Purpose
To investigate somatotropic function in growth retardation by using arginine and insulin to stimulate growth hormone secretion. The mechanism involves a combination of a bolus of amino acid (arginine) with stimulation via the catecholaminergic pathway and insulin-induced hypoglycaemia.
Subject preparation
Fasting for 12 hours and at rest for 30 minutes (except for babies of under one year and hypoglycaemic subjects who should be given 200 millilitres of milk at 5 a.m.).
Product
- Arginine hydrochlorate (Arginine, Veyron®) (400 ml bottle containing 25 grams of arginine).
- Regular insulin
Dose
- Arginine: 0.6 g/kg body weight or 20 g/m2 body surface area (do not exceed 20 g, or 320 ml).
- Insulin: 0.1 U/kg IV (for those at risk of panhypopituitarism or hypoglycaemia, or babies of under one year: cut the dose in half, i.e. 0.05 U/kg).
Protocol
- Commence the perfusion of normal saline 30 minutes before the challenge.
- Samples (dry and fluoride tubes) at time intervals: -15 min (T-15) and 0 (T0).
- Slow IV perfusion (over 30 min) of the correct dose of arginine.
- Draw blood (dry tubes) at T+30, T+45, T+60 and T+90 min after the beginning of perfusion.
- At T+90 min, IV injection of the correct dose of insulin.
- Samples (dry and fluoridated tubes) at time points T+105, T+120, T+135, T+150 and T+180 min.
Samples
After centrifugation, freeze serum at –20°C and store plasma at +4°C.
Side effects
Strict medical supervision is warranted due to the risk of HYPOGLYCAEMIA caused by fasting and the insulin dose: have ready a syringe containing 20 ml 20% glucose solution and a 1 mg vial of glucagon.
Contraindications
Test contraindicated in the newly-born.
Assays
- Growth hormone (GH).
- IGF1.
