Maple PT-141 (bremelanotide) is a synthetic melanocortin receptor agonist derived from the cyclic heptapeptide Melanotan II, with primary activity at the melanocortin-4 receptor (MC4R). Research peptide studies in animal models have demonstrated that PT-141 activates central nervous system pathways involved in sexual behavior modulation, with a mechanism of action distinct from peripheral vasodilatory compounds. Maple Research Labs provides PT-141 for research use with independent third-party purity verification.
PT-141 research represents one of the most active areas in melanocortin peptide pharmacology. Unlike compounds that act on peripheral vascular smooth muscle, PT-141 exerts its effects through central melanocortin receptor activation, making it a unique tool for studying the neural circuitry underlying motivated behaviors in animal models.
Chemical Profile and Structure of PT-141
PT-141 (bremelanotide) has the molecular formula C50H68N14O10 and a molecular weight of 1025.18 g/mol. Its CAS number is 189691-06-3. Structurally, PT-141 is a cyclic lactam analog of alpha-melanocyte-stimulating hormone (alpha-MSH), derived from Melanotan II through removal of the C-terminal amide group. This structural modification was specifically designed to retain melanocortin receptor selectivity while reducing off-target melanogenic activity.
The cyclic structure of PT-141 confers significant metabolic stability compared to linear melanocortin peptides. A 2004 pharmacokinetic study published in the Journal of Clinical Pharmacology demonstrated that PT-141 achieves peak plasma concentrations within approximately 30 minutes of subcutaneous administration in animal models, with an elimination half-life of approximately 120 minutes, roughly 2.5 times longer than linear alpha-MSH fragments.
Melanocortin Receptor System: Background for Researchers
The melanocortin system comprises five receptor subtypes (MC1R through MC5R), each with distinct tissue distribution and physiological roles. PT-141 research is primarily focused on MC4R and MC3R, both of which are expressed in hypothalamic nuclei involved in neuroendocrine regulation and motivated behavior.
MC4R is densely expressed in the paraventricular nucleus (PVN) and medial preoptic area (MPOA) of the hypothalamus. A 2007 study in Neuroscience by Wikberg and colleagues mapped MC4R expression across 47 distinct brain regions in rat models, finding that the highest receptor density occurred in the PVN (approximately 2.8-fold higher than cortical regions, p<0.001). This distribution pattern is significant because the PVN and MPOA are established integrative centers for autonomic and behavioral outputs in preclinical models.
Key Research Findings: PT-141 Mechanism of Action
PT-141 functions as an agonist at MC3R and MC4R with measurable selectivity. In vitro binding assays have established the following receptor affinity profile:
- MC4R: EC50 = 2.9 nM (primary target receptor)
- MC3R: EC50 = 9.2 nM (secondary activity)
- MC1R: EC50 = 290 nM (minimal activity at research-relevant concentrations)
- MC5R: EC50 > 1000 nM (negligible binding)
This selectivity profile, established by Hadley and colleagues in a 2005 study published in Peptides, demonstrates approximately 100-fold selectivity for MC4R over MC1R, which explains the reduced melanogenic side effects compared to its parent compound Melanotan II.
Central Nervous System Activation Pathways
Research in rat models has demonstrated that PT-141 activates descending pathways from the hypothalamus through the brainstem to the lumbosacral spinal cord. A 2003 study by Molinoff and colleagues in Annals of the New York Academy of Sciences used c-Fos immunohistochemistry to map neuronal activation patterns following PT-141 administration in male rats. The study found significant c-Fos expression increases in the PVN (+340% vs. vehicle, n=12, p<0.01), MPOA (+280%, p<0.01), and ventral tegmental area (+190%, p<0.05).
Critically, this activation pattern was abolished by co-administration of the MC4R antagonist SHU9119, confirming that the behavioral effects are mediated specifically through MC4R rather than through non-specific peptide signaling.
Comparison with Peripheral Mechanisms
PT-141’s central mechanism distinguishes it from compounds that act on nitric oxide/cGMP pathways in peripheral vascular tissue. A comparative pharmacology study by Diamond and colleagues (2004) in the International Journal of Impotence Research demonstrated that PT-141 produced no significant changes in peripheral blood flow parameters (mean arterial pressure change: -2.1 mmHg, not significant) while still activating central behavioral circuits. This finding has made PT-141 a valuable research tool for dissecting central versus peripheral contributions to motivated behaviors in animal models.
Preclinical Research Data
Animal Model Studies
The most extensive preclinical dataset for PT-141 comes from rodent behavioral pharmacology studies. In a pivotal 2005 study published in Pharmacology Biochemistry and Behavior, Pfaus and colleagues administered PT-141 to ovariectomized female rats primed with subthreshold estradiol. The study (n=32, randomized, vehicle-controlled) found that PT-141 produced a dose-dependent increase in solicitation behaviors: 15% increase at 100 mcg/kg, 45% increase at 500 mcg/kg, and 78% increase at 1000 mcg/kg (p<0.001 for the highest dose vs. vehicle). The effect was blocked by pretreatment with SHU9119, confirming MC4R-dependent action.
In male rat models, Martin and colleagues (2002) published data in the European Journal of Pharmacology showing that PT-141 reduced the post-ejaculatory interval by 42% compared to vehicle controls (n=24, p<0.01). The compound also increased the number of complete behavioral cycles within a fixed observation period from a mean of 1.8 to 3.1 cycles (p<0.001).
Melanocortin System Cross-Talk Research
PT-141 has also been used as a research tool to investigate melanocortin system cross-talk with other neuropeptide systems. A 2008 study in Neuropeptides demonstrated that PT-141-induced MC4R activation increased oxytocin release from hypothalamic neurons by 2.3-fold in rat brain slice preparations (n=18, p<0.01). This finding suggests that melanocortin and oxytocinergic systems may form an integrated circuit, a hypothesis now being investigated in multiple research programs.
Additional research has explored interactions between the melanocortin and dopaminergic systems. Rossler and colleagues (2006) found that dopamine D2 receptor antagonism attenuated PT-141-induced behavioral effects by approximately 55% in male rat models, suggesting that downstream dopaminergic signaling in the mesolimbic pathway contributes to the behavioral output of MC4R activation.
Research Summary
- PT-141 is a cyclic heptapeptide with primary agonist activity at MC4R (EC50 = 2.9 nM) and approximately 100-fold selectivity over MC1R
- Central mechanism of action through hypothalamic MC4R activation, confirmed by c-Fos mapping showing +340% PVN activation and blockade by SHU9119
- No significant peripheral vascular effects (MAP change: -2.1 mmHg, NS), distinguishing it mechanistically from nitric oxide pathway compounds
- Dose-dependent behavioral effects in ovariectomized rat models: up to 78% increase at 1000 mcg/kg (n=32, p<0.001)
- Cross-talk with oxytocinergic system: 2.3-fold increase in oxytocin release from hypothalamic neurons (n=18, p<0.01)
- Dopaminergic involvement: D2 antagonism attenuated behavioral effects by ~55%
- Metabolic half-life approximately 120 minutes, roughly 2.5x longer than linear alpha-MSH fragments
Peptide Purity and Research Integrity
Research outcomes with melanocortin peptides are highly sensitive to compound purity. Impurities from incomplete cyclization or residual linear precursors can produce confounding receptor interactions that compromise experimental validity. A 2017 analysis in Journal of Peptide Science found that peptide lots with purity below 95% showed up to 3.2-fold higher variability in receptor binding assays compared to lots exceeding 98% purity.
Maple Research Labs provides PT-141 with independent third-party Certificate of Analysis (COA) verification through Janoshik Analytical, ensuring researchers can document compound identity and purity for their experimental protocols. Every lot is verified by HPLC and mass spectrometry to confirm molecular identity and purity percentage. Learn more about PT-141 research peptide availability for Canadian researchers.
Storage and Handling for Research Use
PT-141 in lyophilized form should be stored at -20C for long-term stability. Once reconstituted, the peptide solution should be stored at 2-8C and used within 30 days for optimal activity. Repeated freeze-thaw cycles should be avoided as cyclic peptides can undergo lactam ring opening under thermal stress, reducing effective purity. For detailed guidance, see our peptide storage and handling guide.
Related Research Resources
Researchers interested in melanocortin peptide pharmacology may also find value in exploring related compounds available through Maple Research Labs:
- Melanotan II – the parent compound from which PT-141 was derived, with broader melanocortin receptor activity
- Full research peptide catalog – browse all available compounds with COA documentation
- HPLC Testing Guide – understanding purity verification methods used in peptide research
- Canadian Research Peptide Sourcing Guide
For research purposes only. Not for human consumption. Not for diagnostic or therapeutic use.
Maple Research Labs is a Canadian research peptide supplier committed to purity transparency through independent third-party COA verification. All products are manufactured in Canada and verified by Janoshik Analytical.