Parathyroid hormone (1-34) (human): A Precision Tool for Calcium Homeostasis and Bone Metabolism Research

Executive Summary: Parathyroid hormone (1-34) (human) is a rigorously characterized peptide fragment synthesized to >97.8% purity for scientific research (APExBIO). It acts as a selective agonist of parathyroid hormone receptors PTH1R and PTH2R, mediating cAMP signaling with an IC50 of 0.22 nM in human kidney cells (APExBIO product page). This reagent is indispensable for dissecting bone metabolism, serum calcium regulation, and kidney physiology in vitro and in vivo (Huang et al., 2025). Its solubility profile (≥399.3 mg/mL in DMSO; ≥19.88 mg/mL in water) enables high-concentration dosing and protocol flexibility. In vivo, it drives trabecular and cortical bone mass increases in rodent models, validating its translational utility.

Biological Rationale

Parathyroid hormone (1-34) (human), abbreviated as PTH (1-34), represents the N-terminal bioactive domain of endogenous parathyroid hormone. This 34-amino-acid peptide is derived from the chief cells of the parathyroid glands and is responsible for maintaining serum calcium and phosphate balance. It exerts its effects by binding to G protein-coupled receptors, primarily PTH1R and PTH2R, in bone, kidney, and intestine (APExBIO). Through these receptors, PTH (1-34) regulates both acute and chronic phases of calcium homeostasis, influencing bone resorption, renal calcium reabsorption, and vitamin D activation. In experimental medicine, this peptide fragment is preferred over the full-length hormone due to its stability, well-defined sequence (H2N-SVSEIQLMHNLGKHLNSMERVEWLRKKLQDVHNF-OH), and reproducible activity in model systems (PeptideBridge article).

Mechanism of Action of Parathyroid hormone (1-34) (human)

PTH (1-34) acts as a potent agonist of PTH1R and PTH2R, which are class B G protein-coupled receptors. Upon ligand binding, these receptors activate multiple intracellular signaling cascades, most notably the adenylyl cyclase pathway leading to cyclic AMP (cAMP) accumulation and the phospholipase C pathway resulting in inositol phosphate synthesis (Huang et al., 2025). In human kidney 293 cells transfected with PTH1R, PTH (1-34) stimulates cAMP production with an IC50 of 0.22 nM. At the organ level, PTH (1-34) facilitates:

• Bone: Mobilization of calcium from bone matrix by stimulating osteoclast differentiation via osteoblast signaling.
• Kidney: Reabsorption of calcium and magnesium in the distal tubules and thick ascending limb; decreased phosphate reabsorption.
• Intestine: Indirectly increases intestinal calcium absorption through upregulation of 1,25-dihydroxyvitamin D synthesis.

These actions are temporally regulated: intermittent dosing favors bone formation, whereas continuous exposure promotes resorption (Amyloid.co article). This article extends the mechanistic focus of previous reviews by detailing quantitative receptor activation parameters and downstream signaling readouts.

Evidence & Benchmarks

• PTH (1-34) (human) induces cAMP signaling in HEK293 cells expressing PTH1R with an IC50 of 0.22 nM at 37°C in serum-free medium (APExBIO).
• In male Fisher 344 rats, subcutaneous administration of 10 or 40 μg/kg/day for 4 weeks increases trabecular and cortical bone mass (measured by μCT) in a dose- and time-dependent manner (Huang et al., 2025).
• The peptide is soluble at ≥399.3 mg/mL in DMSO and ≥19.88 mg/mL in water at room temperature; insoluble in ethanol (APExBIO).
• Storage at -20°C under desiccated conditions maintains >97.8% peptide integrity for at least 12 months (APExBIO).
• PTH (1-34) upregulates renal 1α-hydroxylase, enhancing vitamin D activation and thus intestinal calcium absorption (Parathyroid-hormone1-34.com).
• In human kidney progenitor assembloid models, PTH (1-34) can be used to probe PTH/PTHrP receptor signaling and cAMP pathway readouts (Huang et al., 2025).

This article updates the scenario-based approach in Scenario-Driven Solutions by providing explicit quantitative benchmarks and protocol guidance for cAMP and bone mass endpoints.

Applications, Limits & Misconceptions

PTH (1-34) (human) is widely used as a reference agonist for PTH1R in cellular assays, a tool for dissecting calcium homeostasis, and an inducer of bone formation in animal models of osteoporosis. It also serves as a pharmacological probe in engineered kidney organoids and assembloid systems, informing disease modeling and regenerative medicine strategies (Huang et al., 2025). However, its specificity for human and rodent receptors does not always translate to other species. Chronic exposure can paradoxically enhance bone resorption. The product is for research use only and is not intended for therapeutic or diagnostic purposes (APExBIO).

Common Pitfalls or Misconceptions

• Not a therapeutic: This reagent is not approved for clinical use or patient administration; it is strictly for in vitro and preclinical studies.
• Species specificity: PTH (1-34) (human) may display reduced potency in non-mammalian systems due to receptor sequence divergence.
• Continuous vs. intermittent dosing: Chronic, rather than intermittent, administration may promote bone loss rather than formation.
• Stability: Solutions are not stable for long-term storage; freshly prepared aliquots are necessary for reproducibility.
• Solubility limitations: Ethanol is not a compatible solvent; use DMSO or water for stock preparation.

Workflow Integration & Parameters

Parathyroid hormone (1-34) (human) is supplied as a lyophilized solid. For experimental use, dissolve at concentrations up to 399.3 mg/mL in DMSO or 19.88 mg/mL in sterile water. Avoid repeated freeze-thaw cycles and store aliquots at -20°C under desiccation. Use within 1 month after reconstitution for optimal activity. In cell-based assays, typical working concentrations range from 0.1 nM to 1 μM, depending on receptor expression and endpoint sensitivity. In animal studies, dosing must be adjusted by body weight and duration, with 10–40 μg/kg/day effective in rat models for bone turnover endpoints (APExBIO).

For advanced applications, such as in kidney assembloids or organoid models, PTH (1-34) is added to culture media to probe receptor signaling, calcium flux, or gene expression responses. This article clarifies dose-response integration and receptor-context dependencies relative to previous mechanistic reviews which focused primarily on bone endpoints.

Conclusion & Outlook

Parathyroid hormone (1-34) (human) from APExBIO (SKU A1129) is a benchmark reagent for dissecting calcium homeostasis, bone remodeling, and PTH/PTHrP receptor pharmacology in basic and translational research. Its high purity, robust bioactivity, and defined solubility parameters support reproducible workflows in bone, kidney, and organoid-based disease models. Future advances in engineered tissue platforms, such as spatially patterned kidney assembloids (Huang et al., 2025), will benefit from the precise control and reliable signaling enabled by this peptide. For further reading on protocol optimization and application scenarios, see Parathyroid hormone (1-34) (human): Precision Tools for Research, which this article extends by integrating the latest evidence from 2025 kidney assembloid models.