Endocrine rhythms in patients with restless legs syndrome

There is increased evidence that the dopaminergic system plays a major role in the pathophysiology of the restless legs syndrome (RLS). Dopamine is the major inhibitory factor of prolactin release and also influences growth hormone (hGH) secretion. The aim of this study was to measure the endocrine activity of RLS patients, to compare it with that of normal subjects and to detect possibly altered patterns of hormonal secretion in RLS patients. Prolactin, hGH and cortisol plasma levels were measured every 20 min for 24 hours in 10 male never-medicated RLS patients (aged 56 +/- 6 years) who have had mild to moderate symptoms for 15 +/- 10 years and in 8 age-matched male controls (aged 57 +/- 5 years). The blood samples taken during the night were paralleled by polysomnographic recordings including the assessment of periodic leg movements (PLM). Plasma levels as well as frequency and amplitude of the pulses of prolactin, hGH and cortisol were not different between RLS patients and controls. Both groups showed the same rhythms during the night- and daytime for all hormones. Cross correlations resulted in high correlation coefficients for each hormone at lag 0 (0.964,0.943 and 0.971 for mean locations of cortisol, hGH and prolactin, respectively). Concerning sleep parameters, there were no significant differences between the two groups apart from a higher PLMS arousal index in RLS patients (25.9 +/- 17.1) compared with the controls (12.0 +/- 9.2; p < 0.05). It is suggested that a possible dysfunction of the dopaminergic system in RLS does not affect the release of prolactin and hGH from the pituitary gland.