Near-infrared irradiation of the thyroid area: effects on weight development and thyroid and parathyroid secretory patterns

This study evaluates possible changes in weight and the secretory patterns of the thyroid and parathyroid glands irradiated with a 780-nm light-emitting diode (LED) source under conditions allowing their identification in an animal model. The use of near-infrared light sources to detect the parathyroid glands has been a subject of research due to the benefit provided to patients undergoing thyroid and parathyroid surgery. However, few studies have explored possible changes in weight and the secretory patterns of the glands when subjected to light stimulation. Thirty-two male Wistar rats were divided into two groups and subjected to cervical dissection and irradiation of the thyroid-parathyroid region under general anesthesia. The animals in group 1 (irradiated) were exposed to a 780-nm LED light beam for 180 s (dose 1.37 J/cm(2)), whereas the animals in group 2 (control) were not irradiated. Blood samples were collected pre-exposure, 7 min after exposure, and 30 and 60 days after exposure to measure calcium, parathyroid hormone (PTH), triiodothyronine (T-3), thyroxine (T-4), and thyroid-stimulating hormone (TSH) levels in both groups. Weight variations between the evaluation periods were also analyzed. Parametric statistics were used (Student's t test and ANOVA) after assuming normal distribution of continuous variables with the Shapiro-Wilk test. No significant variation was observed in any of the analyzed parameters pre- and postexposure. A significant increase in the calcium level was observed at 30 days in the irradiated group compared with that in the control group (11.156 +/- 1.31 mg/dl vs 10.300 +/- 0.30 mg/dl; df = 30 p < 0.03) but this change was no longer observed at 60 days (9.925 +/- 0.23 mg/dl vs 10.014 +/- 0.18 mg/dl; df = 14 p = 0.21). Irradiated rats gained less weight in the first 30 days after surgery (39.647 +/- 32.39 vs 55.917 +/- 22.61; df = 30 p = 0.146) and at 60 days (84.000 +/- 27.36 vs 84.571 +/- 5.62; df = 14 p = 0.957), no differences were observed between the two groups. No significant variations in weight development or changes in the secretory patterns of the thyroid and parathyroid glands exposed to near-infrared stimulation were observed, confirming the safety of this light source in the identification of the parathyroid glands.