Increased circulating radioreceptor-active growth hormone in insulin-dependent diabetics

A radioreceptor assay (RRA) for GH, using pregnant rabbit liver membranes, was used to evaluate the receptor-hormone interaction of circulating (serum) GH in diabetics. Multiple morning blood samples were taken from 18 fasted insulin-dependent diabetics on three occasions and assayed for GH by the RRA and radioimmunoassay (RIA). Samples from 12 normal subjects (GH secretion stimulated by exercise and hypoglycaemia) and 11 acromegalics were also studied. The RRA/RIA ratio was higher in samples from the acromegalics than in normal subjects (0.85 vs 0.65, P less than 0.01) and only a few samples had RRA values greater than RIA. All the samples from 14 of the diabetics had lower RRA values than RIA, but 40% (39 of 96) of samples from the remaining four diabetics had RRA concentrations markedly in excess of the levels measured by RIA. Sephadex chromatography (G100) of serum samples revealed similar proportions of immunoreactive GH forms in the diabetics with high RRA values compared with the diabetics with low RRA values. These findings may indicate intermittent secretion of highly bioactive GH in some insulin-dependent diabetics. Further studies on the biological properties of circulating GH are needed to clarify the role of GH secretion in the development of diabetic microvascular complications.