there was a change in the ratio of T4/T3 in the blood. The histological patterns of the thyroid gland were characterized by a decrease in the thyrocyte area, growth of follicles, and colloid densification.