Seasonal Variation in Thyroid Gland of the Female Bat, <i>Taphozous Kachhensis</i> (Dobson) During Pregnancy

Abstract

The aim of present study was to compare the changes in thyroid gland during the reproductive cycle of the female bat Taphozous kachhensis . The thyroid gland of the bat was studied morphometrically and histologically, it showed marked seasonal variation in weight, quantity of colloid, epithelial cell height and plasma concentration of thyroid hormones. The thyroid gland was a symmetrical, bilobed, and located on the lateral side of the trachea, between the first and the third tracheal rings, connected by an isthmus. The mean weight of the noted lobes was (2.240±0.121) mg, (2.88±0.05) mg and (2.704±0.067) mg, during early pregnancy, mid pregnancy and late pregnancy respectively. The thyroid hormone showed marked seasonal variations. During early pregnancy there was rise in the level of TSH (1.7 ng/mL) but the slight decrease in the level of T3 (54 ng/mL) and T4 (2.9 ng/mL) was noticed. The level of TSH and T4 was decreases during mid pregnancy but the increase in the level of T3 was noticed and it was highest as compare to other stages and it is found to be 1.4 ng/mL, 1.5 ng/mL, 69 ng/mL respectively. During late pregnancy, TSH and T3 concentration decreases but the increase in the level of T4 was observed and it was found to be 0.9 ng/mL, 60 ng/mL, 2.9 ng/mL respectively. The diameter of colloid in small, medium and large follicle during early pregnancy and late pregnancy were 28 µm, 56 µm, 96 µm and 36 µm, 60 µm, 72 µm respectively. The epithelial cell heights of small, medium and large size follicles during early pregnancy and late pregnancy were 3.6 µm, 4 µm, 8 µm and 4 µm, 8 µm, 8 µm respectively.