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 ? 1- but not ? 2 or ?-adrenoceptors. Activation of ? 2- adrenoceptors induced a small decrease in glycogen levels that could have pre- and postsynaptic components. Activation of ?-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 ? 1-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 ?-adrenoceptors and modulated by intracellular mechanisms by ?- adrenoceptors.