Effect of low-dose dopamine infusion on urinary prostaglandin E2 excretion in sick,preterm infants

In pharmacological doses dopamine (DA) will interact with several endocrine systems and both inhibit (prolactin, thyrotropin) and enhance (renin, angiotensin) hormonal release. In this study we have examined whether DA given to preterm neonates will influence prostaglandin (PG) production. The question is of importance since vasodilatator PGs play a role in postnatal adaptation. We determined the effect of low dose DA infusion on the 24 h urinary PGE₂ excretion rate (an index of renal PGE₂ synthesis) in preterm infants. Six preterm neonates, with a 24-h requirement of 2 g/kg per min DA treatment for oedema, moderate oliguria, poor peripheral perfusion and/or mild systemic hypotension were studied on days 2 (Day 1), 3 (Day 2, the day of DA infusion), and 4 (Day 3, DA discontinued) of life. Six preterm infants (control group) that did not require DA infusion were also studied to monitor possible spontaneous changes in the renal PGE₂ production on days 2, 3 and 4 of life. In the control group urine output (U_v) and PGE₂ excretion rate remained unchanged during the study. In the study group DA administration resulted in nearly two-fold increases in both the U_v (194%) and PGE₂ excretion (182%). Urinary PGE₂ excretion was, however, closely related to urine flow in both the control infants (Day 1–3) and the study group infants (Day 1–2). Since increased diuresis stimulates renal PGE₂ production, our data suggest that the increased PGE₂ excretion on Day 2 in the study group was not due to a direct effect of DA on PGE₂ synthesis. On Day 3, however, urinary PGE₂ excretion in the study group decreased out of proportion to that of the U_v (-66% vs-23%), indicating that discontinuation of the drug infusion directly decreases renal PGE₂ synthesis. In conclusion, the findings of the present study indicate that low dose DA does not directly trigger renal PGE₂ production in the sick preterm infant.Abbreviations DA dopamine - PG prostaglandin - U_v urine output - PGE₂ excr PGE₂ excretion rate - PGE₂ conc PGE₂ concentration - SD standard deviation - U_Na, U_K urinary sodium, potassium excretion