Scientific Glossary

Amino acids share a common structure: a central carbon (alpha-carbon) bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen, and a variable side chain (R group). The R group determines each amino acid's properties — charged, polar, nonpolar, aromatic. Peptide bonds form between the carboxyl of one amino acid and the amino group of the next, with water released. The sequence and composition of amino acids determines a peptide's three-dimensional shape, receptor affinity, and function.

Bacteriostatic water differs from sterile water in that benzyl alcohol (0.9%) acts as a preservative, inhibiting bacterial growth. This allows a single vial to be used multiple times over several weeks once opened (typically up to 28 days when refrigerated), unlike regular sterile water which should be used immediately after opening. The benzyl alcohol also has mild local anesthetic properties. Critical consideration: benzyl alcohol may degrade certain sensitive peptides — some researchers prefer sterile water or sodium chloride for specific compounds.

Dipeptides (2 AA) and tripeptides (3 AA) are the smallest functional peptide units. Despite their small size, they can exert potent biological effects. KPV (Lys-Pro-Val) is a tripeptide with studied anti-inflammatory properties. GHK (Gly-His-Lys) is a tripeptide with broad tissue-remodeling research. Pinealon (Glu-Asp-Arg) and Vilon (Lys-Glu) are dipeptide/tripeptide combinations from Russian longevity research. Small size generally improves oral bioavailability compared to larger peptides.

GLP-1 is released from the gut after meals and exerts multiple metabolic effects: stimulates glucose-dependent insulin secretion from pancreatic beta-cells, suppresses glucagon from alpha-cells, slows gastric emptying (creating satiety), and acts centrally to reduce appetite. GLP-1 has a very short endogenous half-life (~2 minutes) due to DPP-4 degradation. Pharmaceutical GLP-1 receptor agonists are engineered for much longer half-lives (days to weeks).

GIP is the other major incretin hormone. Like GLP-1, it stimulates insulin secretion in response to blood glucose elevation. However, GIP receptors are also expressed in adipose tissue and bone. The GIP receptor's role in fat metabolism is complex — it may promote fat storage in some contexts. Dual GIP/GLP-1 receptor agonists (like tirzepatide) leverage both pathways, potentially explaining their superior weight reduction vs. GLP-1 monotherapy.

GHRH is produced in the hypothalamus and travels to the anterior pituitary where it binds GHRH receptors on somatotroph cells, stimulating GH synthesis and secretion. Endogenous GHRH is released in pulses, particularly during deep sleep. Pharmaceutical GHRH analogues (sermorelin, CJC-1295, tesamorelin) extend this activity by increasing half-life. Importantly, GHRH-based compounds preserve the natural feedback loop — GH levels suppress further GHRH release, maintaining physiological regulation.

GHRPs are synthetic peptides that act on the ghrelin receptor (GHSR-1a) to stimulate GH release. Unlike GHRH, GHRPs do not require GHRH activity — they activate a complementary and synergistic pathway. When GHRH and GHRP are combined, GH pulses are dramatically amplified (2-10x in some studies) compared to either alone. This synergy is the scientific basis for GHRH+GHRP combination research protocols. Examples: ipamorelin, GHRP-6, hexarelin.

GPCRs are transmembrane receptors that couple to intracellular G proteins upon ligand binding. The G protein then activates secondary messengers (cAMP, IP3, DAG) to produce cellular responses. The GLP-1 receptor, ghrelin receptor (GHSR), melanocortin receptors (MC1R-MC5R), GnRH receptor, and KISS1R are all GPCRs. Over 30% of approved drugs target GPCRs, highlighting their pharmaceutical importance. GPCR activation and desensitization mechanisms are critical for understanding peptide pharmacology.

The stomach produces hydrochloric acid (HCl) via parietal cells, creating a pH of 1.5-3.5. This is essential for protein digestion and pathogen killing but can damage the gastric mucosa if the protective mucus barrier is compromised. BPC-157 was originally discovered in research on gastric juice protective proteins — its gastroprotective properties are among its most studied attributes, with animal studies showing protection against NSAID-induced ulceration, alcohol damage, and stress ulcers.

GnRH is released in pulses from the hypothalamus, stimulating pituitary gonadotroph cells to release LH and FSH. LH triggers testosterone production (in males: Leydig cells; in females: corpus luteum) and FSH drives sperm and follicle development. Critically, continuous (non-pulsatile) GnRH receptor stimulation causes receptor downregulation and hormone suppression — this is exploited therapeutically with GnRH agonists for prostate cancer. PT-141 (bremelanotide) acts upstream via melanocortin receptors to influence sexual arousal pathways.

Intranasal delivery offers several advantages: avoids first-pass hepatic metabolism, bypasses BBB via olfactory and trigeminal nerve pathways, enables rapid absorption through highly vascularized nasal mucosa. Particularly relevant for CNS-targeted peptides: Semax and Selank (Russian nootropic peptides) are formulated as nasal drops specifically because they achieve meaningful CNS concentrations via this route. PT-141 (bremelanotide) received FDA approval as an intranasal formulation before transitioning to subcutaneous. Nasal bioavailability varies widely (5-80%) depending on molecular properties.

Kisspeptin neurons in the hypothalamus (arcuate nucleus and AVPV) integrate metabolic and hormonal signals to regulate GnRH pulse frequency and amplitude. Kisspeptin-10 and Kisspeptin-54 are research variants studied for their role in reproductive endocrinology, sexual behavior, and HPA axis regulation. Kisspeptin administration in human studies robustly stimulates LH release. Research interest in kisspeptin spans reproductive disorders, psychosexual function, and understanding metabolic-reproductive axis interactions.

Peptide bonds are amide bonds (-CO-NH-) that link amino acids into chains. The bond has partial double-bond character due to electron delocalization, making it planar and relatively rigid. This rigidity constrains peptide backbone conformation. Peptide bonds are cleaved by proteases (hydrolysis), which is why orally administered peptides are typically degraded in the gut. Chemical modifications that protect peptide bonds (N-methylation, D-amino acid substitution, cyclization) are research strategies to improve oral or metabolic stability.

Proteases are ubiquitous: in digestive secretions (pepsin, trypsin, chymotrypsin), in blood (DPP-4, NEP, ACE), and intracellularly. Most therapeutic peptides are rapidly cleaved by proteases, limiting their half-life and restricting delivery to injectable routes. Semaglutide overcomes this through C-18 fatty acid conjugation (albumin binding) and selective amino acid modifications. Research strategies to resist proteolysis include: D-amino acid substitution, PEGylation, cyclization, and N-terminal acetylation. Understanding proteolytic stability is essential for interpreting peptide pharmacokinetic data.

Most research peptides are manufactured and shipped as lyophilized (freeze-dried) powder to maximize stability and shelf life. Reconstitution involves adding an appropriate sterile diluent (typically bacteriostatic water) to create an injectable solution. The volume of diluent added determines the final concentration (e.g., adding 2mL to 5mg powder = 2.5mg/mL). Proper reconstitution technique is critical for accurate concentration and sterility.

Standard reconstitution process: allow refrigerated vial to reach room temperature; draw appropriate volume of bacteriostatic water into syringe; inject slowly down the vial wall (not directly onto the powder); gently swirl (never shake — shaking damages peptide structure through mechanical stress); allow to fully dissolve; store refrigerated. Concentration is calculated as: mg of peptide ÷ mL of added water = mg/mL. For example: 5mg peptide + 2mL BAC water = 2.5mg/mL = 2,500mcg/mL. Critical: use sterile technique throughout.

Somatostatin (also called growth hormone-inhibiting hormone, GHIH) provides the off-signal in GH regulation, balancing GHRH's stimulatory effects. Endogenous somatostatin release is triggered by high GH levels (negative feedback), hyperglycemia, and high fat/protein intake. Pharmaceutical somatostatin analogues (octreotide, lanreotide) suppress GH in acromegaly treatment. Understanding somatostatin helps explain why timing of research protocols matters — factors that elevate somatostatin (glucose, fatty acids) theoretically blunt GH responses to secretagogues.