Deep-breath frequency in bronchoconstricted monkeys (Macaca fascicularis)

Respiratory mechanics: comparison of Beagle dogs, Göttingen minipigs and Cynomolgus monkeys

INTRODUCTION

When the no observed adverse effect level (NOAEL) is determined by respiratory safety pharmacology, follow-up studies are warranted and may include airway resistance and compliance. Respiratory mechanics in commonly used large animal species (Beagle dogs, Cynomolgus monkeys, and Göttingen minipigs) were compared.

METHODS

Eighteen animals were used (3/sex/species) in an anesthetized model (propofol infusion) with pancuronium as a neuromuscular blocker. Parameters of respiratory mechanics were evaluated at baseline and at peak drug effect. Resistance (Rrs) and elastance (Ers) were measured by applying a single frequency forced oscillation (0.5 Hz) to the subject's airway opening and fitting the flow, volume and pressure data to the single compartment model of the lung. Increasing doses of intravenous (IV) methacholine were administered in all three species, as well as doubling aerosolized concentrations of the same bronchoconstrictor agent before and after inhaled albuterol.

RESULTS

The slope of the IV methacholine dose-response curve for Rrs was similar in dogs and monkeys and both species differed from minipigs, which showed greater reactivity. At the highest IV dose tested, minipigs also reached higher levels of bronchoconstriction than the other two species. They were followed, in decreasing order, by dogs and monkeys. Albuterol induced a significant decrease in the slope of the dose-response curve only in dogs and monkeys.

DISCUSSION

Scientific literature is available on respiratory mechanics in monkeys and dogs but not in minipigs. Our results suggest that minipigs were more reactive than dogs and monkeys to IV methacholine while less sensitive to inhaled albuterol.

Immunopathogenesis of allergic asthma: more than the th2 hypothesis

Asthma is a chronic obstructive airway disease that involves inflammation of the respiratory tract. Biological contaminants in indoor air can induce innate and adaptive immune responses and inflammation, resulting in asthma pathology. Epidemiologic surveys indicate that the prevalence of asthma is higher in developed countries than in developing countries. The prevalence of asthma in Korea has increased during the last several decades. This increase may be related to changes in housing styles, which result in increased levels of indoor biological contaminants, such as house dust mite-derived allergens and bacterial products such as endotoxin. Different types of inflammation are observed in those suffering from mild-to-moderate asthma compared to those experiencing severe asthma, involving markedly different patterns of inflammatory cells and mediators. As described in this review, these inflammatory profiles are largely determined by the involvement of different T helper cell subsets, which orchestrate the recruitment and activation of inflammatory cells. It is becoming clear that T helper cells other than Th2 cells are involved in the pathogenesis of asthma; specifically, both Th1 and Th17 cells are crucial for the development of neutrophilic inflammation in the airways, which is related to corticosteroid resistance. Development of therapeutics that suppress these immune and inflammatory cells may provide useful asthma treatments in the future.

Hypocapnia-dependent facilitation of augmented breaths: observations in awake vs. anesthetized rats

We investigated whether commonly used injectable laboratory anesthetics alter the regulation of augmented breaths (ABs) in different respiratory backgrounds. Male rats were studied on three separate experimental days, receiving one of three injections in randomized order: ethyl carbamate ('urethane'; 1.2mgkg(-1)), ketamine/xylazine (ket/xyl; 80/10mgkg(-1)), or normal saline. Following each of the three interventions, breathing was monitored during 15min exposures to normoxia (room air), hypoxia (10% O(2)) and hypoxia+CO(2) (10% O(2), 5% CO(2)). Urethane anesthesia completely eliminated ABs from the breathing rhythm in room air conditions (p<0.001), and decreased the hypocapnia-dependent component of this response (p<0.001). ket/xyl left the normal incidence of ABs in room air breathing intact but significantly suppressed the hypoxia-induced facilitation of ABs (p=0.0015). These results provide the first clear evidence that laboratory anesthesia can profoundly alter the regulation of ABs including the hypocapnia-dependent component of their facilitation.

Sensory nerves and airway irritability

The lung, like many other organs, is innervated by a variety of sensory nerves and by nerves of the parasympathetic and sympathetic nervous systems that regulate the function of cells within the respiratory tract. Activation of sensory nerves by both mechanical and chemical stimuli elicits a number of defensive reflexes, including cough, altered breathing pattern, and altered autonomic drive, which are important for normal lung homeostasis. However, diseases that afflict the lung are associated with altered reflexes, resulting in a variety of symptoms, including increased cough, dyspnea, airways obstruction, and bronchial hyperresponsiveness. This review summarizes the current knowledge concerning the physiological role of different sensory nerve subtypes that innervate the lung, the factors which lead to their activation, and pharmacological approaches that have been used to interrogate the function of these nerves. This information may potentially facilitate the identification of novel drug targets for the treatment of respiratory disorders such as cough, asthma, and chronic obstructive pulmonary disease.

Animal models of asthma

Studies in animal models form the basis for much of our current understanding of the pathophysiology of asthma, and are central to the preclinical development of drug therapies. No animal model completely recapitulates all features of the human disease, however. Research has focused primarily on ways to generate allergic inflammation by sensitizing and challenging animals with a variety of foreign proteins, leading to an increased understanding of the immunological factors that mediate the inflammatory response and its physiological expression in the form of airways hyperresponsiveness. Animal models of exaggerated airway narrowing are also lending support to the notion that asthma may represent an abnormality of the airway smooth muscle. The mouse is now the species of choice for asthma research involving animals. This presents practical challenges for physiological study because the mouse is so small, but modern imaging methodologies, coupled with the forced oscillation technique for measuring lung mechanics, have allowed the asthma phenotype in mice to be precisely characterized.