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  • Author or Editor: Richard V. Broadstone x
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SUMMARY

Effects of α2-adrenergic receptor stimulation on the cholinergic contractile response of bovine tracheal smooth muscle were studied. To determine the presence and function of α2-adrenergic receptors on cholinergic nerves innervating bovine tracheal muscle, effects of 2 α2-adrenoceptor agonists and an antagonist were determined. Muscular contractions were elicited by either electrical field stimulation (efs) or exogenous acetylcholine (ach).

The contractile response to efs and exogenous ach was examined for each tissue. Electrical field stimulation of bovine tracheal smooth muscle caused contractions that were completely abolished by atropine, indicating the predominant excitatory innervation of bovine trachea is cholinergic. The α2-adrenoceptor agonists clonidine and medetomidine (10-6 M to 10-4 M) concentration-dependently inhibited the contractile response to efs but not the response to exogenous ach. Contractions induced by efs were significantly (P < 0.05) inhibited in clonidine (10-4M)-treated tissues at low frequencies (0.1 to 10 Hz), whereas medetomidine (10-4 M, 10-4 M) inhibited contractions at all frequencies (0.1 to 30 Hz). Inhibitory effects of the α2-adrenoceptor agonists clonidine and medetomidine were attenuated by the (α2-adrenoceptor antagonist tolazoline. The α2-agonists used in this study appear to cause prejunctional inhibition of cholinergic nerves, because the smooth muscle contractions elicited by efs, but not exogenous ach, were inhibited, compared with controls.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate the hemodynamic effects of orally administered carvedilol in healthy dogs with doses that might be used to initiate treatment in dogs with congestive heart failure.

Animals—24 healthy dogs.

Procedure—Dogs were randomly allocated to receive carvedilol PO at a dose of 1.56, 3.125, or 12.5 mg, twice daily for 7 to 10 days; 6 dogs served as controls. Investigators were blinded to group assignment. Hemodynamic variables were recorded prior to administration of the drug on day 1 and then 2, 4, and 6 hours after the morning dose on day 1 and days 7 to 10. Change in heart rate after IV administration of 1 µg of isoproterenol/kg and change in systemic arterial blood pressure after IV administration of 8 µg of phenylephrine/kg were recorded 2 and 6 hours after administration of carvedilol.

Results—Administration of carvedilol did not significantly affect resting hemodynamic variables or response to phenylephrine. The interaction of day and carvedilol dose had a significant effect on resting heart rate, but a significant main effect of carvedilol dose on resting heart rate was not detected. Increasing carvedilol dose resulted in a significant linear decrease in heart rate response to isoproterenol.

Conclusions and Clinical Relevance—In healthy conscious dogs, orally administered carvedilol at mean doses from 0.08 to 0.54 mg/kg given twice daily did not affect resting hemodynamics. Over the dose range evaluated, there was a dose-dependent attenuation of the response to isoproterenol, which provided evidence of β-adrenergic receptor antagonism. (Am J Vet Res 2005;66:637–641)

Full access
in American Journal of Veterinary Research

Summary

Immunohistochemical methods were used to determine the distribution of pulmonary nerves containing either an enzymatic marker of adrenergic nerves, dopamine β hydroxylase, or the putative neurotransmitter neuropeptide Y in 7 equids with healthy lungs. Nerves immunoreactive for these substances were found on airway smooth muscle in nearly all the samples of healthy equine lung examined. These nerves were generally more numerous in the larger airways but could be detected even in noncartilaginous bronchioles. Pulmonary and bronchial vessels also contained numerous immunoreactive nerves. On the basis of these findings, we suggest that dopamine β-hydroxylase- and neuropeptide Y-immunoreactive nerves may be involved in the regulation of airway and vascular diameter in equids.

Free access
in American Journal of Veterinary Research

Summary

Distribution of pulmonary nerves immunoreactive for either substance P or calcitonin gene-related peptide was determined, using immunohistochemical methods on healthy lungs from adult equids. The overall patterns of distribution of substance P and calcitonin gene-related peptide-like immunoreactivity were similar. Distribution of immunoreactive nerves was not uniform throughout the lungs; nerve fibers immunoreactive for these peptides were more frequently observed near the hilus of the lung than in the caudal lobes or in the periphery of the lung. Nerve fibers immunoreactive for substance P or calcitonin gene-related peptide were most abundant in the lamina propria of the trachea and larger airways, particularly within and directly below the airway epithelium; they were also frequently associated with bronchial and pulmonary vessels. Presence of nerve fibers immunoreactive for substance P and calcitonin gene-related peptide in peribronchial neural ganglia indicated that these sensory nerves may modulate parasympathetic regulation of pulmonary function. Nerve fibers immunoreactive for substance P and calcitonin gene-related peptide were, therefore, well placed to detect inhaled agents and to contribute to the pulmonary response to irritants and pathogens.

Free access
in American Journal of Veterinary Research

SUMMARY

The effect of iv administration of the α2-adrenoceptor agonist xylazine hydrochloride (0.5 mg/kg of body weight) was examined in ponies with recurrent obstructive pulmonary disease, commonly called heaves. Six ponies with the disease (principals) were studied during clinical remission and during an acute attack of airway obstruction precipitated by stabling and feeding of dusty hay. Six control ponies were also studied. In principal ponies with airway obstruction, xylazine administration significantly (P < 0.05) decreased pulmonary resistance and increased dynamic compliance, but did not affect Pa o 2 or Pa co 2 . The α2-antagonist yohimbine blocked the pulmonary effects of xylazine. Administration of saline solution was without effect in both groups of ponies at all periods and xylazine did not have effect in controls or in principals in clinical remission.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate nonselective computed tomographic (CT) venography for evaluating the cervical internal vertebral venous plexus (IVVP), define the diameter and area dimensions of the IVVP, and determine the relationship between dimensions of the cervical IVVP and other vertebral components in medium-sized dogs.

Animals—6 healthy dogs that weighed 18 to 27 kg.

Procedure—Helical CT scans were performed from C1 to C7 before and after IV injection of contrast medium (480 mg of iodine/kg) and a continuous infusion (240 mg of iodine/kg). Image data were transferred to a CT workstation, and measurements were performed on displayed transverse images. Diameter and area measurements of the vertebral canal, dural sac, IVVP, and vertebral body were obtained at C3 to C7.

Results—Opacification of vertebral venous structures was achieved in all dogs with no adverse reactions. Sagittal diameters of the IVVP for C3 to C7 ranged from 0.6 to 3.2 mm. Transverse diameters ranged from 2.32 to 5.74 mm. The IVVP area represented 12.4% of the mean vertebral canal transverse area and 30.61% of the mean vertebral epidural space area. Area measurements of the IVVP were significantly correlated with vertebral canal area and dural sac area.

Conclusions and Clinical Relevance—Results indicated that nonselective CT venography is a safe, sensitive method for performing morphometric assessments of the cervical IVVP in dogs. Findings support the theory that there may be a physiologic or developmental relationship between cervical vertebral canal components. (Am J Vet Res 2005;66:2039–2045)

Full access
in American Journal of Veterinary Research

SUMMARY

Objective

To identify the effect of Pasteurella haemolytica lipopolysaccharide (LPS) and leukotoxin (LKT) on spontaneous and calcium ionophore-induced histamine and inflammatory mediator release from isolated bovine lung parenchyma.

Sample Population

Lungs from 8 healthy cattle.

Procedure

Isolated bovine lung parenchyma was incubated in vitro for 2 hours with LKT or LPS, and spontaneous and induced release of inflammatory mediators was determined.

Results

LKT and LPS increased spontaneous release of histamine and leukotriene B4. In addition, incubation with LPS increased spontaneous release of prostaglandin E2. Moreover, a differential effect of the 2 toxins on calcium ionophore-induced inflammatory mediator release was observed. LKT specifically primed isolated lung parenchyma to release leukotriene B4 and thromboxane B2 in response to calcium ionophore, whereas LPS did not alter the profile of prostanoids released by bovine lung tissue exposed to calcium ionophore.

Conclusions

Pasteurella haemolytica toxins have a direct effect on bovine lung parenchyma, causing release of inflammatory mediators, which contribute to response to infection. Furthermore, bacterial toxins (LKT in this study) may sensitize tissues to the effects of other irritant stimuli, amplifying the inflammatory response. (Am J Vet Res 1997;58:1227–1231)

Free access
in American Journal of Veterinary Research