Rythmes endocriniens en période de dépression et de rémission

Les rythmes circadiens dans la dépression

Les auteurs font une présentation générale des connaissances sur les troubles des rythmes circadiens dans la dépression et en proposent une synthèse. Ils soulignent d’abord les difficultés méthodologiques de ces éludes: difficultés liées à la nécessité du recueil d’un nombre considérable de données et difficultés pour analyser ces données et vérifier que les différences observées correspondent bien é des cycles circadiens.

Ils envisagent ensuite les troubles des phases, des taux moyens et des amplitudes. Les phases des cycles circadiens ont été beaucoup étudiées surtout après la proposition du concept d’avance de phase comme caractéristique propre de la dépression, qui avait été faite par Wehr en 1980. II semble actuellement que, plus qu’une avance de phase, ce qui caractérise la dépression c’est une désorganisation des phases. Les taux moyens sont souvent modifiés. Parlois diminués (mélatonine), parfois augmentés (cortisol). Les amplitudes des oscillations sont le plus souvent diminuées. Cette constatation, plus récente que les précédentes, semble être de première importance. Moins un rythme est ample, moins il est stable. Il est possible que désynchronisation et diminution d’amplitude soient deux manifestations d’une «faiblesse» des rythmes circadiens qui serait leur caractère principal dans la dépression.

Ces anomalies n’existent pas que dans la dépression, mais c’est dans son cas qu’elles sont le plus manifestes. En général, elles disparaissent en période de rémission clinique. Pour expliquer ces perturbations, il semble qu’il faille envisager à la fois un trouble de la sensibilité aux synchroniseurs externes et un trouble des systèmes de contrôle interne des rythmes.

Circadian variations in response to protirelin test in major depressive episode

We studied circadian thyrotropin (TSH) and prolactin (PRL) response to synthetic thyrotropin-releasing-hormone (protirelin) infusion (200μg IV) at 8 am and 11 pm in 35 drug-free inpatients with DSM III-R Major Depressive Episode and in 22 hospitalized controls. In each group, maximum TSH and PRL responses were lower at 8 am than at 11 pm. The difference between 11 pm-ΔTSH and 8 am-ΔJTSH (ΔΔTSH) was significantly lower in depressed patients compared to controls. No such blunting was observed in PRL responses to protirelin in depressed patients. In the overall population, TSH response to protirelin (ie8 am-ΔTSH, 11 pm-ΔTSH,ΔΔTSH) correlated significantly with TSH circadian parameters (iemesor and amplitude). These correlations were also observed with PRL (except forΔΔPRL). TSH mesor and amplitude were lower in depressives than in controls. In contrast, PRL mesor and amplitude were not significantly different between diagnostic groups.ΔΔTSH is thus a chronobiological refinement to the measure of thyroid axis dysfunction in major depression. The blunted TSH response to protirelin suggests that the TRH receptors of the pituitary thyrotrophs are hyposensitive in major depression.

Melatonin excretion with affect disorders over age 60

Numerous studies have reported low melatonin secretion in depression, but other studies have suggested no deficit or an increase. Alterations of circadian phase or duration of melatonin secretion have also been described. Since melatonin secretion decreases as we age, it seemed interesting to examine melatonin and depression in an aging sample. Volunteers who complained of mood or sleep problems were recruited for studies in which fractional urine specimens were collected for 24 h, both at home and in the laboratory. The major metabolite, 6-sulfatoxymelatonin (aMT6s), was determined by radioimmunoassay. Of 72 volunteers aged 60-78 years, seven had current major depression and 55% had a lifetime history of an affective disorder. A 55-fold range of home aMT6s excretion rates was observed. A lifetime history of any affective disorder was significantly associated with greater log(10)[mesor] aMT6s excretion in home collections and laboratory collections, but current affective disorders were neither significantly related to melatonin excretion nor to aMT6s acrophase timing, onset, offset or duration. These results are only weakly consistent with a photoperiodic hypothesis of depression.

[Sleep and biological rhythms in depression. Changes caused by antidepressants]

Sleep in depression is characterized by an increase in the number and duration of awakenings, sleep instability, and SWS decrease. REM sleep occurs earlier. REMs density during the 1st REM period is higher than in normal controls matched in age. Accordingly, sleep in depression is similar to sleep in normal aging. Endogenous depression cannot be distinguished from other types of depression by means of polygraphic criteria. Sleep recordings at the beginning of tricyclic compound treatment could be predictive of clinical response to treatment. Sleep modifications induced by antidepressive drugs are reviewed. Sleep recordings enabled us to formulate several physiopathological hypotheses of depression mechanisms: cholinergic-aminergic hypothesis, phase advance, deficiency of process S. Other hypotheses are reviewed: flattening of a hypothetical circadian rhythm of arousal, depressogenic property of sleep in itself (or only of SWS) or timing delay for the start of sleep. A significant phase advance of biological rhythms (temperature, cortisol) is rarely found. A reduction in the amplitude of rhythms (temperature, TSH, melatonine) is more frequent.

Nocturnal melatonin and cortisol secretion in newly admitted psychiatric inpatients. Implications for affective disorders

Melatonin secretion has been suggested as a marker of both circadian and noradrenergic dysfunction in affective disorders. Seventy-two newly admitted psychiatric inpatients [49 with major depressive disorder (MDD), 12 with schizophrenia, and 11 with intermittent depressive disorder (IDD)] underwent neuroendocrine screening at 0200, 0800, 1600 and 2300 hours prior to and the day following dexamethasone administration. All groups showed a drop in cortisol following dexamethasone. Dexamethasone nonsuppression was found in 20 of 49 patients with MDD, in none of the schizophrenics and in none of those with intermittent depressive disorder. Mean melatonin levels decreased significantly after the administration of dexamethasone across all four groups. Overall, the schizophrenic group had a significantly greater mean melatonin level than each of the other three groups, whereas the three depressive groups did not differ significantly from one another. Only at 2300 hours did both the schizophrenic group and the MDD patients with normal dexamethasone suppression show significantly greater melatonin levels than the MDD patients with dexamethasone nonsuppression or the IDD group. The observed trend for a low circadian melatonin profile in IDD patients with superimposed personality disorders is puzzling.