L-tryptophan treatment and the episodic secretion of pituitary hormones and cortisol.

(1) l-Tryptophan, the natural precursor of brain serotonin, was administered to healthy subjects. Plasma free and total tryptophan, somatotropin (growth hormone, GH), follitropin (FSH), lutropin (LH), prolactin and cortisol were analysed after the oral administration of 2 g and 100 mg/kg of l-tryptophan or after 1·28 g of l-leucine, at 08:30 and 11:30. (2) Plasma levels of free and total tryptophan were markedly increased after the oral administration of l-tryptophan. (3) Plasma somatotropin levels were significantly elevated after l-tryptophan treatment at different times of day, but this elevation was not dose-dependent. (4) l-Tryptophan or l-leucine treatment did not affect the pulsatile secretion of follitropin and lutropin. (5) Plasma prolactin was not significantly elevated after the oral administration of l-tryptophan. (6) The morning decline of plasma cortisol was significant with or without l-tryptophan. However, no decline was noticed after l-tryptophan in the middle of day.