Possible effects of melatonin on thymus gland after pinealectomy in rats.

OBJECTIVES

The purpose of this study was to investigate the effects of pinealectomy and pinealectomy plus melatonin administration on thymus weight and histology in adult Wistar-albino rats.

METHODS

The animals were divided into three groups. Group I and Group II were designated as control (sham-pinealectomized) and pinealectomized rats, respectively. They received 10% ethanol (0.1 ml per day s.c.) alone. The rats in Group III were pinealectomized and daily injected with melatonin (3 mg/kg/0.1 ml 10% ethanol per day s.c.) commencing on the day seven after surgical operation. Injections were applied for two months.

RESULTS

The thymus atrophied and its weight decreased after pinealectomy (p<0.001). The cortico-medullary boundary could not be distinguished and in the thymus induced a loss of lymphoid elements, increased number of phagocytic macrophages and enlarged blood vessels. Melatonin prevented the thymic involution.

CONCLUSIONS

These results suggest that pinealectomy decreases thymus weight and that long-term administration of melatonin restores thymus weight to normal levels.