Have you tried this? https://www.qiagen.com/de/products/discovery-and-translational-research/lab-essentials/buffers-reagents/qiazol-lysis-reagent/#orderinginformation

You can also try to preserve your tissue in RNALater if you have trouble with RNA degredation. I used this method to extract RNA from frozen tissue to extract RNA several years after.

With any RNA extraction from animal tissue, it is critical to minimise the time between the animal's death and the protection of RNA by snap-freezing or placing in a preservation solution like RNAlater. This is because as soon as cells are deprived of oxygen, within minutes they start to die and release contents of some cellular compartments - and so the cells' endogenous RNases start to break down RNA. This is especially likely with a tissue that contains high levels of RNase to begin with, and since pancreas secretes digestive enzymes, I am guessing it would be quite challenging to get high quality RNA from.

Here are some of the steps we take to minimise RNA degradation: Begin dissection immediately after sacrificing the animal, ideally within seconds of confirming death. (You will not get good quality RNA from slaughterhouse samples, no matter what you do.) Dissect as rapidly as possible, using chilled buffers and a chilled work surface (I pack a metal lunch box with ice and use the bottom of the lunch box as a cutting surface.) Cut tissue into small pieces to ensure that it freezes or absorbs preservation solution very quickly. If preserving by freezing, snap freeze samples by putting them into dry ice or liquid nitrogen, putting your samples into a freezer is too slow. When doing your RNA extraction, minimise the amount of time your samples begin to defrost before they are homogenised (I begin homogenisation in lysis buffer while my tissue sample is still frozen; other people grind their frozen tissue to powder under liquid nitrogen and then mix the powder with lysis buffer.) Make sure you are using a sufficient volume of lysis/RNA extraction reagent for the amount of tissue that you have - for a tissue high in RNases like pancreas, you might need 2 or even 3 times the volume of reagent suggested by the manufacturer.

Dear Can Kiessling and Laura Leighton,

I appreciated your concrete suggestion.

We didn’t use any RNA stabilization reagent, and could a potential limitation. I hope that the use of RNALater could be the right solution. Thank you so much for your impressive explanation @ Laura Leighton. It is much more useful.