Newborn urimary cyclic. AMP and developmental renal responsiveness to parathyroid hormone

Abstract

Since the renal action of parathyroid hormone (PTH) is known to be mediated via 3′, 5′-adenosine monophosphate (cyclic AMP), urinary cyclic AMP studies were used to determine proximal tubular maturation. Ten formula fed full-term male infants showed a 30 to 60 fold increase in phosphate clearance and excretion with a 3–4 fold increase in urinary cyclic AMP comparing their first and third day 24-hour urines.This 3–4 fold increase in cyclic AMP could reflect increasing pTH renal responsiveness and/or increasing secretion of PTH. One and 3 day old infants and adults were given a one hour PTH infusion (5 μ/kg/hr) measuring urinary cyclic AMP in time periods before and after the infusions. Peak increases in responses from baseline of cyclic AMP were 1.64 ± 0.34, 7.15 ± 1.15 and 36.30 ± 0.73 μmoles/gm creatinine mean ± range on first day, third day and adults respectively with similar relationships of increasing phosphate excretion and decreasing % TRP. Thus, the development of newborn renal responsiveness to parathyroid hormone is on the cellular cyclic AMP level suggesting increasing maturation of the enzyme adenyl cyclase which forms cyclic AMP from ATP.