Differential role of adrenoceptors in control of plasma glucose and fatty acids in carp,Cyprinus carpio(L.)

Carp were cannulated in the dorsal aorta, and after 2 days of recovery they were infused with 1) norepinephrine, 2) yohimbine (α2-antagonist) plus norepinephrine, 3) clonidine (α2-agonist), and 4) isoproterenol (nonselective β-agonist). Norepinephrine lowered the plasma free fatty acid (FFA) level and raised the plasma glucose level for several hours. Norepinephrine in combination with the α2-antagonist yohimbine resulted in retardation of the FFA decrease, indicating the involvement of α2-adrenoceptors. Infusion with the partial α2-agonist clonidine had a smaller effect. Infusion with isoproterenol caused a marked increase of glucose levels, and unexpectedly a decline of plasma FFA levels, indicating a direct involvement of β-adrenoceptors. Combination of isoproterenol with either atenolol (β1-antagonist) or ICI-118,551 (β2-antagonist) showed that both β1- and β2-adrenoceptors were involved in the glucose release by isoproterenol. Remarkably, the decline of FFA levels was augmented in the presence of ICI-118,551, whereas with atenolol present plasma FFA levels were increased by isoproterenol. Thus it is concluded that in carp both β1- and β2-adrenoceptors mediate glucose release, whereas lipolysis is controlled by inhibitory β1-adrenoceptors and stimulatory β2-adrenoceptors, as well as by inhibitory α2-adrenoceptors.