Question

The following hormone does not have any intracellular receptor:

• A. Vitamin D3
• B. Cortisone
• C. Adrenaline
• D. Thyroxine

Hint:

Steroid and thyroid hormones cross the cell membrane and use nuclear receptors; catecholamines cannot cross it and use surface receptors instead.

Answer 1

The Correct Option is C

This question tests whether a hormone signals from inside the cell or from the cell surface, and that depends on whether the hormone can cross the lipid membrane.

1. Vitamin D3: This is a fat soluble, steroid type hormone. It diffuses across the membrane and binds the vitamin D receptor inside the nucleus, so it has an intracellular receptor.
2. Cortisone: A glucocorticoid steroid. It crosses the membrane freely and attaches to the glucocorticoid receptor sitting in the cytoplasm before moving into the nucleus.
3. Adrenaline: A catecholamine built from tyrosine, and it is water soluble and charged. It cannot cross the lipid membrane, so it acts on alpha and beta receptors on the outer cell surface, using cyclic AMP as a second messenger inside the cell. It has no intracellular receptor.
4. Thyroxine: Though it is an amino acid derivative, it behaves like a steroid because it is small and fat soluble. It crosses the membrane and binds a nuclear thyroid receptor.

Three of the four hormones, vitamin D3, cortisone and thyroxine, are lipid soluble and bind receptors inside the cell. Adrenaline stands apart because it is water soluble and must use a surface receptor.

Let's summarize:

• Lipid soluble hormones, steroids, thyroid hormone and vitamin D, use intracellular or nuclear receptors and change gene transcription.
• Water soluble hormones like catecholamines use cell surface receptors and second messengers instead.

So the hormone without any intracellular receptor is adrenaline.