Hi there

Here is an article that you might find useful:

http://www.usp.br/bioterio/Artigos/Procedimentos%20experimentais/Good_practice_lab_animals.pdf

There are a couple of things you need to consider:

Firstly, the activity level of radio-isotope that you wish to administer (this is determined by what you are planning on doing e.g. scintillation counting, imaging..etc, what your radioactivity licence/ethical review board permits (at least in the UK is does), and clearly needs to be a dose that will not make you rats unwell). Secondly, the fluid volume one can safely administer to a rat (regardless of what it contains). I presume you are doing a short-term assay as then half-life of 99m-Tc is quite short? There are other more stable radio-isotopes for labelling studies, if you are not imaging.

Hence it is almost impossible to give you an answer to your question in ml, as it depends on how many MBq os isotope you need to administer, rather than a particular volume of 99mTc.

Rats has a blood volume of 20-35 ml. You should not administer the rat a volume bigger than 10% of this if you want them to survive the study. In the other hand, you need to administer the rat an ammount of 99mTc reasonable to obtain results. If you are performing micro-SPECT studies, you will need at least 1mCi, so you must ensure that your 99mTc concentration is enough to fulfill this 2 conditions. If you detail your experiment, maybe we could help you more.

I agree with Jesus about the ~ 10% for tail vein injection. I did not read and know if there is any sharp line. It was said there is about 7% blood of the body weight and therefore about 1.4 mL for a 20 g mouse. We used to inject 0.1 mL, more than enough for 99mTc labeled solution, unless low labeling efficiency, specific radioactivity, or concentration becomes an issue. For my own experience with mice, there is not any adverse sign if 0.25 mL is used. If injecting 0.4 mL, a mouse may look inactive for a couple of minutes before getting back to normal and active. We do not like to use more than 0.25 mL. I guess there is no difference with rats. Proportional increase may be made. Please note we recently noticed ionic strength is an additional factor to be considered.

Thanks all.

I want to use Tc-99m for Imaging as well as "cut and count assay". is it possible?

Very possible. Can we meet and tell you more about it. I have no much time to write here. Thanks

Thank You all for your contribution

Minor remarks:

"I want to use Tc-99m for Imaging as well as "cut and count assay". is it possible?"

Perfectly possible. For a reliable procedure make sure not to loose urine, e.g. during scanning (tissues to collect it). Especially when injecting higher volumes, this may happen frequently and can ruin results.

If the Tc-99m activity of your sample is too low, you can always consider concentrating (depending on the labelled molecule e.g. with spin colums when working with bigger labelled molecules) rather than increasing the volume to inject.

(Finally, don't forget to have an eye on the pH of your solution, but that's clear anyway.)