Urinary Adenosine 3′,5′-Monophosphate Excretion in Childhood*

Abstract

Total cAMP excretion in relation to creatinine (cAMP/Cr) and glomerular filtration rate (cAMP/GFR) was measured in 2-h morning urine specimens of 437 clinically healthy subjects (227 females and 210 males): 40 infants and children, aged 1 week to 5.9 yr; 377 schoolchildren, aged 7–17.9 yr; and 20 adults, aged 20–40 yr. The cAMP/Cr ratio declined with age (r = −0.63; P < 0.001), reaching adult levels after the age of 16 yr; in contrast, the cAMP/GFR ratio remained relatively constant until this age (mean ± SD, 3.24 ± 0.82 nmol/dl) and decreased thereafter significantly (2.81 ± 0.49 nmol/dl) in 70 female and male subjects, aged 16-40 yr. While the cAMP/GFR values were not different in females and males, the cAMP/Cr ratios were significantly higher in females than in males after the age of 16 yr. In 69 children and adults, a highly significant correlation was found between 24-h and 2-h fasting urinary cAMP when the nucleotide was related to either Cr (r = 0.94; P < 0.001) or GFR (r = 0.81; P < 0.001), indicating that the measurement of cAMP excretion in morning urine specimens is a reliable reflection of 24-h nucleotide excretion. The cAMP/GFR ratio in 2-h fasting urine specimens was markedly elevated in rachitic children with serum immunoreactive parathyroid hormone (PTH) levels exceeding the upper normal range by 2- to 4-fold, but was only slightly raised in children with moderate secondary hyperparathyroidism. In six patients with PTH-deficient or PTH-resistant hypoparathyroidism, the values of the cAMP/GFR ratio overlapped with the low normal range. It is concluded that the measurement of the cAMP/GFR ratio in children under the age of 16 yr provides a useful tool of total cAMP excretion in that it is not age or sex dependent and makes complete 24-h urine collections unnecessary.