Effects of angiotensin II on autonomic components of nasopharyngeal stimulation in male conscious rabbits

Abstract

Angiotensin II (ANG II) is known to activate central sympathetic neurons. In this study we determined the effects of ANG II on the autonomic components of the cardiovascular responses to stimulation of nasopharyngeal receptors with cigarette smoke. Experiments were carried out in conscious New Zealand White rabbits instrumented to record arterial pressure and heart rate. Rabbits were exposed to 50 ml of cigarette smoke before and after subcutaneous osmotic minipump delivery of ANG II at a dose of 50 ng.kg(-1).min(-1) for 1 wk in one group and intracerebroventricular (icv) infusion at a dose of 100 pmol/min for 1 h in a second group. The responses were compared before and after heart rate was controlled by pacing. Autonomic components were evaluated by intravenous administration of atropine methyl bromide (0.2 mg/kg) and prazosin (0.5 mg/kg). ANG II given either systemically or icv significantly blunted the pressor response to smoke (P < 0.05) when the bradycardic response was prevented. This blunted response was not due to an absolute increase in baseline blood pressure after ANG II infusion (71.64 +/- 11.6 vs. 92.1 +/- 19.8 mmHg; P < 0.05) because normalization of blood pressure with sodium nitroprusside to pre-ANG II levels also resulted in a significantly blunted pressor response to smoke. The effect of smoke was alpha(1)-adrenergic receptor-mediated because it was essentially abolished by prazosin in both the pre- and the post-ANG II states (P < 0.05). These results suggest that elevations in central ANG II reduce the sympathetic response to smoke in conscious rabbits. This effect may be due to an augmentation of baseline sympathetic outflow and a reduction in reflex sensitivity similar to the effect of ANG II on baroreflex function.

Central Angiotensin (1-7) Enhances Baroreflex Gain in Conscious Rabbits With Heart Failure

“…HRV was significantly increased in CHF rabbits treated with Ang-(1–7). The HR response to cigarette smoke (a vagally mediated bradycardia) 24 was blunted in CHF animals and restored to control following central Ang-(1–7) infusion. The change in baseline HR following administration of atropine was augmented by central Ang-(1–7) infusion.…”

“…Following baseline recording the response to nasopharyngeal stimulation with 60 ml of cigarette smoke was measured, which our laboratory has used previously to activate and measure vagal tone. 24 …”

Renal denervation modulates angiotensin receptor expression in the renal cortex of rabbits with chronic heart failure

“…After the renal surgery, the effectiveness of renal denervation was tested using the response of the renal vasculature to cigarette smoke. The response to oropharyngeal delivery of cigarette smoke (60 ml) is one intervention to near maximally activate the sympathetic nervous system (41). The five intact animals that did not have their nerves severed during the renal surgery served as the pre-and postpace controls to compare the RBF response to smoke administration.…”

Persistence of the nasotrigeminal reflex after pontomedullary transection

“…However, neural organization is difficult to study in awake behaving animals and laboratory preparations are commonly used to circumvent many of these problems (Panneton et al, 2010b). Indeed, similar responses of apnea, bradycardia and peripheral vasoconstriction are seen in the laboratory after stimulating the nasal mucosa with irritant vapors (Angell James and de Burgh Daly, 1972; White et al, 1974; McRitchie and White, 1974; White et al, 1975; Gandevia et al, 1978; Peterson et al, 1983; Panneton, 1990; Wallois et al, 1991; Nakamura and Hayashida, 1992; Panneton and Yavari, 1995; Houdi et al, 1995; Gieroba et al, 1995; Yavari et al, 1996; McCulloch and Panneton, 1997; McCulloch et al, 1999; Ho and Kou, 2000; Kratschmer, 2001; Nalivaiko et al, 2003; Mousa et al, 2005; Rybka and McCulloch, 2006; Panneton et al, 2008; Panneton et al, 2010b). If the neuronal circuitry for this nasotrigeminal reflex mimics that of diving, profound advances may be made in deciphering the organization of pathways driving the diving response, the most powerful autonomic response known.…”