Some patients with retinal dystrophies present flat diurnal amplitudes of serum melatonin and atypical oscillations of body temperature

Abstract

Abstract: : Purpose: Disturbances of the subjective day/night–rhythm are frequently reported by patients with hereditary retinal dystrophies. This study was performed to investigate diurnal rhythms of serum melatonin and other physiological parameters in retinal dystrophy patients with residual visual perception. Methods: 11 probands (4 male, 7 female) with retinal dystrophies and 7 control subjects were enrolled in this study. Serum melatonin and several other parameters (body temperature, blood pressure etc.) were monitored during a complete standardized 24–hour period in a controlled clinical environment. Blood samples were taken every two hours. Melatonin was quantitatively analyzed using a standardized RIA. Results: Serum concentrations of melatonin presented a typical diurnal rhythm in all probands enrolled in this study. The nightly acrophase of melatonin occurred within the normal time range (samples 0.00 – 4.00 a. m.) in all cases. During lighted daytime a typical through of melatonin levels was found without exception. No signs of desynchronization or dissociation of the diurnal rhythm of melatonin were found in analyzed periodograms. 6 of 11 patients with retinal dystrophies were presenting relatively flat diurnal amplitudes of serum melatonin concentrations (<25 pg/ml). The daily amplitude of melatonin did not correlate to the state of residual retinal function (visual field, electroretinography, visual acuity). Patients with flat amplitudes of serum melatonin were presenting atypical diurnal periodograms of their body temperature including fast high amplitude oscillations and a decreased day/night temperature amplitude. Conclusions: Results of this study demonstrate that the retina of patients with retinal dystrophies provides sufficient synchronization of the endogenous secretion of melatonin with the dark/light–cycle. The discovery of relatively low diurnal melatonin amplitudes in a proportion of patients suggests that in these individuals a degeneration of the pineal gland may be accompanying the progression of retinal disease. Furthermore our results seem to indicate that melatonin may mediate a physiological low pass filter mechanism towards variant diurnal lightening conditions.

Keywords: retinal degenerations: hereditary • melatonin • circadian rhythms