Hypothalamic monoamines and their catabolites in relation to the estradiol-induced luteinizing hormone surge.
Monoamines and non-conjugated catabolites (serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA), 3,4-dihydroxyphenyl-acetic acid (DOPAC), homovanillic acid (HVA), 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG), norepinephrine (NE), and dopamine (DA] were measured in the medial basal hypothalamus (MBH) and preoptic area (POA) of ovariectomized (OVX) and OVX estradiol (E2)-treated rats using high-performance liquid chromatography with electrochemical detection. These E2 treatments were sufficient to induce an LH surge. The use of MHPG/NE ratios as estimates of NE release was validated in the rat hypothalamus by the major decreases of MHPG after injection of the alpha 2-adrenergic agonist, clonidine, and by MHPG increases after the alpha 2-antagonist, yohimbine. The ratio, MHPG/NE, decreased between morning and afternoon in the MBH but not in the POA; there were no differences between OVX and E2-treated rats. Previous studies using a variety of methods indicate that NE turnover increases during LH surges. The present data suggest that unconjugated MHPG is not a sensitive measure of NE release in the rat hypothalamus, but can detect the large changes produced by stimulating or inhibiting the alpha 2-adrenergic autoreceptor. The ratios of DOPAC/DA and 5-HIAA/5-HT in the MBH decreased consistently between morning and afternoon in OVX rats, with or without E2 treatment. This suggests that the release of DA and 5-HT decreases during the day regardless of steroidal milieu.
D000818:Animals; D001679:Biogenic Amines / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D003000:Clonidine / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects*; D007031:Hypothalamus / Q000032:analysis*; D007986:Luteinizing Hormone / Q000378:metabolism*; D010052:Ovariectomy; D051381:Rats; D011919:Rats, Inbred Strains; D015016:Yohimbine / Q000494:pharmacology
D001679:Biogenic Amines; D015016:Yohimbine; D004958:Estradiol; D007986:Luteinizing Hormone; D003000:Clonidine