The objective of this proposed research is to define the regulatory mechanisms, which govern the biosynthesis and secretion of somatostatin, in hypothalamic cells. Somatostatin is an important physiologic regulatory of Growth Hormone (GH) and Thyroid Stimulating Hormone in the pituitary, and of glucagon and insulin in pancreatic islets. A molecule with such diverse function is necessarily under complex control by neural, metabolic, and hormonal influences. In order to study the cellular mechanisms involved in somatostatin production away from these influences, I have developed a method of maintaining somatostatin producing neurons in vitro in a completely defined media. Examination of these cultures reveals that the ontogenesis of somatostatin, the morphology of the neurons, and the types of immunoreactive somatostatin (IRS) produced and secreted are identical to that seen in vivo. Preliminary experiments with cerebral cortical cultures demonstrate their utility in biosynthetic studies as they are capable of incorporating 3H-phenylalanine into somatostatin-14 as well as larger IRS prohormones (using pulse-chase methods), thereby enabling me to determine whether putative feedback factors (e.g. thyroxine, GH, insulin, etc.) affect the rate of IRS synthesis. Similarly somatostatin turnover is sufficiently high in the cultures so that dynamic release studies designed to assess the influences of monoamines and neurotransmitters on somatostatin secretion can be carried out. Cells grown on cover slips allows immunocytochemical analysis, using anti-SRIF antisera, and when combined with autoradiography provides a way to determine if moleculs which influence synthesis or secretion bind directly to somatostatinergic neurons. Elucidation of the regulatory processes in somatostatinergic cells will provide important information in understanding normal and pathological pituitary function and may contribute to defining how somatostatin producing cells in other organs (such as the pancreas) are regulated.
