Characterization of the effects of vasoactive substances on the bulbus arteriosus of the eel, Anguilla rostrata

Abstract

The fish bulbus arteriosus (BA) smoothes cardiac output by expanding during cardiac systole and rebounding during diastole, thereby providing constant perfusion of the gills downstream. Published data have demonstrated innervation of the teleost BA and shown that the tension and compliance of the BA responded to vasoactive agonists, such as epinephrine and acetylcholine, suggesting that the BA was more than a mere ''windkessel.'' To examine vasoactivity in the BA more directly, we measured the responses of isolated tissue rings from the BA of the eel, Anguilla rostrata to a suite of putative vasoactive agonists, which had been shown to affect vascular smooth muscle in a variety of teleosts. The BA of the eel was insensitive to acetylcholine but constricted when endothelin (ET-1) was applied. Nitric oxide, sodium nitroprusside (SNP; NO donor), natriuretic peptides (NP), and prostaglandin E 1 (but not the prostacyclin agonist carbaprostacyclin) produced significant dilation in the BA. Since both ET-1 and sarafotoxin S6c produced concentration-dependent constriction, it appears that endothelin receptor B-type (ET B ) receptors (and possibly ET A receptors) are present. The dilation produced by SNP was also concentration dependent, as were the dilations produced by porcine C-type natriuretic peptide, eel atrial natriuretic peptide (NP receptor agonists), Sulprostone and Butaprost (PGE receptor agonists). Our data demonstrate that the BA of eel is responsive to a variety of vasoactive agonists, suggesting that the BA is under neurohumoral control. The role of agonist-induced changes in BA tension in fish cardiovascular physiology remains to be determined, as do the specific receptor types involved.

Endothelin B receptor Ca2+ signaling in shark vascular smooth muscle: participation of inositol trisphosphate and ryanodine receptors

“…The dogfish shark appears to be unique in that ET-1 stimulation of vascular contraction in dorsal aorta and anterior mesenteric artery (Evans et al, 1996;Evans, 2001), or of increases in [Ca 2+ ]i in anterior mesenteric artery, occurred exclusively via ETBR activation (this study). Evidence for ETBR in teleost fish VSM was demonstrated in the bulbus arteriosus of the eel Anguilla rostrata in studies where there was dose-dependent constriction to ET-1 and SRX (Evans et al, 2003).…”

Chondrichthyans have a bulbus arteriosus at the arterial pole of the heart: morphological and evolutionary implications

“…However, further studies testing the effects of vasoactive substances are needed to verify this notion. Characterization of such effects on the teleost bulbus indicates that it is under neurohormonal control (Evans et al. 2003), a fact which denotes that the bulbus is much more than a ‘Windkessel’ (Von Skramlick, 1935), as classically assumed.…”

“…However, studies in both teleosts and elasmobranchs suggest that the paraphyletic group of fishes relies upon other vasoregulatory mechanisms. These data, mainly derived from ex vivo isolated blood vessels, are often confusing and contradictory (Olson & Villa, 1991; McGeer & Eddy, 1996; Eddy & Tibbs, 2003), but it does appear that NO produces significant dilation of the teleost bulbus arteriosus (Evans et al. 2003).…”

“…It is well known that the teleost bulbus arteriosus smoothes cardiac output, i.e. it (1) reduces both the pulsality of the blood flow to the gill vasculature and haemodynamic afterload of the ventricular muscle by expanding during ventricular systole, and (2) provides constant perfusion of the gills through the ventral aorta by rebounding during ventricular diastole (Icardo et al 1999a,b;Braun et al 2003;Evans et al 2003). The question is whether the function of the chondrichthyan bulbus arteriosus is similar to that of the teleost bulbus.…”

Endothelin receptors in teleost fishes: cardiovascular effects and branchial distribution

“…On the other hand, in the spiny dogfish shark (Squalus acanthias), there is evidence for ET B -like receptors in the gill (6) and aorta (5). In the eel (Anguilla rostrata), pharmacological evidence points toward involvement of an ET B -like receptor in bulbus arteriosus contraction, but the presence of ET A -like receptors could not be ruled out (8). Moreover, Evans and Harrie (7) showed that the ventral aorta of the eel does not respond to the specific ET B receptor agonist SRX S6c.…”