Search

Pancreatic islet beta-cells secrete the hormones insulin, amylin and pancreastatin. To search for further beta-cell hormones, we purified peptides from secretory granules isolated from cultured murine beta TC6-F7 beta-cells. We identified a 34-amino-acid peptide (3948 Da), corresponding to Asp(69)-Leu(102) of the proinsulin-like growth factor II E-peptide, which we have termed 'preptin'. Preptin, is present in islet beta-cells and undergoes glucose-mediated co-secretion with insulin. Synthetic preptin increases insulin secretion from glucose-stimulated beta TC6-F7 cells in a concentration-dependent and saturable manner. Preptin infusion into the isolated, perfused rat pancreas increases the second phase of glucose-mediated insulin secretion by 30%, while anti-preptin immunoglobulin infusion decreases the first and second phases of insulin secretion by 29 and 26% respectively. These findings suggest that preptin is a physiological amplifier of glucose-mediated insulin secretion.

Although most individuals pass through adolescence without excessively high levels of "storm and stress," many do experience difficulty. Why? Is there something unique about this developmental period that puts adolescents at risk for difficulty? This article focuses on this question and advances the hypothesis that some of the negative psychological changes associated with adolescent development result from a mismatch between the needs of developing adolescents and the opportunities afforded them by their social environments. It provides examples of how this mismatch develops in the school and in the home and how it is linked to negative age-related changes in early adolescents' motivation and self-perceptions. Ways in which more developmentally appropriate social environments can be created are discussed.