On the relationship between noradrenergic stimulatory and GABAergic inhibitory systems in the control of luteinizing hormone secretion in female rats.
The relationship between noradrenergic (NA) stimulatory and gamma-aminobutyric acid (GABA)-mediated inhibitory systems in the control of luteinizing hormone (LH) secretion was examined in ovariectomized rats. Stimulation of the GABAA receptor by an intraventricular (i.c.v.) administration of a GABAA agonist, muscimol, significantly attenuated the LH secretory response to the subsequent i.c.v. injection of NA in estrogen-primed rats. On the other hand, blockade of alpha-adrenergic receptors by phenoxybenzamine did not interfere with the stimulatory effect of an i.c.v. injection of a GABAA antagonist bicuculline. In a different series of experiments, ovariectomized animals had been treated with i.c.v. injections of 6-hydroxydopamine (6-OHDA) or its vehicle. An i.c.v. injection of muscimol or phentolamine significantly inhibited the estrogen-induced surge of LH secretion in vehicle-treated rats. Muscimol also inhibited the existing pulsatile LH secretion in vehicle-treated, estrogen-unprimed animals. In animals in which hypothalamic NA terminals were presumed to be destroyed by 6-OHDA, the inhibitory effect of phentolamine was significantly diminished while that of muscimol was unaltered. These results permit the following conclusions: (1) the central GABAergic system inhibits LH secretion via GABAA receptors; (2) this inhibitory GABA system operates without mediation by the NA system, and (3) the GABAergic non-NA-mediated system can affect physiological patterns of pituitary LH secretion in female rats.
Akema
T
T
Department of Physiology, St. Marianna University School of Medicine, Kawasaki, Japan.
Chiba
A
A
Kimura
F
F
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D006892:Hydroxydopamines / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000378:metabolism*; D009118:Muscimol / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D010052:Ovariectomy; D016627:Oxidopamine; D010507:Periodicity; D010643:Phenoxybenzamine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology; D011963:Receptors, GABA-A / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D006892:Hydroxydopamines; D011942:Receptors, Adrenergic, alpha; D011963:Receptors, GABA-A; D010643:Phenoxybenzamine; D009118:Muscimol; D004958:Estradiol; D005680:gamma-Aminobutyric Acid; D016627:Oxidopamine; D007986:Luteinizing Hormone; D009638:Norepinephrine; D001640:Bicuculline