Blockade of steroid-induced leuteinizing hormone release by selective depletion of anterior hypothalamic norepinephrine activity.
Female Sprague-Dawley rats, weighing 200--225 g, were ovariectomized and, 10 days later, were given a single sc injection of 10 micrograms estradiol benzoate/100 g BW. Three days after estradiol benzoate treatment, animals received 50 micrograms progesterone (P)/100 g BW, resulting in a surge in LH release 7 and 9 h later. To determine the locus of the noradrenergic component of the P-induced LH surge, 6-hydroxydopamine (6-OH-DA), a neutrotoxin, was implanted into either the suprachiasmatic region or the median eminence (ME) 24 h before P administration. An implant of 6-OH-DA in the suprachiasmatic region decreased anterior hypothalamic norepinephrine concentration by 83%, anterior hypothalamic dopamine concentration by 24%, and eliminated the P-induced LH surge. ME implant of 6-OH-DA decreased norepinephrine concentration by 57% without affecting dopamine concentration, but was unable to alter the P. induced LH surge. These results indicate that the anterior hypothalamic noradrenergic system is necessary for the P-induced LH surge in ovariectomized rats and that noradrenergic nerve terminals in the ME are not involved in this process.
D000818:Animals; D002369:Castration; D004343:Drug Implants; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D006892:Hydroxydopamines / Q000494:pharmacology*; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood*; D008473:Median Eminence / Q000187:drug effects / Q000502:physiology; D009638:Norepinephrine / Q000502:physiology*; D009897:Optic Chiasm / Q000502:physiology; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats
D004343:Drug Implants; D006892:Hydroxydopamines; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D009638:Norepinephrine