[Catecholaminergic neuronal pathways in homeostatic control of blood circulating mass]

Anti-thirst and anti-diuresis responses have been observed in rats with 50 mg/os of L-dopa and L-methyl-dopa. When rats are given simultaneously either Fla-63, a beta-hydroxylase inhibitory drug, or phentolamine, an alpha-adrenergic blocking agent, the anti-thirst effect is changed in an opposite way; however, the last effect is not statistically significant. These data suggest that the anti-thirst effect observed in the present study could be related to a higher amount of catecholamines synthesized and to the consequent activation of the CNS alpha-adrenergic neuronal pathways. Methyldopa, with long lasting effects, can block the thirst induced by solid food up to the 9th hour. The opposite effect determined by both inhibitory agents indicates that the dopaminergic pathways play a leading role in the thirst regulation system. Furthermore, the alpha-adrenergic pathways seem to be devoided of anti-diuretic effect, since both the above mentioned inhibitory agents do not affect it.