| Summary: | Prostacyclin (PGI2) generation by teleost and elasmobranch fish vascular wall was detected, as 6‐keto‐PGF1α‐like immunoreactivity, in the incubation medium of ventral aorta rings from Anguilla anguilla, Conger conger and Scyliorhinus stellaris. The average yields after 15 min incubation were the following (ng of 6‐keto‐PGF1α‐like/g of wet tissue): A. anguilla =116.8 ±30; C. conger = 7.50; S. stellaris = 58.0 ± 10. Accordingly, the vascular responses to synthetic PGI2were examined on the isolated and saline‐perfused head of four teleost (A. anguilla, C. conger, S corpaena porcus and Solea solea) and two elasmobranch (S. stellaris and Torpedo marmorata) species. In teleosts, PGI2gave a dose‐related increase in overall gill vascular resistance, unaffected by indomethacin, phenoxybenzamine and phentolamine pretreatment or by previous decerebration of the animal. Conversely, in elasmobranchs PGI2elicited a diphasic response, characterized by a transient, not dose‐related constriction, followed by a longer lasting and dosedependent dilation. The effects of PGI2on isolated branchial arch (in A. anguilla, C. conger and S. stellaris) and ventral aorta strips (in C. conger and S. stellaris) were also examined. Both preparations shared the same responsivity of the head in toto, confirming the divergence observed in this respect between teleosts and elasmobranchs. The reactivity of teleost branchial vessels to this autacoid appears to be unique among the other vertebrates examined thus far. Copyright © 1985 Wiley‐Liss, Inc., A Wiley Company
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