I have 2 cats.  They are brother and sister and about 15 1/2 years old.  
The male has been diabetic for about  8 years and other then being fat
is doing pretty good.  I give him two shots a day.

The female has shown very early signs of kidney disease but nothing bad
yet.  Here is the problem.  About a year ago for the first time in her
life she urinated on the carpet in the family room.  I had her checked
out and she had a urinary tract infection.  I gave her meds and it
cleared up.  A few months later she urinated on the carpet a few more
times.  I had her checked out and she was fine.  A month or so ago it
started happening frequently.  I had the vet check her out and I even
shelled out $275 for an ultra sound.  The blood tests all came back fine
and the ultra sound looked ok too.  Its been about 3 weeks since she was
at the vet and she hasn't had an accident since then.

There have been no stressful changes in her life.  She has lived in same
house with her brother for 8 years.  I keep the litter box clean at all
times and added a second litter box too.  I have been racking my brain
trying to think of anything that might be causing her to go outside the
litter box.  She always uses the litter box to move her bowels.  She
only has "accidents" urinating

A year or two ago somebody gave me two soft pads that the cats could lay
on.  Those mats had catnip in them and Betty my female at kept urinating
on them and I eventually took them off the floor so they couldn't use
them anymore.  I have always left a few toys on the floor in the family
room that are soft and when they were bought had catnip in them.  I have
had those toys literally for years but my male cat Barney likes using
them as a pillow so I never threw them away.

I started wondering if there was a link between Bettys urinating on the
carpet and the catnip smell in the toys even though the catnip shouldn't
even exist anymore after all these years.  I decided to pick up all the
toys and left nothing on the carpet in that room.  She has not urinated
on the carpet in the three weeks since I picked up those very old toys.

The bottom line is has anybody every heard of catnip in anyway causing
cats to urinate where they usually do not?  I hope this all makes sense

Thanks

Steve