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1-Adrenoceptor subtypes in rat renal resistance
vessels: in vivo and in vitro studies
Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545
This
study provides new information about the relative importance of
different
1-adrenoceptors during norepinephrine (NE) activation in rat renal resistance vessels. In Sprague-Dawley rats, we
measured renal blood flow (RBF) using electromagnetic flowmetry in vivo
and the intracellular free calcium concentration ([Ca2+]i) utilizing ratiometric
photometry of fura 2 fluorescence in isolated afferent arterioles.
Renal arterial bolus injection of NE produced a transient 46% decrease
in RBF. In microdissected afferent arterioles, NE (1 µM) elicited an
immediate square-shaped increase in
[Ca2+]i, from 90 to 175 nM
(P < 0.001). Chloroethylclonidine (CEC) (50 µM) had no
chronic irreversible alkylating effect in vitro but exerted acute
reversible blockade on norepinephrine (NE) responses both on
[Ca2+]i in vitro and on RBF in
vivo. The RBF response was attenuated by ~50% by the putative
1A-adrenoceptor and
1D-adrenoceptor antagonists 5-methylurapidil (5-MU), and
8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione dihydrochloride (BMY-7378) (12.5 and 62.5 µg/h), respectively. The in
vitro [Ca2+]i response to NE was
blocked ~25% and 50% by 5-MU (100 nM and 1 µM). BMY-7378 (100 nM
and 1 µM) attenuated the NE-induced response by ~40% and 100%.
The degree of inhibition in vitro was similar to the in vivo
experiments. In conclusion, 5-MU and BMY-7378 attenuated the NE-induced
responses, although relatively high concentrations were required,
suggesting involvement of both the
1A-adrenoceptor and
1D-adrenoceptor. Participation of the
1B-adrenoceptor is less likely, as we found no evidence
for CEC-induced alkylation.
norepinephrine;
1A-adrenoceptor;
1B-adrenoceptor;
1D-adrenoceptor; renal
circulation; afferent arteriole; calcium; vascular smooth muscle
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