Cardiotoxicity of β-mimetic catecholamines during ontogenetic development - possible risks of antenatal therapy

Catecholamines are involved in the regulation of a wide variety of vital functions. The β-adrenergic receptor (β-AR) - adenylyl cyclase system has been identified early in embryogenesis before the heart has received adrenergic innervation. The structure of β-receptors in the immature myocardium is similar to that in adults; there are, however, significant quantitative developmental changes in the inotropic and chronotropic responsiveness. Information on the toxic effect of the β-AR agonists in the immature heart is surprisingly scarce, even though these agents are used in clinical practice both during pregnancy and in early postnatal development. Large doses of β-AR agonists induce malformations of the cardiovascular system; the type of change depends upon the time at which the β-AR agonist was administered during embryogenesis. During postnatal ontogeny, the cardiotoxicity of β-AR agonists increased from birth to adulthood. It seems likely that despite interspecies differences, developmental changes in the cardiac sensitivity to β-AR agonists may exist in all mammals, depending on the degree of maturation of the system involved in β-adrenergic signaling. All the existing data draw attention to the possible harmful consequences of the clinical use of β-AR agonists during early phases of cardiac development. Late effects of the early disturbances of the cardiac muscle cannot be excluded.

The cardiopulmonary effects of dobutamine and norepinephrine in isoflurane-anesthetized foals

OBJECTIVE

To evaluate the cardiovascular effects of norepinephrine (NE) and dobutamine (DB) in isoflurane-anesthetized foals.

STUDY DESIGN

Prospective laboratory study.

METHODS

Norepinephrine (0.05, 0.10, 0.20, and 0.40 microg kg(-1) minute(-1)) and dobutamine (2.5, 5.0, and 10 microg kg(-1) minute(-1)) were alternately administered to seven healthy, 1- to 2-week-old isoflurane-anesthetized foals. Arterial and pulmonary arterial blood pressure, right atrial pressure, pulmonary artery occlusion pressure, heart rate, body temperature, cardiac output, arterial and mixed venous blood pH, partial pressure of carbon dioxide, partial pressure of oxygen [arterial partial pressure of oxygen (PaO(2)) and mixed venous partial pressure of oxygen (PvO(2))], and packed cell volume were measured. Standard base excess, bicarbonate concentration, systemic and pulmonary vascular resistance, cardiac index (CI), stroke volume, left and right stroke work indices, oxygen delivery (DO(2)), consumption, and extraction were calculated. Results Norepinephrine infusion resulted in significant increases in arterial and pulmonary arterial pressure, systemic and pulmonary vascular resistance indices, and PaO(2); heart rate was decreased. Dobutamine infusion resulted in significant increases in heart rate, stroke volume index, CI, and arterial and pulmonary arterial blood pressure. Systemic and pulmonary vascular resistance indices were decreased while the ventricular stroke work indices increased. The PaO(2) decreased while DO(2) and oxygen consumption increased. Oxygen extraction decreased and PvO(2) increased.

CONCLUSIONS AND CLINICAL RELEVANCE

Norepinephrine primarily augments arterial blood pressure while decreasing CI. Dobutamine primarily augments CI with only modest increases in arterial blood pressure. Both NE and DB could be useful in the hemodynamic management of anesthetized foals.

Effect of isoproterenol on myocardial mechanical function and cyclic AMP content in the fetal rabbit

The effect of isoproterenol on mechanical function was studied in the isolated arterially perfused heart of the fetal (21st and 28th day of gestation) and newborn rabbits. The inotropic effect of isoproterenol in the fetus was less than in the newborn. In contrast, myocardial cyclic AMP levels after isoproterenol infusion in the fetus were greater than in the newborn. The inotropic effects of dibutyryl cyclic AMP and of calcium in the fetus were less than in the newborn. These data suggest that the process from beta-receptor to cyclic AMP in the fetus was equally or even more responsive to isoproterenol than in the newborn. The diminished inotropic effect of isoproterenol in the fetus may be due, at least in part, to the decreased inotropic effect of calcium.

Maturation of circulatory system in three mammalian models of human development

The review surveys the literature on maturation of vasoconstrictor and vasodilator functions in cerebral, renal and intestinal circulations of three non-primate models of human development. An ovine model has been refined for use at both fetal and neonatal stages of development. Important variables controlling regional circulations in the lamb fetus at term include arterial O2 content and pCO2 (brain), angiotensin-II (kidney) and norepinephrine (small intestine). Blood flow autoregulation to decreasing perfusion pressure has been inferred for the renal circulation of the neonate. A canine model has been employed in the postnatal period, usually later than the first week after birth. Important variables controlling regional circulations in the young puppy include arterial pO2 and pCO2 (brain) and epinephrine and angiotensin-II (kidney). Blood flow autoregulation to decreasing pressure has been demonstrated in the cerebral circulation at birth and in the renal circulation at one week thereafter. The intestinal circulation has not been studied with respect to blood flow control. A porcine model has been examined from birth through at least two months of postnatal life. Important variables controlling regional circulations in swine at birth include adrenergic nerve stimulation, arterial pCO2 (brain), angiotensin-II (kidney) and norepinephrine (kidney and small intestine). Blood flow autoregulation to decreasing perfusion pressure has been demonstrated in the brain by the fourth day, in the kidney by the end of the second week and in the small intestine by the end of the first month after birth. The advantage of each model for further investigation of functional maturation of regional circulatory control is summarized.