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

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Abstract
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,PPPP<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). These results indicated that the decreased response of the kidney to PTH in elderly subjects can be explained mainly by the decreased functional mass of the kidney, possibly with some contribution of down-regulation of PTH receptors owing to increase in the blood level of endogenous PTH in elderly subjects. Further investigations are needed to ascertain why there was decreased response of the kidney to PTH in elderly people.