Possible Protective Role of L-Thyroxin on the Parotid Gland of Adult Male Albino Rat in Carbimazole Induced Hypothyroidism: Histological, Histomorphometry, and Ultrastructural Study

Background: Thyroid disorders are among the most common metabolic disorders worldwide.
Thyroid dysfunction affects salivary glands function, causing hyposalivation. It also provokes
physiological and histological changes in parotid, submandibular, and in particular the sublingual
gland.
The aim of this work: The aim of this work was to clarify the histological and ultrastructural
changes that occur in the parotid gland following carbimazole-induced hypothyroidism in adult
male albino rats. The study also aims to investigate the possible protective role of L-thyroxin
supplementation on the rat parotid glands after long and short duration of hypothyroidism.
Material and Methods: Fifty-five adult male albino rats of Sprague Dawley strain; were divided into
four groups and eleven subgroups, five rats each. G І received nothing. G П given normal saline
orally daily. G Ш (medical Hypothyroidism, short duration – long duration – recovery group) given
Carbimazole orally by gastric tube in a dose of 0.05 mg/kg daily for 3,6 successive weeks for group
(a, b) and for 6 successive weeks then were left without any medication for another 3 weeks in
recovery group c. G IV-b, c (L-Thyroxine supplemented group, short duration-long duration) given
Carbimazole orally daily for 3,6 successive weeks then L-thyroxine was given orally in a dose of
(10 μg/100 g/B.W) daily for another 3 successive weeks. Animals were sacrificed 24 hours after the
last dose of Carbimazole in G III-a, b and 3 weeks after stoppage the drug in G III-c. Animals were
sacrificed 24 hours after the last dose of L- Thyroxine in G IV-b, c. The parotid specimens were
processed for histopathological examination by light and electron microscopy. The medically
induced Hypothyroidism resulted in significant parotid gland damage which was more obvious
with longer duration; as follow: a) most of the acini had irregular outlines and were widely
separated with narrow lumen and cytoplasmic vacuoles. b) some acinar cells contained ill defined,
irregular, pyknotic or hyperchromatic nuclei. c)Vascular changes: dilated and engorged with blood.
d) the interlobular and striated ducts appeared disrupted and dilated. e) extravasated blood with
cellular infiltration were seen in the interstitial space.
In Conclusion: Thyroid hormones (THs) had a significant effect in protection of parotid gland
against damage induced by carbimazole, as it preserved the normal histological architecture of the
parotid gland. This beneficial effect of THs was mostly related to its antioxidant properties. The
expression of BCL-2 has certain regularity in apoptosis after drug administration. Regulation of
glandular atrophy and apoptosis are closely related. The molecular mechanism of the apoptosis of
the gland is not clear, and further study is needed in the future.