Effect of all-trans-retinoic acid on the structure of thyroid glandand pituitary tyrotrophs in streptozotocin-diabetic male rats

BackgroundDiabetes mellitus, a chronic disease with increasing prevalence worldwide, is knownto be associated with thyroid disorders. Retinoic acid, a metabolite of vitamin A, iscurrently used for the treatment of diabetes and obesity.Aim of the workThe present study aimed to evaluate the possibility of using all-trans-retinoicacid (atRA) in reducing the structural changes of the thyroid gland and pituitarythyrotrophs in streptozotocin-induced diabetic rats.Materials and methodsThirty adult male albino rats were divided into three equal groups: group I,control; group II, which included rats in which diabetes was induced by a singleintraperitoneal injection of streptozotocin (100 mg/kg); and group III, which includedrats in which diabetes was induced as in group II, followed by an intraperitonealinjection of atRA (2.5 mg/kg/day) from the third day. After 4 weeks, thyroid andpituitary specimens were processed for light and electron microscopic study.ResultsMost thyroid follicles of diabetic rats were distended with colloid and lined withflattened thyrocytes with hyperchromatic nuclei and vacuolated cytoplasm thatcontained dilated rough endoplasmic reticulum, few colloid droplets, and fewlysosomes. Some exfoliated cells were observed in the lumen. C cells had rarefiedcytoplasm containing a few secretory granules. The number of mast cells showeda nonsignificant change. Thyrotrophs showed dilated rough endoplasmic reticulum,destroyed mitochondria, and decreased secretory granules. The atRA-treateddiabetic group showed almost the same structural alterations in the thyroid gland,with even more changes in thyrotrophs.ConclusionDespite its current use as a novel therapy for diabetes, atRA exerted no amelioratingeffect on diabetes-induced histological changes in the thyroid gland and, moreover,exacerbated the changes of pituitary thyrotrophs.