EXPOSURE TO EITHER GAMMA-IRRADIATION OR A MIXED NEUTRON GAMMA FIELD IRRADIATION MODIFIES VASOACTIVE-INTESTINAL-PEPTIDE RECEPTOR CHARACTERISTICS IN MEMBRANES ISOLATED FROM PIG JEJUNUM/

The effect of acute whole body exposure to ionizing radiation was inve stigated on intestinal vasoactive intestinal peptide (VIP) receptors a nd adenylate cyclase activity in membranes isolated from pig jejunum. Pigs under light anaesthesia were exposed to a single dose (6 Gy) of g amma (gamma) or to mixed neutron/gamma field (ratio 1:1; neutron/gamma ) irradiation. Seven days after irradiation, plasma-membranes were pre pared from Post mortem jejunal mucosal scrapings. Marker enzyme activi ties (sucrase, leucine aminopeptidase (LAP), Na,K-ATPase) were measure d in each preparation. The characteristics (K-D, B-max of VIP receptor s were deter mined using I-125-labelled VIP. In addition VIP-sensitive adenylate cyclase activity was measured. Results showed that enzyme a ctivities were reduced following both gamma (sucrase 67%; LAP 53%; Na/ K-ATPase 29%; N = 7) and neutron/gamma (sucrase 53%; LAP 59%; Na/K-ATP ase 68%; hi = 5) compared with control values (N = 5). VIP receptor af finity was decreased following either type of irradiation (gamma or ne utron/gamma P < 0.01) and receptor numbers increased. Both VIP- and fo rskolin-stimulated adenylate cyclase activities were reduced but the s ensitivity of the enzyme remained the same for VIP (EC(50) values (nmo l dm(-3)) - control- 1.27+/-035; gamma- 2.18+/-0.41; neutron/gamma- 1. 9+/-0.28). In conclusion, exposure to either gamma or- neutron/gamma i rradiation attenuates intestinal enzyme activities and VIP receptor af finity but increases VIP receptor numbers.