Effect of propranolol infusion on the umbilical and uterine circulations of pregnant sheep

Cardiovascular pharmacotherapeutic considerations during pregnancy and lactation

Cardiovascular drugs are often used in pregnancy for the treatment of maternal and fetal conditions. Mothers could also require continued postpartum drug therapy. Most cardiovascular drugs taken by pregnant women can cross the placenta and therefore expose the developing embryo and fetus to their pharmacologic and teratogenic effects. These effects are influenced by the intrinsic pharmacokinetic properties of a given drug as well as by the complex physiological changes occurring during pregnancy. Many drugs are also transferred into human milk and therefore can potentially have adverse effects on the nursing infant. This 2-part article summarizes some of the available literature concerning the risks and benefits of using various cardiovascular drugs and drug classes during pregnancy and lactation. Included in the discussion are cardiac glycosides, antiarrhythmic drugs, drugs used to treat both acute and chronic hypertension, cholesterol-lowering agents, anticoagulants, thrombolytics, and antiplatelet drugs.

Uterine and fetal hemodynamics and fetal cardiac function after atenolol and pindolol infusion. A randomized study

OBJECTIVE

To evaluate the short-term effects of intravenously given atenolol and pindolol on utero- and umbilicoplacental vascular impedance, fetal hemodynamics and cardiac function in patients suffering from pregnancy-induced hypertension.

STUDY DESIGN

A total of 24 women were randomized to receive atenolol or pindolol infusion. By using pulsed color Doppler techniques, uterine, placental arcuate, umbilical fetal middle cerebral and renal arteries were examined before, at the end and 30 min after the end of infusion. Pulsatility indices (PI) were calculated to assess vascular impedance. Fetal myocardial function was evaluated by using pulsed Doppler and M-mode echocardiography. Peak systolic velocities from the ascending aorta and pulmonary trunk, and also inner diameters and fractional shortenings of both ventricles were measured.

RESULTS

Both drugs significantly decreased maternal blood pressure. Immediately after the infusion, maternal heart rate was significantly decreased in both groups; but the decrease was clearer and lasted longer in the atenolol group. Pindolol caused no changes in utero- or umbilicoplacental vascular impedance, while atenolol increased it in the nonplacental uterine artery. After atenolol infusion, PI in the umbilical artery was higher than after pindolol. Pindolol had no effects on fetal hemodynamics, while atenolol decreased PI value in the fetal renal artery. Peak systolic velocity in the pulmonary trunk was decreased after atenolol. Pindolol did not affect the fetal cardiac function. In subgroups with originally increased utero- or umbilicoplacental vascular impedance, the responses in uterine and umbilical vascular impedance and in fetal hemodynamics and cardiac function after atenolol and pindolol were different compared to whole groups.

CONCLUSION

Differently acting antihypertensive agents seem to affect differently uteroplacental vascular impedance. Atenolol may have some direct effects on fetal hemodynamics and cardiac function. According to our results, pindolol seems to be more preferable in the treatment of pregnancy-induced hypertension than atenolol.

New-onset ventricular tachycardia during pregnancy

During evaluation for palpitations, presyncope, or syncope, seven pregnant women had documented ventricular tachycardia. Before pregnancy none had a history of significant cardiac disease or symptomatic arrhythmia. The tachycardia rate ranged from 117 to 250 beats/min and lasted up to 65 seconds. Arrhythmia evaluation in five of the patients suggested catecholamine-sensitive ventricular tachycardia. This diagnosis was supported by either a positive relation to exercise or isoproterenol infusion, suppression of arrhythmia by beta-blockade or sleep, and lack of induction of arrhythmia by programmed electrical stimulation of the heart. The arrhythmias resolved in one patient soon after evaluation and in one other patient after 2 months of controlling therapy. Five other patients continued to receive therapy throughout pregnancy. Delivery was accomplished in all patients without significant maternal or neonatal complications.

Maternal and fetal haemodynamics in hypertensive pregnancies during maternal treatment with intravenous hydralazine or labetalol

Intravenous treatment with 10 mg of hydralazine or 100 mg of labetalol was randomly allocated to 30 hypertensive pregnant women. Umbilical artery flow velocity waveforms were recorded using a pulsed Doppler duplex scanner (ATL Mk V) and umbilical artery pulsatility index (PI) and fetal heart rate (FHR) were derived from these recordings. Maternal blood pressure decreased significantly after both drugs. Maternal pulse rate increased after hydralazine but did not change significantly after labetalol. FHR did not change significantly after hydralazine but decreased after labetalol. PI decreased after hydralazine and increased after labetalol--most fetuses showed little change but a few in each group showed large changes in PI, as did two of five additional patients studied. We attributed the decrease in PI in some fetuses after hydralazine to vasodilation, and the increase in PI in some fetuses after labetalol to vasoconstriction in the fetoplacental circulation, suggesting that fetal beta-blockade may occur after maternal treatment with labetalol.

Response to beta-blockers in maternal and fetal rat hearts in vitro

The effects of beta-blockers on maternal and fetal heart rates have been assessed by comparing isoprenaline concentration-heart rate relationships of hearts isolated from pregnant rats. The normal and maximal heart rates obtained for the maternal and fetal hearts were similar to published data. A slightly but significantly higher concentration of isoprenaline was required to produce 50% of the maximal response of fetal hearts than maternal hearts, suggesting that fetal hearts were less sensitive to isoprenaline than the maternal hearts. The beta-blockers used (propranolol, labetalol, metoprolol and atenolol) all showed a lower affinity to the beta-receptors of fetal hearts than those of maternal hearts, as indicated by significant differences in the pA2 values. Given the similar effects of the beta-blockers in the maternal and fetal hearts it is concluded that pharmacokinetic considerations and beta-blocker selectivity should be used as the basis of choice when treating maternal hypertension during pregnancy.

The influence of beta-adrenergic activity on fetal heart rate and the umbilical circulation during hypoxia in fetal sheep

To determine the importance of beta-adrenergic activity during hypoxia in the fetus, 13 studies were carried out on seven chronically instrumented sheep at nine tenths of gestation. Hypoxia was induced by having the mother breathe gas mixtures that resulted in a reduction of maternal arterial oxygen tension to 32 mm Hg. Hypoxia resulted in a decrease in fetal heart rate (165 +/- 17 to 140 +/- 28 bpm) and fetal oxygen consumption (5.9 +/- 1.3 to 3.0 +/- 1.5 ml/min/kg) and increases in fetal arterial and umbilical venous pressures. There was no change in umbilical blood flow (209 +/- 58 ml/min/kg). Propranolol, 1.1 ml/kg, was rapidly infused into a fetal vein to achieve complete beta-adrenergic blockade. Umbilical vascular resistance increased significantly, fetal heart rate decreased to 112 +/- 22 bpm, and umbilical blood flow decreased to 165 +/- 73 ml/min/kg. There was no further decrease in fetal oxygen consumption. These decreases are approximately twice those seen after propranolol without hypoxia. These findings suggest that during hypoxia there is an increase in beta-adrenergic activity, which tends to maintain fetal heart rate and umbilical blood flow. This activity counteracts the increase in vagal activity with hypoxia, which decreases heart rate.

Maternal and fetal cardiovascular indices during fetal hypoxia due to cord compression in chronically cannulated sheep. I. Responses to timolol

Timolol, one of the newer beta-adrenergic antagonists, has less depressive effects on the heart than propranolol, so that it has the potential for use by pregnant women. In chronically cannulated ewes, timolol at 0.01 and 0.1 mg/kg of body weight induced maternal and fetal bradycardia; the higher dose also depressed uterine blood flow and fetal PaO2. When this higher dose preceded brief compression of the umbilical cord, uterine flow was further depressed and the usual posthypoxia rebound tachycardia did not develop. Both the blocking of fetal responses to hypoxia (precluding detection of fetal distress) and the reduction in uterine flow led us to conclude that timolol taken by a mother could pose particular hazards for her fetus in hypoxic conditions, such as during cord compression at parturition.

Hemodynamic changes after chronic pindolol administration in pregnant renal hypertensive rats

The aim of the present study on pregnant renal hypertensive rats was to investigate the effects on central hemodynamics and uteroplacental blood flow after chronic administration of pindolol, a nonspecific beta-adrenergic receptor blocking agent with intrinsic beta-stimulatory effect. Renal hypertension was induced by partial clamping of both renal arteries four weeks before pregnancy. Pindolol was administered with the food during the entire pregnancy period. Two to four days before expected delivery mean arterial pressure, heart rate, cardiac output, (dye-dilution technique) and utero-placental blood supply (microsphere technique) were determined. The chronic pindolol treatment reduced heart rate by 25 per cent while both mean arterial pressure and cardiac output remained unchanged. However, blood flow to uterus and placentae was reduced by 43 and 64 per cent, respectively, after pindolol treatment. Clinical as well as experimental studies (15, 16) demonstrate a reduced utero-placental blood supply when pregnancies are complicated by hypertension. As pregnancies with severe hypertension are associated with an increased frequency of intrauterine growth retardation and intrauterine asphyxia the present results indicate that the combination of hypertension and long-term treatment with beta-blockers might reduce utero-placental blood flow enough as to seriously interfere with fetal oxygen supply thereby increasing the risk of intra- and extra-uterine asphyxia.

The effect of long term treatment with a beta-adrenoceptor blocker, l-propranolol, on the distribution of cardiac output of the late gestational guinea-pig

1. The effects of daily administration of propranolol on the distribution of cardiac output were studied in the late pregnant guinea-pig. 2. The animals were given either saline, 5 or 50 mg/kg per day of l-propranolol for 15 days during the last trimester of gestation. 3. Blood flow responses were assessed by injecting 15 microns microspheres into the conscious animal one to two days prior to parturition. 4. The fraction of cardiac output reaching the placentas was significantly reduced in both groups (P less than 0.5 and P less than 0.001, respectively), while flow to all other organs studied remained unaltered. 5. It is suggested that propranolol exerts a selective effect on the placental vascular bed in the guinea-pig.

The effect of beta-adrenergic stimulation on fetal cardiovascular function during hypoxemia

The effect of beta-adrenergic stimulation on fetal cardiovascular function during hypoxemia was studied in six lamb fetuses with gestational ages of 119 to 140 days. In chronic preparations, we determined fetal heart rate, umbilical blood flow (by electromagnetic flowmeter), PO2, PCO2, and pH and calculated fetal cardiac output and organ blood flows (using 15 mu nuclide-labeled microspheres). Observations were made during control periods and periods of hypoxemia, beta-adrenergic blockade by propranolol, and hypoxemia superimposed upon the beta-adrenergic blockade. Beta blockade effected a decrease in fetal heart rate both at rest and with hypoxemic stress. Propranolol produced a fall in cardiac output with hypoxemia, but the meaning of this in regard to beta-adrenergic effects is unclear. Beta blockade did not alter fetal arterial pressure or general blood flow distribution. However, we observed a decrease in umbilical blood flow in response to propranolol under both normoxic and hypoxemic conditions.

Ontogenesis of beta-adrenergic receptors in the ovine placenta

Radioligands with high specific activity and high affinity have recently become available to study the beta-adrenergic receptor (BAR). BAR may be important in the placenta for mediating a variety of metabolic and hemodynamic effects of catecholamines including placental hormone synthesis and secretion, placental glycogenolysis, and placental blood flow. Little is known regarding the development of the BAR. We have used the tritiated radioligand dihydroalprenolol to study the ontogenesis of BAR in the fetal and maternal portions of the ovine placenta. The receptor number decreased from 415 fmoles . mg-1 of protein at 120 days' gestation to 226 fmoles . mg-1 at 145 days; this trend was highly significant (r = -0.822, p less than 0.01). Similar changes were noted in the dissociation constant. Downward regulation as a result of fetal neurosympathetic maturation is proposed as an explanation for this observation.

Propranolol and hydrallazine in the management of essential hypertension in pregnancy

A combination of propranolol and hydrallazine was administered to 13 patients with longstanding hypertension during 15 pregnancies. Hydrallazine was continued through labour and delivery in all patients, while in eight patients propranolol was discontinued 2 to 15 days before delivery. Blood pressure control was uniformly good and superimposed pre-eclampsia did not occur during combined therapy. There were 14 livebirths and one unexplained stillbirth. Except for two cases of milk hypoglycemia, there were no neonatal complications.

Long-term propranolol therapy in pregnancy: maternal and fetal outcome

Propranolol, a beta-adrenergic blocking agent, has found an important position in the practice of medicine. Its use in pregnancy, however, is an open question as a number of detrimental side effects have been reported in the fetus and neonate. Ten patients and 12 pregnancies are reported where chronic propranolol has been administered. Five patients with serial pregnancies with and without propranolol therapy are also examined. Maternal, fetal, and neonatal complications are examined. An attempt is made to differentiate drug-related complications from maternal disease--related complications. We conclude that previously reported hypoglycemia, hyperbilirubinemia, polycythemia, neonatal apnea, and bradycardia are not invariable and cannot be statistically correlated with chronic propranolol therapy. Growth retardation, however, appears to be significant in both of our series.

Cardiac output and its distribution and organ blood flow in the fetal lamb during ritodrine administration

The response of the fetal circulation to beta adrenergic stimulation with ritodrine hydrochloride has been investigated by long-term monitoring of the fetal lamb in utero. Ritodrine was infused intravenously either into the ewe or directly into the fetus, and cardiovascular and acid-base responses were measured. Fetal cardiac output and its distribution were measured with the use of radionuclide-labeled microspheres. The output of each ventricle also was measured by means of long-standing implanted electromagnetic flow transducers around the ascending aorta or pulmonary trunk during infusion of ritodrine at various rates into the fetus. Infusion of ritodrine (1.9 mcg. per kilogram per minute) into the ewe caused no change in fetal heart rate, blood pressure, cardiac output, or umbilical blood flow, but did cause an increase in fetal adrenal and myocardial blood flow. Ritodrine infused directly into the fetus produced a marked increase in fetal heart rate and a minimal change in cardiac output. There were no significant changes in fetal or maternal acid-base balance during the ritodrine infusions.

Effect of propranolol on fetal tachycardia in diabetic pregnancy

Propranolol was administered during the last 20 days of pregnancy to a diabetic woman because of fetal tachycardia (heart rate approximately 200 beats/min). With a daily dose of 160 mg of propranolol, a fetal heart rat of 120 to 160 beats/min could be achieved. Blood concentration of propranolol was measured in the mother and infant after birth. The level in the neonatal blood was 20 percent of the maternal sample, which is definitely higher than expected from animal experiments. No undersirable effect of propranolol treatment was detected. Postpartum, the infant demonstrated paroxysmal supraventricular tachycardia, and propranolol was again essential in maintaining a normal rate.

Effect of fenoterol (Th1165a) infusion on uterine and umbilical blood flow in pregnant sheep

The effect of fenoterol (Th1165a) upon uterine artery blood flow (UtBF) and umbilical vein blood flow (UmBF) was investigated in near-term, nonlaboring chronic sheep preparations. During intravenous fenoterol infusions to the ewe in either incremental doses from 0.025 to 0.200 microng per kilogram per minute or constant infusions of 0.025 microng per kilogram per minute for 120 minutes. UtBF and UmBF did not change significantly. Dose-related maternal tachycardia, hyperglycemia, and relative acidemia occurred, but there were no significant changes in mean maternal and fetal arterial pressures or fetal heart rate. The simultaneous infusion of propranolol (2 microng per kilogram per minute) with fenoterol (0.200 microng per kilogram per minute) blocked the maternal tachycardia but resulted in a significant decrease in UmBF and a significant increase in UtBF. In all of the maternal infusions. UtBF significantly rose and plateaued up to 14 per cent above the control level during the 120 minute recovery period after infusion. A non-beta-adrenergic effect of fenoterol is suggested as the cause of this UtBF increase.