Is there a link between hyperthyroidism and aggression and/or
terratoriality towards other cats in a household?

We have a 12 year old male (approx. 18 lbs) with confirmed (but mild)
hyperthyiodism (and arthritis).  He's been sharing the house and yard
with 2 younger new cats (male and female, both about 10 to 12 lbs) for
slightly more than a year.  He gets along with the (very easy-going
male) but there has been the occasional backyard fight which leaves
lots of fur all over the place.  But when he gets the chance (and
we're not around) he tends to stalk or intimidate the (head-strong /
spunky) female and if he corners her (and attacks) the crys that come
from her are blood-curdling (she seems to try harder to get away than
roll and fight).

It's hard not to give him a whoopin when I run to rescue the female.  

He was started on metacam about 3 months ago (initially 3 drops per
week, has been increased to 1 drop per day for the past month).
Kidney and liver tested fine.  Potassium is low.  Noticable
improvement in activity and mobility with the metacam.  (glucosamine
administered for several months prior to that had no effect).

We will start him on tapazol (sp?) and then get him the iodine
treatment later.  Has been diagnosed with a somewhat pronounced heart
murmer for the past few years (3? 4?).  Has had recent surgery to
remove fatty lumps from his chest.  Tolerates anestetic very well.

Besides getting his thyroid under control, we are hoping his
aggressiveness toward the female cat will stop.  I think that if she
either hissed and/or stood her ground and maybe fought back that he'd
back off and "respect" her more and he'd stop attacking her.  Instead
I think he sees her as a prey item because of her behavior in
close-quarters (ie crouch and attempt to flee).  

I also see that amitriptiline (sp?) has been given for aggressive
behavior.  What is the track record for drugs at moderating aggressive
behavior in cats?