Cudd T A, Wood C E
Department of Physiology, University of Florida College of Medicine, Gainesville 32610-0274, USA.
Am J Physiol. 1996 Mar;270(3 Pt 2):R594-8. doi: 10.1152/ajpregu.1996.270.3.R594.
Intravenous mineral acid infusions into fetal sheep stimulate increases in plasma adrenocorticotropic hormone (ACTH) and cortisol concentrations that correlate to the induced changes in arterial pH (pHa). We have recently demonstrated that ACTH and cortisol responses to mineral acid infusion in adult sheep are mediated by thromboxane A2 (TxA2). We designed the present experiments to test the hypothesis that fetal ACTH and cortisol responses are also mediated by TxA2. We infused chronically instrumented fetal sheep with 1 N HCl (0.5 ml/min i.v.) for 60 min, with or without pretreatment with the cyclooxygenase inhibitor flunixin-N-methylglucamine. HCl infusion significantly decreased pHa and significantly increased the arterial partial pressure of O2 (PaO2) and CO2 (PaCO2). Flunixin pretreatment significantly decreased fetal plasma thromboxane B2 (TxB2) concentrations but did not significantly alter the blood gas and pH response to HCl. TxB2 is a stable metabolite of TxA2 and was measured as an index of TxA2 generation. HCl increased fetal heart rate only in the flunixin group. Plasma ACTH and cortisol concentrations were increased significantly in both groups; flunixin did not significantly alter the responses. HCl infusion did not significantly alter plasma TxB2 concentrations. We conclude that the fetal ACTH and cortisol responses to HCl infusion are not mediated by TxA2 or other prostanoids whose synthesis depends on cyclooxygenase activity.
向胎羊静脉内输注无机酸可刺激血浆促肾上腺皮质激素（ACTH）和皮质醇浓度升高，且这些升高与动脉血pH值（pHa）的诱导变化相关。我们最近证明，成年羊对无机酸输注的ACTH和皮质醇反应是由血栓素A2（TxA2）介导的。我们设计了本实验来检验胎羊ACTH和皮质醇反应也由TxA2介导这一假说。我们对长期植入仪器的胎羊静脉内输注1N盐酸（0.5ml/min），持续60分钟，同时给予或不给予环氧化酶抑制剂氟尼辛 - N - 甲基葡糖胺预处理。输注盐酸显著降低了pHa，并显著升高了动脉血氧分压（PaO2）和二氧化碳分压（PaCO2）。氟尼辛预处理显著降低了胎羊血浆血栓素B2（TxB2）浓度，但并未显著改变对盐酸的血气和pH反应。TxB2是TxA2的一种稳定代谢产物，被作为TxA2生成的指标进行测量。盐酸仅在氟尼辛组增加了胎羊心率。两组血浆ACTH和皮质醇浓度均显著升高；氟尼辛并未显著改变这些反应。输注盐酸并未显著改变血浆TxB2浓度。我们得出结论，胎羊对输注盐酸的ACTH和皮质醇反应不是由TxA2或其他其合成依赖于环氧化酶活性的前列腺素介导的。
