催產素
催產素是一種由下丘腦室旁核和視上核合成，並儲存於垂體後葉的九肽激素。在獸醫學中，它主要作為子宮收縮劑，用於引產或增強分娩時的子宮收縮、治療產後胎盤滯留和子宮內膜炎、促進子宮復舊，以及在無乳症情況下促進排乳。 **臨床要點：** * **偏好微量給藥 (Mini-dosing)：** 現代獸醫產科學強烈建議使用「微量劑量」（例如狗的總劑量為 0.25-4 單位），而非傳統的高劑量。高劑量會導致強直性、無效的子宮收縮，透過壓迫胎盤損害胎兒氧氣供應，並增加子宮破裂的風險。 * **鈣依賴性：** 催產素的功效高度依賴細胞外鈣離子。給藥前必須糾正低血鈣或低血糖。鈣能增加收縮的「強度」，而催產素增加的是「頻率」。 * **子宮頸狀態：** 如果子宮頸未開或存在未經矯正的阻塞性難產，絕對不可使用催產素。
作用機制: Oxytocin exerts its effects by binding to specific **G-protein coupled oxytocin receptors (OXTR)** on the cell membrane of uterine myofibrils and myoepithelial cells of the mammary gland. * **Uterine Contraction:** Binding to OXTR activates the **Gq/11 pathway** → stimulates **Phospholipase C (PLC)** → increases inositol triphosphate (**IP3**) and diacylglycerol (**DAG**) → triggers the release of intracellular calcium from the sarcoplasmic reticulum. Calcium binds to calmodulin, activating **Myosin Light Chain Kinase (MLCK)**, leading to smooth muscle contraction. The threshold for oxytocin-induced contraction is significantly lowered late in pregnancy due to upregulation of oxytocin receptors by high estrogen levels. * **Milk Let-down:** Oxytocin stimulates the contraction of myoepithelial cells surrounding the mammary alveoli, forcing milk into the larger ducts and cisterns. It does *not* have galactopoietic (milk-producing) properties.
各物種劑量
- For retained placenta in patients with uterine atony · 10-20 Units oxytocin. · IM/IV · Once · Limited value after 48 hours postpartum. Note for CAMELIDS (NW): 5-10 Units IM at 10-minute intervals for retained placenta (Adams 2008).
- For mild to moderate cases of acute post-partum metritis · 5-10 Units IM 3-4 times a day for 2-3 days · IM · TID to QID · 2-3 days
- For retained placenta in patients with uterine atony · 10-20 Units oxytocin. · IM/IV · Once · Limited value after 48 hours postpartum.
- For mild to moderate cases of acute post-partum metritis · 5-10 Units IM 3-4 times a day for 2-3 days · IM · TID to QID · 2-3 days
- To control post-extraction cervical and uterine bleeding after internal manipulations · 10-20 Units IV, may repeat SC in 2 hours · IV/SC · Once, may repeat in 2h
- To promote uterine involution after uterine prolapse manual reduction · 0.5-5 Units IM OR 5-10 Units (total dose) IM · IM · Once · Extrapolated from dog doses.
- To treat primary uterine inertia · 0.25 Units (total dose) SC or IM to a maximum dose of 4 Units per queen. Generally not given more frequently than hourly. · SC/IM · q1h · Given 15 minutes after calcium gluconate.
- For adjunctive treatment of metritis · 0.5-5 Units IM · IM · Once · May be used if birth occurred less than 24 hours prior.
給藥途徑
禁忌症
- Dystocia due to abnormal fetal presentation (unless corrected)
- Closed or unrelaxed cervix
- Known hypersensitivity to oxytocin
- Significant cephalopelvic disproportion
- Obstetrical emergencies where surgical intervention (C-section) is warranted
- Pregnancy (for nasally administered oxytocin)
不良反應
- Uterine cramping and discomfort
- Tetanic uterine contractions (at high doses)
- Uterine rupture
- Fetal compromise or death (due to placental compression)
- Water intoxication (with prolonged high-dose infusions)
- Hypersensitivity reactions (more common with non-synthetic products)
藥物相互作用
- Thiopental · May delay thiopental anesthesia (reported in humans; clinical significance in animals is not firmly established).
- Vasoconstrictors (Sympathomimetics) · Concurrent use post-partum may result in severe hypertension. Monitor closely.
監測
- Uterine contractions (frequency, duration, and strength via tokodynamometry if available)
- Status of the cervix (must be dilated)
- Fetal monitoring (heart rate/distress)
- Maternal calcium and glucose levels
過量
Effects of overdosage on the uterus depend on the stage of the uterus and the position of the fetus(es). * **Uterine Effects:** Hypertonic or tetanic contractions can occur, leading to tumultuous labor, uterine rupture, fetal injury, or fetal death due to compromised placental blood flow. * **Water Intoxication:** Can occur if large doses are infused for a long period, especially with large volumes of electrolyte-free IV fluids. * *Early signs:* Listlessness, depression. * *Severe signs:* Coma, seizures, death. * *Treatment:* Stop oxytocin therapy, restrict water access. Severe cases may require osmotic diuretics (mannitol, urea, dextrose) with or without furosemide.
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