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Microvascular bed structure and functions are known to vary throughout the brain. Microvascular responses to high doses of pentobarbital sodium might therefore differ among brain areas. This possibility was examined by measuring local cerebral blood flow (LCBF) with [14C]iodoantipyrine in 52 brain areas at 5, 10, 25, and 60 min after intraperitoneal administration of pentobarbital (50 mg/kg). From 5 to 60 min, LCBF was significantly lowered in 17 of 25 forebrain gray matter areas but in only 1 of 18 hindbrain gray matter structures, the pontine nuclei. Smaller, shorter duration lowering of LCBF was also observed in ten other brain areas. In both control and treated rats, LCBF was found to vary within individual brain structures. The pattern of these LCBF variations was columnar in the cerebral cortex and the hippocampus but was patchy in the caudate-putamen, thalamus, and inferior colliculus. These results indicate that pentobarbital anesthesia more strongly alters LCBF in the forebrain than in the hindbrain and produces different patterns of changes in LCBF than in local cerebral glucose utilization, which was measured with 2-deoxyglucose in a companion study.

It is sometimes desirable to obtain a specified blood level which obeys a prescribed mathematical form. Following an approach based on impulse analysis via Laplace Transform techniques, a general method for an input injection schedule which will achieve this goal is derived. Specific infusion schedules are given which attain blood levels that are constant, increase linearly, decay exponentially, and increase exponentially. Further, simpler approximate infusion schedules are also derived whose outputs achieve the desired function after a short time. Two illustrative experimental examples-one for [14C]EDTA-Ca in anesthetized rhesus monkeys and the other for 2-deoxy-D-[1-14C]glucose in the conscious rat-are presented in detail. The assumptions are discussed and an error analysis is performed.

Am. L Physinl.: 2kart I&c*. 2hyCL $3): H299-~3~1j 1978. - Vascular permeability P in different cerebral regions of the conscious rat was determined, independently of blood flow, for “C tracers of glycerol, mannitol, sucrose, and inulin. A tracer was injected intravenously, arterial plasma concentrations were monitored, and regional brain concentrations were measured at specific times thereafter. A plasma-brain two-compartment model was used to calculate mean regional values of P, letting capillary area equal 240 cm”*g? P was Z4 X 10+ cm * s-* for glycerol, 0.95-1.4 X lop7 for mannitol, 2.53,O x 10mH for sucrose, and 1.0-1.4 x IO-!) for inulin. Cerebrovascular permeability coefficients correspond to coefficients at single cell membranes and lipid bilayers, but are 1,000 times less than at muscle capillaries, The relation between cerebrovascular prmeability and octanol/water partition suggests that saccharides diffuse into the brain through homogeneous endothelial cell membranes and not through capillary pores or by means of vesicles. Estimated cerebral distribution volumes for the tracers indicate that glycerol distributes rapidly within the brain extracellular and intracellular compartments and may be incorporated into the metabolic pool, that mannitol distributes extracellularly and partially intracellularly, and that sucrose remains within the extracellular space.