This hormone analog's mechanism of action likely resembles which type of endocrine hormone?

Question

A pharmaceutical company is experimenting with a new hormone analog whose mechanism of action is contingent on binding to extracellular receptors of target cells. The hormone analog's mechanism of action likely resembles which type of endocrine hormone?

A) Antidiuretic hormone

B) Cortisol

C) Nitric oxide

D) Testosterone

Answer 1

Correct: A

Explanation #1:

Nonsteroid hormones must bind to surface receptors embedded in the target cell’s membrane because they are unable to diffuse across the phospholipid bilayer membrane of the target cell. 

Antidiuretic hormone (ADH) is a nonsteroid, peptide-derived hormone molecule. Also known as vasopressin, ADH is a polar molecule with hydrophilic and hydrophobic properties. ADH will not penetrate through the target cell’s phospholipid bilayer membrane. ADH exerts its physiologic effects by binding to receptors embedded in the target cell’s membrane.

Based on their biochemical structure, hormones exist in two main types: steroid hormones and nonsteroid hormones. Nonsteroid hormones are amino-acid derived (amine/peptide/polypeptide/protein) molecules, which are lipid-insoluble. Lipophobic (lipid-insoluble), nonsteroid hormones will not diffuse across the target cell’s phospholipid bilayer membrane and must instead bind to surface receptors embedded in the target cell’s membrane. Examples of nonsteroid hormones are given the table below:

Nonsteroid Hormones (Amino-acid based)

Site of Secretion

1. Amine: Thyroxine (T4),triiodothyronine (T3)
2. Thyroid gland (follicle cells).
3. Peptide: Prolactin, adrenocorticotropic hormone (ACTH)

Anterior pituitary

1. Polypeptide: Antidiuretic hormones, oxytocin
2. Posterior pituitary (produced in hypothalamus but stored and released from the posterior pituitary)
3. Protein: Growth hormone
4. Anterior pituitary

 

Steroid hormones are lipid-derived molecules and are, therefore, lipophilic or lipid-soluble. Steroid hormones will invariably diffuse across the target cell’s phospholipid bilayer membrane and bind to intracellular receptors located either in the cytosol or the nucleus. The adrenal cortex and the gonads (testes and ovaries) are the essential glands that secrete steroid hormones. Examples of steroid hormones include:

Steroid Hormones

Site of Secretion

1. Aldosterone
2. Adrenal Cortex (Zona Glomerulosa)
3. Cortisol
4. Adrenal Cortex (Zona Fasciculata

Androgens, dehydroepiandrosterone, DHEA

1. Adrenal Cortex (Zona Reticularis)

Testosterone

1. Testes (Leydig cells in the seminiferous tubules of the testes)

Estrogen and Progesterone

1. Ovaries

Figure 1 showing mechanism of action of steroid hormones.

Nonsteroid hormones are amino-acid derived (peptide/amine) molecules which are lipid-insoluble. Lipophobic (lipid-insoluble), nonsteroid hormones will not diffuse across the target cell’s phospholipid bilayer membrane and must instead bind to surface receptors embedded in the target cell’s membrane.

Figure 2 showing classification of hormones by chemical class

(Choice B) Cortisol is a steroid hormone produced by the adrenal cortex. The phospholipid bilayer of a target cell’s membrane enables the diffusion of all lipophilic hormones, including steroid hormones across the target cell’s membrane. Upon diffusing across the target cell’s cell membrane, steroid hormones bind to intracellular receptors located either in the cytosol or the nucleus.

(Choice C) Nitric oxide is a gaseous hormone that diffuses freely across the target cell’s phospholipid bilayer membrane and, in turn, bind to intracellular receptors. 

(Choice D) Testosterone is a lipid-soluble, steroid hormone produced by the testes. Lipid-soluble or lipophilic hormones, like testosterone, can penetrate through the target cell’s phospholipid bilayer membrane and, in turn, enter inside the cell directly where it binds to intracellular receptors. 

Educational objective:

Property	Steroid Hormones	Nonsteroid Hormones (Peptide/Amine Hormones)
Interaction with Target Cell Membrane	Diffusion through cell membrane	Binding to receptor on cell membrane
Receptor	In Cytosol or Nucleus	Embedded on Cell Membrane