Atrial natriuretic peptide (ANP) is produced primarily in the cardiac atria. Several hormones and neurotransmitters, such as endothelin, arginine-vazopressin, and cathecolamines, directly stimulate the secretion of atrial natriuretic peptide. Increased atrial-wall tension, reflecting increased intravascular volume, is the main stimulus for its release. ANP exerts its effects primarily on the cardiovascular system by reducing the blood pressure and on the kidneys by increasing natriuresis, fractional sodium excretion and fraction of filtration.
To research the role of ANP in weight loss of the newborn in the postnatal first week and in their adaptation to extra-uterine life.
Sixty-one newborns with a mean gestational age of 40 weeks (range 38-42 weeks) were enrolled in the study. We obtained aldosterone and ANP levels from the umbilical artery on the postnatal first day and from the venous blood on the postnatal third and tenth days. Fractional sodium excretion (FENa) was calculated simultaneously.
ANP increased from 12.32 ± 8.94 mmol/L on the postnatal first day to 33.34 ± 17.84 mmol/L on the postnatal third day (p<0.01). Aldosterone levels also increased from 98.69 ± 32.07 pg/ml on the postnatal first day to 222.46 ± 102.22 pg/ml on the postnatal third day (p<0.001). There was a slight increase in FENa from 0.74 ± 0.66 ion the postnatal first day to 0.81± 0.54 on the postnatal third day despite a rise in aldosterone concentration. On the postnatal tenth day the levels of ANP and aldosterone decreased to levels similar to those on the postnatal first day. FENa on the tenth day decreased to levels below those on the postnatal first and third days.
The increase in FENa despite the rise in aldosterone levels was attributed to the effect of ANP which might act by inhibiting apical Na + channel function or proximal tubular sodium reabsorption. A rise in ANP levels may contribute to weight loss of the newborn during the first five days.
Keywords: ANP, weight loss, newborn