Reduction of pituitary GnRH receptors in immature rats treated with monosodium glutamate.
The number of pituitary gonadotropin-releasing hormone (GnRH) receptors increases during sexual maturation in the rat and probably reflects changes in hypothalamic GnRH secretion. As GnRH is synthesized in various hypothalamic nuclei, including the arcuate nucleas (ARC), we investigated the effects of monosodium glutamate (MSG)-induced lesions of the ARC in the rat. In males and females treated with MSG during the first 10 days of life, GnRH receptor content (GnRH-RC) was unchanged from controls at 10 days but was decreased at 20 and 30 days of age (P less than 0.01). Serum concentrations of luteinizing hormone (LH) were similar in MSG-treated and control males but were significantly lower in 10-day-old females (P less than 0.01). Injections of GnRH (3 micrograms every 8 h on days 18 and 19) restored GnRH-RC to control values in MSG-treated rats. Both MSG and untreated control rats showed similar LH responses to acute injections of GnRH, but responses were attenuated (P less than 0.05) after 2 days pretreatment with GnRH in rats that had received MSG. Ovarian GnRH-RC was similar in both MSG-treated and untreated controls. These data indicate that MSG-induced lesions of the ARC reduce pituitary GnRH-RC in immature rats, and the more marked effects in females suggest a more significant role in the ARC in the control of GnRH secretion during maturation in females. The lack of MSG-induced changes in ovarian GnRH-RC indicates that GnRH from the arcuate nucleus is not responsible for the increase in ovarian GnRH receptors seen during sexual maturation.
Dalkin
A C
AC
Duncan
J A
JA
Regiani
S
S
Marshall
J C
JC
D000818:Animals; D005260:Female; D005971:Glutamates / Q000494:pharmacology*; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism* / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood; D010053:Ovary / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D011966:Receptors, LHRH; D012970:Sodium Glutamate / Q000494:pharmacology*
D005971:Glutamates; D011956:Receptors, Cell Surface; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D012970:Sodium Glutamate