Effect of Melatonin upon Thyroid Hormone Secretion Rate and Endocrine Glands of Chicks.

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Abstract
The normal TSR of a group of 55 male and female chicks was determined starting at 4 weeks of age. They were then divided into 3 groups of equal TSR. The mean TSR of a control group and groups injected with 50 and 100 pig of melatonin/100 g bw/day determined starting at 7 weeks were approximately equal, indicating that melatonin had no effect upon the TSR of immature chickens. However, at 10 weeks of age melatonin significantly reduced the testes weights 94% (P< .001) and ovaries 67% (P<.025) at the higher level as well as the adrenal and thymus glands. The pituitary gland weights of the females were progressively increased on the 2 levels of melatonin while the males were unaffected. The pineal glands were increased in both sexes at the lower level. At the higher level, the males showed an increase but the females showed a slight decrease.