Unilateral Orchidectomy in Mature Cats is Not Followed by Compensatory Hypertrophy GG Romero 1 , C Barbeito 2 , P Fernandez 2 , E Gimeno 2 and C Gobello 1 1 Laboratory of Reproductive Physiology, Faculty of Veterinary Medicine, National University of La Plata – CONICET, La Plata, Argentina; 2 Institute of Pathology, Faculty of Veterinary Medicine, National University of La Plata – CONICET, La Plata, Argentina Contents The aim of this study was to describe the effect of unilateral orchidectomy on testicular characteristics of mature domestic cats. Five, 1- to 2-year-old, cross-bred male cats were unilaterally orchidectomized on day 0 (right) and day 60 (left). The testes were processed for histological and immu- nohistochemical evaluation and groups compared by Stu- dent’s t-test. No significant differences (p > 0.05) were found between testes groups for any of the gross (volume and gonadosomatic index) and microscopic (tubular diameters, axis, area, length and perimeter, germinal epithelium height, spermatogonias, spermatocytes, spermatids, spermatozoa, Sertoli and Leydig cells, intertubular compartment, lumen, cellular debris, tubular- intertubular proportion and basement membrane) parameters assessed. According to these biometric and morphometric results, mature cats do not develop compensatory hypertrophy within 60 days of unilateral orchidectomy. Introduction In the domestic cat (Felis catus), surgical removal of one diseased testis is a frequent practice after unilateral trauma, neoplasm, inflammation or torsion. In addition, the use of hemicastrated animals, theoretically, offers advantages over the use of intact males in studying testicular effect of drugs as interindividual variability could be eliminated. In both clinical and research settings, the question arises whether the remaining testis suffers any post-surgery effect. After hemicastration, compensatory hypertrophy of the remaining testis occurs in bulls (Johnson 1978), boars (Kittok et al. 1984), rams (Voglmayr and Mattner 1968) and stallions. Such hypertrophy, however, has not been detected in mice (Fawke et al. 1972). In rats, the magnitude of this response depends on the age at which hemicastration is performed (Cunningahm et al. 1978). In adult dogs, the reports are contradictory (Taha et al. 1982; Gunzel-Apel et al. 1989), while in the authors’ knowledge, there is no information concerning the effect of unilateral castration in feline species. The aim of this study was to describe the effect of unilateral castration on testicular characteristics in sexually mature cats. Materials and Methods Animals Five healthy, 1- to 2-year- old, cross-bred male cats were unilaterally orchidectomized on days 0 (right testis) and 60 (left testis). The animals were exposed to more than 12 h of light per day for two months before and after the first hemicastration. Surgery and gross examination of the testes General anaesthesia was induced with xylazine (1–3 mg/ kg IM; Kensol, Ko¨ing, Argentina) and ketamine (15– 25 mg/kg IM; Ketmin-50, Holiday, Argentina) and complemented with local anaesthesia using lidocaine 1% (maximum 0.5 ml). After surgery, ketoprofen (1 mg/kg; Ketofen, Fort Dodge, Argentina) was injected SC (once) and then orally every 24 h for four additional days. This study was approved by the Faculty Institutional Care and Animal Use Committee (IACUC, Number 129/09). Immediately after surgical removal, the testes were weighed (g) and measured [length (cm) and width (cm)] using laboratory callipers. Testicular volume (cm 3 ) and gonadosomatic index (%; Franca and Godinho 2003) were also calculated. Histological evaluation The testes were longitudinally sectioned and placed in Bouin’s fixative. After processing, 5-lm sections were cut and stained with haematoxylin and eosin. Micro- scopic images were obtained at 910 and 940 (Olympus BX50, Tokyo, Japan) through an attached video camera (Sony DXC 151 A CCD, Tokyo, Japan) and digitalized in a 24-bit true colour TIFF format. Fifteen to 20 tubular profiles, which were round or nearly round, were chosen randomly and measured for each animal. The maximum, minimum and medium tubular diame- ters (lm), major and minor axis (lm), area (lm 2 ) and perimeter (lm) of seminiferous tubules were measured at 910 by planimetry (Image Pro Plus, Media Cyber- netics, Silver Spring, MA, USA). The germinal epithe- lium height (lm) was also recorded. The volume (cm 3 ) of the testicular tissue components was determined by light microscopy using a 441-intersection grid placed on 940 magnification. For this, 15 fields were chosen randomly (6615 points) and scored for each animal. Points were classified as one of the following: sperma- togonia, primary and secondary spermatocytes, rounds spermatids, elongated spermatids, spermatozoa, Sertoli and Leydig cells, intertubular compartment, basement membrane, lumen, cellular debris and tubular–intertu- bular compartment proportion. The total length of seminiferous tubules (metre) was also calculated (Franca and Godinho 2003). Sertoli cells were immunohistochemically marked (Monoclonal Mouse Anti-Vimentin Clone 9, Dako, Carpinteria, CA, USA). The EnVision System Kit (Dako, Carpinteria, CA, USA) was used as inmunohis- tochemical detection system. Positively stained cells © 2012 Blackwell Verlag GmbH Reprod Dom Anim 47 (Suppl. 6), 226–228 (2012); doi: 10.1111/rda.12024 ISSN 0936–6768