Efectos de la castración y administración de testosterona sobre la regulación del sistema kisspeptina en el hipotálamo de machos adultos de lubina (Dicentrarchus labrax L.)

Abstract

Currently, the existence of two diferent kiss and gpr54 genes, whose products probably play a critical role in the regulation of the gonadotropic axis, has been reported in sea bass (Dicentrarchus labrax L.). The objective of the present study was to investigate how the kisspeptin system is involved in mediating the action of testosterone (T) in the regulation of GnRH and gonadotropin release in male sea bass. To this end, three groups of 33-36 adult males (152.37±0.58 g and 23.6±9.07 cm) during early gonadal recrudescence (gonadosomatic index, GSI<0.07) were established, as follows: gonad-intact fish containing empty silastic implants (sham-control), castrated fish (Gx) implanted with either testosterone containing (Gx+T) or empty (Gx-T) silastic implants. Implants were administrated in gonadectomized or sham-operated fish, 15 days after the initial surgery. Blood, brain and pituitary samples were periodically collected from day 0 to 105 after T replacement for hormonal and molecular analysis. Plasmatic levels of T in the control group were maintained at 3.96±0.75 ng/ml, whereas changes in circulating T concentrations following castration and implantation of testosterone-filled or empty silastic implants were 29.84±5.61 and 1.68±0.20 ng/ml, respectively. On the other hand, plasma levels of 11-ketotestosterone in control fish ranged of 0.77-23.25 ng/ml, whereas this steroid was maintained at 4.67±1.16 ng/ml in castrated fish with T replacement and at 1.82±0.6 ng/ml in castrates containing empty silastic implants. At the present time, gonadotropin expression in association with kiss/gpr54 mRNA levels are performed in the pituitary and hypothalamus, respectively. The participation of sexual steroids in the feedback control of the kisspeptin and GnRH/gonadotropin systems are discussed.