ENDOCRINE PROFILE OF CATCH-UP GROWTH IN THE CYNOMOLGUS MONKEY

We studied catch-up growth following withdrawal of glucocorticoid admi nistration in seven intact prepubertal cynomolgus monkeys. To reduce s tress during blood sampling, a vascular access port was implanted subc utaneously in each animal for the duration of the study. After a basel ine observation period of 50 weeks, the monkeys received injections of dexamethasone at a dose of 100 mug.kg-1.day-1 for 15 weeks. Growth ve locity was monitored every 3 weeks by measuring lower leg length and b ody weight. Spontaneous serum growth hormone (GH) concentrations and G H levels after insulin and L-dopa stimulation, as well as serum insuli n-like growth factor I (IGF-I) and plasma thyrotropin, triiodothyronin e and thyroxine, were measured during the study. Differences between a nimals were analyzed by repeated measures analysis of variance and Stu dent's paired t-test. Mean +/- SEM growth velocity (mm/3 weeks) decrea sed 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 var iation during the study. Peak GH during the L-dopa test decreased from 15.4 +/- 3.2 mug/l during the baseline period to 6.2 +/- 2.4 mug/l du ring the period of growth retardation (p < 0.05), and increased to 23. 0 +/- 5.9 mug/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. increa sed 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. Plas ma thyroxine and triiodothyronine levels did not vary during the study , whereas thyrotropin decreased during the period of growth retardatio n. We conclude that GH secretion increases after L-dopa during catch-u p growth in this primate model, suggesting that GH may play a role in the accelerated growth observed during this period.