Brooks V L, Kane C M, Van Winkle D M
Department of Physiology and Pharmacology, Oregon Health Sciences University, Portland, USA.
Am J Physiol. 1997 Sep;273(3 Pt 2):R960-6. doi: 10.1152/ajpregu.1997.273.3.R960.
Two studies were performed to determine whether the attenuation of baroreflex control of heart rate during late pregnancy in conscious rabbits is due to changes in parasympathetic (Para) or sympathetic (Sym) control of the heart. In the first, baroreflex relationships between arterial pressure and heart rate were generated before and after treatment with propranolol (Pro) to block Sym or with methscopolamine (Meth) to block Para. Each rabbit was studied in both the pregnant and nonpregnant state. Pregnancy decreased maximum baroreflex gain from 14.9 +/- 4.0 to 4.8 +/- 0.9 beats.min-1.mmHg-1 (P < 0.01) and decreased heart rate range from 177 +/- 6 to 143 +/- 10 beats/min (P < 0.01), primarily by increasing minimum heart rate (114 +/- 6 to 134 +/- 8 beats/min; P < 0.01). The difference between pregnant and nonpregnant rabbits in baroreflex gain was not altered by Meth but was abolished by Pro, suggesting that it is due to decreased Sym control of the heart. The elevated minimum heart rate of pregnancy persisted after Pro, but was abolished by Meth, suggesting that it is mediated by decreased Para control of the heart. In the second study, isolated buffer-perfused hearts from pregnant and nonpregnant rabbits were treated with increasing doses of isoproterenol (0.3-300 mM) or acetylcholine (0.3-10,000 microM), and the heart rate responses were determined. Hearts from pregnant rabbits were more sensitive to isoproterenol (P < 0.05), but less responsive to acetylcholine (P < 0.05). In conclusion, pregnancy-induced decreases in cardiac reflex gain and range appear to be mediated by alterations in Sym and Para, respectively. The change in Sym occurs proximal to the heart, whereas the decreased contribution of Para may be due, at least in part, to decreased sensitivity of the heart to acetylcholine.
进行了两项研究以确定清醒兔妊娠晚期心率压力反射控制的减弱是否归因于心脏副交感神经（Para）或交感神经（Sym）控制的变化。在第一项研究中，在用普萘洛尔（Pro）阻断交感神经或用甲基东莨菪碱（Meth）阻断副交感神经之前和之后，建立动脉血压与心率之间的压力反射关系。对每只兔子在妊娠和非妊娠状态下都进行了研究。妊娠使最大压力反射增益从14.9±4.0降至4.8±0.9次·分钟⁻¹·mmHg⁻¹（P<0.01），并使心率范围从177±6降至143±10次/分钟（P<0.01），主要是通过增加最低心率（从114±6升至134±8次/分钟；P<0.01）。妊娠兔与非妊娠兔之间压力反射增益的差异未被Meth改变，但被Pro消除，提示这归因于心脏交感神经控制的降低。妊娠时升高的最低心率在使用Pro后持续存在，但被Meth消除，提示它是由心脏副交感神经控制的降低介导的。在第二项研究中，用递增剂量的异丙肾上腺素（0.3 - 300 mM）或乙酰胆碱（0.3 - 10,000 μM）处理来自妊娠和非妊娠兔的离体缓冲液灌注心脏，并测定心率反应。来自妊娠兔的心脏对异丙肾上腺素更敏感（P<0.05），但对乙酰胆碱反应性较低（P<0.05）。总之，妊娠引起的心脏反射增益和范围的降低似乎分别由交感神经和副交感神经的改变介导。交感神经的变化发生在心脏近端，而副交感神经贡献的降低可能至少部分归因于心脏对乙酰胆碱敏感性的降低。
