Effects of calcium channel blockers on "dynamic" and "steady-state step" renal autoregulation.
Renal autoregulation (AR) mechanisms provide the primary protection against transmission of systemic pressures and hypertensive renal damage. However, the relative merits of the "step" change vs. "dynamic" methods for the assessment of AR capacity remain controversial. The effects of 48-72 h of orally administered amlodipine (L-type) and mibefradil (T-type) calcium channel blockers (CCBs) on step and dynamic AR in Sprague-Dawley rats were compared. Both CCBs significantly impaired "steady-state step" AR (autoregulatory indexes = approximately 0.5 vs. approximately 0.1 in controls, P < 0.05; n = 9-10/group). By contrast, dynamic AR compensation in separate conscious rats (n = 12) was not significantly altered by either amlodipine (n = 10) or mibefradil (n = 6; fractional gain in admittance approximately 0.4-0.5 in all groups at frequencies in the range of 0.0025-0.025 Hz). However, both CCBs tended to attenuate the myogenic resonance peak along with shifting it to a significantly slower frequency (P < 0.001) during dynamic AR, but no consistent effects were observed on the tubuloglomerular feedback resonance peak. While the reasons for the insensitivity of dynamic vs. steady-state step AR capacity estimates to CCBs remain to be established, the present data indicate that dynamic AR methods may have a limited utility for assessing AR capacity but may provide potentially important insights into the operational characteristics of AR control mechanisms. A strong correlation was also observed between the average conductance and the admittance gain at the heart beat frequency (r = 0.77, P < 0.001), suggesting that such parameters may provide additional and possibly more meaningful indexes of BP transmission in conscious animals during dynamic AR.
Griffin
Karen A
KA
Loyola Univ. Medical Ctr., 2160 South First Ave., Maywood, IL 60153, USA. kgriffi@lumc.edu
Hacioglu
Rifat
R
Abu-Amarah
Isam
I
Loutzenhiser
Rodger
R
Williamson
Geoffrey A
GA
Bidani
Anil K
AK
D017311:Amlodipine / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D005246:Feedback; D006706:Homeostasis / Q000187:drug effects*; D007668:Kidney / Q000187:drug effects*; D007678:Kidney Glomerulus / Q000187:drug effects / Q000502:physiology; D008279:Magnetic Resonance Imaging; D008297:Male; D020748:Mibefradil / Q000494:pharmacology; D009929:Organ Size / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012079:Renal Circulation / Q000187:drug effects
D002121:Calcium Channel Blockers; D017311:Amlodipine; D020748:Mibefradil