Calcitriol

Yay, Just found this info: Calcitriol as the active form of Vitamin D. The ingredients to make the calcitriol must first make their way through the liver and then migrate to the kidneys which if healthy do the final step of making the calcitriol. Calcitriol helps your pet's body absorb calcium and phosphate from food and put it in growing bones, where extra calcium and phosphate is stored. A molecule called parathyroid hormone (PTH) works with calcitriol at bone to release calcium to blood. When too high, PTH becomes a serious health problem and we wish to lower it which we can do by giving calcitriol. If your pet's kidneys are failing and no longer doing their job of making enough calcitriol the parathyroid glands (around the thyroid gland in the throat area) produce more PTH in an attempt to normalize calcium and phosphate in the blood. The PTH is not too damaging until it reaches about 3 times the upper limit of its normal level in the blood as this is when toxicity due to the PTH first appears. This is usually happening about when your pet first appears to be ill. The PTH increase is worsened by the failure of the sick kidneys to eliminate phosphorus from blood which then gets too high a level. This both slows calcitriol formation and also prevents calcitriol from working at the parathyroid gland to block the PTH excess. When at very high levels late in kidney failure the phosphorus combines with blood calcium to precipitate into soft tissues damaging them. Although very injurious, this only happens at late stages of disease and use of calcitriol should prevent getting to such stages nearly as soon as would happen in pets not given calcitriol. The high levels of PTH directly damage kidney cells long before the mineral precipitation phase of renal injury. See http://members.verizon.net/~vze2r6qt/calcitriol/calcitriol2.htm