Effect of initial blood pressure level on cardiovascular reflexes caused by intraperitoneal neurotensin

The reflex changes of systemic blood pressure (BP) and heart rate (HR) induced by intraperitoneal (IP) injections of neurotensin-containing solutions (NTCS) were measured in anesthetized guinea pigs whose BP was raised up by intravenous (IV) infusions of either angiotensin II (ATII) or noradrenaline (NA), and compared to those observed in control animals (i.e., saline-infused guinea pigs with low initial BP level). The amplitudes of reflex pressor and tachycardic responses to IP NTCS were either not affected or reduced in animals whose BP was raised with ATII or NA. However, no hypotensive effect was observed, following IP NTCS, in any of the animals tested. The results indicate that high initial BP levels tend to attenuate the reflex increases of BP and HR caused by IP NTCS, the level of inhibition being largely determined by the type of vasopressor agent utilized to raise up the BP. They also suggest that the initial BP level is unlikely to be an important factor in determining whether the activation of capsaicin-sensitive visceral afferents will produce hypotensive or hypertensive effects in this animal model.