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Fetal cardiovascular reactions during labour and asphyxia modified by adrenergic receptor agonists and antagonists
In the human fetus the adrenergic system develops morphologically at an early stage. The development of adrenergic receptors occurs to a large extent before birth. The human fetus is capable of a large production of catecholamines, particularly during the last two months of fetal life. Normal labour and delivery elicits an increased release of catecholamines, a reaction that is markedly enhanced by asphyxia. beta-Receptor stimulants not only relax the uterine smooth muscle but also tend to modify the concentration of surfactant in lung fluid. beta-Receptor blocking agents, both non-selective and cardioselective, create a problem in clinical medicine since they provide an effective means of treating hypertension in pregnancy. Theoretical implications of such treatment present a risk to the fetus. Experimental evidence from the fetal sheep preparation indicate that beta-receptor blockade carriers an immediate risk to the severely asphyxiated fetus when the blockade is induced acutely. In this situation heart muscle contractility, heart rate and cardiac output fall abruptly while the capacity for anaerobic glycolysis is greatly diminished. Even though such acute animal experiments are far removed from clinical practice the results suggest that great caution should be exercised in the use of adrenergic blocking agents in obstetric practice.
In the human fetus the adrenergic system develops morphologically at an early stage. The development of adrenergic receptors occurs to a large extent before birth. The human fetus is capable of a large production of catecholamines, particularly during the last two months of fetal life. Normal labour and delivery elicits an increased release of catecholamines, a reaction that is markedly enhanced by asphyxia. beta-Receptor stimulants not only relax the uterine smooth muscle but also tend to modify the concentration of surfactant in lung fluid. beta-Receptor blocking agents, both non-selective and cardioselective, create a problem in clinical medicine since they provide an effective means of treating hypertension in pregnancy. Theoretical implications of such treatment present a risk to the fetus. Experimental evidence from the fetal sheep preparation indicate that beta-receptor blockade carriers an immediate risk to the severely asphyxiated fetus when the blockade is induced acutely. In this situation heart muscle contractility, heart rate and cardiac output fall abruptly while the capacity for anaerobic glycolysis is greatly diminished. Even though such acute animal experiments are far removed from clinical practice the results suggest that great caution should be exercised in the use of adrenergic blocking agents in obstetric practice.