Objective      To determine the impact of 5-aminolevulinic acid mediated photodynamic therapy (5-ALA PDT) on the morphology and function of rat parathyroid glands and surrounding tissues.       Methods      A total of 64 female SD rats

weighing 150-200 g

were randomly divided into 16 groups (n=4) according to the dose of photosensitizer (0

100

300 and 500 mg/kg) and irradiation time (0

10

15 and 20 min). The parathyroid gland and surrounding tissues were surgically exposed

followed by treatment with different doses of photosensitizer for different irradiation times. Before and after PDT

the serum levels of parathyroid hormone (PTH)

thyroxine (T4)

triiodothyronine (T3) and thyroid-stimulating hormone (TSH) were determined by ELISA. Histological observation was carried out before and after treatment.       Results      5-ALA PDT or irradiation alone had no significant change in parathyroid function. PDT induced parathyroid function reduction in a short time

but had no effect on thyroid function. With the increase of photosensitizer dose and irradiation time

the treatment showed significant effect on thyroid function. When the photosensitizer dose was 500 mg/kg and irradiation time was 10

15 and 20 min

the serum level of PTH was 75.24±6.06

47.23±5.18

and 39.10±4.03 ng/L

respectively

with significant difference as compared with control group (0 mg/kg and 0 min

128.19±4.75 ng/L

P0.05). After PDT

histological examination displayed integrated envelope of parathyroid

normal proliferation of fibrous connective tissue

increased number of vacuolated fat cells

and decreased number of gland cells compared with normal parathyroid

but no significant change was observed in the thyroid and surrounding muscles.       Conclusion      5-ALA PDT specifically disrupts the morphology and function of parathyroid glands in rats.