A type of internal secretion or hormone-like substance produced by body tissues that inhibits or regulates biological processes.
From Greek 'chalao' meaning 'to slacken' or 'to relax,' combined with the chemical suffix '-one'. The term was coined in early endocrinology to describe inhibitory substances before the hormone concept was fully developed.
Chalones were discovered before scientists understood hormones—they noticed that tissues somehow told other tissues to calm down, which was mystifying until the endocrine system's complexity was revealed.
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