Upsala J Med Sci 92: 85-88, 1987 The Effect of Cysteamine on the Somatostatin Content of Guinea-pig Islets Birger Petersson Department of Medical Cell Biology, University of Uppsala, Uppsala, Sweden ABSTRACT Cysteamine is known to deplete the immunoreactive somatostatin content in different organs from rat and mouse. The aim of the present work was to test if cysteamine also affects the somatostatin content in guinea-pig islets, since guinea-pigs have a carbohydrate metabolism different from that of other labora- tory animals. Cysteamine was injected to guinea-pigs and the pancreatic islets were isolated four hours later. Cysteamine was also incubated in vitro with isolated pancreatic islets from untreated guinea-pigs. Cysteamine depleted the somatostatin content in the pancreatic islets in both the in vivo and in vitro studies. INTRODUCTION It is well known that the ulcerogenic substance cysteamine (2-amino-ethan- ethiol), injected in vivo, causes a selective depletion of somatostatin in many organs in both the mouse and rat (7, 6, 3 ) . Besides somatostatin, cysteamine also depletes prolactin ( 3 ) . In addition, cysteamine is known to decrease the somatostatin content of pancreatic islets in vitro (4, 5 ) . The guinea-pig is associated with several biochemical peculiarities and both its insulin and glucagon amino acid sequences are different from those of other animals. The general amino acid sequence for somatostatin seems, however, to be conserved in guinea-pigs ( 1 ) . In view of its biochemical peculiarities,it is of particular interest to follow the effect of cysteamine on somatostatin in the guinea-pig. In the present study we therefore measured somatostatin in isolated pancreatic islets of guinea-pigs after administration of cysteamine in vivo and after exposure of the islets to cysteamine in vitro. 85 MATERIALS AND METHODS Each of six guinea-pigs received a subcutaneous injection of 60 mg/kg body weight of cysteamine (Aldrich, Beerse, Belgium) dissolved in distilled water. The animals were killed four hours after the injections. Three control animals remained untreated and were killed together with the injected animals. The pan- creatic glands were rapidly removed and islets were isolated by means of a collagenase digestion technique ( 2 ) . Groups of 25 islets from each animal were then sonicated and extracted in 250 u l of ice-cold acid alcohol (0.18 mol/l HC1 in 70 % alcohol) at 4OC overnight. The somatostatin content was determined as described below. / Effects of cysteamine in vitro were studied in collagenase-isolated islets from nine normal guinea-pig pancreases. Groups of 25 islets were exposed for four hours at 3 7 O C to cysteamine dissolved at a concentration of 10 or 100 ug/ / ml in tissue culture medium (Parker 199) containing 10 % (v/v) calf serum. The somatostatin content of the islets was determined after sonication and extrac- tion in ice-cold acid alcohol as described above. For determination of the somatostatin content, the acid alcohol extracts of the islet homogenates were centrifuged at 2000 rpm for 20 minutes and the soma- tostatin content of the supernatant was assayed by a radioimmunological method (Kit nr. 038192; Immuno Nuclear Corp. ,Stillwater, Minnesota 5508, USA) using synthetic somatostatin-I4 as standard. The sensitivity of the method was approx- imately 3 pg per tube. Probabilities (P) of chance differences between groups were calculated by Stu- dent's t-test. Results are expressed as mean values 2 standard errors of the means (m%EM). RESULTS Four hours after the subcutaneous administration of cysteamine the somato- statin content of the pancreatic islets was significantly depleted compared with that in the control animals ( 1 7 6 1 1 pg/islet versus 934 2 47 pg/islet). In vitro incubation of islets with cysteamine for four hours at a concentration of 100 ,ug/ml resulted in a marked depletion of somatostatin, but at 10 /ug/ml cysteamine did not have this effect. The somatostatin values were 331 2 47 pg/ islet with 100 (see figs. 1 and 2 ) . ug/ml, 640 2 116 with 10 / / u g h 1 and 8 7 3 2 139 in the controls DISCUSSION The present results show that not only treatment with cysteamine in vivo but also exposure to cysteamine in vitro causes a rapid and marked depletion of immunoreactive somatostatin in pancreatic islets from guinea-pigs. This is in accordance with previous observations in islets from mice and rats (4, 5). 86 control cystearnine Fig. 1 . The bars show the somatostatin content of pancreatic i s , e t s from control guinea-pigs a n d from guinea-pigs treated with cysteamine ( 6 0 mg/kg B . W . ) four hours before the animals were k i l l e d . The numbers of batches a r e given within parentheses. Means S.E.M. a r e given. xxx: P < 0.001 i n r e l a t i o n t o the control g r o u p . ( 1 7 ) ( 1 7 ) (17) control cysteamine cystearnine 10,uglml 100,uglml Fig. 2. The bars show the somatostatin content of pancreatic guinea-pig i s l e t s incubated f o r four hours with and without cysteamine in the medium. The numbers of batches a r e given within parentheses. Means 2 S.E.M. a r e given.NS: P > 0.05; xxx: P < 0 . 0 0 1 in r e l a t i o n t o the control g r o u p . 87 Other studies indicate that the loss of immunoreactive somatostatin occurs without changes in the pancreatic insulin or glucagon content (6). Although the mechanism for the cysteamine action is not known, there is support for the view that the action is intracellular ( 6 ) . Since in many aspects the guinea-pig has a metabolism different from that of many other laboratory animals, it is of in- terest to note that the depletion of immunoreactive somatostatin by cysteamine is pronounced in this animal, also. ACKNOWLEDGEMENTS Supported by grants from the Swedish Medical Research Council (Project No 2297 1 . REFERENCES 1. Conlon, J.M.: Isolation and structure of guinea-pig gastric and pancreatic 2. Howell, S.L. & Taylor, K.W.: Potassium ions and the secretion o f insulin by 3. Parsons, J.A., Peterson, E.K. & Hartfel, M.A.: Effects of cysteamine on pi- somatostatin. Life Sciences 35: 213 - 220, 1984. islets of Langerhans incubated in vitro. Biochem J 108: 17 - 24, 1968. tuitary, MtTWI5 tumor, and serum prolactin levels measured by rat lymphoma cell bioassay and radioimmunoassay. Endocrinology 114: 1812 - 1817, 1984. 4. Patel, Y.C., Pierzchala, I . , Amherdt, M. & Orci, L.: Effects of cysteamine and antibody to somatostatin on islet cell function in vivo. J Clin Inv 75: 1249 - 1255, 1985. 5. Petersson, B. & Hellerstrom, C.: Rapid depletion of somatostatin in isolated mouse pancreatic islets after treatment with cysteamine. Acta endocrinol (Kbh.) 110: 227 - 231, 1985. 6. Sorenson, R.L., Grouse, L.H. & Elde, R.P.: Cysteamine blocks somatostatin secretion without altering the course of insulin o r glucagon release. Dia- betes 32: 377 - 379, 1983. 7. Szabo, S. & Reichlin, S.: Somatostatin in rat tissue is depleted by cyste- amine administration. Endocrinology 109: 2255 - 2257, 1981. Address for reprints: Dr. Birger Petersson Department of Medical Cell Biology P.O. Box 571 S-751 23 UPPSALA 88