Circadian variation of catecholamine excretion in rats: correlation with locomotor activity and effects of drugs.

Rats housed in metabolic cages were used to study the circadian variation in the urinary excretion of free catecholamines. Small samples of urine (25-100 microliter) were analyzed for adrenaline, noradrenaline and dopamine by high pressure liquid chromatography (HPLC) and electrochemical detection. Various ways in which the values for excretion of catecholamines can be expressed (per min; per ml; per mmol creatinine; as ratio over dopamine) were calculated and discussed. Correction for excretion of creatinine resulted in the lowest variations coefficient among the experimental data. The correction for creatinine removed the circadian rhythm present in the output of noradrenaline (NA) and dopamine (DA). Adrenaline corrected for creatinine still displayed a pronounced circadian variation which was related to the overall locomotor activity of the animals (as recorded by photocells). Collection of 1 hr samples instead of 3 hr samples resulted in a worsening of the relationship between the excretion of adrenaline and locomotor activity. Finally, the possibility that the DA antagonist haloperidol, the DA agonist dipropyl-5,6-2-amino-6,7-dihydroxytetrahydronaphtalene (dipropyl-5,6 ADTN) and the alpha-antagonist phentolamine, could modify the excretion of free urinary catecholamines was investigated. Haloperidol and 5,6-dipropyl-ADTN did not change the output of the catecholamines, but phentolamine induced a strong increase in the excretion of NA. The latter observation suggest that at least part of the excretion of NA may originate from peripheral noradrenergic neurotransmission.