Cardiovascular actions of dogfish urotensin I in the dogfish, Scyliorhinus canicula

A synthetic replicate of dogfish urotensin I (U-I), a 41-amino-acid residue peptide isolated from an extract of the caudal spinal cord region of the European spotted dogfish Scyliorhinus canicula was prepared in order to study its cardiovascular actions in the species of origin. Bolus intraarterial injections of dogfish U-I (0.3-30 nmol/kg body wt) into the celiac artery of unanesthetized dogfish produced a transient fall in arterial blood pressure (P < 0.05 in the dose range 1-3 nmol/kg) followed by a sustained and dose-dependent rise in pressure (P < 0.05 in the dose range 1- 30 nmol/kg). The maximum depressor response (to 3 nmol/kg) was 0.25 ± 0.08 kPa and the maximum pressor response (to 30 nmol/kg) was 1.08 ± 0.09 kPa. There was no significant effect on heart rate at any dose tested. Pretreatment of the animals with the α-adrenergic receptor antagonist phentolamine significantly (P < 0.05) attenuated the pressor response to injections of dogfish U-I (1 nmol/kg and 10 mol/kg), demonstrating that the effects of the peptide are mediated, at least in part, through release of catecholamines. The data suggest that U-I, released together with potent pressor peptide urotensin II from the caudal neurosecretory system, may play a physiological role in cardiovascular regulation in elasmobranchs.