醋酸甲羥孕酮

醋酸甲羥孕酮 (MPA) 是一種強效的合成**孕激素**（黃體素衍生物）。 過去在獸醫學中，它常被用於行為修飾（例如：遊蕩、雄性間的攻擊行為、噴尿）和皮膚疾病（如貓心因性脫毛）。然而，由於其**引發嚴重副作用的風險極高**，目前的使用已大幅減少。 **臨床要點：** 對於行為問題，現在強烈建議使用更安全的替代方案（如 SSRIs、TCAs 或外科結紮）。MPA 偶爾仍用於特定的生殖適應症，例如懷孕母犬的黃體功能不全、良性前列腺肥大的短期管理，或德國牧羊犬的腦下垂體侏儒症。由於其具有深遠的全身性影響，在使用前必須仔細權衡潛在益處與引發內分泌及生殖系統併發症的巨大風險。

作用機制: MPA mimics endogenous progesterone by binding to intracellular **progesterone receptors**, translocating to the nucleus, and altering gene transcription. It transforms the proliferative endometrium into a secretory endometrium and inhibits spontaneous uterine contractions. * **Endocrine/Reproductive:** Exerts negative feedback on the hypothalamus and pituitary, decreasing **GnRH** → suppressing **FSH** and **LH** release, thereby inhibiting estrus and spermatogenesis. It also possesses anti-estrogenic properties and decreases plasma testosterone. * **Glucocorticoid Activity:** MPA has significant intrinsic affinity for **glucocorticoid receptors**, leading to profound suppression of the hypothalamic-pituitary-adrenal (HPA) axis (decreased ACTH and cortisol release). * **Metabolic Effects:** Induces peripheral insulin resistance, which can precipitate **diabetes mellitus**. * **Growth Hormone:** In dogs, progestins can stimulate the mammary glands to produce growth hormone, potentially leading to acromegaly.

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