Direct influence of melatonin on the thyroid and comparison with prolactin

✍ Scribed by Wright, Mary L.; Cuthbert, Karen L.; Donohue, Maura J.; Solano, Samantha D.; Proctor, Krista L.

• Book ID: 101226992
• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 172 KB
• Volume: 286
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/(sici)1097-010x(20000501)286:6<625::aid-jez9>3.0.co;2-q

✦ Synopsis

Melatonin administered in vivo had previously been shown to inhibit thyroid cell proliferation and subsequent in vitro thyroxine (T 4 ) secretion in anuran tadpoles. Melatonin in vitro also directly reduced the sensitivity of the thyroid to thyrotropin (TSH). The present work sought to determine whether melatonin directly affected baseline, unstimulated T 4 secretion, and to compare its effect with that of prolactin (PRL). Thyroids from larval Rana catesbeiana or adult Rana pipiens were incubated in control or melatonin (0.01 to 100 µg/ml) media. Melatonin directly inhibited T 4 secretion by thyroids from both tadpoles and frogs at all concentrations of melatonin used and at both prometamorphic and climax tadpole stages. PRL, used in vitro at 10 µg/ml, did not influence the response of the thyroid to TSH (0.2 µg/ml) in young tadpoles, or the baseline secretion of T 4 by thyroids at any stage of larval life except climax, when T 4 secretion was significantly decreased by the third day of culture. Thus although both melatonin and PRL have been shown to antagonize the action of T 4 in vitro, and to decrease metamorphic rate, melatonin is a much more effective thyroid gland inhibitor than PRL.