Effect of Melatonin on Thyroid Hormone Secretion Rate and Feed Consumption of Female Rats.

Abstract

TSR estimation of Sprague-Dawley-Rolfsmeyer strains of rats at 55 and 85 days of age was found to be significantly reduced by 22.8% and 14.8%, respectively, with subcutaneous injection of 50 [mu]g melatonin/rat at 55 days, and 75 [mu]g/rat at 85 days. An injection of 100 [mu]g/rat at 115 days of age caused no change. These results indicate that melatonin depresses TSR but the effect appears to be reduced with advancing age. Feed consumption was reduced 8.76%, a nonsignificant reduction, in 115-day-old rats injected s/c with 100 [mu]g melatonin/day/rat for 12 days. The effect may be cumulative due to increasing doses of melatonin during each TSR estimation at monthly intervals. At the end of the experiment, the mean ovarian weight showed a significant reduction of 30.1% and the pituitary weight of 34.6% compared with the control group. In contrast, the mean adrenal weight showed a significant increase of 22.7%.