Effects of PGD2 and PGF2 alpha on longitudinal and circular muscles of guinea-pig isolated proximal colon.

The mechanical effects of PGD2 and PGF2 alpha on longitudinal and circular muscles of the guinea-pig isolated proximal colon were investigated. PGD2 and PGF2 alpha (1 nM - 10 microM) produced a dose-dependent contraction in longitudinal and circular muscles. The contractile action of PGD2 was more potent than that of PGF2 alpha in circular muscle and was less potent in longitudinal muscle. Contractions induced by PGD2 or PGF2 alpha (1 microM) were unaffected by atropine(1 microM) in both muscles, but tetrodotoxin(1 microM) slightly inhibited these contractions in longitudinal muscle. The results suggest that in longitudinal muscle PGD2 and PGF2 alpha have largely a direct action on the muscle cells and a partial neuronal action on the non-cholinergic intrinsic nerves, whereas in circular muscle these PGs have only a direct action on the muscle cells.