An alternative to allosteric interactions as causes of sigmoid dose versus response curves. Application to glucose-induced secretion of insulin.

It is shown that a sigmoid dose vs. response curve will occur in any biological system in which the stimulant compound must diffuse significant distances to reach responding cells, even when the cells themselves respond according to Michaelis-Menten kinetics. Isolated pancreatic islets releasing insulin in response to glucose stimulation have been used as a specific example. Since diffusion and/or other physical processes can produce global effects which could account for the sigmoidal nature of a dose vs. response curve, the existence of complex molecular mechanisms of hormone-receptor interaction can not be inferred solely from the character of a dose vs. response relation.