Modulation of norepinephrine release through alpha 1- and alpha 2-adrenoceptors in rat isolated kidney.
The aim of this study was to investigate alpha-adrenoceptor modulation of norepinephrine (NE) release from sympathetic nerves in rat isolated perfused kidney. After preincubation with [3H]NE, the renal nerves were stimulated. The stimulation-induced (S-I) outflow of radioactivity was used as an index of NE release. Clonidine (0.1 mumol/L) decreased the S-I outflow of radioactivity. This effect was abolished by the alpha 1-adrenoceptor antagonist idazoxan (0.1 mumol/L) but not by the alpha 2-adrenoceptor antagonist prazosin (0.1 mumol/L). Methoxamine (10 mumol/L) also had an inhibitory effect; this was abolished by prazosin (0.1 mumol/L), but not by idazoxan. Individually, these alpha-blocking drugs and the alpha 1-adrenoceptor antagonist corynanthine (0.3 mumol/L) enhanced S-I outflow of radioactivity. In the presence of indomethacin (10 mumol/L), the inhibitory effect of methoxamine was abolished but clonidine still inhibited S-I outflow of radioactivity. The facilitatory effect of prazosin was also unaltered by indomethacin. These results suggest the existence of inhibitory prejunctional alpha 1- and alpha 2-adrenoceptors in the kidney. The inhibitory effect of methoxamine seems to be mediated through prostaglandin inhibition of NE release. However, the evidence for inhibitory prejunctional alpha 1-adrenoceptors rests solely on the facilitatory effects of prazosin and corynanthine.
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D004146:Dioxanes / Q000494:pharmacology; D004558:Electric Stimulation; D019329:Idazoxan; D066298:In Vitro Techniques; D007668:Kidney / Q000294:innervation / Q000378:metabolism*; D008297:Male; D009638:Norepinephrine / Q000378:metabolism* / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology
D000316:Adrenergic alpha-Agonists; D004146:Dioxanes; D011942:Receptors, Adrenergic, alpha; D003000:Clonidine; D009638:Norepinephrine; D011224:Prazosin; D019329:Idazoxan; D010646:Phentolamine