l-carnitine male fertility benefits Evaluation of Potential in Improvement of Enhancing Male Fertility Through Nutrition:

Differentially expressed between tissues, SLC22A4 is notably highly expressed both on the apical membrane of the small intestine where it functions in a pH-dependent fashion to take ergothioneine up from the diet (Reference Harwood, Zhang and Pathak29) and on the apical membrane of proximal tubular cells in the kidney where it functions in renal reabsorption (Reference Nakanishi, Fukushi and Sato30)

Intern Med 1994;33(2):82-86 7

As yet, there is no direct evidence to suggest that orally administered Glyteine can reach the human brain [17]

Pigeolot, E., Corbisier, P., Houbion, A., Lambert, D., Michiels, C., Raes, M., Zachary, M.O