Comparison of the effect of hypothalamic neuropeptides upon luteinizing hormone secretion by cultured rat anterior pituitary cells.
Bovine median eminence contains a factor difference from gonadotropin-releasing hormone (GnRH) than increases basal luteinizing hormone (LH) secretion and potentiates GnRH-stimulated LH release. We compared the effect of hypothalamic neuropeptides on basal and GnRH-stimulated LH secretion using rat pituitary cells under static incubation conditions to determine if any of them mimics the LH-releasing activity no attributable to GnRH present in bovine median eminence extracts. Both, galanin and neurotensin (10(-9)-10(-5)) stimulated basal LH secretion in a dose-response manner. Galanin increased 3-4 fold and neurotensin doubled the basal LH secretion. The GnRH antagonist Nal-Glu 10(-6) M abolished the effect of 10(-7) M GnRH and 10(-5)M neurotensin, but did not block the LH-releasing activity of galanin. Leucin-enkephalin, beta-endorphin, substance P and neuropeptide Y (NPY) did not alter basal LH secretion. Neuropeptides produced three types of response on GnRH-stimulated LH release. First, leucine-enkephalin and beta-endorphin (10(-9)-10(-5) M) showed a dose-dependent inhibition of GnRH-stimulated LH release. At 10(-5) M the inhibition was complete with leucine-enkephalin and only 30% with beta-endorphin. Both were blocked by naloxone. Second, substance P showed an inverted U type response on GnRH-stimulated LH secretion. At 10(-9) M this peptide potentiated the action of GnRH. This effect decreased when the dose of substance P was increased to 10(-7) M and turned inhibitory at 10(-5) M when 10(-7) M GnRH was used. Third, galanin and NPY potentiated the effect of GnRH on LH secretion. Neurotensin had no effect on GnRH-stimulated LH release. In conclusion, rat gonadotrophs present diverse responses to neuropeptides at physiological concentrations, and -apart from GnRH-galanin is most likely the other factor present in bovine median eminence extracts that stimulates LH secretion. The data lend further support to a role of galanin in the control of LH secretion.
Leiva
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Instituto Chileno de Medicina Reproductiva, Santiago, Chile.
Croxatto
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D000818:Animals; D002417:Cattle; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D006065:Gonadotropins, Pituitary / Q000502:physiology*; D007986:Luteinizing Hormone / Q000378:metabolism*; D009479:Neuropeptides / Q000502:physiology*; D009496:Neurotensin / Q000494:pharmacology; D010903:Pituitary Gland, Anterior / Q000378:metabolism; D051381:Rats; D013373:Substance P / Q000494:pharmacology
D006065:Gonadotropins, Pituitary; D009479:Neuropeptides; D013373:Substance P; D007987:Gonadotropin-Releasing Hormone; D009496:Neurotensin; D007986:Luteinizing Hormone