Q: When my 10-year-old German short - haired pointer started to suffer greatly from arthritis, the veterinarian told me that because painkillers would be bad for his health at his age, I should just keep him warm and walk him regularly. Then a friend recommended that I give him the dietary supplement DLPA (DL-Phenylalanine), which I found in a health food store. The change in my dog in one week was miraculous. He is now bounding around like a puppy, and his appetite has increased. Why didn't the vet know about this nutrient?--M.D. A: DL-Phenylalanine is an essential amino acid. An English study showed that DLPA seems to lead to improvement and pain relief in humans. I am unaware of any studies being done for dogs and/or cats. DPLA seems to function by inhibiting the enzymes that destroy endorphins, thus prolonging the effect of these naturally produced painkillers. It is reported that DLPA may be combined with other arthritis therapies without interfering with their effects and often enhancing the benefits. Other treatments include drugs (from cortisone to a wide range of non-steroidal anti-inflammatories) and acupuncture-acupressure.