I M McIntyre

Human Melatonin Suppression by Light is Intensity Dependent

Five intensities of artificial light were examined for the effect on nocturnal melatonin concentrations. Maximum suppression of melatonin following 1 hr of light at midnight was 71%, 67%, 44%, 38%, and 16% with intensities of 3,000, 1,000, 500, 350, and 200 lux (lx), respectively. In contrast to some previous reports, light of 1,000 lx intensity was sufficient to suppress melatonin to near daytime levels, and intensities down to 350 lx were shown to significantly suppress nocturnal melatonin levels below prelight values. On the basis of these data, it is suggested that when examining the melatonin sensitivity of patient groups (such as bipolar affective disorders) to artificial light, an appropriate light intensity should be established in each laboratory. Light of less intensity (e.g., 200–350 lx) may be more suitable to dichotomize patient groups from control subjects.

Serotonergic effects of isatin: an endogenous MAO inhibitor related to tribulin.

A study of the acute effects of isatin, an endogenous MAO inhibitor related to tribulin, on rat brain serotonergic function was undertaken. A single dose of isatin significantly increased 5-HT concentrations in the hypothalamus and cortex but did not significantly alter 5-HIAA concentrations. Synaptosomal 5-HT uptake was unaffected but there was a trend for the number of3H-ketanserin binding sites was to be decreased. The results of the study are discussed in terms of the relationship of isatin to tribulin and their possible causal role in stress.

Clinical Pharmacokinetics of Dothiepin

SummaryThe pharmacokinetics of dothiepin were evaluated in 9 depressed patients following a single oral dose of 75mg. Blood and plasma concentrations of dothiepin and 2 major metabolites, northiaden and dothiepin S-oxide, were measured by gas chromatography/mass fragmentography. The mean (±SD) peak plasma concentrations of dothiepin were 49 ±27 μg/L at 3 ± l.2h. Mean (± SD) estimates of other parameters were as follows: absorption half-life 1.1 ± 1.1h; distribution half-life 2.2 ± 0.8h; elimination half-life 25 ± 7h; apparent volume of distribution 70 ± 62 L/kg; and oral clearance 2.1 ± 1.6 L/kg/h.The mean (±SD) peak plasma concentration of dothiepin S-oxide was 125 ± 43 μg/L at 3.5 ± 1.3h with an elimination half-life of 22 ± 12h. The mean peak plasma concentration of northiaden was 6 ± 3 μg/L at 4.5 ± 1.1h, with an elimination half-life of 31 ±12h. No significant differences were found in pharmacokinetic parameters compared with a previous study in 7 healthy volunteers.When data for the patients and healthy volunteers were combined (n = 16), pharmacokinetic parameters were not found to be affected by age. However, a significant difference was found between males and females for the elimination half-lives of dothiepin and northiaden, and for the apparent volume of distribution of dothiepin.The 24-hour blood/plasma concentrations of dothiepin and dothiepin S-oxide accurately predicted the steady-state concentrations obtained following 4 weeks’ treatment with dothiepin 150mg nocte.

Plasma immunoreactive β-endorphin in dexamethasone suppressors and non-suppressors of cortisol

Immunoreactive plasma beta-endorphin level was assayed in 33 patients with major affective disorder and in 16 psychiatrically normal controls before and after dexamethasone (1 mg) administration at 23.00 h. There were 18 cortisol suppressors and 15 non-suppressors among the patient group. All controls suppressed cortisol. Plasma beta-endorphin before dexamethasone was significantly different between suppressors, non-suppressors and controls (P less than 0.05, ANOVA). Concentrations of beta-endorphin were 4.7 +/- 0.7, 3.1 +/- 0.3 and 2.8 +/- 0.3 pmol/l for non-suppressors, suppressors and controls respectively. Following dexamethasone, beta-endorphin concentrations were again significantly different between groups (P less than 0.005, ANOVA). Concentrations were 4.6 +/- 0.7, 2.3 +/- 0.2 and 1.6 +/- 0.2 pmol/l for non-suppressors, suppressors and controls respectively. The implications of these findings are discussed.

Blood and plasma concentrations of dothiepin and its major metabolites and clinical response.

Ten patients suffering from primary depressive illness were treated with 150 mg/d of dothiepin for 4 weeks. Blood and plasma concentrations of dothiepin and two metabolites, dothiepin S-oxide and northiaden were measured by gas chromatography-mass spectrometry. Severity of depression was assessed using the Hamilton Depression Rating Scale. No significant correlation was found between amelioration score or percentage change and either blood or plasma concentrations of dothiepin, its metabolites or total drug and metabolite concentrations at week 4.