Abstract
Simple SummaryIn cats, semen is collected by pharmacological stimulation. The administration of a drug that stimulates α2-adrenoceptors causes the expulsion of spermatozoa into the urethra. However, as the results are not always satisfactory, this method needs to be improved. There are nine subtypes of adrenoceptors that are involved in the contraction of smooth muscle, including those in the reproductive tract, so adrenoceptors other than the α2-subtype are potential targets in any new, optimized protocol. The aim of this study was to analyze the immunolocalization of the adrenergic receptors in the reproductive tract of the male cat for the first time in this species. The expression of all adrenoceptor subtypes was noted in the peritubular smooth muscle in cats, indicating a potential clinical application for agonists of these receptors for the optimization of the pharmacological semen collection in felids. In a broader context, the development of a new procedure for semen collection in the male cat, using active substances from groups other than those currently used, will support the wider application of reproductive biotechnologies in felids.Adrenoceptors mediate the action of the sympathetic nervous system, including the contraction of the epididymis and vas deferens. The aim of this study was to immunolocalize the adrenergic receptors in the reproductive tract of the male cat, as this information is not yet available. The epididymis and vas deferens of domestic cats and rats (the biological controls) were analyzed by immunohistochemistry to determine the localization of the α1A-, α1B-, α1D-, α2A-, α2B-, α2C-, β1-, β2-, and β3-adrenoceptors. All the receptors were expressed in the peritubular smooth muscles of the cat, but the α1D-, α2C-, and β1-adrenoceptors were not detected in this tissue in the rat. For the α2A-adrenoceptor, the intensity of immunostaining differed significantly between the caput epididymis (weakest staining) and the vas deferens (strongest staining). The presence of all the types of the receptors was also detected in the cytoplasm of the epithelial cells in all the regions of the reproductive tract. The strong expression of the α2A-adrenoreceptor suggests it has a leading role in the contraction of the reproductive tract in the cat. The presence of other adrenergic receptors in the smooth muscle of the epididymis and vas deferens indicates a potential clinical application for α1-mimetics in the optimization of pharmacological semen collection in felids.
Highlights
There was a punctate, diffuse immunostaining of the investigated receptors in the cytoplasm for all the subtypes, a positive signal for the α1B-adrenoceptor was observed in single individuals, and many individuals did not show a signal for the α1D, α2C, and β1-adrenoceptors, especially in the caput or corpus epididymis (Table 1)
There was no positive reaction in the smooth muscle for the α1D, α2C, or β1-adrenoceptors (Figures 2–4)
The signals for the α1B- and α2Badrenoceptors were absent from the epididymis and present only in the vas deferens
Summary
Adrenoceptors (adrenergic receptors) are targets for norepinephrine and epinephrine and play a crucial role in the central and peripheral actions of these catecholamines, which are mediators of the sympathetic nervous system. Three families of adrenergic receptors have been described (α1-, α2-, and β-adrenoceptors), with each family divided into three subtypes, meaning that nine distinct adrenoceptors are recognized: α1A, α1B, α1D, α2A, α2B, α2C, β1, β2, and β3 [1]. Adrenoceptors are recognized most commonly for their regulation of cardiac action, their constriction and relaxation of smooth muscle (e.g., vasoconstriction, bronchodilatation), and their effect on the central nervous system (e.g., the sedative action of the α2-adrenoceptors), they are widely distributed throughout the body and mediate various physiological functions, including, e.g., lipid metabolism [3,4]
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