Evidence of melatonin synthesis in the ram reproductive tract

Abstract

SUMMARYMelatonin is a ubiquitous molecule found in a wide range of fluids, one of them being ram seminal plasma, in which it can reach higher concentrations than those found in blood, suggesting an extrapineal secretion by the reproductive tract. In order to identify the source of the melatonin found in ram seminal plasma, we first tried to determine whether the melatonin levels were maintained during the day. For this purpose, melatonin concentrations were measured in seminal plasma obtained from first ejaculates of six rams at 6:00 a.m. in total darkness, at 10:00 a.m. and at 14:00 p.m. The melatonin concentration was higher (p < 0.05) in ejaculates collected at 6:00 a.m. than at 10:00 and 14:00. There was no statistical difference between the latter. To further corroborate an extrapineal secretion of melatonin, the presence of the two key enzymes involved in melatonin synthesis, arylalkylamine-N-acetyltransferase (AANAT) and Nacetylserotonin-O-methyltransferase (ASMT) was analyzed by RT-PCR, q-PCR and Western-blot in ram testes, epididymis, and accessory glands. The RT-PCR showed the presence of the m-RNA codifying both AANAT and ASTM in all the tissues under study, but the q-PCR and Western-blot revealed that gene expression of these enzymes was significantly higher in the testis (p < 0.05). Immunohistochemistry confirmed the presence of AANAT and ASMT in the testis and revealed that they were found in the Leydig cells, spermatocytes, and spermatids. Also, measurable levels of melatonin were found in testicular tissue and the tail of the epididymis. In conclusion, our study indicates that the testes are one of the likely sources of the high levels of melatonin found in ram seminal plasma, at least during the day.

Melatonin MT1 and MT2 Receptors in the Ram Reproductive Tract

“…In the female, granulosa cells surrounding the oocyte can synthesize melatonin [42], and the melatonin receptors have been found in the ovary [43], uterus [13,44], and mammary gland [14]. In the male, melatonin is secreted in the testes [34,45], and although there are several reports of the presence of melatonin receptors MT 1 and/or MT 2 in various organs of the male reproductive tract, such as the testes [16,17], epididymis [18], or prostate [19], to the best of our knowledge this is the first time that the presence of melatonin receptors MT 1 and MT 2 have been studied in the whole male reproductive tract of one species, the sheep.…”

“…We have also measured seasonal variations of the melatonin concentration in ram seminal plasma [33], and we have recently demonstrated that the melatonin synthesizing enzymes are expressed in the ram testes [34], mainly in the Leydig cells, spermatocytes and spermatids. The testicular melatonin could protect the developing spermatozoa from oxidative damage [35], one of the possible mechanisms of action being through melatonin receptors in the cells [36].…”

Evaluación de los parámetros de calidad seminal y cinemática espermática en tres razas ovinas de lana en condiciones de trópico alto colombiano

“…Por otro lado, se ha reportado la importancia de variables como la viabilidad y la velocidad curvilínea (VCL) como predictores de la fertilidad en ovinos (21), relacionado con las tres subpoblaciones espermáticas descritas para esta especie, según el patrón de cinemática que presentan (lenta, no lineal; rápida, lineal; rápida, no lineal) (28). También se ha comprobado que los espermatozoides de ovinos con alta fertilidad presentan mayores valores de viabilidad, VCL y VSL que los de ovinos de baja fertilidad (29).…”

“…El eyaculado mamífero es muy heterogéneo y contiene subpoblaciones espermáticas con importantes diferencias en sus características cinemáticas (30), o en procesos como apoptóticos, capacitados y reaccionados (acrosoma), procesos que involucran cambios en la membrana plasmática (28). Tales condiciones pueden explicar la presencia de diferentes patrones de motilidad (cinemática) que caracterizan a las subpoblaciones espermáticas, y cambios en la proporción de estas poblaciones pueden afectar el éxito en el proceso de fertilización como se ha descrito en ovinos (4), en venado rojo ibérico (31), humano (32), entre otras especies.…”

Responses of Transgenic Melatonin-Enriched Goats on LPS Stimulation and the Proteogenomic Profiles of Their PBMCs

“…Melatonin (MT) ( N -acetyl-5-methoxytryptamine) is an important molecule secreted mainly by the pineal gland as well as immune cells and the digestive and reproductive systems [14,15,16,17,18]. This molecule exhibits pleiotropic physiological functions.…”