Tough one, but you could adjust the pressure, rather than the flow rate, by elevating the reservoir of perfusion fluid.  If the volume is great enough, the pressure won't drop much over time.

I thought of that, but it would require to use a very big volume of colagenase solution (expensive!)  so I dropped it.

I thought of that too.  Inject the collagenase into thekrebs ringer bufffer line near to the liver at concentration and rate that will dilute it appropriately.

Ian, you mean to use a fill a big flask with KRB , connect it with the liver by a T-connector tube and once the flushing is complete, to open the T-connector so that the collagenase could flow in ?

That would work.  You'd need to make sure the head of pressure was appropriate or maintian flow rates.

I was thinking a bit differently. Because I was concerned about having the KRB gassed and warmed, and not wanting to try to do that with the collagenase solution, I wondered if you couldn't inject 10X collagenase into the inflow at 1/10th the approximate flow rate of the KRB........

Hi Petar, I do perfussions regularly with cannula, syringe and 10 ml of collagenase buffer. According to the my experience, the essential point is the collagenase concentrastion.Once you find the optimal concentration of your enzyme lot, you can get nice hepatocytes. Good luck!

The flow rate for isolating mouse hepatocytes is so low, you could probably regulate it with a gravity drip system.  Just put your solution above your isolation table and regulate it with a clamp.  If you have access to IV bags, I would use those.  If you need to increase pressure you could apply pressure directly to the bag.  The flow rate won't be regulated, but it should work.

I wouldn't recommend the 10x collagenase, as you would overdigest closest to the vascular system, and it would stop your flow once it collapses.