Atrial natriuretic peptide and extracellular volume contraction after birth

Plasma concentrations of atrial natriuretic peptide (ANP) were measured in full-term newborns immediately after birth and on the 3rd, 5th, 7th and 10th day of life. The ANP concentrations were within the normal range in the first hours of life. Plasma concentrations of ANP had increased significantly on the 3rd and 5th day of life, while body weight decreased continuously. After the 5th day of life ANP concentration decreased continuously reaching its minimum on the 10th day whereas body weight increased. The mechanism behind ANP release shortly after birth is not known. The increase in ANP concentration in plasma may however induce changes in body fluid compartments shortly after birth which would result in physiological weight loss.

Influence of dopamine on atrial natriuretic peptide level in premature infants

The role of dopamine (DA) in the activation and/or release of atrial natriuretic peptide (ANP) was investigated in 11 premature infants during the early postnatal period. Mean plasma concentration of ANP and free DA level before DA infusion was 252.6 +/- 210 fmol/ml, and 0.4 +/- 0.2 ng/ml, respectively. DA infusion in a dose of 2 micrograms/kg/min caused a rise in plasma free DA level to 59.7 +/- 21.5 ng/ml and a significant increase in GFR, diuresis, sodium excretion and fractional sodium excretion. The plasma concentration of ANP, however, remained unchanged (252.6 +/- 210.0 vs. 213 +/- 143.0 fmol/ml). Thus, our data failed to demonstrate a stimulatory effect of DA on ANP release in premature infants. The role of the high plasma concentration of ANP in preterm neonates immediately after birth has to be clarified.

Dopamine causes inhibition of Na+-K+-ATPase activity in rat proximal convoluted tubule segments

We studied the effect of dopamine (DA) on Na+-K+-ATPase activity in proximal convoluted tubule (PCT) segments dissected from perfused rat kidneys. DA inhibited Na+-K+-ATPase activity in a dose-dependent manner. Inhibition was significant with 10(-7) M DA and maximal with 10(-4) M DA. The inhibition was reversible. Enzyme inhibition occurred in the presence of DA and a DA antagonist, metoclopramide, but not when 10(5) M of the DA1 and DA2 agonists fenoldopam mesylate and LY 171555 were added in the absence of DA. In PCT segments incubated with the DA precursor dopa, Na+-K+-ATPase activity was also inhibited. However, dopa did not inhibit the sodium pump if dopa decarboxylase activity was blocked with benserazide. These findings suggest an intracellular site of action of DA. In tubules incubated in different K concentrations, 10(-5) DA decreased the maximal activity (Vmax) and increased the Km. DA 10(-5) M caused an almost immediate swelling of PCT segments. Swelling did not occur in the presence of both DA and 10(-5) M amiloride. The DA-induced tubular swelling was probably due to inhibition of Na+-K+-ATPase-mediated Na+-transport. We conclude that in rat PCT segments, DA causes a rapid and reversible inhibition of apparent Na+-K+-ATPase activity and an apparent reduction in the affinity for K. The site of action appears to be intracellular.

Acute oliguria in preterm infants with hyaline membrane disease: interaction of dopamine and furosemide

Ten premature infants with hyaline membrane disease and with acute oliguria were treated with furosemide or furosemide and dopamine. Furosemide alone did not increase diuresis. Furosemide when combined with dopamine, however, caused significant increases in urine output, sodium excretion, fractional sodium excretion and creatinine clearance. These data suggest that the increase in the sodium excretion was due not only to a reduction in the tubular sodium reabsorption but also to an increase in the glomerular filtration rate. Since in premature neonates the creatinine clearance is not a very precise index of the glomerular filtration rate, the extent of contribution of the increase in the glomerular filtration rate to the enhanced sodium excretion cannot be determined. Despite the increase in the sodium excretion, the serum sodium concentration did not fall significantly. We conclude that the combined treatment with dopamine and furosemide is useful for treating furosemide-resistant, severe functional renal failure in preterm infants with hyaline membrane disease.

The effect of dopamine administration on the activity of the renin-angiotensin-aldosterone system in sick preterm infants

Nine premature infants with birth weight of 1150 to 2500 g and gestational age of 28 to 35 weeks were given dopamine in a dose of 2-4 micrograms/kg/min to treat cardiopulmonary distress. In addition to monitoring of blood gases, blood pressure, acid-base balance, urine flow and urinary sodium excretion, plasma renin activity (PRA) and plasma aldosterone concentration (PA) was also determined prior to and during dopamine therapy. The dopamine-induced increase in urine flow and urinary sodium excretion was associated with a significant increase of PRA from 18.2 +/- 5.1 ng/ml/h to 33.0 +/- 5.6 ng/ml/h (P less than 0.025), while PA and blood pressure remained unaltered by dopamine administration. It is suggested that the angiotensin II-stimulated aldosterone production is overridden by the inhibitory effect of dopamine.

Effect of low-dose dopamine infusion on prolactin and thyrotropin secretion in preterm infants with hyaline membrane disease

The effect of low-dose (2-4 micrograms/kg/min) and long-term (greater than or equal to 46 h) dopamine infusion on serum prolactin and thyrotropin concentrations was investigated in 8 preterm infants with hyaline membrane disease. Dopamine was administered for systemic hypotension and/or for impending renal failure. Serum prolactin decreased from 1,314.5 +/- 422.7 microU/ml to 489.9 +/- 464.1 microU/ml (p less than 0.005), while serum thyrotropin fell from 3.77 +/- 2.27 microU/ml to 1.01 +/- 0.25 microU/ml (p less than 0.025) during dopamine infusion. Our data indicate that exogenous dopamine exerts an inhibitory effect on the secretion of prolactin and thyrotropin even in the sick preterm neonate. The role of prolactin in fetal lung maturation and in regulation of the neonatal tissue water stores is discussed. The results of the present study are also useful in explaining the renal effects of long-term low-dose dopamine infusion in the sick preterm infant.

The use of dopamine for the prevention of the renal side effects of indomethacin in premature infants with patent ductus arteriosus

To determine if dopamine would prevent the renal side effects of indomethacin, fifteen preterm infants were randomized into two groups: seven received indomethacin alone, and eight received indomethacin together with low dose dopamine infusion. Infants who received indomethacin together with dopamine had significantly higher UV (p less than 0.005), CNa (p less than 0.005), Cosm (p less than 0.005) and FENA (p less than 0.005) than those of infants who received indomethacin alone. There was, however, no significant difference in Ccr and FNa between the groups. These data indicate that dopamine overcomes indomethacins renal side effects of tubular origin, but it cannot prevent the renal vasoconstrictive action of vasoconstrictor hormones following the inhibition of prostaglandin synthesis by indomethacin. Considering that RBF and GFR turn to normal approximately 12 hours after the last dose of indomethacin, and that with the use of dopamine systemic blood pressure and peripheral circulation can also be normalized and to some extent myocardiac contractility improved, low doses of dopamine can be used instead of furosemide in the sick preterm infant with PDA when indomethacin therapy is indicated.

Cardiovascular response to dopamine in hypotensive preterm neonates with severe hyaline membrane disease

The effect of low dose (2, 4, and 8 micrograms/kg per min) dopamine infusion on blood pressure, heart rate and renal function was studied in 18 hypotensive, preterm infants with severe hyaline membrane disease (HMD). Significant dose-related effects found during dopamine infusion were systolic and diastolic blood pressure elevation and diuretic effect, while heart rate increase occurred only with 8 micrograms/kg per min of the drug. This indicates, that in the preterm neonate, dopamine at low doses has a pronounced effect on the alpha- and dopamine-receptors, while its beta-receptor stimulating activity is minimal. We demonstrated a significantly decreased metabolic clearance rate of dopamine in preterm infants. Thus, beside the differences in the vascular receptors' maturation, the decreased metabolic clearance rate should also be taken into account when explaining the cardiovascular and renal effects of low dose dopamine infusion in these babies. Dopamine was found to be useful in normalizing low arterial blood pressure, in improving impaired peripheral circulation, and in producing a marked diuresis in hypotensive preterm neonates with severe hyaline membrane disease.

[Tolazoline and dopamine in the treatment of the persistent fetal circulation syndrome]

The combined application of Tolazoline and Dopamine for the treatment of the persistent fetal circulation syndrome showed that Dopamine prevented the most common side effects of Tolazoline i.e. systemic hypotension and oliguria. The authors emphasize the importance of continuous monitoring of the systemic blood pressure in infants during this treatment.

Effects of dopamine on renal functions in premature neonates with respiratory distress syndrome

The renal effects of dopamine have been studied in preterm infants with RDS. Dopamine has been given in doses of 0.5-2.0 microgram/kg/min as a continuous intravenous infusion in cases of peripheral circulatory disturbances. As a result, the circulation became stable and some renal parameters improved. There was a + 106% increase of urine output as well as a + 73%, + 140%, + 21% increase in Na-excretion, FeNa, creatinine clearance respectively. In accordance with the marked increase in phosphorus excretion the titratable acidity was also increased. There was a significant decrease in the renal urea excretion and free water clearance. These alterations were probably caused by an intrarenal hemodynamic redistribution. The possible mechanism of the renal changes are also discussed. The observations demonstrate the functional maturity of renal dopaminergic receptors in the preterm infants.