The influence of gabaergic drugs upon LH secretion from the pituitary of the common carp: an in vitro study.

In the present study, the perifusions of whole pituitary glands of spermiating male common carp were performed in the presence of several GABAergic drugs. Muscimol (agonist of GABA(A) receptors) and bicuculline (the antagonist of the same type of GABA receptors) did not modify basal LH release. LH basal secretion was not modified when pituitaries were perifused with baclofen--an agonist of GABAB receptors. On the other hand, baclofen at doses of 10(-8) and 10(-4) M significantly decreased GnRH-A-induced LH release to about 86% and 88% of LH levels in control group, respectively. In our previous study we have shown that GABA decreased basal and GnRH-A-stimulated in vivo and in vitro LH release. In conclusion, it can be suggested that in the mature male carp GABA exerts an inhibitory influence on GnRH-stimulated LH release, probably through the inhibition of the GnRH action on gonadotropes. This inhibition seems to be mediated by the B type of GABA receptors.