Does laser phototherapy influence the proliferation of myoepithelial cells in the salivary gland of hypothyroid rats?

- This study demonstrated an in vivo model of hypothyroidism.
- Myoepithelial cells in the euthyroid group increased when λ660 nm was evaluated.
- LPT did not influence cells from submandibular gland in rats with hypothyroidism.

Thyroid hormones influence both development and growth of organs and tissues and guarantee metabolic demands that interfere with the quality of digestive secretions, including those of the salivary glands. Laser phototherapy - LPT can modulate various biological phenomena and its diverse effects permit the action on different cell types. The aim of this study was to evaluate the influence of laser phototherapy on myoepithelial cells of salivary glands of hypothyroid rats. Forty-two albino Wistar rats were divided into two main groups: euthyroid (EU) and hypothyroid (HYPO). Hypothyroidism was induced using propylthiouracil (PTU) for 4 weeks. Each group was divided into subgroups: control (without laser) and laser groups (Red/infrared - IR). LPT was used on the submandibular gland and was carried out using a diode laser (λ660 or λ780 nm, 40 mW, spot size 0.04 cm2, irradiation area 1 cm2, 300 s, 6 J/cm2 per gland, 12 J/cm2 per session) and started two weeks after PTU treatment. LPT was repeated every other day for two weeks. After animal death, the glands were removed, dissected and processed for immunohistochemical analysis. It was observed an increase in the number of myoepithelial cells of hypothyroid control rats in comparison to euthyroid controls (p = 0.001). Visible LPT (λ660 nm) caused significant higher proliferation of myoepithelial cells in EU rats when compared to IR LPT (λ 780 nm)(p ≤ 0.001).It is concluded that, despite the LPT protocol used did not influence myoepithelial proliferation on hypothyroid rats it significantly increased the proliferation on euthyroid animals.