Arginine enhances the growth hormone-releasing activity of a synthetic hexapeptide (GHRP-6) in elderly but not in young subjects after oral administration - Ghigo, E; Arvat, E; Rizzi, G; Bellone, J; Nicolosi, M; Boffano, G M; Mucci, M; Boghen, M F; Camanni, F (J Endocrinol Invest, 1994)