Melanocortin system, sexual health
Libido.
Melanocortin receptor agonists acting centrally on sexual behaviour and erectile mechanisms. Includes FDA-approved (PT-141) and unapproved (Melanotan II) substances.
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PT-141
Bremelanotid
PT-141 (bremelanotide) is a synthetic cyclic heptapeptide and an agonist at melanocortin receptors, particularly MC3R and MC4R. It is a metabolite of Melanotan II but contains no acetyl group at the N-terminus. Unlike peripheral vasodilators (e.g. PDE-5 inhibitors), PT-141 acts primarily centrally via the hypothalamus and other CNS areas involved in regulating sexual desire. MC4R activation in the hypothalamus is postulated as the main mechanism of its pro-sexual effect.
Melanotan II
MT-2
Melanotan II is a synthetic cyclic heptapeptide and a non-selective agonist at melanocortin receptors (MC1R, MC3R, MC4R, MC5R). Activation of MC1R in melanocytes stimulates melanin synthesis, leading to increased skin pigmentation. MC4R activation in the hypothalamus is associated with effects on sexual desire and erectile mechanisms. Unlike PT-141 (bremelanotide, a metabolite), Melanotan II has broader receptor selectivity and an additional N-terminal acetylation, resulting in a different side-effect profile.
Kisspeptin
Kisspeptin-10
Kisspeptin is a neuropeptide derived from the KISS1 gene, occurring in several biologically active forms (KP-10, KP-13, KP-14, KP-54). It binds the G-protein-coupled receptor KISS1R (formerly GPR54) on hypothalamic GnRH neurons and is regarded as a central regulator of pulsatile GnRH release — the master pacemaker of the hypothalamic-pituitary-gonadal axis. Kisspeptin mediates the activation of puberty, governs the cyclic release of LH/FSH and mediates the negative and positive feedback mechanisms of sex hormones at the hypothalamic level. Exogenous kisspeptin administration reliably stimulates LH and FSH pulses and, downstream, testosterone and oestrogen.
Gonadorelin (GnRH)
Gonadorelin
Gonadorelin is the synthetic form of the body's own gonadotropin-releasing hormone (GnRH), a decapeptide from the hypothalamus. It binds to GnRH receptors in the pituitary gland and there governs the release of the gonadotropins LH and FSH. The pattern is decisive: pulsatile administration stimulates the gonadotropic axis, whereas continuous, sustained stimulation paradoxically down-regulates it (desensitisation).
HCG
Humanes Choriongonadotropin
Human chorionic gonadotropin (HCG) is a glycoprotein hormone of two subunits (α and β), produced by the placenta during pregnancy. Its β-subunit resembles luteinising hormone (LH); HCG therefore binds to the LH receptor. In men it stimulates the Leydig cells of the testes to produce testosterone; in women it stimulates the ovaries (ovulation trigger). In fertility medicine it is used to mimic the body's own gonadotropic action.
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