Serum-insulin changes following administration of L-leucine to children.

There have been many published accounts of idiopathic leucine-sensitive hypoglycaemia of infancy since its description by Cochrane, Payne, Simpkiss, and Woolf in 1956, and raised plasmainsulin levels after the administration of L-leucine have been found in children with this condition (DiGeorge, Auerbach, and Mabry, 1960; Grumbach and Kaplan, 1960; Harmer and Sinclair, 1964). Similar changes in insulin have been found in patients with islet-cell tumours (Floyd, Fajans, Knopf, and Conn, 1964) and in healthy subjects pretreated with sulphonylurea drugs (Floyd, Fajans, Knopf, and Conn, 1963). Smaller increases in plasma-insulin after leucine administration have been reported in normal subjects (Floyd et al., 1963), and it has been suggested that the effect of L-leucine on plasma-insulin in idiopathic leucine-sensitive hypoglycaemia is an exaggeration of a normal phenomenon (Fajans, 1965). Changes in blood sugar after a leucine load may be difficult to interpret in children with persistent, severe hypoglycaemia, even when control tests without leucine are carried out, and in these cases the measurement of serum-insulin may help in establishing a diagnosis of leucine-sensitive hypoglycaemia. There is, however, little information available on the size of increase in serum-insulin which can be expected after the administration of leucine to leucine-insensitive children. This paper describes the serum immunoreactive insulin changes observed during leucine tolerance tests which were carried out in 28 children who had been admitted to hospital for investigation of either mental retardation or hypoglycaemia.