bs_bs_banner
Equine Veterinary Journal ISSN 0425-1644 DOI: 10.1111/evj.12201
Plasma cortisol concentration increases within 6 hours of stabling in RAO-affected horses J. J. SHABA, A. BEHAN BRAMAN and N. E. ROBINSON* Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, USA. *Correspondence email: [email protected] Received: 20.05.13; Accepted: 11.10.13
Summary Reasons for performing study: In many inflammatory diseases plasma cortisol concentration (CORT) increases at the onset of acute inflammation, but the situation in recurrent airway obstruction (RAO) of horses is unknown. Study design: Split-plot repeated measures design with one grouping factor (disease) and two repeated factors (day and 3-hour intervals). Objective: To test the hypothesis that CORT increases as acute exacerbations of RAO develop. Methods: Four RAO-susceptible and 4 control horses were placed in a low dust environment (LDEnv) for 2 days followed by 2 days in a high dust environment (HDEnv). Exacerbations of RAO were indicated by increases in maximal change in pleural pressure (ΔPplmax) and decreases in breathing frequency variability (BFV), which was continuously measured by respiratory inductance plethysmography. Plasma samples for determination of CORT were collected every 6 h. Results: In control horses, ΔPplmax and BFV were unaffected by the HDEnv, whereas in RAO-affected horses ΔPplmax increased and BFV decreased significantly. In the LDEnv, there was a circadian variation in CORT in both control and RAO-affected horses. In HDEnv, CORT was unaffected in control horses, but increased significantly in RAO-affected horses between 6 and 12 h after entering the HDEnv. Conclusions: Plasma cortisol concentration increases concurrently with the development of acute exacerbations of RAO. Keywords: horse; RAO; cortisol; heaves; circadian; inflammation
Introduction The clinical signs that occur when horses affected with recurrent airway obstruction (RAO) are housed in an organic dust rich environment are a consequence of airway obstruction resulting from airway inflammation [1]. The onset and progression of airway obstruction can be monitored by measurement of the maximal change in pleural pressure (ΔPplmax) [2] and breathing frequency variability (BFV) by respiratory inductance plethysmography (RIP) [3]. The latter measures breathing pattern and has detected reduced BFV within 6 h of stabling RAO-affected horses [3]. Pulmonary inflammation in RAO-affected horses also occurs within 6 h of stabling [4], involves both the innate and adaptive (Th2) immune system [5,6] and leads to neutrophil influx into the lung. In other species, including man, activation of these branches of the immune system, for example by endotoxin [7] or an acute allergen challenge [8], increases the plasma concentration of the endogenous anti-inflammatory hormone cortisol (CORT). It is likely that this increase in endogenous CORT has beneficial effects through reduction of inflammation and, in the case of airway disease, through facilitation of β2 adrenergic receptor function [9]. Previous measurements of CORT in horses with RAO have focused only on the adrenal response to corticosteroid therapy [10,11]. The measurement of CORT during the development of an acute exacerbation of RAO has not been reported. Based on the aforementioned reports of an increase in CORT during acute inflammation, it was hypothesised that inducing RAO in susceptible horses would lead to an increase in airway obstruction accompanied by an increase in CORT. For this reason, CORT was measured every 6 h throughout a protocol in which both RAO and control horses moved from a clean air environment to a high dust environment known to induce exacerbations of RAO.
Materials and methods Eight mixed-breed horses (5 geldings and 3 mares) were used: 4 horses (15–21 years of age, mean ± s.d., 17.3 ± 2.6) that fulfilled the phenotypic description of RAO [1] and 4 control horses (9–21 years, 13 ± 5.5 years) that did not develop airway obstruction when stabled, were paired. Before this study, animals were maintained on pasture and supplemented with a pelleted diet as needed. During the study, animals were housed in 2 different stables. For the first 48 h, the horses were in a low dust environment (LDEnv) that was provided by a well ventilated stable, where
642
horses ate a complete pelleted feed and were bedded on moistened low dust wood pellets. To initiate lower airway obstruction, horses were then transferred to a high dust environment (HDEnv), which was a poorly ventilated stable where horses ate hay and were bedded on straw: they remained there for the final 48 h. Horses were assigned into paired groupings of RAO-susceptible and control horses. Prior overnight dexamethasone suppression tests (40 μg/kg bwt i.m.) strongly indicated that pituitary pars intermedia dysfunction was not present in the horses [12]. On the day before initiation of the study protocol, a pair of horses was transferred from pasture into the LDEnv in the early afternoon to be outfitted with RIP bands and an i.v. jugular catheter. Venous blood sampling began at 08.00 h on Day 1 and continued every 6 h for the remainder of the protocol. The ΔPplmax was measured once daily in the morning, and at that time the RIP bands were calibrated. Respiratory inductance plethysmography data recording began at 10.00 h and continued until the next ΔPplmax measurement approximately 22 h later, during which time there was limited access to the stable. Airway function was monitored by daily ΔPplmax measurement [13] and by continuous use of RIP for BFV calculations [3]. Throughout the sampling period, blood was collected every 6 h from an indwelling i.v. catheter. The CORT was measured by radioimmunoassay. The assay was conducted at the Diagnostic Centre for Population and Animal Health at Michigan State University using the Coat-a-count kita (interassay CV = 8%, intra-assay CV = 3%). The Institutional Animal Care and Use Committee at Michigan State University approved all protocols. The BFV was calculated as the standard deviation (s.d.) of breathing frequency using 3 h blocks of data. Data were analysed by a factorial analysis of variance (ANOVA) with random horse and fixed disease, day and sampling period. When main effects or interactions were significant, means were compared by Tukey’s test with P
Equine Veterinary Journal ISSN 0425-1644 DOI: 10.1111/evj.12201
Plasma cortisol concentration increases within 6 hours of stabling in RAO-affected horses J. J. SHABA, A. BEHAN BRAMAN and N. E. ROBINSON* Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, USA. *Correspondence email: [email protected] Received: 20.05.13; Accepted: 11.10.13
Summary Reasons for performing study: In many inflammatory diseases plasma cortisol concentration (CORT) increases at the onset of acute inflammation, but the situation in recurrent airway obstruction (RAO) of horses is unknown. Study design: Split-plot repeated measures design with one grouping factor (disease) and two repeated factors (day and 3-hour intervals). Objective: To test the hypothesis that CORT increases as acute exacerbations of RAO develop. Methods: Four RAO-susceptible and 4 control horses were placed in a low dust environment (LDEnv) for 2 days followed by 2 days in a high dust environment (HDEnv). Exacerbations of RAO were indicated by increases in maximal change in pleural pressure (ΔPplmax) and decreases in breathing frequency variability (BFV), which was continuously measured by respiratory inductance plethysmography. Plasma samples for determination of CORT were collected every 6 h. Results: In control horses, ΔPplmax and BFV were unaffected by the HDEnv, whereas in RAO-affected horses ΔPplmax increased and BFV decreased significantly. In the LDEnv, there was a circadian variation in CORT in both control and RAO-affected horses. In HDEnv, CORT was unaffected in control horses, but increased significantly in RAO-affected horses between 6 and 12 h after entering the HDEnv. Conclusions: Plasma cortisol concentration increases concurrently with the development of acute exacerbations of RAO. Keywords: horse; RAO; cortisol; heaves; circadian; inflammation
Introduction The clinical signs that occur when horses affected with recurrent airway obstruction (RAO) are housed in an organic dust rich environment are a consequence of airway obstruction resulting from airway inflammation [1]. The onset and progression of airway obstruction can be monitored by measurement of the maximal change in pleural pressure (ΔPplmax) [2] and breathing frequency variability (BFV) by respiratory inductance plethysmography (RIP) [3]. The latter measures breathing pattern and has detected reduced BFV within 6 h of stabling RAO-affected horses [3]. Pulmonary inflammation in RAO-affected horses also occurs within 6 h of stabling [4], involves both the innate and adaptive (Th2) immune system [5,6] and leads to neutrophil influx into the lung. In other species, including man, activation of these branches of the immune system, for example by endotoxin [7] or an acute allergen challenge [8], increases the plasma concentration of the endogenous anti-inflammatory hormone cortisol (CORT). It is likely that this increase in endogenous CORT has beneficial effects through reduction of inflammation and, in the case of airway disease, through facilitation of β2 adrenergic receptor function [9]. Previous measurements of CORT in horses with RAO have focused only on the adrenal response to corticosteroid therapy [10,11]. The measurement of CORT during the development of an acute exacerbation of RAO has not been reported. Based on the aforementioned reports of an increase in CORT during acute inflammation, it was hypothesised that inducing RAO in susceptible horses would lead to an increase in airway obstruction accompanied by an increase in CORT. For this reason, CORT was measured every 6 h throughout a protocol in which both RAO and control horses moved from a clean air environment to a high dust environment known to induce exacerbations of RAO.
Materials and methods Eight mixed-breed horses (5 geldings and 3 mares) were used: 4 horses (15–21 years of age, mean ± s.d., 17.3 ± 2.6) that fulfilled the phenotypic description of RAO [1] and 4 control horses (9–21 years, 13 ± 5.5 years) that did not develop airway obstruction when stabled, were paired. Before this study, animals were maintained on pasture and supplemented with a pelleted diet as needed. During the study, animals were housed in 2 different stables. For the first 48 h, the horses were in a low dust environment (LDEnv) that was provided by a well ventilated stable, where
642
horses ate a complete pelleted feed and were bedded on moistened low dust wood pellets. To initiate lower airway obstruction, horses were then transferred to a high dust environment (HDEnv), which was a poorly ventilated stable where horses ate hay and were bedded on straw: they remained there for the final 48 h. Horses were assigned into paired groupings of RAO-susceptible and control horses. Prior overnight dexamethasone suppression tests (40 μg/kg bwt i.m.) strongly indicated that pituitary pars intermedia dysfunction was not present in the horses [12]. On the day before initiation of the study protocol, a pair of horses was transferred from pasture into the LDEnv in the early afternoon to be outfitted with RIP bands and an i.v. jugular catheter. Venous blood sampling began at 08.00 h on Day 1 and continued every 6 h for the remainder of the protocol. The ΔPplmax was measured once daily in the morning, and at that time the RIP bands were calibrated. Respiratory inductance plethysmography data recording began at 10.00 h and continued until the next ΔPplmax measurement approximately 22 h later, during which time there was limited access to the stable. Airway function was monitored by daily ΔPplmax measurement [13] and by continuous use of RIP for BFV calculations [3]. Throughout the sampling period, blood was collected every 6 h from an indwelling i.v. catheter. The CORT was measured by radioimmunoassay. The assay was conducted at the Diagnostic Centre for Population and Animal Health at Michigan State University using the Coat-a-count kita (interassay CV = 8%, intra-assay CV = 3%). The Institutional Animal Care and Use Committee at Michigan State University approved all protocols. The BFV was calculated as the standard deviation (s.d.) of breathing frequency using 3 h blocks of data. Data were analysed by a factorial analysis of variance (ANOVA) with random horse and fixed disease, day and sampling period. When main effects or interactions were significant, means were compared by Tukey’s test with P
