Purification of anterior pituitary and hypothalamic hormones.

Pure preparations of pituitary and hypothalamic hormones are needed mainly for (1) their chemical characterisation, which increases our understanding of their biochemistry and makes their synthesis possible; (2) replacement therapy, in which contamination with other pituitary hormones is undesirable; and (3) the development of specific diagnostic assays. Pituitary hormones were first isolated from tissue by fractionation procedures involving precipitation by various salts and solvents. However, the development of chromatographic materials has lessened the problems of fractionation and purification. The strategy usually depends on the particular pituitary hormone or class of pituitary hormone. Since the hypothalamic hormones are present in very low concentrations their isolation poses quite difficult problems, which will be discussed at the end of the paper. Before trying to isolate a hormone an assay must be available. Ideally, this should be a biological one which can measure the potency of material obtained at each fractionation stage. In the early days this was impossible as the assay sometimes took longer than the isolation procedure. Recently, the development of biological assays using tissue slices and isolated cells has made a quick assessment of biologically active fractions possible. Radioimmunoassay is another rapid method but has the obvious limitation that the hormone must have been purified on an earlier occasion for the assay to have been developed. Since anterior pituitary hormones are speciesspecific we will restrict discussion to the isolation of the human hormones, as these are obviously more important clinically.