在哺乳類動物中，由下視丘及腦下腺前葉產生一些化學物質，稱為激素；藉血流輸送，與特定細胞膜上專一接受器結合後，會活化細胞內第二傳訊者，進而引起一連串的訊號反應而生成新的激素或其他生化作用。本文以雄性素為例，綜述激素的分類、激素的特性及激素的作用機制，提供讀者對激素之基礎瞭解，或可應用於未來之研究。

In mammals, the chemicals released from hypothalamus and anterior pituitary gland are called hormones and combine with their receptors in the target cells to activate the 2nd messengers, and then induces a cascade reactions. This review makes an introduction for "hypothalamuic-pituitary-testis axis", to introduce the hormone classifications, characteristics, and the action mechanism. We hope to provide some informations for the readers to understand the physiology and regulation of the hormone, e. g. androgen and to create idea in the future studies.