Catecholamine contents and activities of catecholamine synthesizing and inactivating enzymes in the salivary glands of young growing rats

The catecholamine concentrations and activities of tyrosine hydroxylase, DOPA decarboxylase, dopamine β-hydroxylase, catechol 0-methyltransferase and monoamine oxidase in the submandibular and sublingual glands of developing rats ranging in age from 1 to 70 days were measured. The total concentration of catecholamines and the total activities of tyrosine hydroxylase and monoamine oxidase increased markedly up to 56 days and then remained at about the same levels. The total activities of dopamine β-hydroxylase increased steadily between 1 and 70 days of age. The total activity of DOPA decarboxylase increased rapidly to approximately 55-fold up to 21 days of age, thereafter decreasing markedly and at 70 days of age was only 2.6-fold higher than that at 1 day of age, probably because endogenous inhibitors are present in the submandibular gland of rats older than 42-days. The total activity of catechol 0-methyltransferase increased 38-fold up to 56 days of age, and thereafter decreased. Catecholamine concentrations and activities of the enzymes per unit weight reached maximal levels at the age of 14 or 21 days except for catechol 0-methyltransferase which reached maximal activity at 42 days of age. After 14 days, the catecholamine concentrations remained at almost the same level. The activity of dopamine β-hydroxylase and catechol 0-methyltransferase increased 2–3-fold reaching maxima at 21 and 28 days respectively. The monoamine oxidase activity remained at about the same level after birth.