Sulphate conjugation limits fluctuations in free catecholamines in phaeochromocytoma

More than 80% of total noradrenaline (NA) and adrenaline (A) and nearly 100% of dopamine (DA) circulate in blood as sulphates, and it has been proposed that sulphate conjugation contributes to the inactivation of catecholamines (CA). Sulphate conjugation rapidly responds to changes in sympathetic activity and may buffer the haemodynamic and metabolic consequences of wide fluctuations in CA release in phaeochromocytoma. This hypothesis was tested in seven patients with phaeochromocytoma by consecutive measurements of plasma-free and conjugated NA, under resting conditions, before operation and at least 4 weeks after tumour removal. Free and total (free + sulphates) NA were markedly elevated before compared with 1-4 months after surgery. Similar elevations were seen in free and total A and free DA. Before surgery consecutive measurements of total NA, 5 min apart, were markedly different (17 +/- 4.1 and 13.7 +/- 4.4 ng/ml, respectively), whereas only small differences in free NA levels were present (4.1 +/- 1.5 and 4.3 +/- 1.8 ng/ml). These differences between total and free levels were also apparent for A and DA, but to a lesser degree. In three patients, fluctuations in total NA concentration greater than 12 ng/ml were associated with either no change (one patient) or changes of 0.6 and 2.8 ng/ml in free levels for the other two patients, respectively. Mean blood pressure (BP) varied less than 8 mmHg in these patients. These findings suggest that sulphate conjugation is a dynamic process which may limit wide fluctuations in free CA concentration during episodic secretory activity in phaeochromocytoma.