EFFECTS OF PROSTAGLANDINS AND THROMBOXANE ANALOGUES ON BULLOCK AND DOG IRIS SPHINCTER PREPARATIONS

Abstract

1 The bullock iris sphincter was contracted by low concentrations of prostaglandin E₂ (PGE₂), 16,16-dimethyl PGE₂ and 17,18,19,20-tetranor-16-p-chlorophenoxy PGE₂. Other compounds with thromboxane-like actions, for example 11,9-epoxymethano PGH₂, were also potent spas-mogens. ZK 36374, a stable carbacyclin, was a partial agonist on the PGE-sensitive system of this tissue. 2 The thromboxane antagonist, EP 045, had little effect on the action of PGE₂ and 16,16-dimethyl PGE₂ on the bullock iris. 3 The dog iris sphincter was sensitive to PGF_2α but not to PGE₂ and 11,9-epoxymethano PGH₂. 4 16,16-Dimethyl PGE₂ had very low activity on the dog iris in contrast to its high activity on the bullock iris. The reverse was found with the 17,18,19,20-tetranor-16-m-trifluoromethylphenoxy analogue of PGF_2α (ICI 81008). This indicates a considerable selectivity of action of the two analogues. 5 The results are discussed in relation to the existing knowledge of prostanoid receptors.