Peptide hormones are initially synthesized as which of the following?

Peptide hormones are initially synthesized as preprohormones. This term refers to the initial form of the hormone that contains not only the peptide sequence destined to become the active hormone but also additional sequences that are often referred to as signal peptides. These signal peptides are essential for directing the nascent polypeptide into the endoplasmic reticulum (ER) during translation.

Once the preprohormone is synthesized, it undergoes several processing steps where the signal peptide is removed, leading to the formation of a prohormone. The prohormone is still not in its active form and may require further cleavage or modification before becoming the active peptide hormone that can exert its physiological effects.

Thus, the sequence of events starts with the synthesis of preprohormones, making this option the correct answer. Understanding this process is crucial as it highlights the complexity of hormone biosynthesis and the maturation process that peptide hormones undergo before they are released into circulation.