[Effects of met-enkephalin on the testis. I. Structural study].

We performed a structural study on rat testis using the hematoxylin-eosin and azocarmine staining methods. For the study, we utilized 105 male Wistar rats weighing 280-300 gms. Thirty rats comprised the control group, and 75 comprised the study group. Rats in the study group received a single, acute intracardiac dose of met-enkephalin (100 microliters of 50% met-enkephalin solution) and were sacrificed at 15, 30 and 60 minutes following injection, or a chronic intramuscular dose (50 microliters of 40% met-enkephalin solution) for 10 or 20 days. We observed marked numeric and morphologic changes in Leydig cells, as well as a blockade of spermatogenesis that led to a fall in spermatozoids and secondary spermatocytes. These changes were observed in all rats that had been submitted either to acute or chronic treatment, and were more marked in those where the interval between commencement of treatment and sacrifice was longer. These findings demonstrate that enkephalins (endogenous opiates) can cause profound endocrine and seminal lesions in the rat testis.