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Abstract
Total urinary cyclic AMP (UcAMP) and nephrogenous cyclic AMP (NcAMP) were measured in 4, 20 and 24 h urine in forty-eight healthy volunteers. There were no significant differences between 4, 20 and 24 h excretion rate of UcAMP and NcAMP whether it was corrected for the glomerular filtration rate ([UcAMP]GF, [NcAMP]GF), creatinine corrected (UcAMP/Crea)U, or expressed as actual excretion rate (NcAMP, n), nor any sex differences. Mean values ± one standard deviation (SD) for these parameters:
[UcAMP]GF: 30.4 ± 9.4 nmol/1; 27.7 ± 7.0 nmol/min; 28.1 ± 6.9 nmol/1 in 4, 20 and 24 h urine, respectively.
[NcAMP]GF: 13.4 ± 8.5 nmol/1; 10.6 ± 7.7 nmol/1; and 11.1 ± 7.2 nmol/1 in 4, 20 and 24 h urine, respectively.
(NcAMP, n): 1.45 ± 0.90 nmol/min; 1.14 ± 0.80 nmol/min; 1.17 ± 0.73 nmol/min in 4, 20 and 24 h urine, respectively, NcAMP accounts for about 40% of UcAMP.
A positive correlation was found between plasma cyclic AMP and [UcAMP]GF (r = 0.41, P<0.001), whereas this relationship could not be demonstrated between plasma cyclic AMP and [NcAMP]GF (r = -0.008, P>0.1). The calculation of [NcAMP]GF therefore corrects for unsuspected high or low plasma cyclic AMP values, and is therefore the preferred parameter of the PTH effect on the kidney tubular cells.
No correlation could be demonstrated between [NcAMP]GF and concentration of ionized calcium in plasma. An advantage of [NcAMPlGF compared to the actual excretion rate (NcAMP, n) is that the former expression can be calculated from the concentration of cAMP and creatinine in urine and plasma without measuring the diuresis.
Plasma cyclic AMP, ionized calcium, and parathyroid hormone (PTH), were regulated within narrow limits, without any significant difference between men and women.
Our data do not reveal any significant variation between 4 and 24 h urine collection. The choice between a 4 or 24 h test therefore mostly depends on the practicability of the test.