Alpha-2 mediated inhibition of water and urea permeability in the
rat imcd.
Rouch, Alexander J., and L_cia H. Kudo.
Oklahoma State University College of Osteopathic Medicine, 1111
West 17th Street, Tulsa, OK 74107 and Faculdade de Medicina,
Universidade de S<o Paulo, S<o Paulo, Brasil
APStracts 3:0075F, 1996.
These studies were conducted to determine if the alpha-2 ([alpha]2)
agonists epinephrine and dexmedetomidine inhibit osmotic water
permeability (Pf) and urea permeability (Pu) in the rat inner
medullary collecting duct (IMCD). Wistar rat IMCD segments were
perfused via standard methods, and Pf & Pu were determined in
separate studies. The control period was followed by adding 220 pM
arginine vasopressin (AVP) or 10-4 M dibutyryl cyclic AMP (DcAMP) to
the bath. Epinephrine or dexmedetomidine, both at 1[mu]M, was then
added to the bath and this period was followed by adding 1[mu]M
atipamezole, a selective [alpha]2-antagonist. The phosphodiesterase
inhibitor 3-isobutyl-1-methyl-xanthine was present in all experiments
with DcAMP. Epinephrine inhibited AVP- and DcAMP-stimulated Pf 90%
& 80%, respectively. Dexmedetomidine inhibited AVP- and DcAMP
-stimulated Pf 98% & 97%, respectively. Epinephrine inhibited AVP-
and DcAMP-stimulated Pu 70% & 60%, respectively. Dexmedetomidine
failed to affect Pu. Atipamezole reversed all inhibitory effects.
These data confirm an [alpha]2-mediated mechanism in the IMCD which
modulates Pf & Pu, and they indicate that inhibition occurs via
post-cAMP cellular events.
Received 21 November 1995; accepted in final form 15 February
1996.
APS Manuscript Number F396-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 23 April 96