PARATHYROID HORMONE-RELATED PROTEIN IN LOWER-VERTEBRATES

1. Parathyroid hormone-related protein (PTHrP) is an important mediato r of humoral hypercalcaemia of malignancy in humans. Normal human subj ects have very low levels of PTHrP in their circulation. 2, Parathyroi d hormone-related protein has recently been demonstrated in high level s in the circulation and tissues of the sea bream and the dogfish,lead ing to the hypothesis that PTHrP may be a 'classical' hormone in fish. 3, Immunohistochemistry and in situ hybridization were performed to i nvestigate the evolutionary history of PTHrP, Tissues were examined fr om a number of lower vertebrates, including lungfish, lamprey and seve ral species of bony and cartilaginous fish. Parathyroid hormone-relate d protein was localized to the skin and to kidney tubules in all anima ls studied. In the developing lungfish, PTHrP was observed in the noto chord, developing brain and skeletal muscle layers, These results sugg est that PTHrP is of ancient origin and has a basic and fundamental fu nction in vertebrates.