Magness R R, Rosenfeld C R
Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas 75235.
Am J Obstet Gynecol. 1988 Jul;159(1):252-61. doi: 10.1016/0002-9378(88)90531-5.
Attenuated pressor responses to angiotensin II and alpha-agonists normally occur during ovine pregnancy; however, for alpha-agonists it is not known to what extent this reflects alterations in cardiac output. We therefore compared peripheral and cardiac responses to alpha-agonists in pregnant (n = 6) and nonpregnant (n = 6) sheep, measuring mean arterial pressure, heart rate, and cardiac output before and during steady-state dose responses to norepinephrine (0.458 to 45.84 micrograms/min) and phenylephrine (1.29 to 129 micrograms/min). Both alpha-agonists caused dose-dependent increases in mean arterial pressure and systemic vascular resistance, more so in nonpregnant than pregnant sheep (p less than 0.01), and decreases in cardiac output and heart rate (p less than 0.01). In both nonpregnant and pregnant sheep the percent change in systemic vascular resistance generally exceeded the percent change in mean arterial pressure, reflecting decreases in cardiac output; however, at equivalent increases in percent change in mean arterial pressure and percent change in systemic vascular resistance, the fall in the percent change in cardiac output was greatest in pregnant sheep (p less than 0.05). Also, at similar increases in mean arterial pressure the percent change in heart rate was greatest in pregnant sheep (p less than 0.01). In contrast to angiotensin II, the attenuated pressor responses to alpha-agonists observed during ovine pregnancy are partly a result of reflex decreases in cardiac output mediated mainly through falls in heart rate.
在绵羊怀孕期间，对血管紧张素II和α-激动剂的升压反应通常会减弱；然而，对于α-激动剂而言，尚不清楚这种情况在多大程度上反映了心输出量的变化。因此，我们比较了怀孕（n = 6）和未怀孕（n = 6）绵羊对α-激动剂的外周和心脏反应，在对去甲肾上腺素（0.458至45.84微克/分钟）和去氧肾上腺素（1.29至129微克/分钟）进行稳态剂量反应之前和期间，测量平均动脉压、心率和心输出量。两种α-激动剂均导致平均动脉压和全身血管阻力呈剂量依赖性增加，未怀孕绵羊比怀孕绵羊增加得更多（p < 0.01），并导致心输出量和心率降低（p < 0.01）。在未怀孕和怀孕绵羊中，全身血管阻力的百分比变化通常超过平均动脉压的百分比变化，反映了心输出量的降低；然而，在平均动脉压百分比变化和全身血管阻力百分比变化等量增加时，怀孕绵羊的心输出量百分比变化下降最大（p < 0.05）。此外，在平均动脉压相似增加时，怀孕绵羊的心率百分比变化最大（p < 0.01）。与血管紧张素II不同，在绵羊怀孕期间观察到的对α-激动剂的升压反应减弱部分是主要通过心率下降介导的心输出量反射性降低的结果。
