β-Adrenoceptors in Equine Trachea and Heart

The density and subtype pattern of -adrenoceptors in equine tracheal epithelium, tracheal smooth muscle and heart from 6–9 horses were investigated by radioligand binding studies using the non-selective -adrenoceptor antagonist 125I-cyanopindolol (ICYP). The specific binding of ICYP was 341±162 fmol/mg protein (mean±SD) for epithelium, 42±13 fmol/mg for smooth muscle and 124±39 and 101±19 fmol/mg for the cardiac atrium and ventricle, respectively. The Kd value of ICYP was 6.7–10.2 pmol/L.In competition studies, different concentrations of either the 2-selective drug ICI 118551 or the 1-selective CGP 20712A competed with 25 pmol/L ICYP for the binding sites. The competition curves for tracheal smooth muscle and epithelium were monophasic with an approximate Kd value for ICI 118551 of 1 nmol/L and for CGP 20712A of 10 000 nmol/L. This corresponds to known Kd values for these substances binding to 2-adrenoceptors. 2-Adrenoceptors were also found in the heart, most pronounced in the atrium, where the density was 29%±6% (mean±SD) of the total receptor density. CGP 20712A and ICI 118551 bound to the dominating binding site of 1-adrenoceptors in the heart with Kd values of approximately 1 nmol/L and 100 nmol/L, respectively.     

Equine glaucoma: Where are we now?

The following article discusses the pathophysiology, clinical signs, diagnosis, medical treatment and surgical management of glaucoma in the horse.     

Equine eosinophilic keratitis: An emergent ocular condition?

Eosinophilic keratitis (EK) is considered an immune mediated disorder associated with an underlying type I or IV hypersensitivity reaction to parasitic or environment allergens. It is believed that the persistency of inflammatory mediators and recruitment of eosinophils into the conjunctival tissue have detrimental effects on the corneal surface. Epithelial cells are consequently damaged, particularly by eosinophilic toxic proteins, which determine the lack of epithelial healing and plaque formation. Although some clinical signs are common to other corneal diseases, the location of the lesion, presence of corneal plaques and time of the year, may help practitioners to identify EK. Topical therapy with steroids or immune-modulators seems to be the most effective treatment in small, localised lesions while large epithelial defects will benefit from a thorough debridement and/or early keratectomy, before secondary microbial infection may occur.     

Hyperactivated Sperm Motility: Are Equine Sperm Different?

A recent study has suggested a central role for hyperactivated sperm motility in successful equine in vitro fertilization, as the highest apparent fertilization rates reported yet were obtained using exogenous stimulation of hyperactivated motility in sperm that had been incubated for capacitation. Hyperactivated motility has been studied intensively in other species, but little data are available in this area in the horse. Hyperactivated motility is associated with an influx of calcium from the extracellular space, and in other species this occurs because of an increase in intracellular pH during capacitation. Influx of calcium seems to trigger changes in flagellar function through calcium–calmodulin–calmodulin kinase-related effects on dynein function, but the exact mechanisms resulting in hyperactivated motility are still unclear. We have been exploring the physiology of hyperactivated motility in stallion spermatozoa and have found many of the mechanisms present in other species to be in place in the stallion. Further research is needed to determine why stallion spermatozoa seem to fail to undergo hyperactivation in response to capacitating environments that support this activity in other species.