Evidence that alpha-1-adrenergic stimuli specifically increase gluconeogenesis of the isolated proximal convoluted tubule in the rat.

Isolated kidney-cortical tubule suspensions and microdissected nephron segments from fed rats were used to study the action of catecholamines on gluconeogenesis. Gluconeogenesis from rat tubule suspension incubated with 5 mM pyruvate was stimulated maximally by 10(-5) M methoxamine, an alpha 1-selective agonist, and 10(-6) M noradrenaline by 29.2 +/- 5.2% (mean +/- SEM) and 32.6 +/- 2.9%, respectively. These effects were completely inhibited by 10(-7) M prazosin, a beta 1-selective antagonist. Yohimbine, an alpha 2-antagonist, also inhibited the effect, but only at a higher concentration (5 X 10(-5) M). Gluconeogenesis was not stimulated by isoproterenol, a alpha-agonist, at any concentrations between 10(-5) and 10(-7) M. With microdissected nephron segments, only the proximal tubule possessed gluconeogenic activity. Within the proximal tubule, the proximal convoluted tubule (PCT) revealed higher gluconeogenic activity than the proximal straight tubule (PST). Methoxamine at 10(-5) M stimulated gluconeogenesis in PCT, whereas in PST no increase of gluconeogenesis was observed. From these results, it can be concluded that an alpha 1-adrenergic agonist specifically stimulates renal gluconeogenesis in PCT, but not in PST.