Scientific Glossary

GnRH is released in pulses from the hypothalamus, stimulating pituitary gonadotroph cells to release LH and FSH. LH triggers testosterone production (in males: Leydig cells; in females: corpus luteum) and FSH drives sperm and follicle development. Critically, continuous (non-pulsatile) GnRH receptor stimulation causes receptor downregulation and hormone suppression — this is exploited therapeutically with GnRH agonists for prostate cancer. PT-141 (bremelanotide) acts upstream via melanocortin receptors to influence sexual arousal pathways.

Kisspeptin neurons in the hypothalamus (arcuate nucleus and AVPV) integrate metabolic and hormonal signals to regulate GnRH pulse frequency and amplitude. Kisspeptin-10 and Kisspeptin-54 are research variants studied for their role in reproductive endocrinology, sexual behavior, and HPA axis regulation. Kisspeptin administration in human studies robustly stimulates LH release. Research interest in kisspeptin spans reproductive disorders, psychosexual function, and understanding metabolic-reproductive axis interactions.

Pulsatile secretion is physiologically important because continuous receptor stimulation leads to desensitization. The pituitary gland releases GH in 6-12 pulses per day (largest pulse shortly after sleep onset). GnRH must be pulsatile to maintain gonadotropin secretion — continuous GnRH agonist exposure paradoxically suppresses LH/FSH. Research into GHRH and GHRP combinations aims to amplify these natural GH pulses rather than create continuous supraphysiological exposure. Mimicking natural pulsatile patterns is a key design principle in hormone research.

When receptors are continuously exposed to high levels of an agonist, cells often compensate by reducing the number of receptors on the cell surface (downregulation) or making existing receptors less responsive (desensitization). This is why research studies often use pulsatile or cyclical administration rather than continuous exposure. For example, GHRH receptors downregulate with continuous GHRH stimulation — this is why pulse administration is studied more than continuous infusion for GH secretagogues.