Hi, Normally Rats killed by cervical dislocation to get the smooth muscle or tissues. But cervical dislocation is very painful for rats. there is anesthetia i give them prior to kill which may not effect on the Rats smooth muscles.
Very easy, have been doing that for years to get hearts and perfuse them. None of the classic anesthetics, they all affect organ/tissue/muscle performance. A very short administration of ether would do. And after you did it, it up to you.