Angiotensin II stimulates norepinephrine uptake in hypothalamus-brain stem neuronal cultures

Abstract

In this study we have characterized the uptake of [3H]norepinephrine (NE) into neuronal co-cultures of rat hypothalamus and brain stem and have examined the effects of angiotensin II (ANG II) on this uptake. Neuronal co-cultures prepared from the brains of 1-day-old Sprague-Dawley (SD) or Wistar-Kyoto (WKY) rats exhibited sodium-dependent and sodium-independent portions of the total [3H]NE uptake. The sodium-dependent uptake was abolished by blockers such as maprotiline, desmethylimipramine, and xylamine (0.1-100 microM) and is presumably neuronal uptake. The sodium-independent uptake was unaffected by these drugs and is presumably non-neuronal, since nonneuronal co-cultures from SD rats exhibited no significant sodium-dependent or blocker-sensitive uptake. In SD or WKY neuronal co-cultures, ANG II (0.1 nM-10 microM) caused increased [3H]NE uptake during short-term incubations (1-5 min). This stimulatory effect of ANG II was on neuronal NE uptake. Furthermore, it was inhibited by preincubation with saralasin (1-10 microM). Construction of saturation curves and kinetic analyses revealed that ANG II caused an increase in the maximal velocity of uptake of neuronal [3H]NE, but the affinity of the transporter for NE was not altered. With longer-term incubations (15-30 min), ANG II caused a reduction in neuronal [3H]NE uptake. This effect was also blocked by saralasin. However, reliable kinetic analysis was not possible with the longer-term incubations, and it is likely that the inhibitory action of the peptide represents a stimulation of NE release. Therefore, using neuronal co-cultures, we have identified a previously unseen stimulatory action of ANG II on neuronal [3H]NE uptake, which precedes the already documented inhibitory actions.