Comparison of renal responses to synthetic human PTH(1-34) administration in normal young and elderly male subjects.

A parathyroid hormone (PTH) loading test with synthetic human PTH(1-34) was performed in 7 young and 6 elderly normal males. The elderly subjects had significantly higher mean basal levels of serum PTH than the young subjects (0.262 +/- 0.035(SE) vs 0.097 +/- 0.012 ng Eq/ml, P less than 0.001). When human PTH(1-34) at a dose of 100 U was administered to these subjects, the mean increases in urinary excretions of adenosine cyclic 3',5'-monophosphate(cAMP) and inorganic phosphorus (Pi), expressed as increases in absolute amounts per unit time, were significantly lower in the elderly subjects. (3.65 +/- 1.02 vs 7.41 +/- 1.05 mumol/h, P less than 0.05 for cAMP and 14.7 +/- 6.3 vs 41.8 +/- 8.6 mg/2h, P less than 0.05 for Pi) and an inverse correlation was found between the serum PTH levels and the increases in urinary cAMP excretion (mumol/hr; r = -0.63, P less than 0.05). However, when corrected for the glomerular filtration rate (GFR) and the units of PTH administered per kg body weight, the increases were not significantly different in the two groups (elderly 52.1 +/- 7.5 vs young 60.0 +/- 19.2 nmol . kg/100 ml GFR . U . h for cAMP and 0.315 +/- 0.061 vs 0.186 +/- 0.044 mg . kg/100 ml GFR . U . 2 h respectively for Pi).(ABSTRACT TRUNCATED AT 250 WORDS)