Vomiting: only nocturnally

My 12 year old male tabby is exhibiting behaviour that has my vet stumped.
For the last few weeks he vomits once a day. The vomiting always occurs
somewhere between midnight and 6 a.m. The vomit consists of a small amount
of liquid that looks like the residue of the dry cat food he is fed. On two
occasions there has been a small amount of blood in the vomit.

Here are some facts that may be relevant:

1) He gets his main feeding around 8 a.m. It consists of about 39 g (1.4
oz) of canned food. In addition, we put out a bowl of dry food that is
shared by him and the two other cats in our household. The three cats graze
on the dry food until it is gone (which usually is by 10 p.m.).
2) We took him to the vet and she performed a physical exam, did a blood
work-up, and x-rayed his abdomen. She found nothing abnormal.
3) On the chance that the nocturnal vomiting might be the result excess
stomach acidity, she prescribed an antacid (Sucralfate). He has been on the
antacid for 5 1/2 days. The antacid has had no effect.
4) Other than the nocturnal vomiting, there is no indication of a change in
his behaviour or mood. He has a good appetite, urinates and defecates
regularly, is alert, playful, has a healthy coat, etc., etc.

The vet has mentioned other things she could do, including testing him for
pancreatitis, administering barium and then taking more x-rays, and, as a
last resort, doing exploratory surgery on his abdomen.

If anyone has encountered a similar situation, what was the cause? Any
information will be greatly appreciated.


Jay