Cardiorespiratory activity of C-terminal pentapeptide of substance P in anaesthetized rats

• Cardiovascular and respiratory effects of substance P and AWL2077 were compared.
• AWL2077 affected respiratory variables less than substance P.
• Fall in arterial blood pressure was of equal intensity for both peptides.
• Involvement of lung vagi referred to respiratory timing.

Experiments were performed in anaesthetized, spontaneously breathing rats to: (1) analyse the respiratory and cardiovascular effects of C-terminal fragment of substance P (AWL2077) as referred to those exerted by the parent undecapeptide, (2) determine the involvement of lung vagal afferents to these responses.Each peptide was injected intravenously at a dose of 0.3 μmol/kg into neurally intact or midcervically vagotomized rats.Administration of both compounds decreased tidal volume, minute ventilation, mean arterial blood pressure and heart rate, showing stimulatory (SP) and depressive (AWL2077) effects on the rate of breathing. Midcervical vagotomy reversed (post-SP) and precluded (post-AWL2077) respiratory rate responses and eliminated bradycardia evoked by both peptides.These findings indicate that the examined C-terminal pentapeptide was convergent with, but less potent than substance P in central depression of tidal volume and displayed divergence in the peripheral effect on respiratory timing.