Histopathological and biochemical alterations of the parotid gland induced by experimental hypothyroidism in adult male rats and the possible therapeutic effect of Nigella sativa oil.

Thyroid hormones are essential for metabolic rate regulation and play a role on the integrity of the salivary glands. Nigella sativa is a widely used plant in medicine. This study aimed to evaluate the effect of Nigella sativa oil (NSO) on the hypothyroidism-induced parotid gland pathological alterations. Rats were divided into four groups: control group, hypothyroid group: received daily oral carbimazole for 3 weeks, hypothyroid-NSO group: NSO was orally given for 4 weeks after hypothyroidism induction and NSO group: administrated NSO only for 4 weeks. After 7 weeks, all rats were sacrificed, serum thyroid hormones were estimated, and parotid glands were assessed by histopathological, immunohistochemical, ultrastructural and morphometric analyses. Hypothyroid group showed a significant decrease in thyroid hormones with increase in thyroid-stimulating hormone (TSH) levels and decrease in body and parotid weights compared to the control rats that were improved with NSO treatment. Sections of the hypothyroid group showed fibrosis, acinar cytoplasmic vacuolations, vascular congestion, ductal dilatation, wide intercellular canaliculi, nuclear pyknosis and decreased number of secretory granules. Also, there were decreased B-cell lymphoma 2 (Bcl-2) and increased p53, Bcl-2 Associated X (Bax) and alpha-smooth muscle actin (α-SMA) immune-expressions; with decreased Bax/ Bcl-2 ratio that all were attenuated by NSO. NSO ameliorates hypothyroidism-induced parotid changes by altering p53, Bax and Bcl-2 pathway.