Inhibition of prostaglandin effects by ouabain in the canine vascular tissue

Abstract

The effects of prostaglandins on the isolated mesenteric vein and artery of the dog were investigated. Prostaglandin E 1 (PGE 1 ) inhibited spontaneous contractions of the tissue whereas prostaglandin F 1α (PGF 1α ) and prostaglandin F 2α (PGF 2α ) stimulated them. The effects of prostaglandins were not influenced by pretreatment with atropine, phenoxybenzamine, propranolol, or tetrodotoxin. The norepinephrine-induced contractions were inhibited by PGE 1 and enhanced by PGF 1α and PGF 2α Both these contrasting effects were enhanced in a low concentration of K + (1.2 mM) and diminished when the media contained K + in high concentration (23.2 mM). Pretreatment of the tissue with ouabain in sufficiently high concentration (1.5 × 10 −5 M) produced an initial contracture followed by relaxation. PGE 1 and PGF 1α had no effect on the ouabain-treated tissue but PGF 2α still induced dose-dependent contractions. In the ouabain-treated tissue the effects of PGE 1 and PGF 1α on the norepinephrine-induced contraction were also absent. From these experiments it is concluded that the transport enzyme (Na + + K + )-dependent ATPase is necessary for PGE 1 and PGF 1α to elicit their action on vascular tissue. The PGF 2α effect is probably mediated by an enzyme which is not sensitive to ouabain.