Homologous desensitization to prostaglandins in rabbit ileum

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Abstract
Prostaglandins (PG's) increase short-circuit current (Isc), inhibit NaCl absorption, and stimulate Cl secretion in rabbit ileum. These changes occur with the following PGs; E2, E1, nitrilo-I2 and, to a lesser extent, with A2, D2, and F2 alpha. Arachidonic acid (AA) also stimulates secretion. The PG- or AA-stimulated Isc does not persist, however, and on prolonged exposure tachyphylaxis develops. Resensitization of the Isc response to PGE2 is rapid, being essentially complete in 15 min after the PG is removed. Desensitization to AA is not reflected by diminished PG generation. PGE2 release from the mucosa after AA addition is constant, although the AA-stimulated Isc decreases. Isc measurements indicate that PGE2 at slightly below its EC50 partially desensitizes and a near-maximal concentration completely desensitizes to PGE2 but does not, however, inhibit the subsequent change in Isc caused by theophylline or vasoactive intestinal peptide (VIP). Adenosine 3',5'-cyclic monophosphate (cAMP) measurements suggest that desensitization applies to cAMP production. PGE2 (10(-5) M) increases mucosal cAMP three- to sevenfold, but this elevation is transient; a second challenge dose, which fails to elicit a Isc change, also fails to increase mucosal cAMP. Adenylate cyclase measurements from untreated and PGE2-treated enterocytes demonstrate a decrease in stimulation by PGE2 but not in stimulation by VIP, fluoride, or 5-guanylylimidodiphosphate.

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