It has been suggested that conformational and structural similarities between SP and GnRH could allow the neuropeptide to interact with the GnRH receptor. In fact, high concentrations of SP can displace [125I]GnRH binding in membrane preparations of rat pituitary tissue. To ascertain whether the stimulatory effect of SP on LH release from porcine gonadotrophs involved activation of GnRH receptors, we examined the influence of the potent GnRH antagonist antide on gonadotropin secretion in response to SP. buy ampicillin
Results from these experiments demonstrated that antide does not affect SP-stimulated LH release, whereas it completely blocks the stimulatory ability of GnRH. This observation indicates that the SP effect on LH release is not mediated via the GnRH receptor. It has been suggested that in the rat, SP exerts its neuroendocrine function on gonadotrophs through an interaction with its specific NK1 receptor. Consistent with this notion are reports showing that iodinated SP is bound and internalized in rat gonadotrophs and RT-PCR studies that demonstrate the presence of specific SP receptors of the NK1 type in rat pituitary. Hence, in light of our present results, it seems reasonable to propose the existence of specific SP receptors in porcine gonadotrophs that would mediate the stimulatory action of this neuropeptide.