Modification of plasma dopamine-beta-hydroxylase activity by adrenal and pineal extirpations, and time of day dependency of changes.

Plasma level of dopamine-beta-hydroxylase (DBH; EC 1.14.2.1) activity has been considered important both as a diagnostic aid and as an indicator of temporal changes in sympathetic activity. The present study sought to evaluate the possible dependency of some phases of the circadian rhythm in plasma DBH on adrenal and pineal glands. Male Holtzman (albino) rats were shamoperated, adrenalectomized (AX), pinealectomized (PX) or both adrenalectomized and pinealectomized (AXPX) at 32-35 days of age and after acclimation to controlled conditions with a fixed, 12-h, daily photoperiod (LD 12:12). Animals were killed at selected times 15 days postoperatively, and plasma DBH was measured using a sensitive radioenzymatic method. Results from two successive experiments showed that there was significant reduction in plasma DBH in the AXPX animals, but that this was evident only during the middle of the dark phase. PX and AX alone did not bring about any change in the DBH activity at any of the two times tested. These results show that combined endocrine manipulations can alter the circulatory DBH activity level and that such changes can be evaluated only within the definition of a circadian pattern.