La Función Endócrina del Testículo en el Carnero Criollo Mexicano Durante las Diferentes Epocas del Año y su Control Opioidergico Durante el Anestro
Authors: Fuentes V. , Sanchez V. , Gonzalez H. , Fuentes P. , Garcia A. , Rosiles R. 
Published: May 2010

SummaryThis work was carried out with the objective of studying the endocrine function of the testes in the Mexican Crossbred Ram (Suffolk × Hampshire) during the different seasons of the year in a latitude of 19°13′N. Also studied was the opioidergic control of this gland during anoestrus. For this purpose 8 rams were used, from which 3 ml of jugular blood were obtained three times a week to study the seasonal fluctuations in plasma testosterone. The experiment was carried out from May 1993 until June 1994. The androgen was determined by radioimmunoassay. To study the opioidergic control of androgen secretion during seasonal anoestrous (May—June) four of the rams were selected at random and treated with 0.5 mg naloxone at 12 h intervals during 3 continuous weeks. It was observed that blood testosterone was lowest during long days, and concentration was highest during the breeding season. Chronic naloxone medication during anoestrus resulted in a significant increase in blood testosterone (P < 0.001), an effect that was evident after the first week of treatment. When naloxone administration was discontinued, blood testosterone levels returned to basal. With this experiment it was demonstrated that an opioid antagonist such as naloxone administered in low doses, is capable of altering plasma testosterone concentration in the anoestrus ram, giving further support to endogenous opioids as important modulators of reproduction in seasonal breeders such as sheep.ResumenCon el proposito de estudiar la función endócrina del testículo en el carnero criollo mexicano (Suffolk × Hampshire) a una latirud de 19° 13′ N; y asimismo tambien estudiar su control opiodergico durante la epoca de anestro. Se utilizaron 8 carneros machos de los cuales se obtuvieron muestras sanguineas tres veces por semana para deterrninar las concentraciones de testosterona por radio immunoanálisis desde mayo de 1993 hasta junio de 1994. Durante el periodo de anestro estacional; del grupo de ocho; se escogieron al azar cuatro borregos, y fueron medicados con 0.5 mg/12 horas de naloxona durante tres semanas. La concentración sanguinea de testosterona mostró una variación circanual, con los niveles hormonales mas bajos durante el fotoperiodo largo; y los mas altos durante la época de empadre. La medicación crónica con naloxona incrementó significativamente (p < 0.001) los niveles sanguíneos de testosterone, efecto que se hizo evidente hasta la segunda semana de tratamiento. Al descontinuar la administración del antagonista opioide los niveles sanguíneos de testosterona regresaron a los niveles basales iguales a los del grupo no medicado. Este experimento demuestra que dosis bajas del antagonista opioide naloxona pueden modificar los patrones endócrines reproductivos de los animales poliestricos estacionales, como la oveja y respalda el postulado de que los opioides endógenos estan jugando un papel importante en la reproducción de los animales domésticos.