Peripheral cardiorespiratory effects of bombesin in anaesthetized rats

The respiratory effects evoked by systemic injection of bombesin were studied in spontaneously breathing rats that were (i) neurally intact and subsequently bilaterally vagotomized, (ii) intact, before and after pharmacological blockade of the bombesin BB1 and BB2 receptors. An intravenous bolus of bombesin (10 μg/kg) evoked sighs, decrease in the breathing rate, augmentation of tidal volume and an increase in mean arterial blood pressure.Midcervical vagotomy abolished all respiratory changes evoked by bombesin challenge, but did not prevent the increase in blood pressure. Blockade of BB1 and BB2 receptors with an intravenous dose of 50 μg/kg of [D-Phe]12-bombesin, reduced significantly the cardio-respiratory effects due to bombesin administration. The BB1 receptors antagonist, BIM 23127, at a dose of 100 μg/kg did not block the response to bombesin. These results indicate that bombesin given systemically stimulates ventilation by activation of BB2 receptors affecting mainly the tidal component of the breathing pattern, and that the response is mediated by the lung vagi. The hypertensive effect of bombesin resulted from the excitation of BB2 receptors, but occurred outside vagal afferentation from the lungs.