The author studied in conscious rats the local spinal blood flow (SCBF) and metabolic effects of intrathecally administered bupivacaine. Fourteen rats received 0.75% bupivacaine, 15 microliters, through a chronically implanted lumbar subarachnoid catheter. Twelve control animals were treated identically, except that they received only an equal volume of saline intrathecally. Ten minutes after intrathecal drug injection, either local SCBF or glucose utilization was measured in the lumbar spinal cord of seven experimental and six control animals with the quantitative autoradiographic iodo-[14C]antipyrine or 2-[14C]deoxyglucose methods, respectively. Intrathecal bupivacaine produced a limp tail, absent hindlimb withdrawal to pinch, and 25-30 min of analgesia on the tail-flick test. Mean arterial blood pressure decreased 14% (P less than 0.01) after bupivacaine was administered, but there was no change in arterial blood gases, pH, or rectal temperature. Subarachnoid bupivacaine reduced both local SCBF and glucose utilization, but the SCBF effect was larger. Local SCBF decreased 27-34% (P less than 0.01) in all five spinal gray and three white matter areas measured, and there was little regional variability in the response. The reduction in spinal glucose utilization was regionally selective and less marked. For example, glucose utilization decreased 15% (P less than 0.05) and 21% (P less than 0.05) in lateral and anterior spinal white matter, respectively, but only decreased approximately 3% in laminae I-III and dorsal white matter (P greater than 0.1). A trend toward metabolic depression was also evident in laminae VIII (-15%, P = 0.06), VII (-13%, P = 0.09), and IV-VI (-11%, P greater than 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)