Thyroxine is a peptide hormone, but its mechanism is different from other peptide hormones. Which of the following statements is true concerning this difference?
1) Thyroxine is synthesized in the hypothalamus.
2) Thyroxine acts through a cell surface receptor.
3) Thyroxine is involved in the regulation of blood sugar levels.
4) Thyroxine is released by the adrenal glands.