PT-141

Central Mechanism: The Brain Desire Circuit

The distinction between PT-141 and conventional sexual health treatments is fundamental:

Peripheral approach (PDE5 inhibitors): Sildenafil/tadalafil inhibit phosphodiesterase 5, increasing cGMP in vascular smooth muscle → vasodilation → improved genital blood flow. They require sexual stimulation. They treat physical response, not desire.

Central approach (PT-141): Activates MC4R in the medial preoptic area (mPOA) and arcuate nucleus of the hypothalamus. MC4R activation:

1. Increases dopamine release in the nucleus accumbens (mesolimbic reward pathway)
2. Activates oxytocin neurons in the PVN
3. Reduces inhibitory signalling from somatostatin interneurons in the mPOA

The result: intrinsic sexual motivation is increased, independent of external stimulation or vascular status.

MC3R vs MC4R: Different Roles

MC4R: Primary mediator of PT-141’s sexual effects. Expressed in the hypothalamus, brainstem, and limbic system. MC4R knockout mice have markedly reduced sexual behaviour. MC4R also regulates energy homeostasis - explaining the mild appetite suppression sometimes noted.

MC3R: Expressed in the limbic system and modulates presynaptic autoinhibition of melanocortin signalling. MC3R activation by PT-141 may contribute to the anxiolytic component of its effects.

FDA Approval Context

The bremelanotide Phase 3 programme (RECONNECT trials) enrolled 1267 premenopausal women with HSDD:

• Primary endpoints: satisfying sexual events and distress scores
• Results: significant improvement in both endpoints vs placebo
• Approval dose: 1.75mg subcutaneous, 45 minutes before anticipated sexual activity, max 1 dose per 24 hours

Storage

Reconstitution: use bacteriostatic water; swirl gently until dissolved, do not shake. After reconstitution: keep refrigerated (2-8°C), protect from light, and use within 30 days.

For research purposes only. Not for human consumption.