Our previous studies have indicated that (a) alterations in cyclic AMP(cAMP), cyclic GMP (cGMP) metabolism and/or cAMP-dependent protein kinase (PK) activity occur early after exposure of colonic mucosa to the carcinogens 1,2 dimethylhydrazine (DMH) (lower cAMP, lower PK activity ratio, higher soluble Type I PK), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) (higher cGMP) or acetylaminobiphenyl (AAB) (higher cGMP); (b) alterations in cGMP are mediated by reactive derivatives of the carcinogens; (c) fatty acid dependent microsomal oxidation, linked in part to endogenous prostaglandin(PG) synthesis may be the preferred pathway for local drug and procarcinogen metabolism by colonic mucosa; (d) endogenous PG synthetic activity in colonic mucosa is an important local determinant of cAMP and cGMP; and (e) cAMP acts as a negative signal to cell proliferation in this tissue. The proposed studies are aimed at clarifying the potentially important relationships among fatty acid dependent procarcinogen oxidation, PG synthesis, and cyclic nucleotide metabolism, an understanding of which may suggest methods of pharmacologic and/or dietary modification of carcinogen and PGE metabolism. Accordingly, the goals of the proposed study are: 1) examine in cultured colonic explants of rat and human colons and in microsomal fractions fatty acid dependent oxidation of benzo(a)pyrene, DMH and azoxymethane and determine the extent to which potentially carcinogenic derivatives are formed by assessing the binding of these derivatives to nucleic acid; 2) examine the relationships among colonic mucosal fatty acid dependent procarcinogen oxidation, PG synthesis, cAMP and cGMP metabolism; 3) compare the effects of diets high and low in saturated versus unsaturated fatty acids or cholesterol on colonic PG synthesis, and on fatty acid versus NADPH induced procarcinogen oxidation; 4) examine the relationships between colonic mucosal PG synthesis and proliferative activity by assessing the effects of stimuli and inhibitors of PG synthesis on proliferation in colonic explants; 5) examine the roles of cAMP and cGMP in the control of colonic epithelial proliferative activity (DNA, RNA, and protein synthesis) and the possibility that cAMP induced inhibition of proliferation in this tissue is associated with phosphorylation of specific nuclear or membrane proteins.
