Our further study of the effects of rgLh (0.5, 2.5, 5, 10 ig) on T and E2 secretion with different treatment time (2, 6, 12, and 24 h) suggests that rgLh can stimulate sex steroid hormone secretion in a time-dependent manner.
Gonadotropin secretion in vertebrates is mainly regulated by the brain-pituitary-gonadal axis. It is produced in the pituitary by the stimulation of GnRH produced in the hypothalamus and acts on the gonad to produce androgens and estrogens.
The whole metabolic process is regulated by neural and endocrine mechanisms, including negative and positive feedback loops, to maintain the dynamic and physiological balance among various hormones. In the present in vivo study, marked increases were observed in the mRNA levels of lhb in the pituitary, hypothalamus, and gonad of immature groupers. These results are consistent with the findings that sex steroids exert a strong inhibitory effect on lhb mRNA levels in sexually immature and maturing goldfish. It is possible that the in vivo effect of sex steroids is mediated via their effect on the brain to modulate the secretion of Gnrh or dopamine.