Plasma homovanillic acid and prolactin in systemic lupus erythematosus

Prolactin (PRL) is an important immunoregulator and might have a role in the pathogenesis of systemic lupus erythematosus (SLE). The regulation of pituitary prolactin secretion is complex and involves a negative feedback process in the hypothalamus, in which dopamine plays the principal role. However, the main source of serum prolactin in lupus patients is still not clearly established. Since homovanillic acid (HVA), the principal metabolite of dopamine (DA), is removed from the brain into the blood, it would indirectly reflect DA metabolism. It is assumed that the turnover of a neurotransmitter can be determined through an analysis of its metabolites. The objective of this study was to analyse plasma samples from SLE patients to see if there were any alterations in neurally functioning DA through its principal metabolite, HVA. We also measured the levels of PRL and compared HVA and PRL with the clinical activity of the disease. Twenty-four SLE patients and fifteen healthy controls were studied. The investigation was done over a period of 3 months. The results of this study show significantly low levels of HVA in lupus patients compared to controls (P < 0.0001). This corresponds to a decrease in dopamine turnover. Hyperprolactinemia was observed in nine patients, and the average level of prolactin in lupus patients was higher than in healthy controls (P < 0.001). For the duration of the study, a significant percentage of variation was observed in the levels of HVA in the clinically active patients (P < 0.05) compared to inactive patients. When PRL was compared in these groups, throughout the study, no significant percentage of variation was observed. The relationship between HVA and PRL in healthy controls was r = 0.47, P = 0.08, and in patients was r = 0.04, P = 0.84. It is suggested that there is a probable association between plasma levels of HVA and PRL in the healthy controls and not in the SLE patients.