Endocrine Abstracts

Insulin like growth factor-1 (IGF-1) has been shown to co-vary with renal function in a number of physiological and pathological conditions. However, this relationship and possible co-variants have not been specifically explored in untreated growth hormone deficient adults (GHDA). To examine this issue, we studied 24 GHDA subjects (14M, 10F) in the fasted state twice after obtaining consent and ethical approval. The Cockcroft and Gault equation was used to calculate creatinine clearance (CrCl) from plasma creatinine.

Subjects' age [median (interquartile range)] was 50.5 (37.5-61.0) yrs and body mass index (BMI) was 27.1 (25.1-28.6) kg per m ². Serum total IGF-1 (nanograms per millilitre) was 162.5 (79.0-244.5) in males and 34.2 (21.5-174.7) in females; Mann-Whitney test P=0.05), GH (picograms per millilitre) was 44.3 (10.5-136.8), IGF binding protein-3 (IGFBP-3, nanograms per millilitre) was 2034 (1673-3227) and CrCl (millilitre per minute) was 92 (76-109, with only 4 subjects having CrCl below normal range), no sex difference for GH, IGFBP-3 or CrCl was found.

Univariate analysis showed significant correlations between IGF-1 and CrCl (Spearman's rank [rho] =0.56, P=0.003), IGF-1 and GH (rho= 0.58, P=0.002), IGF-1 and IGFBP-3 (rho=0.85, P<0.0001), CrCl and age (rho= - 0.63, P=0.0009), CrCl and BMI (rho=0.42, P=0.03), CrCl and IGFBP-3 (rho=0.54, P=0.006). No significant correlations of either CrCl or IGF-1 were found with other variables including GHD duration, the number of deficient pituitary hormones, insulin or thyroxine levels. Using forward stepwise multiple linear regression, IGF-1 (coefficient= 0.08, P=0.002), BMI (coefficient=2.9, P< 0.0001) and age (coefficient= - 1.1, P <0.0001) were independent and significant determinants of CrCl.

In conclusion, growth hormone deficiency per se in adults is not associated with reduced renal function. Nevertheless, IGF-1 remains a strong determinant of creatinine clearance, thus supporting a physiological role of IGF-1 in regulating renal haemodynamics.