Neurokinin receptors in recurrent airway obstruction: a comparative study of affected and unaffected horses.

The purpose of the study was to compare in vitro airway responses to neurokinin A & B (NKA and NKB) and expression of NK-2 receptors in airways of horses affected and unaffected with recurrent airway obstruction (RAO). Neurokinin-A, an inflammatory mediator belonging to the tachykinin family of neuropeptides, causes bronchoconstriction by binding to NK-2 receptors. Neurokinin-B is a lesser-known neuropeptide that acts on NK-3 receptors. Horses were placed into RAO-affected and RAO-unaffected groups based on their history, clinical scoring, and pulmonary function testing. Lung tissue from each lobe was collected for immunohistochemical staining for NK-2 receptors. Cumulative concentration-response relationships were determined on bronchial rings (4-mm wide) collected and prepared from the right diaphragmatic lung lobe to graded concentrations (half log molar concentrations 10(-7)M to 10(-4)M) of NKA and NKB. The results showed that NKA caused significantly greater contraction than NKB in both groups. In RAO-affected horses, both agents produced significantly greater bronchial contractions than those in the RAO-unaffected horses. Immunohistochemical staining showed that the overall NK-2 receptor distribution was significantly increased in bronchial epithelium and smooth muscles of bronchi and pulmonary vessels of RAO-affected than RAO-unaffected horses. The findings indicate that NK-2 receptors are up-regulated in RAO, suggesting that NK-2 receptor antagonists may have some therapeutic value in controlling the progression of airway hyperreactivity in horses affected with RAO.

Rhodamine 123 permeability through the catfish intestinal wall: Relationship to thermal acclimation and acute temperature change.

Temperature is known to influence xenobiotic retention in fish. The effect of acute and acclimatory temperature change upon Rhodamine 123 (Rho123) permeability through an in vitro catfish multi-segment (3) everted sac intestinal wall model was examined in a 9 cell matrix of acclimation and assay temperatures (10, 20 and 30 degrees C). Changes in Rho123 permeability were examined in context with membrane fluidity, xenobiotic solubility and intestinal morphology. When assayed at the acclimation temperature greater Rho123 permeability was noted at warmer acclimation temperatures for the proximal and middle intestinal segments, while the distal segment exhibited little change and apparent compensation across temperatures. Rho123 permeability was increased as assay temperatures were elevated above the acclimation temperature for most comparisons. Cold acclimation significantly increased total intestinal length (43.2%) and proximal intestine weights while total body weights did not differ. Brush border membranes (BBM) increased fluidity with increased assay temperatures, however, composite anisotropy lines were not significantly different between acclimation treatments. In an additive manner, the membrane probe DPH exhibited increased solubility in BBM with increases in acclimation and assay temperatures. Compositely, these results suggest that acclimation and acute temperature change may differentially influence xenobiotic permeability among intestinal segments with interacting mechanisms.

Endothelin receptor alterations in equine airway hyperreactivity.

The purpose of this study was to evaluate the role of endothelin-1 (ET-1) and its receptors in the airway hyperreactivity of horses with obstructive pulmonary disease associated with summer pasture (SPAOPD). The right diaphragmatic lobe of the lung of 8 clinically healthy (unaffected) and 8 SPAOPD-affected horses was collected immediately after euthanasia. Bronchial rings (4 mm wide) were prepared and mounted in organ baths and attached to force transducers interfaced with a polygraph. Four rings were used to study each ET-1 receptor; 1 ring served as the control, and the other 3 were incubated with 10(-9), 10(-7), or 10(-5) M of either BQ-123, an ET(A)-receptor antagonist, or IRL-1038, an ET(B)-receptor antagonist. Cumulative concentrations (10(-8.5) to 10(-6) M) of ET-1 were applied to all rings. Using pooled pulmonary tissue from different regions of the lung, we performed a reverse-transcription polymerase chain reaction (RT-PCR) to determine ET(B)-receptor gene expression. Although ET-1 caused concentration-dependent bronchial ring contraction in both groups of horses, the rings of SPAOPD-affected horses had significantly greater contraction than the rings of unaffected horses. Whereas ET(A)-receptor blockade significantly increased the response to ET-1 in unaffected horses, ET(B)-receptor blockade significantly decreased the response in affected horses. The pA2 values showed a nonsignificant decrease in ET(A)-receptor affinity and a significant increase in ET(B)-receptor affinity in affected horses compared with unaffected horses. The ET(B)-receptor mRNA expression of the pooled pulmonary tissue showed a nonsignificant increase in affected horses compared with unaffected horses. The airway hyperreactivity to ET-1 observed in the bronchial rings from the affected horses appears to be due in part to activation of pulmonary ET(B) receptors, which appear to be inactive in unaffected horses.

Role of endothelium and nitric oxide in modulating in vitro responses of colonic arterial and venous rings to vasodilatory neuropeptides in horses.

The objective of this study was to determine and compare the in vitro responses of equine large colon arterial and venous rings to vasodilatory neuropeptides; calcitonin gene-related peptide (CGRP); substance P (SP); vasoactive intestinal polypeptide (VIP); and acetylcholine (ACh), a standard nonpeptide endothelium-dependent vasodilator. Responses of vessel rings to graded concentrations (10(-11) M to 10(-5) M) of each drug were determined in endothelium-intact, denuded, and Nomega-nitro-L-arginine methyl ester (L-NAME, 10(-5) M)-treated rings that were pre-contracted with norepinephrine. Percentage maximal relaxation (PMR), defined as the % decrease from the contracted state, was determined. Because all rings did not relax at least 50%, EC50 values could not be consistently calculated. Arterial rings with intact endothelium were more sensitive to CGRP, compared with VIP and SP, and venous rings of all conditions were more sensitive to VIP than CGRP or SP. Overall, arteries had a greater PMR for ACh compared with SP and VIP. Intact and L-NAME treated arteries had a greater PMR than denuded arteries; there were no differences in PMR of intact and L-NAME treated arteries. Veins had a greater PMR for VIP than CGRP, SP, or ACh. Calcitonin gene-related peptide caused greater relaxation in intact arteries, whereas VIP causes greater relaxation in veins. Arterial relaxation was dependent upon the presence of intact endothelium. The response of veins to VIP among the conditions tested was not different, suggesting VIP has direct actions on venous smooth muscle. These neuropeptides modulate vasomotor tone via vasorelaxation in colonic arteries and veins.

Pharmacologic evaluation of neurokinin-2 receptor antagonists in the guinea pig respiratory tract.

OBJECTIVE: To evaluate 3 neurokinin-2 (NK2) receptor antagonists on the basis of their ability to block neurokinin A (NKA)-induced contractile responses in various regions of the guinea pig respiratory tract. ANIMALS: 48 clinically normal guinea pigs. PROCEDURE: After euthanasia, the trachea and lungs were removed en bloc. The spirally cut trachea was divided into lower, middle, and upper portions. The main bronchus was spirally cut. A lung strip was cut from the edge of the lung. Tissue strips were mounted in organ baths containing Tyrode solution at 37 degrees C and attached to force transducers interfaced with a polygraph. Lung strips were set at a tension of 1 g; other tissue strips were set at 2 g. After 45 minutes of equilibration, cumulative concentration-response (CR) relationships to graded concentrations of NKA were determined. In the treatment groups, tissues were incubated (30 minutes) with antagonists (MEN 10376, SR 48968, and SR 144190) at 3 concentrations (10(-9), 10(-7), and 10(-5)M) before CR relationships were determined. Effectiveness of SR 48968 against NKA was also tested in vivo. RESULTS: Lung strips failed to contract, but all others responded in a concentration-dependent manner. Bronchial spirals were most sensitive. SR 48968 had the highest pA2 value and effectively blocked NKA. CONCLUSIONS AND CLINICAL RELEVANCE: The bronchial region where airflow resistance is high was the most sensitive to NKA, suggesting the importance of NKA in bronchoconstriction. Nonpeptide antagonists (SR 48968 and SR 144190) were more potent than the peptide antagonist (MEN 10376), indicating their greater therapeutic potential as antiasthmatic agents.