Losartan increases renal blood flow during isoflurane anesthesia in sheep.
BACKGROUND
Inhaled anesthetics cause a transient reversible depression of renal function by direct renal effects or indirectly by changes in neurohumoral systems or cardiovascular performance. When the sympathetic nervous activity is decreased during anesthesia, other vasoactive systems like vasopressin (AVP) and particularly the renin angiotensin system (RAS) are of importance for blood pressure maintenance. Little is known about how the renal circulation is affected by angiotensin receptor blockade during isoflurane anesthesia.


METHODS
The study was performed on isoflurane anesthetized sheep equipped with flow probes (placed around a femoral and a renal artery) and a pulmonary artery catheter. During stable conditions the sheep were given one or more of the following substances: isotonic saline (NaCl); losartan (LOS) 10 mg x kg(-1); prazosin (PRAZ) 0.2 mg x kg(-1) and a vasopressin V1-receptor antagonist (AVP-a) 10 microg x kg(-1).


RESULTS
LOS and AVP-a did not affect mean arterial pressure (MAP), whereas PRAZ lowered MAP significantly (from 98+/-12 to 65+/-7 mmHg). Renal blood flow (RBF) increased after LOS treatment (148+/-34 to 222+/-33 ml x min(-1)). The other substances were without effect on RBF. Femoral blood flow remained unchanged after all treatments.


CONCLUSIONS
We conclude that the sympathoadrenal system is still the major determinant for blood pressure maintenance during isoflurane anesthesia in sheep. The apparently increased activity of the renin angiotensin system in this situation causes a reduction in renal blood flow, which is counteracted by angiotensin II AT1-receptor blockade.
Ullman
J
J
Dept of Anesthesiology and Intensive Care, Karolinska Hospital, Stockholm, Sweden. johan.ullman@ks.se
Eriksson
S
S
Rundgren
M
M
D000758:Anesthesia; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology*; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D006614:Hindlimb / Q000098:blood supply; D007530:Isoflurane / Q000494:pharmacology*; D019808:Losartan / Q000494:pharmacology*; D009994:Osmolar Concentration; D011224:Prazosin / Q000494:pharmacology; D012039:Regional Blood Flow / Q000187:drug effects; D012079:Renal Circulation / Q000187:drug effects*; D012756:Sheep; D014667:Vasopressins / Q000037:antagonists & inhibitors
D018685:Anesthetics, Inhalation; D000959:Antihypertensive Agents; D014667:Vasopressins; D007530:Isoflurane; D019808:Losartan; D011224:Prazosin