Effect of α-adrenergic agonists on gluconeogenesis and 45Ca efflux in rat kidney tubules

Tubule fragments were isolated from renal cortex of fed rats and incubated with 5 mM lactate. Noradrenaline and phenylephrine (α-agonist) stimulated gluconeogenesis at all extracellular Ca 2+ concentrations. Oxymetazoline (α-agonist) was ineffective at low extra-cellular Ca 2+ concentrations, but stimulated the process at higher calcium concentrations. Noradrenaline stimulated 45Ca efflux from prelabelled tubules. Oxymetazoline had no effect on this process. The effect of noradrenaline was blocked by thymoxamine (α-blocker) but not by propranolol (β-blocker). It is suggested that noradrenaline may promote the mobilization of an internal Ca 2+ store whereas oxymetazoline may influence Ca 2+ movement at the cell surface.