Parathyroid hormone-like immunoreactivity in brains of tetrapod vertebrates

Heat-stable nondialyzable immunoreactive (IR) parathyroid hormone (PTH)-like activity, that coelutes with authentic PTH on Sep-Pak C18 columns and reverse-phase high-performance liquid chromatography, was measured in the brain, hypothalamus, and pituitary of amphibian, reptilian, avian, and mammalian species, using two specific antisera raised against the 48-64 region of the intact PTH molecule. In each case the IR PTH concentration was greater than that present in peripheral plasma and in rats was not affected by dietary calcium status. Extracts of muscle, liver, and kidney tissue were without IR PTH activity. These results demonstrate the extraparathyroidal occurrence of PTH-like peptides in nontumorous neuroendocrine tissues of vertebrate species. These findings may have evolutionary significance, since IR PTH was present in the brain and plasma of species that lack encapsulated parathyroid glands.