Excitatory aminoacids as modulators of gonadotropin secretion

The effects of quinolinic acid (QUIN) and quisqualate (QA) on the secretion of GnRH from MBH and LH and FSH from AP of 50 day old male rats have been evaluated by means of an 'in vitro' perifusion technique. QUIN (100 μM) is able to increase GnRH secretion with an action mediated by an NMDA receptor type, as shown by the inhibitory effect exerted by both a competitive (AP-5) and a non-competitive (MK-801) specific antagonist. QA 'per se' at the concentrations tested (1-100 μM) does not modify GnRH and gonadotropin secretion, but in the presence of a specific KA/QA receptor antagonist (DNQX) exerts a stimulatory effect at both levels. This observation might indicate that of the two QA receptor subtypes (ionotropic and metabotropic), this agonist binds to the metabotropic one with very low affinity: thus it is likely that a higher dose is required in order to have any effect on gonadotropin secretion. However, in the presence of DNQX, which binds to the ionotropic receptor, all the available QA can bind to the metabotropic one and can exert its action at MBH AP levels.