Objective: 

Although pituitary adenylate cyclase - activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) exert diverse actions on heart and blood vessels along the vertebrate phylum, no information is currently available concerning the potential role of these peptides on the regulation of the baroreflex response, a major mechanism for blood pressure homeostasis. Consequently, the goal of this study was to examine in our experimental model, the unanesthetized rainbow trout, whether PACAP and VIP are involved in the regulation of the cardiac baroreflex sensitivity (BRS).

Methods: 

For this purpose, we investigated the effects of intracerebroventricular (ICV) and intra-arterial (IA) injections of trout PACAP and VIP (25–100 pmol) on BRS in unanesthetized trout. Cross spectral analysis techniques using a fast Fourier transform algorithm were employed to calculate the coherence, phase and gain of the transfer function between spontaneous fluctuations of systolic arterial blood pressure and R-R intervals of the electrocardiogram. The BRS was estimated as the mean of the gain of the transfer function when the coherence between the two signals was high and the phase negative.

Results: 

Compared with vehicle, ICV injections of trout PACAP and trout VIP dose-dependently reduced the cardiac BRS to the same extent with a threshold dose of 50 pmol for a significant effect. When injected IA at the same doses as for ICV injections, only the highest dose of VIP (100 pmol) significantly attenuated the BRS.

Conclusions: 

Our findings indicate new roles for PACAP and VIP, functioning as neurotransmitters or neuromodulatory peptides, for the control of neural pathways involved in the cardiac baroreflex sensitivity in trout.