Hi Valerie,
I have had great results just post-fixing the livers in 4% PFA for 3 hours at room temp, followed by 30% sucrose overnight at 4 degrees before freezing down in OCT in the cryostat, or -20C.
Perfusion wasn't necessary. Also, I am not familiar with perfusion using saponin in the mix. 
But I do always use TritonX on my actual cut slides before staining, anytime I use 4% PFA fixed tissues. Detergents help permeabilize the cells, facilitating your antibody binding. 

Hope this helps, 
Melissa

Message: 10
Date: Fri,  1 Jul 2005 09:37:13 -0500
From: vsailes@nd.edu
Subject: [Histonet] Recipe for 4%PFA w/saponin
To: histonet@lists.utsouthwestern.edu
Message-ID: <1120228633.42c5551975837@webmail.nd.edu>
Content-Type: text/plain; charset=ISO-8859-1

Hi Histonetters,
I'm working with mice and we want to stain the livers for albumin. I have an
antibody that appears to work but we would like to perfect the technique if
possible. I have done some literature searches and some of them suggested that
to perfuse the animal with 4% paraformaldehyde containing saponin would give a
more homogenous staining pattern but I really could not find information
telling the percentage of saponin to use.
If anyone out there has experience with this would you please help shed some
light on this matter.
Thank you in advance for your help.
Have a great holiday weekend.
Valerie








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