Asymmetric reflex responses of the nasal and tracheal vasculatures of the dog

Characterization of nasal obstruction in the allergic guinea pig using the forced oscillation method

INTRODUCTION

This is the first report to evaluate changes in nasal resistance in a preclinical animal model using the forced oscillation method.

METHODS

The method involves characterizing pressure-flow relationships of the respiratory system due to external oscillatory forces.

RESULTS

First, we evaluated changes in nasal resistance using an established small-animal rhinometric technique. In these studies, aerosolized ovalbumin (3%) administered to the nasal cavity of ovalbumin-sensitized guinea pigs increased nasal resistance at 30 min by 99 +/- 14%. The histamine H1 antagonists, chlorpheniramine (1 mg/kg i.v.) and pyrilamine (1 mg/kg i.v.), blocked the increase in nasal resistance due to ovalbumin provocation (50 +/- 17% and 39 +/- 11% over baseline, respectively). The alpha-adrenergic agonist phenylpropanolamine (3 mg/ kg i.v.) had no effect on the nasal actions of ovalbumin. In separate studies, nasal resistance was measured at 2 Hz by forced oscillation and ovalbumin (3%) increased nasal resistance by 91 +/- 14%. Chlorpheniramine (1 mg/kg i.v.) significantly attenuated the increase in nasal resistance due to ovalbumin. Finally, changes in nasal resistance for each treatment group were evaluated at frequencies of 1 - 18 Hz. Area under the curve analysis demonstrated that chlorpheniramine blocked the nasal obstructive effect of ovalbumin. In contrast, a pharmacologically active dose of phenylpropanolamine (3 mg/kg i.v.) did not produce decongestant activity.

DISCUSSION

The current data are inconsistent with the well-established clinical efficacy of alpha-adrenergic agonists as nasal decongestants. Consequently, we suggest that allergic nasal obstruction in the guinea pig may not be the best preclinical approach to assess the nasal decongestant activity of vasoconstrictor alpha-adrenergic agonists. Additionally, our studies demonstrate the utility of the forced oscillation technique in assessing changes in nasal resistance in small laboratory animals.

The Effects of Vagal Stimulation on Laryngeal Vascular Resistance and Intraluminal Pressure in the Dog

In anaesthetized dogs (sodium pentobarbitone 30 mg/kg, i.v.) laryngeal vascular resistance was measured by unilateral perfusion at constant flow of the branch of the cranial superior thyroid artery that supplies the larynx. Arterial perfusion was at constant flow and inflow pressure was divided by flow to give laryngeal vascular resistance (R(LV)). Intraluminal laryngeal pressure (P(L)) and systemic arterial blood pressure (BP) were also measured. Stimulation (20 V, 20 Hz, 0.2 milliseconds) of the central end of cervical vagus caused an increase in R(LV) (+22.9+/-6.1%) and a decrease in P(L) (-12.1+/-4.4%). Stimulation (10 V, 10 Hz, 0.2 milliseconds) of the central end of the recurrent laryngeal nerve (RLN) reduced RLV (-3.4+/-0.8%) and P(L) (-7.5+/-4.1%). Stimulation of the peripheral end of the RLN decreased R(LV) (-7.1+/-1.9%) and increased PL (+21.6+/-7.7%). Stimulation of the central end of the superior laryngeal nerve (SLN) increased R(LV) (+17.9+/-3.2%) and P(L) (+59.8+/-2.7%), whereas stimulation of the peripheral end of the SLN decreased R(LV) (-4.8+/-1.6%) and P(L) (-4.1+/-2.4%). After treatment with alpha-adrenoreceptor antagonist phentolamine (0.5 mg/kg, i.v.), stimulation of the central end of cervical vagus nerve reduced R(LV) by 25% and decreased BP. Phentolamine caused a decrease in BP and reduced the magnitude of increase in R(LV) in response to stimulation of central end of SLN. After atropine sulphate (0.5-2.0 mg/kg, i.v.), the stimulation of both central and peripheral ends of RLN reduced R(LV). The decrease in R(LV) during stimulation of peripheral end of SLN was reduced by atropine. Thereafter, pancuronium bromide (0.06-0.1 mg/kg, i.v.) was given and dogs were artifically ventilated. After paralyzed, stimulation of the central end of the SLN decreased R(LV) (+26.0+/-4.5%) but produced no change in P(L), It is concluded that parasympathetic motor fibers in the RLN and SLN are effective for the laryngeal vascularity and non-adrenergic system may be responsible for laryngeal vasoconstriction. laryngeal vasculature; vagal stimulation; phentolamine; atropine

Chemical control of laryngeal vascular resistance in anesthetized dogs

The branch of the cranial superior thyroid artery that supplies the larynx was perfused unilaterally at a constant flow rate in dogs anesthetized with pentobarbitone sodium (30 mg.kg-1, i.v.). Laryngeal vascular resistance (RLv) was calculated. Intraluminal laryngeal pressure (PL) was determined. Asphyxia caused a diminution in PL (-27.7 +/- 4.2%) (p < 0.01) and an initial decrease followed by an increase in RLv (-10.9 +/- 2.3% and +12.8 + 2.8%) (p < 0.001). Following vagotomy, asphyxia decreased PL (-17.1 +/- 4.2%) and increased RLv (+45.5 +/- 11.0%). Systemic hypoxia induced by breathing 8% O2-N2 increased RLv (+8.4 +/- 1.3%) (p < 0.001) and decreased PL (-24.9 +/- 3.7%) (p < 0.001). In chemodenervated dogs, the response of PL to hypoxia was abolished while that of RLv was similar to that in intact animals. Breathing of 7% CO2 in air caused an increase in RLv (+6.1 +/- 1.6%) (p < 0.001) and a decrease in PL (-20.9 +/- 3.2%) (p < 0.001). Following chemodenervation, hypercapnia still increased RLv (+11.3 +/- 3.2%) (p < 0.01) and diminished PL (-29.9 +/- 2.5%). Bilateral vagotomy reduced the response of PL to hypercapnia (-13.3 +/- 6.9%) (p < 0.05). Local intra-arterial injection of KCN produced an increase in RLv and PL (+7.0 +/- 1.2%, +9.0 +/- 1.0%). After peripheral chemodenervation KCN injection slightly increased PL (+2.0 +/- 0.9%). The response of RLv was almost abolished. In conclusion, laryngeal vasoconstriction in response to systemic hypoxia after chemodenervation is probably mediated by increased sympathetic discharge to the larynx due to hypoxia of the CNS. Laryngeal responses to hypercapnia may be due to the action of central chemoreceptors.

Asymmetry in reflex responses of nasal muscles in anesthetized guinea pigs

Nasal reflexes elicited by mechanical or electrical stimulation of nasal afferents were studied in anesthetized guinea pigs. Probing the nasal cavity of one side evoked a greater activation of the contralateral than the ipsilateral nasal muscles and, occasionally, sneezing. Similarly, electrical stimulation of the ethmoidal nerve often caused sneezing, with a greater activation of the nasal muscles and a greater increase in resistance on the contralateral side. Asymmetrical activation of the nasal muscles in response to mechanical stimuli induces asymmetrical airflows, especially during sneezing, between the two sides of the nasal cavity. Most of the expired air is forcibly blown out through the ipsilateral nostril, thus improving the elimination of irritants from the nose.