Maturational response of colonic and renal Na+,K(+)-ATPase activity to K+ load and betamethasone in preterm rats.
Preterm human infants demonstrate high fecal K+/Na+ ratio that is inversely related to maturation. Renal and colonic basolateral membrane-located Na+,K(+)-adenosine triphosphatase (Na+,K(+)-ATPase) governs K+ excretion and is enhanced by both steroid administration and K+ loading. However, the response of premature kidney or colon to these stimuli is not well studied. We measured basal as well as stimulated levels of renal and colonic Na+,K(+)-ATPase activity in response to betamethasone and K+ load given separately and betamethasone given after K+ load in premature, mature, and 4-day-old Sprague-Dawley rats. Although preterm rats showed a higher basal level in the kidneys (p < 0.004), an increase in enzyme activity in response to the stimuli was achieved only in the colon (p < 0.001 for betamethasone, p < 0.0001 for K+ load, and p < 0.0007 for the combination). At term and at 4 days of postnatal age, however, the kidneys showed much higher levels than the colon in response to stimuli (p < 0.0001 for all) except for betamethasone at term. The response of colonic tissue of preterm and term rats to betamethasone given 4 days after a K+ load was less marked than response to betamethasone or K+ load given separately (p < 0.001). The stimulated levels achieved in the preterm colon were higher than the basal preterm renal values (p < 0.001). The tissue K+ content increased in response to K+ load in only the preterm colon (p < 0.05). We have demonstrated a tissue specificity in the development of Na+,K(+)-ATPase activity in K+ excretory organs of rats.(ABSTRACT TRUNCATED AT 250 WORDS)
Verma
R P
RP
Division of Neonatology, International Institute for Infant Nutrition and Gastrointestinal Disease, Philadelphia PA.
Horvath
K
K
Blochin
B
B
Lu
R B
RB
Wang
W J
WJ
Lebenthal
E
E
D000375:Aging / Q000378:metabolism*; D000818:Animals; D001623:Betamethasone / Q000494:pharmacology*; D003106:Colon / Q000201:enzymology* / Q000254:growth & development; D005865:Gestational Age; D007668:Kidney / Q000201:enzymology* / Q000254:growth & development; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D001623:Betamethasone; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium