Serotonin and Melatonin Lower Progesterone

Also see:
Melatonin Lowers Body Temperature
Tryptophan, Sleep, and Depression
Carbohydrate Lowers Free Tryptophan
Gelatin > Whey
Serotonin, Fatigue, Training, and Performance
Gelatin, Glycine, and Metabolism
Whey, Tryptophan, & Serotonin
Tryptophan Metabolism: Effects of Progesterone, Estrogen, and PUFA

In 1994 A.V. Sirotkin found that melatonin inhibits progesterone production but stimulates estrogen production, and it’s widely recognized that melatonin generally inhibits the thyroid hormones, creating an environment in which fertilization, implantation, and development of the embryo are not possible. This combination of high estrogen with low progesterone and low thyroid decreases the resistance of the organism, predisposing it to seizures and excitotoxic damage, and causing the thymus gland to atrophy. -Ray Peat, PhD

Although melatonin sometimes antagonizes serotonin in a protective way, in itself it can lower body temperature and alertness, suppressing thyroid and progesterone. (Sirotkin, 1997) -Ray Peat, PhD

Exp Clin Endocrinol Diabetes. 1997;105(2):109-12.
Melatonin and serotonin regulate the release of insulin-like growth factor-I, oxytocin and progesterone by cultured human granulosa cells.
Schaeffer HJ, Sirotkin AV.
The direct influence of indoleamines on ovarian peptide hormones and growth factor secretion, in contrast to steroidogenesis, is yet to be thoroughly investigated. The aim of our in vitro experiments was to investigate the influence of melatonin and serotonin (5-hydroxy-tryptamine) (0.01-10 micrograms/ml) on the release of insulin-like growth factor-I (IGF-I), oxytocin and progesterone by cultured human granulosa cells. It was observed that both melatonin and serotonin stimulate IGF-I release. Melatonin also stimulated oxytocin output. Serotonin increased oxytocin secretion only at the highest dose (10 micrograms/ml). Both melatonin and serotonin were potent inhibitors of progesterone release. The present results suggest a possible involvement of the indoleamines melatonin and serotonin in the direct regulation of growth factor, nonapeptide and steroid hormone secretion by human ovarian cells.