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PEPTIDES OF THE BOMBESIN/GRP GROUP IN THE ATLANTIC COD, Gadus morhua.

ANN-CATHRINE J~NSSON & SUSANNE HOLMGREN, Comparative Neuroscience Uni t , Department of Zoophysiology Un ive rs i t y of G~teborg, Sweden.

Bombesin and gast r in re leas ing pept ide (GRP) l i k e peptides are known to be present in mammals, but the in format ion about these peptides in lower ver tebrates is scarce. The present study was star ted to inves t iga te the presence of bombesin/GRP-like immunoreact iv i ty (IR) in the gas t ro in tes t i na l t r ac t of the cod by histochemical and radioimmunochemical techniques using d i f f e r e n t ant isera (R6704, R6902 (GRP); GO7, L89/90 (bombesin)). Muscle s t r ips from the gas t ro in tes t i na l canal were used to study the e f fec ts of bombesin and GRP on gut m o t i l i t y . Previous immunohistochemical (IHC) studies (Thorndyke et al 1984, Regul. Pept. 9:350; Jensen & Holmgren 1985, Comp. Biochem. Physiol . 82C:81-89) describe the presence of bombesin-l ike IR in the stomach and i n tes t i ne respec t i ve ly . In the present study we have found a s t r i k i n g d i f ference in the i n t e n s i t y of the bombesin IR between nerves of the stomach and other parts of the gut, with an intense react ion in the stomach and a much weaker react ion in theother parts. Endocrine ce l l s are frequent in the py lo r i c stomach and occur in a low number throughout the rest of the gut. RIA measured low amounts of bombesin-l ike IR (acet ic acid ex t rac ts ) in muscle and mucosa throughout the gas t ro in tes t i na l t r a c t . The highest amounts were present in the cardiac stomach. The leve ls of bombesin-l ike IR were higher in the mucosa than in the musclelayer in the i n tes t i ne . Frac t ionat ion of ext racts from the whole gastro- i n t es t i na l t r a c t on Sephadex G50 (super f ine, 16x500 mm) showed a peak of IR running in the same pos i t ion as synthet ic bombesin, and, occas iona l ly an e a r l i e r e lu t i ng peak. Exogenous bombesin has an e x c i t a t o r y e f fec t on the stomach (Thorndyke et al 1984) whi le the e f fec t on the i n tes t i ne is weak and i n h i b i t o r y and occurs only in high concentrat ions (Jensen & Holmgren 1985). The e f fec t on the rectum is weak or non-ex is tent (present study). The e f fec t on iso la ted s t r i p preparat ions of stomach smooth muscle is an increase in rhythmic a c t i v i t y of ten combined with an increase in basic tonus in long i tud ina l muscle, whi le the e f fec t on c i r c u l a r muscle is mainly an increase in tonus. GRP has the same e f fec t as bombesin on stomach muscle s t r i ps , but is s l i g h t l y less potent. I t is concluded that one or maybe two bombesin-l ike peptides are present in the cod gut. I t is possible that the peptide in the i n t es t i na l nerves d i f f e r from that of the stomach nerves, or that they have separate funct ions.

EFFECTS OF THE SOMATOSTATIN ANALOGUE (SMS 201-995) ON STREPTOZOTOCIN-INDUCED INSULINOMAS IN RATS

C.F. Johnston and K.D. Buchanan Department of Medicine, The Queen's University of Belfast, Belfast, Northern Ireland.

Insulinomas were raised in 20 female Wistar rats by administration of streptozotocin (50mg/Kg

i.v.) and nicotinamide (350mg/Kg x 2 i.p.). After 18 months the random blood glucose was

1.3-3.4mmoi/I (control rat level 3.5-6.8mmoi/i). Rats were divided into two groups, one receiving

20Ng/Kg of SMS 201-995/day s.c. in a single bolus, whilst the remainder received vehicle alone.

Animals were sacrificed at various times between 2 weeks and 3 months after commencement of

treatment. Blood was taken for assessment of insulin and glucose levels. Tumours from the

pancreata were fixed and processed to wax to enable assessment by specific immunocytochemistry.

Post mortem examination confirmed that all animals possessed insulinomas. However, no difference

was observed in either the size (range 500~ - 8mm diameter) or numbers (range 1-5 per animal) of

tumours between the treated and the untreated groups. All tumours stained for insulin and some

contained small numbers of cells immunoreactive for both PP and glucagon in the tumour periphery. Normal islets from both groups of animals stained strongly for glucagon, PP and somatostatin.

Insulin immunoreactive cells stained with reduced intensity in the untreated insulinoma-bearing

animals when compared with either animals treated with SMS 201-995 or non tumour-bearing controls. Whereas the blood glucose levels of the untreated groups were unaltered, those of the treated

animals were comparable with the control animals (range 2.8-5.6mmoi/i). Plasma insulin levels in

the treated group were similar to the controls (76-125mU/i) whereas the untreated

insulinoma-bearing animals possessed higher levels (100-540mU/l). Active insulinomas appear to

cause a down-regulation of insulin synthesis by the normal islet 8 cells, as demonstrated by the

observed reduction in intensity of insulin immunofluorescence. That the 8 cells stain with normal intensity in the SMS 201-995 treated insulinoma-bearing animals indicates that secretion and not synthesis is reduced. This preliminary study indicates that, in the short term at least, SMS

201-995 normalizes both blood glucose and insulin in this animal model but may not influence tumour growth.