Radioimmunoassay of ligandin

A sensitive and specific radioimmunoassay has been developed for rat ligandin, capable of measuring this protein in the manogram range. The assay employs [125I] ligandin prepared by the chloramine-T method and rabbit antiserum to rat ligandin, with a double antibody method of separating antibody-bound from free ligandin. Using the radioimmunoassay, ligandin concentration was measured in the cytosol of various tissues in normal and phenobarbital-treated adult and newborn rats. In the adult rat, ligandin showed a widespread tissue distribution with the highest concentrations in liver, kidney, small-intestinal mucosa, testis, ovary and adrenal gland. Lesser quantities were measured in salivary gland, mucosa of stomach and colon, pancreas, pituitary, lung, thyroid, bladder, heart and seminal vesicles. Rat tissue cytosol gave immunochemical displacement curves parallel with the standard curve while tissue cytosol from other species either gave non-parallel curves (mouse and guinea pig) or showed no cross reaction (rabbit). Gel filtration analysis of the cytosol of liver, kidney, small intestinal mucosa, testis and myocardium revealed immunoreactivity in these tissues to correspond to the elution volume of ligandin. Hepatic and renal ligandin concentrations in rats soon after birth were 4 and 6% of adult values. Phenobarbital treatment in adult rats resulted in significant increases in hepatic, renal and small intestinal mucosa ligandin concentrations with no change in the testis. © 1977.