<Li> Interstitial: RBP3 </Li> <Li> Plasma: RBP4 </Li> <P> Retinol plays a crucial role in the growth and differentiation of various body tissues, and it has been previously characterized that embryos are extremely sensitive to alterations in retinol concentration that can lead to spontaneous abortion and malformations occurring during development . Within a mature animal, retinol is transported from the liver via the circulatory system while bound to RBP to the desired target tissue . RBP is also bound to a carrier protein, transthyretin . The process by which RBP releases retinol for cellular availability is still unknown and not concisely determined . </P> <P> Traditionally, RBP is synthesized within the liver with secretion being dependent upon retinol concentrations . However, the concentrations levels do not appear to have an effect upon transcription of RBP messenger RNA (mRNA) which remains constant . Literature reveals that the bovine endometrium has also been identified as a location of RBP synthesis, as well as, the conceptus and extraembryonic tissues of various livestock species . </P>

Retinol bound to retinol binding protein is a good measure of