title: Age-related changes in parathyroid hormone and parathyroid hormone action in normal humans.
abstract: We evaluated parathyroid function in 158 normal subjects, aged 23-85 yr. Calcium, phosphorus, creatinine, and cAMP were measured in blood and urine in the fasting state and after a 1-g oral calcium challenge. Serum immunoreactive PTH (iPTH) was measured with a goat antiserum developed against human PTH, using (43Tyr) human PTH-(44-68) as tracer and standards. With age, a decrease in total serum Ca (r = -0.14; P less than 0.05) was attributable to a fall in serum albumin (r = -0.40; P less than 0.001). Creatinine clearance fell from 124 ml/min at age 20 yr to 61 ml/min at age 80 yr (r = -0.44; P less than 0.001). iPTH rose with age in men (r = 0.21; P less than 0.05) and women (r = 0.31; P less than 0.001) from 29 pg/ml at age 20 yr to 48 pg/ml at 80 yr. iPTH was also correlated with creatinine clearance (r = -0.32; P less than 0.001. When renal function was controlled in the analysis, the regression of iPTH with age was no longer significant. Other significant correlations with age include a decrease in renal phosphorus reabsorption (r = -0.17; P less than 0.05) and an increase in urinary nephrogenous cAMP excretion (r = 0.34; P less than 0.01). The rise in nephrogenous cAMP was not accompanied by a change in total urinary cAMP, since plasma, and therefore filtered, cAMP decreased with age. Basal calcium excretion was stable, but the calciuric response to oral calcium decreased (r = -0.27; P less than 0.01). We conclude that loss of renal function is the major cause of rising iPTH levels with age.
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging; D000469:Alkaline Phosphatase / Q000097:blood; D002112:Calcifediol / Q000097:blood; D002118:Calcium / Q000097:blood / Q000652:urine; D003401:Creatine / Q000097:blood; D000242:Cyclic AMP / Q000652:urine; D005215:Fasting; D005260:Female; D006801:Humans; D008297:Male; D008657:Metabolic Clearance Rate; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood* / Q000502:physiology; D010758:Phosphorus / Q000097:blood / Q000652:urine
chemical_list: D010281:Parathyroid Hormone; D010758:Phosphorus; D000242:Cyclic AMP; D000469:Alkaline Phosphatase; D003401:Creatine; D002112:Calcifediol; D002118:Calcium