We examined the biological and histologic characteristics of a new experimental model of acute necrotizing pancreatitis induced by excessive doses of arginine in rats. Rats were given a single intraperitoneal injection of 500 mg/100 g body weight of L-arginine. At 12-24 hr after the arginine injection, serum levels of amylase, lipase, and anionic trypsin(ogen) reached respective peak values 2, 5, and 20 times those of control rats without arginine and returned to control levels after 24-48 hr. The contents of pancreatic protein, DNA, and digestive enzymes were markedly reduced after the arginine injection and reached their nadirs at 72 hr. After 14 days these levels were almost normal. Histologic examination revealed a number of small vesicles within acinar cells at 6 hr, which were identified as markedly swollen mitochondria by the electron microscope. Other intracellular organelles and nuclei also showed degenerative changes. At 12 hr interstitial edema appeared, and acinar cell necrosis was seen after 24 hr. The extent and severity of necrotic changes of pancreatic exocrine tissue with inflammatory cell infiltration were maximal at 72 hr. At seven days, pancreatic acinar cells began to regenerate, and pancreatic architecture appeared almost normal after 14 days. The present study has demonstrated that the administration of excessive doses of arginine induces a new, noninvasive experimental model of acute necrotizing pancreatitis.

In cultured vascular smooth muscle cells, angiotensin II

In cultured rat aortic smooth muscle cells, angiotensin II induced tyrosine phosphorylation of at least 9 proteins with molecular masses of 190, 117, 105.82,79,77,73,45 and 40 kDa in time-and dose-dependent manners. Other vasoconstrictors such as [Arglvasopressin, 5-hydroxytryptamine and norepinephrine induced the tyrosine phosphorylation of the same set of proteins as angiotensin II. The tyrosine phosphorylation of these proteins was mimicked by the protein kinase C-activating phorbol ester, phorbol 12 myristate 13-acetate, and the CaZ+ ionophorc, ionomycin. These results demonstrate that the vasoconstrictors stimulate the tyrosine phosphorylation of several proteins in vascular smooth muscle cells and suggest that the tyrosine phosphorylation reactions are the events distal to the activation of protein kinase C and Ca2+ mobilization in the intracellular signalling pathways of the vasoconstrictors.

In unstimulated cultured vascular smooth muscle cells (VSMC), mRNA of an inducible macrophage-type of nitric oxide synthase (iNOS) was barely detectable. Interferon y (IFNy) and tumor necrosis factor a (TNFcc) markedly increased iNOS mRNA levels in time-and dose-dependent manners. The induction of iNOS mRNA paralleled the cytokine-induced nitrite production. Actinomycin D abolished the IFNp and TNFa-induced increases in iNOS mRNA and nitrite production. Cycloheximide, which abolished both the IFNy-and TNFcc-induced increases in nitrite production, had no effect on the IFNy-induced increase in iNOS mRNA but markedly inhibited the TNFa-induced one. These results suggest that IFNy directly induces the expression of the iNOS gene whereas TNFa mainly induces it via the induction of an intermediary protein in cultured VSMC.

In cultured vascular smooth muscle cells, the baseline mRNA and protein levels of an inducible type of nitric oxide synthase were barely detectable. Interferon gamma, tumor necrosis factor-a, and interleukin-1/9 each markedly increased mRNA and protein levels of this enzyme in parallel with the production of nitrite, a stable oxidative metabolite of nitric oxide. Actinomycin D abolished the cytokine-induced increases in mRNA levels and nitrite production. Cycloheximide, which abolished the cytokine-induced increase in nitrite production, had no effect on the interferon-gamma-induced increase in mRNA levels but partially inhibited that induced by interleukin-1/3 and markedly inhibited that induced by tumor necrosis factor-a. Transforming growth factor-/31, which inhibited the interferon gamma-, interleukin-1^-, and tumor necrosis factora-induced nitrite production, did not affect the increases in mRNA levels caused by these cytokines. Transforming growth factor-/31, however, significantly inhibited the increase in protein levels caused by these cytokines. These findings suggest that interferon gamma directly induces the expression of the inducible nitric oxide synthase gene, whereas tumor necrosis factor-a and interleukin-1/3 induce it, at least in part, via the induction of intermediary protein(s), and that transforming growth factor-01 inhibits cytokine-induced nitric oxide production by blocking the posttranscriptional synthesis of inducible nitric oxide synthase.