In addition, aromatase activity may reflect the response of Lhb in the pituitary in vivo. The effects of GnRH and its various analogs on gonadotropin have been extensively studied in mammals and teleosts. It has been determined that GnRH is secreted from the hypothalamus in a pulsatile fashion, which parallels the pulsatile release of LH and FSH, and that a feedback regulation exists between them. It has also been demonstrated that GnRH is capable of stimulating cga, fshb, and lhb mRNA levels in the goldfish pituitary following 24 h of treatment in vivo.
In studies on rats, treatment of pituitary cells with GnRH increased LHb mRNA levels between 12 and 24 h. In this study, the mRNA level of gnrh decreased in the hypothalamus after intraperitoneal injection of rgLh, which suggests that there is a negative feedback regulation in Gnrh secretion.
In conclusion, the present study has shown that biologically active rgLh can be produced using the baculovirus expression system in insect cells. This recombinant hormone could be employed to improve artificial production in the aquaculture industry by replacing current methods that rely on hormones such as hCG, which show low activity in stimulating sex steroid hormone synthesis and secretion. It is also expected to be helpful in elucidating the physiological function of rgLh in gonadal development and the mechanism of Ihb and cga gene expression and regulation in the orange-spotted grouper.