Norepinephrine reuptake is impaired in skeletal muscle of hypertensive rats in vivo

Certain forms of experimental hypertension are characterized by organ-speci fic alterations of catecholaminergic pathways. The purpose of this study wa s to evaluate, in the same awake and freely moving normotensive Wistar-Kyot o rats (WKY) and spontaneously hypertensive rats (SHR) before and after the development of arterial hypertension, the norepinephrine (NE) turnover and , in particular, the neuronal NE reuptake activity that ends its effects on ce released from nerve terminals, in subcutaneous adipose tissue and in ske letal muscle, whose sympathetic efferents are respectively independent or d ependent from baroreflexes. Plasma and tissue interstitial NE and 3,4-dihyd roxyphenylethylene glycol (DHPG), its major deaminated metabolite, were mea sured before and after blockade of NE reuptake by tissue perfusion of desip ramine through microdialysis probes. Arterial pressure and plasma NE in SHR were similar to those in WKY at 5 weeks of age but increased at 16 weeks o f age. In contrast, plasma DHPG was already higher in young SHR. Basal inte rstitial NE and DHPG were increased in both tissues of young and old SHR co mpared with age-matched WKY. Desipramine induced a higher rise of interstit ial NE in SHR of both ages, with a lesser increase in the skeletal muscle o f old compared with young SHR. These results indicate an increased NE turno ver in prehypertensive and hypertensive SHR in both baroreflex-dependent an d -independent tissues, not shown by plasma NE levels in young SHR. In the skeletal muscle, where sympathetic efferents are baroreflex dependent, the reduced interstitial NE reuptake contributes to the higher availability of interstitial NE for postsynaptic effects in old SHR.