Acetylcholine and Norepinephrine Stimulate the Release of Corticotropin-Releasing Factor-41 from the Rat Hypothalamusin Vitro*

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Abstract
The effects of the two putative neurotransmitters acetylcholine and norepinephrine on immunoreactive CRF-41 release from incubated rat hypothalami were studied. Acetylcholine at concentrations of 10-11 to 10-7 M stimulated CRF-41 release. This effect was blocked in a dose-dependent manner by the muscarinic antagonist atropine (10-9 to -7 M). The nicotinic antagonist hexamethonium was ineffective at a dose of 10-7 M, but produced slight inhibition of this response at 10-5 M. Norepinephrine at concentrations of 10-10 to 10-6 M also produced a dose-dependent stimulation of CRF-41 release. The .beta.-adrenoceptor antagonists propranolol (10-5 M) and timolol (10-6 M) blocked norepinephrine-induced CRF-41 release. The .alpha.1-adrenoceptor antagonists thymoxamine (10-5 M), prazosin (10-5 M), and corynanthine (10-4 M), and the .alpha.2-antagonist idazoxan (10-5 M), were ineffective. Potasssium depolarization (56 mM) caused stimulation of CRF-41 release which was dependent on the presence of calcium in the incubation medium. Authenticity of immunoreactive CRF-41 released was demonstrated by chromatographic criteria using gel filtration and reversed phase HPLC. These results provide evidence for a stimulatory role of acetylcholine and norpinephrine on CRF-41 release, and consequently on hypothalamo-pituitary-adrenal axis in the rat, through actions at a hypothalamic level. The stimulatory effect of acetylcholine is mediated principally through muscarinic receptors and that of norepinephrine through .beta.-adrenoceptors.

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