Growth hormone (GH) responses to sleep, insulin hypoglycaemia and arginine infusion

Abstract

A few children with no apparent cause for their short stature, continue to grow poorly despite normal GH responses (>15mU/L) to pharmacological stimuli. It has been suggested that their GH secretion during sleep may more accurately reflect their true GH reserve. We have compared sleep related GH secretion (GH-Sleep) with GH responses to insulin hypoglycaemia (GH-I) and arginine infusion (GH-Arg.) in 19 children referred to our Growth Clinic. Blood was withdrawn continuously through an indwelling thromboresistant catheter (Cormed SL-65 Continuous Blood Withdrawal Pump) and divided into 15 minute aliquots, throughout approximately 5 hours of EEG monitored sleep. The following morning and insulin hypoglycaemia/arginine infusion test was performed. GH was measured by radioimmunoassay. 2 patients had normal GH-Arg. responses but GH-Sleep peaks less than 15mU/L. Correlation coefficients, r, for peak serum GH levels were :- for GH-I & GH-Sleep 0.55 (p<0.02), GH-Arg. & GH-Sleep 0.52 (p<0.02) and GH-I & GH-Arg. 0.56 (p <0.02). We conclude that sleep studies of GH reserve are indicated only when the results of stimulation tests are inconsistent with clinical findings.