title: Regulation of glycogen content in rat pineal gland by norepinephrine.
abstract: In the rat pineal gland the glycogen stores were cytochemically localized in astrocytes and pinealocytes. Moreover, it was found that norepinephrine (NE) induced a time- and concentration-dependent reduction in pineal glycogen content and yielded lactic acid. The NE effect was prevented by blocking alpha1- but not alpha2 or beta-adrenoceptors. Activation of alpha2-adrenoceptors induced a small decrease in glycogen levels that could have pre- and postsynaptic components. Activation of beta-adrenoceptors with 10(-12)-10(-3) M isoproterenol (ISO) induced a bell shape concentration-response curve, presumably due to desensitization, since the response induced by 10(-4) M ISO was greater with shorter period of stimulation. On the other hand, activation of alpha1-adrenoceptors with 10(-12)-10(-3) M phenylephrine (PHN) induced a hyperbolic concentration-response curve with a maximum at concentrations above 10(-8) M. Moreover, treatment with ISO drastically reduced the response induced by PHN concentrations lower but not higher than 10(-6) M, favoring a concentration-dependent response between 10(-6) and 10(-4) M PHN, similar to that induced by equimolar NE concentrations. Thus, the NE-induced reduction in glycogen content of the rat pineal gland is mainly mediated by alpha1-adrenoceptors and modulated by intracellular mechanisms activated by beta-adrenoceptors.
authors.affiliation: Departamento de Ciencias Fisiológicas, Facultad de Ciencias Biólogicas, Pontificia Universidad Católica de Chile, Santiago.
authors.forename: E A
authors.initials: EA
authors.lastname: Eugenín
authors.forename: C G
authors.initials: CG
authors.lastname: Sáez
authors.forename: G
authors.initials: G
authors.lastname: Garcés
authors.forename: J C
authors.initials: JC
authors.lastname: Sáez
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D006003:Glycogen / Q000378:metabolism*; D007150:Immunohistochemistry; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology*; D010870:Pineal Gland / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000316:Adrenergic alpha-Agonists; D006003:Glycogen; D007545:Isoproterenol; D009638:Norepinephrine