Prostaglandins and hormone signaling — identify the incorrect statement Which one of the following statements about prostaglandins and lipophilic hormones is incorrect?

Introduction:
Prostaglandins are lipid-derived mediators that usually act locally through GPCRs, whereas classic lipophilic hormones (steroids and thyroid hormone) generally signal through intracellular receptors that regulate gene expression. Distinguishing these categories helps clarify where receptors are located and how signals are transduced.

Given Data / Assumptions:

• Prostaglandins derive from arachidonic acid via cyclooxygenase pathways.
• They act primarily in a paracrine/autocrine fashion and bind cell-surface GPCRs.
• Steroid and thyroid hormones are lipophilic and commonly use intracellular nuclear receptors.

Concept / Approach:

The incorrect claim would conflate “principal lipophilic hormones” with prostaglandins at plasma membranes. While prostaglandins are lipidic and have membrane GPCRs, the principal lipophilic hormones in endocrine physiology are steroids and thyroid hormone, which predominantly use intracellular receptors, not plasma-membrane receptors.

Step-by-Step Solution:

Verification / Alternative check:

Endocrinology texts classify glucocorticoids, mineralocorticoids, sex steroids, and thyroid hormone as lipophilic endocrine hormones acting via intracellular receptors; prostaglandins are eicosanoids with local GPCR signaling.

Why Other Options Are Wrong:

Option B is correct: biosynthesis from arachidonic acid is textbook.

Option C is correct: they are paracrine/autocrine mediators.

Option E is correct: it accurately contrasts steroid/thyroid signaling with membrane receptors.

Option D (“None of the above”) cannot be correct because A is incorrect.

Common Pitfalls:

Assuming all lipophilic messengers use the same type of receptor; overlooking that prostaglandins are not typically endocrine “principal hormones.”

Final Answer:

The principal lipophilic hormones that bind to receptors located in plasma membranes are prostaglandins