RESUMO
A study of urinary osmolarities and plasmatic level of arginine-vasopressin (AVP) 48 hours after birth in a group of 70 newborns (30 of which are normal and 40 of which have acute perinatal hypoxia), selected according to previously established criteria is carried out. An evolutionary study of urinary osmolarities of newborns with acute perinatal hypoxia, osmolar index and its relation to plasmatic levels of AVP during the first week of life is also considered. AVP 48 hours after birth was blatantly more elevated among those newborns who had shown acidosis at birth (p less than 0.001) which correlated significantly with urinary osmolarity, although it showed low figures (p less than 0.05). This same correlation (p less than 0.001 and p less than 0.05) appears with osmolar index and urinary osmolarity on successive days, but it is important to point out that vasopressin decreased to base values at the end of the first week of life while osmolarities in urine increased. Conclusions are: 1) AVP is higher after 48 hours of life among those newborns with acute perinatal hypoxia and decreases progressively during the first week of life, being comparable to values obtained from normally born children 48 hours after birth at the eight day of life. 2) Renal response to this hormone is slight during the first days of life.