Pantothenic acid is found in feeds in both bound (largely as CoA) and free forms. It is necessary to liberate the pantothenic acid from the bound forms in the digestive process prior to absorption. Pantothenic acid, its salt, and the alcohol are absorbed primarily in the jejunum by a specific transport system that is saturable and sodium ion dependent (Fenstermacher and Rose, 1986). The alcohol form, panthenol, which is oxidized to pantothenic acid in vivo, appears to be absorbed somewhat faster than the acid form. After absorption, pantothenic acid is transported to various tissues in the plasma from which it is taken up by most cells via another active-transport process involving cotransport of pantothenate and sodium in a 1:1 ratio (Olson, 1990). Within tissues, pantothenic acid is converted to CoA and other compounds where the vitamin is a functional group (Sauberlich, 1985). Free pantothenate appears to be efficiently absorbed; in the dog between 81% and 94% of an oral dose of sodium [14C]pantothenate was absorbed (Taylor et al., 1974). Measurement of pantothenic acid bioavailability in adult men consuming a typical United States diet ranged from 40% to 61%, with an average of 50% (Sauberlich, 1985). Urinary excretion is the major route of body loss of absorbed pantothenic acid, and excretion is prompt when the vitamin is consumed in excess. Most pantothenic acid is excreted as the free vitamin, but some species (e.g., dog) excrete it as beta-glucuronide (Taylor et al., 1972). An appreciable quantity of pantothenic acid (~15% of daily intake) is oxidized completely and is excreted across the lungs as CO2.
Livestock do not appear to have the ability to store appreciable amounts of pantothenic acid; organs such as the liver and kidneys have the highest concentrations. The majority of pantothenic acid in blood exists in red blood cells as CoA, but free pantothenic acid is also present.
