Salmon GnRH and its analogues bind the human placental receptor.

OBJECTIVE: The presence of GnRH receptors in the human placenta has been recognized for a number of years. However, mammalian GnRH, which is expressed in placental tissues, has limited affinity for the chorionic receptor. On the basis of immunological and bioactivity data, we have previously proposed that the chorionic GnRH may differ from mammalian GnRH.
METHODS: We have studied the affinity of another isoform of GnRH (ie, salmon GnRH and stable analogues of this GnRH isoform), and compared their receptor affinity to that of mammalian GnRH and its analogues.
RESULTS: Using our receptor assay method with the labeled mammalian GnRH analogue Buserelin, salmon GnRH had a twofold greater affinity for the placental GnRH receptor than did mammalian GnRH and for the stable salmon GnRH analogue the affinity was increased tenfold. Using a homologous receptor assay method with a stable salmon GnRH analogue as label, the affinity for this salmon GnRH analogue had a K(d) of 101 nmol/L.
CONCLUSION: The presence of these higher affinity receptors for non-mammalian GnRH in the human placenta has led us to propose that the chorionic tissues may express more than one isoform of GnRH and that non-mammalian GnRH, such as salmon GnRH, may be potent regulators of placental functions.