Endocrine profile of catch-up growth in the cynomolgus monkey

Abstract

We studied catch-up growth following withdrawal of glucocorticoid administration in seven intact prepubertal cynomolgus monkeys. To reduce stress during blood sampling, a vascular access port was implanted subcutaneously in each animal for the duration of the study. After a baseline observation period of 50 weeks, the monkeys received injections of dexamethasone at a dose of 100 μg·kg−1·day−1 for 15 weeks. Growth velocity was monitored every 3 weeks by measuring lower leg length and body weight. Spontaneous serum growth hormone (GH) concentrations and GH levels after insulin and l-dopa stimulation, as well as serum insulin-like growth factor I (IGF-I) and plasma thyrotropin, triiodothyronine and thyroxine, were measured during the study. Differences between animals were analyzed by repeated measures analysis of variance and Student's paired t-test. Mean±sem growth velocity (mm/3 weeks) decreased from 0.90±0.08 during the baseline period to 0.29±0.07 (p< 0.001) during the period of growth retardation, and increased to 1.23±0.2 (p< 0.001) during the period of catch-up growth. Spontaneous GH and peak GH levels following insulin did not show any significant variation during the study. Peak GH during the l-dopa test decreased from 15.4±3.2 μg/l during the baseline period to 6.2±2.4 μg/l during the period of growth retardation (p<0.05), and increased to 23.0±5.9 μg/l during the period of catch-up growth (p<0.05). Serum IGF-I levels were 3.0±1.0 mU/l during the baseline period, increased to 9.5±1.3 mU/l (p<0.05) during the period of dexamethasone administration and decreased to 6.1±1.0 mU/l during catch-up. Plasma thyroxine and triiodothyronine levels did not vary during the study, whereas thyrotropin decreased during the period of growth retardation. We conclude that GH secretion increases after l-dopa during catch-up growth in this primate model, suggesting that GH may play a role in the accelerated growth observed during this period.