Tuberoinfundibular Peptide 39 Binds to the Parathyroid Hormone (PTH)/PTH-Related Peptide Receptor, but Functions as an Antagonist**This work was supported by grants from the NIH, NIDDK (DK-11794), the Swedish Foundation for International Cooperation in Research and Higher Education (to K.B.J.), and the Deutsche Forschungsgemeinschaft (JO 315/1–2; to M.R.J.).