title: Effects of drugs which modify catecholamine activity on amplification of LH release induced by locus coeruleus electrical stimulation.
abstract: Norepinephrine may be the neurotransmitter responsible for triggering the surge release of luteinizing hormone (LH) in proestrous and steroid-treated ovariectomized rats. In a previous study, we electrically stimulated (ES) the locus coeruleus (LC), a norepinephrine cell body region from which some axons project to the hypothalamus. These studies were performed in estradiol-treated rats in which the medial preoptic nucleus (MPN) initially had been electrochemically stimulated (ECS) to partially depolarize luteinizing hormone-releasing hormone (LH-RH) neurons. We observed that LC-ES markedly amplified the amount of LH released after preoptic-ECS. The purpose of the present study was to determine if these amplifying effects of LC-ES were due to the release of a catecholamine and if so which neurotransmitter was involved in this response. All rats in this study were ovariectomized and 7 days later (day 0) they were treated with estradiol for 2 days (day 2). On day 2, all animals were anesthetized with chloral hydrate. In control rats, the MPN was electrochemically stimulated (100 microA/60 s DC) and 30 min later the LC was electrically stimulated for 15 min. MPN-ECS significantly increased plasma concentrations of LH and LC-ES markedly amplified these plasma LH levels. Thereafter, 3 studies were performed and the following drugs were given: (1) alpha-methyl-p-tyrosine (MPT, 300 mg/kg i.p.); (2) phenoxybenzamine (PX, 15 mg/kg i.p.) and (3) propranolol (PROP, 15 mg/kg i.p.). MPT and PROP were administered 15 min prior to MPN-ECS and PX was given 90 min before MPN-ECS. None of these drugs affected the amount of LH released after preoptic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D008125:Locus Coeruleus / Q000187:drug effects / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D008781:Methyltyrosines / Q000494:pharmacology*; D010052:Ovariectomy; D010643:Phenoxybenzamine / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors; D019805:alpha-Methyltyrosine
chemical_list: D008781:Methyltyrosines; D010643:Phenoxybenzamine; D004958:Estradiol; D019805:alpha-Methyltyrosine; D007986:Luteinizing Hormone; D011433:Propranolol; D014446:Tyrosine 3-Monooxygenase