Bile salt stimulation of colonic epithelial proliferation. Evidence for involvement of lipoxygenase products.

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Abstract
Prostaglandin E2 (PGE2) and several other prostaglandins synthesized by colon suppress the proliferative activity of colonic epithelium. However, bile salts stimulate colonic epithelial proliferation despite the actions of bile salts to enhance the release of arachidonate and consequent colonic synthesis of PGE2. The current study was conducted to assess whether bile salt-induced increases in colonic formation of arachidonate metabolites other than PGE2 were linked to the stimulation of the proliferative activity of colonic epithelium. Within 10 min of addition, deoxycholate markedly stimulated the in vitro release of [14C]arachidonate from prelabeled rat colon. When given in vivo by intracolonic instillation deoxycholate (10 mumol) increased colonic accumulation of immunoreactive prostaglandin E (PGE), thromboxane B2 (TXB2), and the lipoxygenase product 12-hydroxyeicosatetraenoic acid (12-HETE) by two to fourfold over control in 30 min. This effect of intracolonic deoxycholate was followed by a ninefold increase in mucosal ornithine decarboxylase activity (4 h), and a subsequent two to threefold increase in [3H]thymidine [( 3H]Thd) incorporation into DNA of either mucosal scrapings or isolated pools of proliferative colonic epithelial cells (24 h). Intracolonic instillation of indomethacin (50 mumol) suppressed to low or undetectable levels both basal colonic accumulation of PGE and TXB2 and the increases in each parameter induced by subsequent instillation of deoxycholate. By contrast, indomethacin enhanced accumulation of 12-HETE in both control colons and those subsequently exposed to deoxycholate. The increases in 12-HETE induced by indomethacin alone were correlated with stimulation of mucosal ornithine decarboxylase activity and [3H]Thd incorporation into mucosal DNA. Indomethacin also enhanced the increases in these parameters induced by deoxycholate. Intracolonic instillation of phenidone (25-100 mumol) suppressed accumulation of PGE, TXB2, and 12-HETE in control colons and the increases in these parameters induced by a subsequent instillation of deoxycholate. Phenidone alone did not alter mucosal ornithine decarboxylase activity or [3H]thymidine incorporation into mucosal DNA. However, phenidone suppressed or abolished increases in these parameters induced by a subsequent instillation of deoxycholate. 4-(2-[IH-imidazol-1-yl]ethoxy) benzoic acid hydrochloride UK 37,248, which selectively reduced colonic TXB2 to undetectable levels without altering PGE or 12-HETE, had no effect on control or deoxycholate-induced increases in mucosal ornithine decarboxylase activity or [3H]Thd incorporation into DNA. Neither indomethacin nor phenidone altered the increases in [(14)C]arachidonate release induced in vitro by deoxycholate. Chenodeoxycholate and cholate also stimulated [(14)C]arachidonate release from colon in vitro within 10 min, and increased colonic 12-HETE (30 min) and mucosal ornithine decarboxylase activity (4 h) upon intracolonic installation. Prior installation of phenidone inhibited the increases in both 12-HETE and ornithine decarboxylase activity induced by these bile salts. The results support a role for bile salt-induced increases in colonic accumulation of lipoxygenase products, as reflected by 12-HETE, in the subsequent stimulation of the proliferative activity of colonic epithelium.