We evaluated the influence of age on the response to infusion of PTH (1-34) in healthy children (n=8) and adults (n=12). Basal TP/GFR was inversely associated with basal UcAMP/GF levels (p<0.0359). By multiple regression analysis PTH stimulated TP/GFR was inversely correlated with peak stimulated UcAMP/GF (p<0.0007), dependent on age (p<0.0001) and the interaction of age group with UcAMP/GF (p<0.0076). In 6 patients with pseudo-hypoparathyroidism (HP), stimulated TP/GFR was also correlated with peak UcAMP/GF (r=0.96, p<0.002). Furthermore, peak PTH stimulated fractional excretion of P (FEP) was found to be directly correlated with UcAMP/GF (p<0.0002), and also influenced by the interaction of age group with UcAMP/GF (p<0.0034), in a multiple regression analysis p<0.0013, r2=0.61. The slope of the regression of FEP with UcAMP/GF was steeper in children than adults. Addition of serum P level as a covariate in the regression model was not statistically significant. In contrast, 2 children with HP had very high PTH stimulated UcAMP/GF but FEPs considerably below those expected from the normative data.
The effect of PTH infusion on P excretion is correlated with the UcAMP/GF level in an age dependent manner. Consideration of this relationship may permit a more detailed clinical assessment of responsiveness to PTH in individuals with bone mineral disorders and abnormalities of mineral regulating hormones. (Supported by a grant from Rhone-Poulenc-Rorer.)
