ESMOLOL HYDROCHLORIDE, SODIUM-NITROPRUSSIDE, AND ISOFLURANE DIFFER INTHEIR ABILITY TO ALTER PERIPHERAL SYMPATHETIC RESPONSES

To demonstrate that esmolol, sodium nitroprusside, and isoflurane diff er in their abilities to alter adrenal medullary blood flow and other peripheral sympathetic responses to hypotension, 16 mongrel dogs anest hetized with pentobarbital were allocated randomly to one of four test groups and given two hypotensive stimuli, separated by 1 h, to a mean arterial blood pressure of 60 mm Hg for 10 min. The first stimulus, i nduced by blood loss into a pressurized bottle system, constituted the control for each animal. The second hypotensive stimulus was created by either repeat blood loss (Group 1), esmolol infusion (Group 2), sod ium nitroprusside infusion (Group 3), or isoflurane administration (Gr oup 4). Before and 10 min into hypotension, the variables of abdominal organ blood flow, adrenal medullary blood flow, arterial norepinephri ne and epinephrine concentrations were measured. In the control animal s (Group 1), comparable decreases in abdominal organ blood flow and si milar increases in adrenal medullary blood flow, norepinephrine, and e pinephrine were elicited by the first and second hypotensive stimulus. Esmolol-induced hypotension (Group 2) abolished the increase in adren al medullary blood flow and attenuated the increase in epinephrine by 65% (P < 0.03). The decrease in abdominal organ blood flow and the inc rease in norepinephrine were similar to that observed during baseline hemorrhagic hypotension. In contrast, sodium nitroprusside-induced hyp otension (Group 3) abolished abdominal organ vasoconstriction whereas the increases in adrenal medullary blood flow, norepinephrine, and epi nephrine were comparable to baseline hemorrhagic hypotension. In fact, abdominal organ blood flow increased 2.5-fold (P < 0.001) during hypo tension with SNP. Isoflurane 2%, 1.54 minimum alveolar anesthesia conc entration (Group 4), abolished the increases in adrenal medullary bloo d flow, norepinephrine, and epinephrine observed during baseline hemor rhagic hypotension and attenuated the decrease in abdominal organ bloo d flow by 70% (P < 0.001). These data demonstrate that esmolol, sodium nitroprusside, and isoflurane differ radically in their ability to al ter or blunt peripheral sympathetic responses to hypotension, and sugg est that isoflurane is the drug most effective in blunting multiple re sponses of the peripheral sympathetic system.