Objective: 

The present study aims to examine the effect of zinc supplementation and zinc deficiency on the secretion of leptin and NPY in experimental hyperthyroidism in rats.

Methods: 

This study included 50 adult male Sprague-Dawley rats which were divided into 5 groups: Group 1, general control; group 2, sham-hyperthyroidism; group 3, hyperthyroidism (the group which was injected 0.3 mg/kg/day ip thyroxine for 4 weeks); group 4, hypothyroidism and zinc-deficient group (the group which was injected 0.3 mg/kg/day ip thyroxine and fed on a zinc-deficient diet "0.65 ppm/zinc/g/diet" for 4 weeks); and group 5, hyperthyroidism + zinc-supplemented group (the group which was administered 0.3 mg/kg/day ip thyroxine and 3 mg/kg/day zinc sulfate for 4 weeks). At the end of the 4-week procedures, all the animals were decapitated and their blood samples were analyzed to determine plasma melatonin, leptin and NPY levels by RIA.

Results: 

The highest melatonin levels in the study were found in the hyperthyroidism groups (groups 3, 4 and 5) (p<0.001). Leptin and NPY levels in the hyperthyroidism (group 3) and zinc-deficient hyperthyroidism (group 4) groups were higher than those in all other groups (p<0.001).

Conclusions: 

Results of the study indicate that hyperthyroidism brings about important alterations in the secretion of leptin and NPY, while zinc supplementation prevents these changes.