NEUROENDOCRINE ASPECTS OF PRIMARY ENDOGENOUS-DEPRESSION .15. MATHEMATICAL-MODELING OF NOCTURNAL MELATONIN SECRETION IN MAJOR DEPRESSIVES AND NORMAL CONTROLS

We previously reported a trend toward a higher mean nocturnal serum me latonin (MEL) concentration, based on 30-min blood sampling over 24 h, in 23 female definite endogenous depressives compared to 23 matched n ormal female control subjects, and no significant difference in 15 mal e depressives compared to their controls (Rubin et al., 1992). In both groups of patients vs. their controls, there also were trends toward an earlier MEL rise time, by about 30 min, and a later MEL peak time, by about 90 min. Because the offset of MEL secretion was not estimated in that study, the total duration of MEL secretion could not be deter mined. To further delineate the nocturnal MEL secretion curve, we mode led the MEL data by a linear-Beta model, a four-parameter adaptation o f the Beta function. One parameter accounted for baseline (diurnal) ME L concentration, two accounted for the shapes of the ascending and des cending phases of the nocturnal secretion curve, and the fourth accoun ted for the area under the curve. The model permitted estimation of th e start, peak, and end times of nocturnal MEL secretion. There again w as a trend toward a higher mean nocturnal MEL concentration in the fem ale depressives compared to their matched controls. There were no sign ificant patient-control differences in secretion onset or peak times i n either the women or the men except for nocturnal MEL offset time: th e female patients had a trend toward a later offset time, by about 40 min, than their controls; this difference was not present in the men. With women and men analyzed together, the difference in nocturnal MEL offset time between patients and controls just reached significance (P < 0.05). The linear-Beta model appears to satisfactorily fit the MEL data and provides estimators of the onset, peak, and offset times of t he activation phase of MEL secretion. This model may be applicable to more severely skewed 24-h hormone secretion curves, such as ACTH and c ortisol. (C) 1997 Elsevier Science Ireland Ltd.