The secretion of newly synthesized insulin in vitro.

1. An immunological method for the purification of small quantities of insulin has been devised. 2. This method has been used to isolate labelled insulin secreted from pancreas slices incubated in vitro. The insulin had previously been labelled by incubation of the slices with [(3)H]leucine in vitro. 3. There is some release of labelled insulin when such slices are further incubated in media of low glucose content. When the glucose content of the medium is raised, little additional radioactive insulin is released in the first hour after labelling. However, there is a marked increase in specific radioactivity of insulin released from slices in response to a high concentration of glucose in the second and third hours. Release of labelled insulin is again diminished in the final phase, 4hr. from the start of the experiment. 4. These results are discussed in relation to possible mechanisms of insulin release from the beta-cell.