Exposure to either gamma or a mixed neutron/gamma field irradiation modifies vasoactive intestinal peptide receptor characteristics in membranes isolated from pig jejunum

Abstract

The effect of acute whole body exposure to ionizing radiation was investigated on intestinal vasoactive intestinal peptide (VIP) receptors and adenylate cyclase activity in membranes isolated from pig jejunum. Pigs under light anaesthesia were exposed to a single dose (6 Gy) of gamma (gamma) or to mixed neutron/gamma field (ratio 1:1; neutron/gamma) irradiation. Seven days after irradiation, plasma-membranes were prepared from post mortem jejunal mucosal scrapings. Marker enzyme activities (sucrase, leucine aminopeptidase (LAP), Na,K-ATPase) were measured in each preparation. The characteristics (KD, Bmax) of VIP receptors were determined using 125I-labelled VIP. In addition VIP-sensitive adenylate cyclase activity was measured. Results showed that enzyme activities were reduced following both gamma (sucrase 67%; LAP 53%; Na/K-ATPase 29%; N = 7) and neutron/gamma (sucrase 53%; LAP 59%; Na/K-ATPase 68%; N = 5) compared with control values (N = 5). VIP receptor affinity was decreased following either type of irradiation (gamma or neutron/gamma P < 0.01) and receptor numbers increased. Both VIP- and forskolin-stimulated adenylate cyclase activities were reduced but the sensitivity of the enzyme remained the same for VIP (EC50 values (nmol dm-3)-control-1.27 +/- 0.35; gamma-2.18 +/- 0.41; neutron/gamma-1.91 +/- 0.28). In conclusion, exposure to either gamma or neutron/gamma irradiation attenuates intestinal enzyme activities and VIP receptor affinity but increases VIP receptor numbers.

Potential role of the membrane in the development of intestinal cellular damage after whole-body gamma irradiation of the rat

“…The activities of sucrase, LAP, and Na + /K + -ATPase are decreased 4 days after irradiation, whereas the activity of LAP was slightly increased 1 day after total body irradiation. Such changes are in agreement with those reported for different species and irradiation configurations (Becciolini et al 1995;Griffiths et al 1996;Lebrun et al 1998). In addition to modifications of membrane enzyme activities, we observed, 4 days after whole body irradiation, an increased effect of carbachol on fluid transport, as measured by short-circuit current changes in Ussing chambers.…”

“…In particular, changes in electrolyte fluxes, basal electrical parameters, agonist-stimulated short-circuit current and conductance, receptor characteristics, and membrane enzyme activities have been observed within a week after irradiation (Becciolini et al 1995;Harari et al 1994;Griffiths et al 1996;Lebrun et al 1998). However, the causes of these different radiation-induced functional alterations are to date unclear.…”

Alterations of the VIP-stimulated cAMP pathway in rat distal colon after abdominal irradiation

“…Modifications of VIP receptor characteristics have already been observed after irradiation (21). Increase of VIP concentration in colon may be responsible for modification of VIP receptor characteristics.…”

“…The adenylyl cyclase activity was measured on crude homogenate of distal colonic mucosa as described previously by Griffiths et al (21). In brief, the mucosa was removed by scraping, weighed, and homogenized (Ultra-Turrax 20,000 rpm, 2 ϫ 30 s) in sucrose buffer (250 mM sucrose, 2 mM Tris ⅐ HCl, pH 7.4) containing protease inhibitor 1 mM phenylmethylsulfonyl fluoride.…”

“…Adenylyl cyclase activity was measured as described previously for pig jejunal plasma membranes (21). Colonic mucosa from two rats was pooled and used for each sample.…”