After an equilibration period for at least 1 h, the perfusate was collected at a perfusion rate of 0.1 µl/min every 60 min into collection tubes containing 2 µl of 0.5 N perchloric acid.
If the perfusion rate is sufficiently slow, the analytes reach concentration equilibrium between the perfusate and the extracellular space of the brain.
Phenol (1 300 mM) was delivered directly to the liver via the MD probe at a perfusion rate of 1 μl min−1 which consistently resulted in a relative delivery of 77 85% of the phenol in the perfusate to the tissue over a 3 day experimental time frame.
In experiments at 37°C 50 µM of BaCl2 was added to the perfusate, instead, because the 10 mM BaCl2 in the lower electrode space seemed to be less effective probably due to higher perfusion rate at 37°C.
In this equation, Vi initial perfusion rate, nl/min) is calculated by dividing the cpm of C in the collected fluid by the cpm/nl of C in the initial perfusate and by the time of the collection period; Vo (collection rate, nl/min) is measured directly from the collection; and L (mm) is the length of the tubule perfused, measured with an ocular micrometer.
This might however not be a problem in the case of the isolated perfusion of tumour-bearing limbs by an extracorporeal circuit as performed clinically, since perfusion pressure can be regulated by enhancing or lowering perfusate flow rate by means of an external pump.
Application of the vehicle alone resulted in only a slight decrease in perfusion pressure by 2% of the baseline value so that the perfusate flow rate remained almost constant during vehicle administration.
An inverse relationship exists between perfusate flow rate and analyte extraction fraction, where the percent of relative in vivo recovery declines exponentially as the flow rate is increased.
Perfusate flow rate was varied (range: 0.27 2.63 ml min−1) to achieve a constant perfusion pressure (PP) of approximately 100 to 140 mmHg in order to maintain an adequate tissue perfusion which might otherwise be impaired with PP approximately 15 mmHg below the systemic MABP (Fontijne et al, 1985a, b).
Additionally, the microdialysis experiments sampling from the mPFC used a lower perfusate flow rate than the striatal experiments.
