Amino acid uptake in the rat parotid gland: II. Effects of surgical sympathectomy and parasympathectomy.

The effects of surgical denervation and pharmacologic stimulation on amino acid transport have been investigated. Uptake of a nonmetabolizable amino acid, [14C]alpha-aminoisobutyric acid (AIB), was measured in an in vitro system of parotid lobules prepared from surgically denervated glands. Despite atrophic changes indicated by morphologic and biochemical examination, lobules prepared from sympathectomized glands showed a 22% (P less than .05) increase in [14C]AIB uptake. Uptake by lobules prepared from parasympathectomized glands had a similar average increase, but results were more variable (P greater than .05). Analysis of initial flux data for AIB suggested that a small increase in Vmax and a small decrease in Km occur after sympathetic or parasympathetic denervation. Norepinephrine, at a concentration of 10(-6) M, caused acceleration of AIB uptake in normal lobules (60%) and further increase in parasympathectomized lobules (150%) and sympathectomized lobules (200%). Acceleration of AIB uptake was only evident, however, after 1 hr of incubation, suggesting an intermediate event. The pattern of in vitro uptake of [3H]norepinephrine over a period of 3 hr was studied and revealed a biphasic pattern of uptake in control and parasympathectomized tissue. Early rapid increase in radioactivity was followed by slow decline. A different pattern was observed in sympathectomized glands, in which radioactivity increased steadily but at a reduced rate. These results suggest that the initial rapid phase of uptake may be the result of neuronal uptake followed by gradual degradation and release of radioactive metabolites. [3H]Norepinephrine uptake by parasympathectomized glands averaged 20% greater than controls, suggesting a possible expansion of the sympathetic component after surgery.