title: Role of intrarenal alpha(2)-adrenoceptors in the renal responses to xylazine in rats.
abstract: This study examined the contribution of intrarenal alpha(2)-adrenoceptor mechanisms to the enhanced urine flow rate (V) and urinary sodium excretion (U(Na)V) responses in ketamine-xylazine-anesthetized rats. Ten minutes after left renal artery (LRA) injection, the alpha(2)-adrenoceptor antagonist yohimbine (5 microg) significantly decreased V from 58 +/- 8 to 35 +/- 7 microl. min(-1). g kidney wt(-1) and U(Na)V from 2.8 +/- 0.4 to 2.1 +/- 0.4 microeq. min(-1). g kidney wt(-1) without altering right kidney function. The renal effects of the LRA injection of yohimbine were completely abolished in chronic bilaterally renal-denervated (RDNX) rats. In RDNX rats, a higher LRA dose of yohimbine (15 microg) significantly reduced left and right kidney V, with no effects on U(Na)V. In separate bladder-catheterized rats, yohimbine (0.5 mg/kg), 20 min after intravenous injection, significantly decreased V from 63 +/- 9 to 13 +/- 2 microl. min(-1). g kidney wt(-1 )and U(Na)V from 4.5 +/- 0.5 to 1.1 +/- 0.1 microeq. min(-1). g kidney wt(-1). In RDNX rats, this dose of yohimbine reduced V and U(Na)V, but the magnitude was blunted compared with intact rats. In contrast, 0.1 mg/kg iv yohimbine significantly reduced V and U(Na)V to similar magnitudes in intact and RDNX groups. Together, these findings indicate that intravenous xylazine acts by renal nerve-dependent and -independent mechanisms to enhance renal excretory function in ketamine-anesthetized rats. Because the effects of the LRA dose of yohimbine were abolished in renal-denervated animals, it appears that xylazine has a direct renal action to augment the renal excretion of water and sodium via a presynaptic alpha(2)-adrenoceptor pathway that inhibits the release of neurotransmitters from renal sympathetic nerve terminals.
authors.affiliation: Department of Physiological Sciences, Federal University of Espirito Santo, Vitoria, Espirito Santo, Brazil 29040-090.
authors.forename: R G
authors.initials: RG
authors.lastname: Menegaz
authors.forename: D R
authors.initials: DR
authors.lastname: Kapusta
authors.forename: A M
authors.initials: AM
authors.lastname: Cabral
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D007269:Injections, Intra-Arterial; D007275:Injections, Intravenous; D007649:Ketamine / Q000494:pharmacology; D007668:Kidney / Q000737:chemistry* / Q000187:drug effects* / Q000294:innervation; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*; D012077:Renal Artery; D012964:Sodium / Q000652:urine; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology; D014556:Urine; D014991:Xylazine / Q000494:pharmacology*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D018691:Excitatory Amino Acid Antagonists; D018341:Receptors, Adrenergic, alpha-2; D014991:Xylazine; D015016:Yohimbine; D007649:Ketamine; D012964:Sodium