Insulin
Also known as: Regular insulin, Human insulin
Insulin is a peptide hormone produced by beta cells in the pancreas that regulates blood glucose by promoting cellular uptake of sugar. Insulin is essential for metabolism and was the first peptide to be sequenced and synthesized. Many peptide therapies affect insulin signaling, including GLP-1 agonists.
Last updated: January 21, 2026
How Insulin Works
Insulin regulates blood glucose through multiple mechanisms:
- Glucose uptake - Promotes glucose entry into muscle and fat cells
- Glycogen synthesis - Stimulates glucose storage in liver and muscle
- Protein synthesis - Promotes amino acid uptake and protein building
- Fat storage - Inhibits fat breakdown, promotes fat synthesis
- Gluconeogenesis inhibition - Reduces liver glucose production
Insulin Release Pattern
| Trigger | Response |
|---|---|
| Rising blood glucose | Rapid insulin release |
| Amino acids (especially leucine) | Moderate insulin release |
| Incretins (GLP-1, GIP) | Enhanced insulin release |
| Glucagon | Insulin release (counter-regulation) |
| Low blood sugar | Insulin suppressed |
Insulin Structure
Insulin is a 51-amino acid peptide with two chains:
- A chain: 21 amino acids
- B chain: 30 amino acids
- Connected by disulfide bonds
This structure makes insulin larger than most “peptides” but it’s historically grouped with peptide hormones.
Insulin and Type 2 Diabetes
In type 2 diabetes:
- Early stages: Insulin resistance (cells don’t respond well)
- Compensation: Pancreas produces more insulin
- Later stages: Beta cell exhaustion, reduced insulin production
- Treatment goal: Improve sensitivity and/or provide insulin
GLP-1 Agonists and Insulin
GLP-1 receptor agonists affect insulin in several ways:
Enhanced Secretion
- GLP-1 amplifies insulin release in response to meals
- Effect is glucose-dependent (reduces hypoglycemia risk)
- Restores first-phase insulin response
Preserved Beta Cells
- May protect beta cells from stress
- Potentially delays disease progression
- Active area of research
Insulin vs GLP-1 Agonists
| Feature | Insulin | GLP-1 Agonists |
|---|---|---|
| Mechanism | Provides hormone directly | Enhances natural release |
| Hypoglycemia risk | Higher | Lower |
| Weight effect | Often gain | Loss |
| Glucose control | Powerful | Effective |
| Timing flexibility | Varies by type | Weekly options available |
Types of Insulin Therapy
Rapid-acting
- Lispro, Aspart, Glulisine
- Onset: 15 minutes
- Used for meal coverage
Long-acting
- Glargine, Detemir, Degludec
- Duration: 24+ hours
- Provides basal coverage
Historical Significance
Insulin holds a special place in peptide science:
- 1921: Discovered by Banting and Best
- 1923: Nobel Prize awarded
- 1955: First protein sequenced (Sanger)
- 1978: First recombinant human protein produced
- Today: Over 100 years of life-saving use
Frequently Asked Questions
Is insulin a peptide or protein?
Insulin is on the border—with 51 amino acids, it’s larger than typical peptides (2-50 AA) but smaller than most proteins. It’s historically classified as a peptide hormone and was the first peptide to be sequenced.
Why don’t GLP-1 agonists cause hypoglycemia like insulin?
GLP-1 agonists enhance insulin release only when blood glucose is elevated (glucose-dependent action). When blood sugar is normal or low, the GLP-1 effect on insulin diminishes, providing a built-in safety mechanism that injected insulin doesn’t have.
Can you take GLP-1 agonists with insulin?
Yes, they’re sometimes used together, especially in type 2 diabetes when GLP-1 alone isn’t sufficient. The combination can allow for lower insulin doses and may provide better outcomes than higher insulin doses alone.
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Disclaimer: This glossary entry is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider for medical questions.