Amino Acid Derivatives and Steroid Hormones

Amino Acid Derivatives

• Catecholamine hormones are neurohormones and neurotransmitters, including epinephrine and norepinephrine, produced by the adrenal gland and water-soluble.
• Tryptophan is the precursor to serotonin and melatonin.
• Glutamic acid is converted to histamine.

Steroid Hormones

• Derived from cholesterol and differ only in ring structure and side chains.
• Lipid-soluble and not packaged, but synthesized and immediately released.
• All steroid hormones are derived from the same parent compound: cholesterol.
• Not water-soluble, so carried in the blood complexed to specific binding globulins.
• In some cases, a steroid is secreted by one cell and converted to the active steroid by the target cell (e.g., androgen to estrogen).

Fatty Acid Derivatives (Eicosanoids)

• Arachidonic acid is the precursor of hormones.
• Stores of arachidonic acid are present in membrane lipids and released through the action of various lipases.
• Eicosanoids are rapidly inactivated by being metabolized and are typically inactive for only a few seconds.
• The principal group of hormones of this class are prostaglandins, prostacyclins, leukotrienes, and thromboxanes.

Regulation of Hormone Secretion

• Sensing and signaling: a biological need is sensed, the endocrine system sends out a signal to a target cell whose action addresses the biological need.
• Key features of this stimulus-response system are:
  • Control of endocrine activity
  • Concentration of hormones in blood and extracellular fluid are determined by rate of production, delivery, and degradation/elimination.

Hormone-Receptor Interaction

• Receptor: a protein that binds to a ligand with high affinity and low capacity.
• Requires a receiver to get the message (receptor).

Principal Functions of Hormones

• Maintenance of the internal environment in the body (maintaining the optimum biochemical environment).
• Integration and regulation of growth and development.
• Control, maintenance, and instigation of sexual reproduction.

Types of Hormones

• Peptide/protein hormones are water-soluble (e.g., ADH, oxytocin, insulin).
• Steroid hormones are lipid-soluble and derived from cholesterol.
• Thyroid hormones (T3, T4) and catecholamines (dopamine, norepinephrine, epinephrine) are derived from tyrosine.
• Tryptophan-based hormones include serotonin and melatonin.