PT-141 (Bremelanotide) (10mg)

PT-141 Peptide and Reproductive Functions

Initial investigations into PT-141, also known as Bremelanotide, revealed its agonistic activity toward melanocortin receptors, akin to the natural hormone alpha-MSH. Comprising seven amino acids, this cyclic synthetic peptide is derived from the metabolism of melanotan II. Early studies indicated that melanocortin hormones play a role in regulating various physiological functions, with a particular focus on reproductive processes. Administration of PT-141 to test animals reportedly led to heightened reproductive functions, making it a focal point of ongoing research in the field.

Overview

Research findings propose that PT-141 exhibits agonistic effects on melanocortin receptors, specifically MC3R and MC4R, potentially triggering heightened responses in the central nervous system. MC3R, predominantly expressed in the hypothalamus, is speculated to play a role in energy homeostasis and might modulate the actions of other melanocortin receptors in this region. It is further hypothesized that MC3R could influence feeding behavior, impacting appetite, food intake, and participating in metabolic processes such as glucose and lipid regulation. On the other hand, MC4R is considered crucial in appetite control and energy expenditure, potentially contributing to weight reduction upon activation. Additionally, MC4R is tentatively associated with reproductive functions, including the potential regulation of penile tissues and overall reproductive behavior. Notably, researchers suggest that PT-141 binding with MC3R and MC4R receptors leads to the activation of neurons in the hypothalamus, resulting in increased immunoreactivity and potentially stimulating sexual arousal in murine models.

PT-141 Chemical Makeup

Molecular formula: C50H68N14O10
Molecular weight: 1025.2 g/mol
Other Known Titles: Bremelanotide

Scientific Investigations and Clinical Trials

PT-141 Peptide Exploratory Investigations

In this early exploration conducted around the year 2000, a study aimed to investigate the potential impact of PT-141 peptide on sexual behavior in murine models. The study employed female rats as subjects to assess how the peptide might influence various aspects of their sexual behavior.(5) Upon administration, the female rats reportedly displayed an increase in sexual desire, with no discernible changes in sexual pace, lumbar lordosis, or other related behaviors. The analysis conducted by researchers suggested that PT-141 may not have a direct effect on generalized motor activation but could exert a selective pharmacological influence, possibly stimulating the central nervous system, particularly melanocortin receptor activities. This stimulation was hypothesized to result in heightened sexual arousal. The researchers concluded that “The ability of PT-141 to enhance solicitation in two distinctive testing environments indicates that the effect is selective and stable, and suggests that central melanocortin systems are part of the neurochemical network that evokes appetitive sexual behavior in female rats.”(5)

PT-141 Peptide and Erectile Response Mechanism

The potential interaction of PT-141 with MC4R may induce an upregulation in the production of vasodilators, such as nitric oxide (NO), within penile tissues, contributing to improved erectile potential, as suggested by research findings.⁽⁶⁾ Recognized as a metabolite of Melanotan-2 (MT-II), both PT-141 and MT-II seem to activate similar receptors. Previous studies have proposed that melanocortin agonists might elicit concentration-dependent increases in cavernosal pressure. An agent known as SHU 9119, presumed to be a non-selective antagonist of MC3R and MC4R, did not appear to significantly affect cavernosal or systemic blood pressure but seemingly counteracted the induced increases in cavernosal pressure by melanocortin agonists. This agent also inhibited the depressor response produced by melanocortin agonists. Furthermore, when a combination of phentolamine mesylate, papaverine, and PGE1 was introduced directly into cavernosal tissue, it reportedly resulted in a 4-fold increase in cavernosal pressure. The study also explored the potential role of the NO-cyclic GMP-dependent pathway in the melanocortin agonists-induced increases in cavernosal pressure. Bilateral transection of pudendal nerves and NO synthase inhibition using L-NAME were employed, suggesting that either removing pudendal nerves or pretreating with L-NAME might negate melanocortin agonists-induced increases in intracavernosal pressure in anesthetized murine models. The gathered data tentatively inferred that the activation of central melanocortin receptors by melanocortin agonists might increase cavernosal pressure, possibly achieved through the neuronal release of NO.⁽⁶⁾

PT-141 Peptide and Neuroanatomical Specificity

Explorations into PT-141 have been directed at unraveling the peptide’s potential impact on the central nervous system (CNS), with a particular focus on select brain regions.⁽⁷⁾ A study conducted in murine models with heightened levels of female reproductive hormones delved into the sexual behaviors of rats, specifically appetitive behaviors such as increased pace and agitation, along with consummatory behaviors like lordosis. Following the introduction of the peptide, increased appetitive behavior of solicitation was observed, leaving the sexual pace and lordosis seemingly unaffected. Notably, PT-141’s actions were noted after both peripheral and direct introductions into the lateral ventricles or medial preoptic area (mPOA), excluding the ventromedial hypothalamus. The mPOA, considered a significant region for displaying appetitive sexual behaviors across species, is an ongoing area of exploration. Peripheral introduction of PT-141 appeared to activate the mPOA and other hypothalamic and limbic brain regions linked to sexual behavior. The study suggests that PT-141 might operate by potentially activating dopamine terminals in the mPOA, although further research is warranted for confirmation. Researchers remarked that the peptide “appears to possess the behavioral, pharmacological, and neuroanatomical specificity required” for potential influence on sexual function.⁽⁷⁾

Exploring the intricacies of these mechanisms, a comprehensive study utilized psychometric evaluations, functional neuroimaging techniques, and hormonal analyses. This randomized, double-blinded, placebo-controlled, crossover clinical investigation sought to assess the effects of MC4R agonism on sexual brain processing. Results suggested that MC4R agonists, exemplified by PT-141, could potentially heighten sexual desire for up to 24 hours when compared to a placebo. Notably, during the functional neuroimaging phase, MC4R agonism seemingly enhanced activity in the cerebellar and supplementary motor areas while potentially deactivating the secondary somatosensory cortex, particularly in response to erotic stimuli, in contrast to the placebo. Additionally, MC4R agonists were hypothesized to enhance the functional connectivity between the amygdala and the insula when subjects were exposed to erotic stimuli, further distinguishing them from the placebo. These findings contribute to a deeper understanding of how MC4R agonists like PT-141 might impact sexual brain processing, offering valuable insights into the exploration of this peptide class.⁽⁸⁾
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