High concentration of somatostatin immunoreactivity in chicken pancreas

Diabetologia, May 1976

G. C. Weir, P. C. Goltsos, E. P. Steinberg, Y. C. Pate

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High concentration of somatostatin immunoreactivity in chicken pancreas

High Concentration ot Somatostatin Immunoreactivity in Chicken Pancreas G. C. Weir 0 P.C. Goltsos 0 E.P. Steinberg 0 Y.C. Patel 0 0 Diabetes Unit of Massachusetts General Hospital, and Endocrine Division, Tufts-New England Medical Center Hospital , Boston, Massachusetts USA Summary. Extracts of discrete lobes of chicken pancreas were assayed for somatostatin (SRIF), insulin, and glucagon immunoreactivity. The distribution of hormone concentration was correlated appropriately with the known distribution of A, B, and D-cells. Concentrations of all three hormones were highest in the splenic lobe. The glucagon content of the ventral and dorsal lobes was low. Evidence is presented that the SRIF-like material in the pancreatic extracts is very similar to synthetic cyclic SRIF; parallel immunoassay displacement curves and similar chromatographic elution profiles were obtained. The SRIF concentration in chicken pancreas is 21 times higher than that found in the rat. Chicken pancreas may provide a useful model for studies of somatostatin physiology. Chicken pancreas; somatostatin; insulin; glucagon - Somatostatin (SRIF) is a cyclic fourteen amino acid peptide originally isolated from the hypothalamus [ 1 ]. In addition to inhibiting growth hormone secretion it has also been found to inhibit the release of insulin, glucagon, gastrin, secretin, ACTH, prolactin and TSH [ 2-7 ]. Furthermore it is capable of inhibiting gastric acid [3] and pancreatic exocrine secretion [ 7, 8, 9 ]. The presence of somatostatin in extraneural tissues was first suggested by Dubois who demonstrated somatostatin immunoreactivity in pancreatic islets of mammals and birds by immunofluorescence techniques [ 10 ]. Somatostatin immunoreactivity was also found in extracts of rat islets [ 11 ] and of whole pancreas [ 12 ] using specific radioimmunoassays. Furthermore the gel filtration elution profiles of the rat islet extracts were identical t o those of synthetic cyclic somatostatin (unpublished observations of Patel, Reichlin and Weir). Somatostatin immunoreactivity has also been found in gastrointestinal tissue [12 and unpublished observations of Patel, Reichlin and Weir]. The cell of origin of somatostatin in both the pancreas and gut appears to be the D-cell [ 13 ]. Because of the large number of D-cells in the avian pancreas it was decided to evaluate the somatostatin content of the chicken pancreas. Materials and Methods Five-week old White Leghorn chickens were sacrificed and individual pancreatic lobes (ventral, dorsal, third, and splenic) were dissected out, weighed, and placed in iced Hanks solution. As soon as possible they were individually homogenized with a Ten Broeck pyrex homogenizer in 5 ml of 2 N acetic acid. Tubes containing these homogenates were then suspended in boiling water for five minutes to inactivate proteolytic pancreatic enzymes and the extracts frozen pending assay. Before dilution for assay aliquots of the extracts were neutralized with NaOH. The radioimmunoassay for somatostatin (method of Patel, and Reichlin, unpublished) utilized a rabbit antiserum obtained following immunization with SRIF conjugated to thyroglobulin. This antiserum was highly specific for SRIF with negligible or no crossreactivity with insulin, glucagon, gastrin, cholecystokinin-pancreozymin, cholecystokinin octapeptide (C8-CCK), secretin, vasoactive peptide (VIP), substance P and neurotensin. [1251]Tyrl-SRIF was iodinated with chloramine T. Synthetic cyclic somatostatin (kindly provided by the Ayerst Company, Montreal, Canada) was used as standard. The buffered diluent was 0.05 M PO 4 with 0.1% crystalline BSA at a pH 7.5. The incubation volume was 0.7 ml and dextran-charcoal separation was employed [ 14 ]. The detection limit for t h e assays done in this study was 3-4 pg of SRIF per incubation tube. Glucagon concentrations were determined with radioimmunoassay methods previously described [ 15 ] utilizing antiserum 30K provided by Dr. Roger Unger. Pork glucagon (lot GLF 599A, EliLilly and Company) was used as standard. The insulin radioimmunoassay method was that of Albano et al. [ 16 ] and chicken insulin (lot 615-1082B-249) was kindly donated by Dr. Ronald Chance of Eli Lilly and Company. Results The hormone concentration of individual lobes of the chicken pancreas is presented in Table 1. The concentration of all three hormones is greatest in the splenic lobe, with the glucagon concentration being strikingly high. It is noteworthy that the glucagon concentration of the ventral and dorsal lobes is very low. When the total hormonal content of each lobe is determined (Table 2) it c a n b e appreciated that the splenic lobe contributes little to total amount of insulin or SRIF, but contains at least half of the total a Calculations could only be made for five total pancreata because a third lobe from one of the six chickens was lost. glucagon. The contribution of the splenic lobe may actually be slightly higher (...truncated)


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G. C. Weir, P. C. Goltsos, E. P. Steinberg, Y. C. Pate. High concentration of somatostatin immunoreactivity in chicken pancreas, Diabetologia, 1976, pp. 129-132, Volume 12, Issue 2, DOI: 10.1007/BF00428977