The kinetics of insulin, glucagon and somatostatin release was studied in human 
pancreatic islets. Batches of 10-15 islets were perifused and the hormones 
measured with RIA in 30-sec fractions. Increase of glucose from 3 to 20 mm 
resulted in a brief pulse of glucagon coinciding with suppression of basal 
insulin and somatostatin release. There was a subsequent drop of glucagon 
release concomitant with the appearance of a pronounced pulse of insulin and a 
slightly delayed pulse of somatostatin. Continued exposure to 20 mm glucose 
generated pulsatile release of the three hormones with 7- to 8-min periods 
accounting for 60-70% of the secreted amounts. Glucose caused pronounced 
stimulation of average insulin and somatostatin release. However, the nadirs 
between the glucagon pulses were lower than the secretion at 3 mm glucose, 
resulting in 18% suppression of average release. The repetitive glucagon pulses 
were antisynchronous to coincident pulses of insulin and somatostatin. The 
resulting greater than 20-fold variations of the insulin to glucagon ratio might 
be essential for minute-to-minute regulation of the hepatic glucose production.