Development of tetrahydrobiopterin and GTP cyclohydrolase in salivary glands of rats.

A significant amount of 5,6,7,8-tetrahydrobiopterin (BH4), an essential cofactor of tyrosine hydroxylase, and the activity of GTP cyclohydrolase (GTP cycl), the first and rate-limiting enzyme in BH4 biosynthesis, were found in rat salivary glands, in which adrenergic transmitters are localized, from day 4 through 56 after birth. About 90 ng of BH4 per g wet weight were determined in the glands (submandibular and sublingual) of adult rats. The levels of them which were maintained from 2 weeks after birth up to the adult stage correlated with a previous finding in the maintenance of catecholamine concentration during the same stage in rat salivary glands.