Zhu Y S, Szeto H H
Department of Pharmacology, Cornell University Medical College, New York, New York.
J Pharmacol Exp Ther. 1989 Apr;249(1):78-82.
A dose-response analysis of the effects of morphine on fetal heart rate (FHR) and blood pressure (FBP) was conducted in 28 chronically instrumented fetal lambs. Morphine was infused directly to the fetus at doses ranging from 0.075 to 40 mg/hr. At doses below 0.15 mg/hr, morphine did not result in significant changes in FHR or FBP. With increasing doses of morphine, fetal tachycardia was observed without significant changes in FBP, and the peak response (38.3 +/- 8%) in FHR was reached at a dose of 2.5 mg/hr. Further increases in dose were associated with a decrease in the magnitude of response. This resulted in a bell-shaped dose-response curve. This tachycardia was completely abolished by either naloxone or propranolol pretreatment. These results indicate that i.v. morphine administrated produces tachycardia in unanesthetized unrestrained fetal lambs, and this effect is mediated via specific opioid receptors and involves the beta adrenergic system.
对28只长期植入仪器的胎羊进行了吗啡对胎儿心率（FHR）和血压（FBP）影响的剂量反应分析。吗啡以0.075至40毫克/小时的剂量直接注入胎儿体内。在剂量低于0.15毫克/小时时，吗啡未导致FHR或FBP出现显著变化。随着吗啡剂量的增加，观察到胎儿心动过速，而FBP无显著变化，在剂量为2.5毫克/小时时达到FHR的峰值反应（38.3±8%）。剂量进一步增加与反应幅度的降低相关。这导致了一条钟形剂量反应曲线。这种心动过速可通过纳洛酮或普萘洛尔预处理完全消除。这些结果表明，静脉注射吗啡会使未麻醉、不受约束的胎羊产生心动过速，且这种效应是通过特定的阿片受体介导的，并且涉及β肾上腺素能系统。
