Geoclimatology and sleep in Africa: A mini-review.

Sleeping habits and morningness-eveningness questionnaires (chronotype), and polysomnography (internal sleep organization) were proposed to healthy volunteers living under natural climates from different locations in West Africa (Niger, Côte d'Ivoire) and Central Africa (Angola, Congo). Under the Sahelian dry climate, 138 Niger medical students (130 had afternoon naps) completed 1792 sleep questionnaires during 7-day sessions in the cool-dry and hot-dry seasons. As everywhere else on Earth, daily sleep lasted 7 to 8hours. In Abidjan (hot-humid climate), 78 medical students reported shorter sleep time, because of course schedules. Also in Abidjan, 23 African sportsmen and Expatriate soldiers slept at night and in afternoon naps. They reported similar sleep amounts than Niger students. In Congo villages, during a 5-year human African trypanosomiasis (HAT) research campaign, 45 healthy volunteers expressed morning chronotypes. The 71 HAT patients shifted from the indifferent chronotype towards morningness type. Chronotyping such patients may help evaluating treatment efficacy on brain function alterations. French soldiers executing missions in Africa were typed for morningness-eveningness. Regarding malaria prophylaxis and mosquito control, morning chronotype was more compliant than evening type. Polysomnography demonstrated internal sleep organization differences in different geoclimatic zones. The Sahelian climate promoted N3 slow-wave sleep in Africans and Expatriates during both the cool-dry and hot-dry seasons, with higher amounts in the hot-dry season. Increasing heat load by physical exercise further augmented N3. Rapid-eye-movement R sleep was high compared with values from temperate and hot-humid climates. Supramaximal exercise triggered a surprising R stage increase in the hot-dry season. In Côte d'Ivoire, Caucasian and African volunteers fragmented their sleep, although internal sleep organization approached that of temperate climates. Sleep patterns were also similar in Angola high hills and on Congo River shores. Therefore, Africans and Caucasians living in Niger hot-dry Sahelian climate exhibited major differences with those exposed to hot-humid or temperate climates.

Disruption of endocrine rhythms in sleeping sickness with preserved relationship between hormonal pulsatility and the REM-NREM sleep cycles.

In human African trypanosomiasis (sleeping sickness), sleep and wake episodes are sporadically distributed throughout the day and the night. To determine whether these sleep disturbances affect the 24-h hormone profiles and the normal relationships between hormone pulsatility and sleep stages, polygraphic sleep recordings and concomitant hormone profiles were obtained in 6 African patients with sleeping sickness and in 5 healthy African subjects selected from Abidjan on the Ivory Coast. Polysomnographic recordings were continuous, and blood was taken every 10 min throughout the 24-h period. Plasma was analyzed for cortisol, prolactin, and plasma renin activity (PRA). The 24-h rhythm of cortisol, considered to be an endogenous circadian rhythm, was attenuated in all of the patients except one. However, as in normal subjects, slow wave sleep (SWS) remained associated with the declining phases of the cortisol secretory episodes. Prolactin and PRA profiles, which are strongly influenced by the sleep-wake cycle, did not manifest the nocturnal increase normally associated with the sleep period; instead, they reflected a sporadic distribution of the sleep and wake episodes throughout the 24-h period. In patients with sleeping sickness as in normal subjects, rapid eye movement (REM) sleep began during the descending phases of prolactin pulses. In both groups, PRA reflected the sleep stage distribution with non REM (NREM) sleep occurring during the ascending phases and REM sleep during the descending phases of the PRA oscillations. However, in sleeping sickness patients, the marked sleep fragmentation often did not allow sufficient time for PRA to increase significantly, as is normally the case in subjects with regular NREM-REM sleep cycles. These results demonstrate that, together with the disruption of the sleep-wake cycle, there are profound differences in the temporal organization of the 24-h hormone profiles in humans with African trypanosomiasis. However, the relationship between hormonal pulses and specific sleep stages persists, indicating the existence of a robust link between hormonal release and the internal sleep structure.

Lactate exchange and removal abilities in sickle cell patients and in untrained and trained healthy humans.

Arterial blood lactate concentrations obtained on seven black males with hemoglobin sickle cell disease (SC) before, during, and after graded bicycle exercise up to exhaustion were compared with those of seven untrained (HU) and seven trained (HT) healthy males of the same ethnic origin. Lactate recovery curves were fitted by a biexponential time function consisting of a rapidly increasing and a slowly decreasing component. Higher work rates were reached by the HU and HT than by the SC group. Blood lactate rose distinctly over the corresponding preexercise resting values after the 25-, 50-, and 100-W exercise steps for the SC, HU, and HT groups, respectively. The arterial oxygen content was significantly lower for the SC than for the HU group at rest and at the end of exercise. The velocity constants of the slowly decreasing component of the lactate recovery curves were similar for the SC, HU, and HT groups despite the fact that they cycled up to different absolute work rates. The velocity constant of the rapidly increasing component was significantly higher for the HT. In terms of the functional meaning given to these constants and in view of their inverse relationship with absolute work rate (Freund et al. J. Appl. Physiol. 61: 932-939, 1986), these results indicate that, relative to the HU, the HT and the SC display improved and impaired abilities, respectively, to exchange and to remove lactate.

Twenty-four-hour plasma cortisol and prolactin in human African trypanosomiasis patients and healthy African controls.

We have previously demonstrated that human African trypanosomiasis (sleeping sickness) at the stage of meningoencephalitis results in a major disruption of the circadian rhythmicity of sleep and wakefulness that is proportional to the severity of the disease. This paper examines the corresponding 24-hourly secretion in cortisol and prolactin and compares it with the hourly distribution of sleep composition in infected patients and healthy African subjects. The secretion of cortisol in humans follows a circadian rhythm relatively independent of the sleep-wake cycle, whereas that of prolactin exhibits fluctuations over the 24-hr day that are strongly related to the sleep-wake cycle. After the clinical classification of the patients according to the severity of the disease, hourly blood samples were taken over 24 hr via an indwelling catheter. Plasma cortisol and prolactin were analyzed by radioimmunoassay, and the variations in the hourly concentrations were analyzed for the presence of a potential 24-hr rhythm (circadian). All of the healthy African subjects showed significant circadian rhythms in both cortisol and prolactin secretion, similar to data on humans from temperate regions, and a sleep-related anamnestic afternoon peak of prolactin. Major disruptions in the circadian rhythms of plasma cortisol and prolactin were found in the three patients with the most severe illness, in contrast to the four who were less severely ill and the healthy controls. Thus, it appears that as the disease progresses in severity, major disruptions begin to occur in body circadian rhythms, not only in the sleep-wake cycle as reported elsewhere, but also in cortisol and prolactin secretion, suggesting that sleeping sickness affects the circadian timing system.

Sleep-wake cycle in human African trypanosomiasis.

Sleeping sickness patients are classically described as sleepy by day and restless by night. Prior to this study, we had objectively confirmed this description by recording 24-h sleep patterns in a patient with human African trypanosomiasis. We report 24-h polysomnographic recordings (EEG, electrooculogram, electromyogram, electrocardiogram, and nasal, buccal, and thoracic respiratory traces) performed on two eight-channel electroencephalographs in eight patients with untreated sleeping sickness at an early stage of meningoencephalitis. As in our previously reported patient, there was no hypersomnia. The patients presented mainly a disorganization of the circadian alternation of sleeping and waking, with no or little alteration in the states of vigilance at this early stage of the disease. The disorganization was proportional to the degree of severity of the clinical symptoms. It may be due to an alteration in biological clock mechanisms.

Electroencephalographic and polygraphic features of 24-hour recordings in sleeping sickness and healthy African subjects.

Electroencephalographic (EEG) and polygraphic features were analysed in six healthy control subjects and eight patients suffering from sleeping sickness meningoencephalitis in order to determine possible functional relationships. One patient was disqualified because of intermittent metabolic disease. Twenty-four h polygraphic recordings-EEG, electrooculography (EOG), electromyography (EMG), nasal and buccal air flow, chest respiratory movements-were performed continuously both on paper and on cassette tapes. Tapes were played back on paper (paper speed: 15 mm/s). Traces were analyzed for normal and pathologic features, and transient activation phases and paroxysmal hypnopompic hypersynchrony events were counted. During wakefulness, slow theta and delta waves occurred in four patients, but alpha reactivity was present. During sleep, normal features were seen. However, transient activation phases were decreased in the patients. During slow-wave sleep, four patients presented predominantly monophasic frontal delta bursts along with paroxysmal hypnopompic hypersynchrony events. In conclusion, in sleeping sickness patients, although dampened, the waking process remains responsive and slows down only during the late stage of meningoencephalitis.

Cardiorespiratory and metabolic responses to exercise in HbSC sickle cell patients.

PURPOSE: Relative to healthy control individuals with normal hemoglobin (Hb), patients carrying the double heterozygous form of sickle cell disease (HbSC) display an impaired oxygen transport capacity. The present study was undertaken to determine the influence of the decreased oxygen availability associated with the presence of HbSC on the cardiorespiratory and metabolic responses to endurance exercise. METHODS: Eleven black men affected by the double heterozygous form of the sickle cell disease (HbSC group) and seven healthy subjects with normal Hb (HbAA group) of the same ethnic origin submitted successively to an incremental exercise test to exhaustion on a cycle ergometer for the determination of their maximal tolerated power and to a 20-min endurance exercise. RESULTS: The HbSC had a significantly lower exercise tolerance than the HbAA. During the endurance exercise, they exhibited furthermore significantly lower VO2, VCO2, and minute ventilation V(E) than the HbAA. Despite the fact that the HbSC exercised at a significantly lower mean absolute work rate than the HbAA, except for the ventilatory equivalent for CO2 (V(E)/VCO2), which was higher (P < 0.001) in the HbSC group, the other parameters recorded during the 20-min endurance exercise (heart rate, arterial PaO2, PaCO2, pH, lactate, and VE/VO2, the ventilatory equivalent for O2) and during the subsequent recovery (blood lactate) were similar for both groups. CONCLUSION: The study underscores the importance of considering relative work rate as well as absolute work rate to arrive at a correct interpretation of exercise and recovery data. The results give evidence that the modifications of homeostasis brought into play by exercise were shifted toward distinctly lower absolute work rates in HbSC patients.

[Blood levels of protein markers of inflammation and nutrition in the meningo-encephalitis phase of human African trypanosomiasis]. / Valeurs sériques des marqueurs protéiques de l'inflammation et de la nutrition dans la phase méningo-encéphalitique de la trypanosomose humaine africaine.

Two acute phase proteins; C-reactive protein and acid alpha 1-glycoprotein and three nutritional markers; prealbumin, retinol binding protein and transferrin have been evaluated in 8 patients suffering from trypanosomiasis in meningoencephalitic state and compared to those obtained from 15 normal control subjects. Findings show a markly decrease of nutritional markers without change of sera acute phase proteins. We concluded that in meningo-encephalitic state of human african trypanosomiasis, denutrition was a major biological or clinical feature in association with lymphoid cells stimulation as revealed by beta 2-M levels.

Disruptions in the secretion of cortisol, prolactin, and certain cytokines in human African trypanosomiasis patients.

It has been shown previously that sleeping sickness at the stage of meningoencephalitis manifests itself as a significant disturbance in the circadian rhythm of sleep-wakefulness. The objective of the current study was to examine the extent of circadian disruption in infected patients by measuring 24 hours patterns of plasma cortisol, an example of a classical circadian rhythm relatively independent of sleep, and prolactin, a primarily sleep-related rhythm. Plasma levels of certain cytokines were also measured to examine the immunopathogenesis of human African trypanosomiasis. An attempt was made to relate any circadian disruptions to the severity of the disease. The three most advanced patients demonstrated circadian disruptions in cortisol, prolactin and sleep-wake rhythms. The prime cytokine factor that correlated with the progression of the disease in humans was interferon-gamma, levels being 7- to 12-fold higher in the patients without any circadian rhythms. Our findings support the hypothesis that human African trypanosomiasis induces selective changes in the suprachiasmatic nucleus, important as a pacemaker for biological rhythms, resulting in disruptions of circadian rhythmicity in advanced stages of the disease.

[The nyctohemeral rhythm of melatonin is preserved in human African trypanosomiasis]. / Le rythme nycthéméral de la mélatonine (MLT) est conservé dans la trypanosomose humaine africaine.

We studied plasma melatonin profiles by radioimmunoassay in nine patients suffering from human african trypanosomiasis and six healthy controls matched according to the age and the photoperiodic conditions. The circadian periodicity of the sleep-wake cycle was disturbed proportionally to the degree of severity of the disease. On the contrary, the patients' plasma melatonin profile was similar to the controls' one. These results suggest that, beside the master clock generating the main circadian rhythms (sleep-wake, melatonin and core temperature rhythms), an additional regulating system of the melatonin rhythm could be involved.

[Maintenance of the relation between the pulsed secretion of hormones and the internal sleep structure in human African trypanosomiasis]. / Maintien des relations entre la sécrétion pulsatile des hormones et la structure interne du sommeil dans la trypanosomiase humaine africaine.

In order to determine whether sleep disturbances would affect the hormonal patterns and the normal relationships between hormone pulses and sleep stages, the 24-hour profiles of cortisol, prolactin and plasma renin activity (PRA) were analysed in 6 sleeping sickness patients studied at Brazzaville and in 5 healthy African controls studied in Abidjan. Polysomnographic recordings were done continuously and blood was taken every 10 minutes throughout the 24-hour period. Plasma was analyzed for cortisol, prolactin and PRA. The circadian rhythm of cortisol, considered as an example of an endogenous rhythm was attenuated in all the patients but one, but as in normal subjects, slow wave sleep (SWS) remained associated with the declining phases of the secretory episodes. Prolactin and PRA profiles, which are strongly influenced by the sleep-wake cycle did not show the increase normally associated with long sleep periods and reflected the spreading of sleep and wakefulness throughout the 24-hour period. However, rapid-eye movement (REM) sleep began in sleeping sickness patients, as in normal subjects, during the descending phases of prolactin pulses. In both groups, PRA reflected the sleep stage distribution with non rapid-eye movement (NREM) sleep occurring during the ascending phases and REM sleep during the descending phases of the oscillations. However, in sleeping sickness patients, the marked sleep fragmentation often did not allow sufficient time for PRA to increase significantly, as observed with regular NREM-REM sleep cycles. These results demonstrate that, together with the disruption of the sleep-wake cycle, there are profound differences in the temporal organization of the 24 hour hormone profiles in human African trypanosomiasis.(ABSTRACT TRUNCATED AT 250 WORDS)

[The distribution of sleep and wakefulness in human African trypanosomiasis]. / Distribution du sommeil et de la veille dans la trypanosomose humaine africaine.

Last century, patients with human African trypanosomiasis were described as sleepy by day and restless by night, and physicians referred to this condition as sleeping sickness. Such a description could have evoked a disturbance of circadian rhythms. However, it is only in 1989 that the first 24-hour recording was performed by our team in Niamey (Niger) in a patient with sleeping sickness. The patient was a Niger-born farm worker who had contracted the disease near Gagnoa (Côte d'Ivoire). Polysomnographic recordings (electroencephalogram, EEG, electrooculogram, electromyogram, electrocardiogram, buccal and nasal airflow, and chest respiratory movements) showed a disappearance of the circadian distribution of sleep and wakefulness, which tended to occur evenly throughout day and night, with a sleep-wake alternation of approximately 80 minutes. Two investigations were conducted thereafter. The first one was done at Daloa (Côte d'Ivoire) in 8 patients who were recorded during two 24-hour periods, with and without hourly blood samples; the second at Brazzaville (Congo) in 10 patients recorded for 24 hours before and after treatment with melarsoprol. All patients were at the stage of early meningoencephalitis. At Daloa, polysomnographic recordings were taken on two 8-channel EEG machines (Alvar Minihuit, and T3-ECEM), as well as on a portable Oxford Medilog 9000 system from the same electrodes. Sleep and wake structure was altered in the most severely sick patient, the EEG trace being loaded with slow waves. Stages 1 and 2, and stages 3 and 4 could not be distinguished from one another. In the other patients, all sleep stages were easily scored. No difference was seen between recordings, regarding blood collection.(ABSTRACT TRUNCATED AT 250 WORDS)

[Circadian analysis of sleep, rectal temperature and immunological and endocrinological variables in sleeping sickness: preliminary study]. / Analyse circadienne du sommeil, de la température rectale et de variables immunologiques et endocrinologiques dans la maladie du sommeil: etude préliminaire.

A multidisciplinary study was conducted in 8 patients with neurological Human African Trypanosomiasis. The sleep-wake cycle followed an ultradian pattern which was more pronounced in patients with more severe symptoms. The EEG trace was consistently interrupted by numerous cyclic activation patterns with K complexes, rapid low amplitude elements and slow high voltage elements. Circadian rhythmicity was also disturbed in other physiological (rectal temperature), immunological (interleukins) or hormonal (cortisol, prolactin) variables, the disturbance being greater in severely hit patients.

[Tobacco consumption of students ages 8 to 22 in Abidjan, 2002]. / Tabagisme des élèves et étudiants âgés de 8 à 22 ans à Abidjan en 2002.

BACKGROUND: To update full time educated youth data on smoking prevalence related to gender and to assess perception and behaviour related to smoking, we have led a self-administrated question-study from January to June 2002 in Abidjan with students from 8 to 22 years old. METHODS: Our population was divided in 3 groups: T1 (812 years), T2 (13-17 years) and T3 (18-22 years). The size of each group has been determined using the smoking estimated rate in each of them. RESULTS: 2742 students had returned a well-full questionnaire, with the following rates, expressed by mean and standard deviation in%: a total smoking rate at 7.9 +/- 0.5, with statistic difference between boys and girls (11 +/- 0,8 versus 3,7 +/- 0,5; p<0.001). This rate increased with age: 3.7 +/- 0.8 in T1; 12.9 +/- 1.0 in T2 and 17.1 +/- 1,1% in T3. Globally, the rate was 0.7 +/- 0.2 for regular smokers (>or=1 cigarette/day) (10% of C.D.T.) and 1.7 +/- 0.2% for ex-smokers. 99.2% of current smokers used cigarettes only. On average, the tobacco consumption was 3.4 cigarettes/day. In non-smokers group, 88% had respiratory symptoms linked to smoke exposure, with 17% of major dyspnea. Non smokers reported public places as the most frequent (66.7 +/- 1.3%) and the highest long time exposure (44.3 +/- 1.9%) places to second hand smoke. DISCUSSION: A similar smoking prevalence between asthmatics and non-asthmatics subjects, and between sporty type and non sporty type subjects, suggested that students had superficial knowledge or under assessment on smoking detrimental effect. However, their perception of smoking health hazard was sufficient to give 95 +/- 1% favourable opinions on necessary smoking place regulations and 85 +/- 1% favourable opinions on tobacco product advertising ban. CONCLUSION: The epidemiological and behaviour information given by this study might contribute to the development of a national youth tobacco control program, provided a complementary national survey would be led including non educated youth.

[Pulmonary hypertension in patients with emphysema]. / L'hypertension artérielle pulmonaire des emphysémateux.

Fifty-three patients with chronic and stabilized emphysema, mostly of the panlobular type, and without any associated disease likely to interfere with the cardio-pulmonary function, were used to analyze the physiological factors responsible for their pulmonary hypertension, moderate at rest but marked at exercise. The study showed that the main responsibility for pulmonary hypertension, both at rest and during exercise, lay on mechanical respiratory factors and on passive regulation of the lesser circulation. It also showed that the predictive value of SaO2 was higher than that of PaO2 but lower than that of CvO2 which depends on a relative tissue hypoxia of cardiovascular origin responsible for vasoconstrictive acidosis at exercise. In this study, destruction of the pulmonary capillary bed, often different from destruction of the alveolar surface, had a predictive value for PAP higher than that of hypoxia. In these cases of pure, stabilized chronic emphysema hypoxia does not have the preponderant hypertensive role for which it is blamed in the literature in all circumstances.

[Domestic and occupational pneumo-allergens among workers with tropical wood in Abidjan (Ivory Coast)]. / Pneumallergènes domestiques et professionnels des travailleurs de bois tropicaux à Abidjan (Côte-d'Ivoire).

The authors realized an epidemiologic research by skin test method in a furniture factory in Abidjan (Ivory Coast). 19 wood workers underwent these tests: their professional risk to wood dust exposure was over 13 years. The results show the importance of allergenic work atmosphere and mainly the high allergic potential of five exotic woods currently used. This article proposes an approach of the specific immunological pathways through a prospective allergological enquiry conducted at furniture factory in Abidjan (Ivory Coast).

[Effect of smoking on PaO2 at rest and during moderate exercise]. / Effet du tabagisme sur la PaO2, au repos et au cours d'un effort physique modéré.

The most data on smoker's arterial oxygen tension (PaO2) were carried out at rest and from non arterial blood sample. The aim of this retrospective study was to compare smokers and nonsmoker's arterial oxygen tension (PaO2) at rest and during a moderate exercise. 98 male smokers between 23 and 69 years old and 98 male nonsmokers with the same age bracket were recruited among subjects submitted to arterial blood gas analysis according to the following protocol: 2 arterial blood samples were taken at rest, with an interval of 5 minutes, followed by a third one taken at the end of a moderate effort (50 watts during 5 minutes) on a bicycle in the supine position. Wilcoxon's test was used to compare the measured biological parameters between smokers and nonsmokers. Unlike nonsmokers, smoker's PaO2 increased meaning fully during moderate exercise. However, like at rest, it remained lower than nonsmoker's PaO2.: 87.6 +/- 15.8 mmHg Versus 94.1 +/- 10.4 mmHg (p < 0.0001). These beneficial effects of exercise on smoker's PaO2, although limited among heavy smokers group, suggested that hypoxia observed at rest must be due to troubles in ventilation/perfusion ratio in the lungs. In comparison to nonsmokers, the most significantly hypoxia was founded in smokers between 40 and 59 years old. The variation of PaO2 in nonsmokers was normal in comparison with age, but strongly disturbed in smokers at rest as well as during a moderate exercise, despite the lack of correlation between PaO2 and the intensity of tobacco consumption (expressed as number of pack-years). Thus, the smokers' PaO2 deterioration concerned together its value and its variation in comparison with age.

Lactate exchange and removal abilities in sickle cell trait carriers during and after incremental exercise.

Arterial blood lactate concentrations and pH were measured on seven black male sickle cell trait (SCT) carriers before, during and after incremental exhaustive bicycle exercise (25 W increments per minute) and compared with those of six control individuals of the same ethnic origin having a similar physical fitness level. The object of the experiment was to determine if SCT has an effect on lactate kinetics. At volitional exhaustion which was reached at a comparable overall mean absolute work rate for both groups, oxygen consumption expressed per kilogram body mass was significantly lower for the SCT carriers than for the control volunteers. Lactate concentrations were higher for the SCT carriers after the 150 W exercise step but differences reached statistical significance only at exhaustion. Concentrations were distinctly higher for the SCT group during the following 40 minutes of recovery. While there were no observable differences in blood pH between the SCT and control subjects during the exercise, this variable became significantly lower for the SCT than for the control group 8 minutes after the end of exercise. Lactate recovery curves were fitted by a biexponential time function where the two velocity constants inform on the body's overall ability to exchange and remove lactate. The ability to remove lactate was comparable for the two groups. The present results do not warrant drawing a definite conclusion on impairment of the ability to exchange lactate in the presence of SCT. However, SCT carriers are likely to produce more lactate than control subjects reaching exhaustion at similar mean absolute work rate during exhaustive incremental bicycle exercise.

Sickle cell trait as a limiting factor for high-level performance in a semi-marathon.

Of 1506 black males participating in the first Abidjan semi-marathon, 123 subjects with sickle cell trait (SCT) were detected, i.e., 8.7%. Twenty-nine of these subjects with hemoglobin S (HbS) were ranked among the first 332 participants to finish the race, a percentage of 8.2. These percentages did not significantly differ from the prevalence of SCT observed in the general Ivory Coast population (12.0%). Only one subject with SCT was found among the 22 internationally-ranked athletes. The concentration of HbS found in this athlete (37.7%), his mean globular volume (87 fl), and his hemoglobin concentration (13.8 g/100 ml) suggest the coexistence of alpha-thalassemia with SCT. These results indicate that the percentage of SCT individuals participating in a semi-marathon is equal to the prevalence of SCT found in the local population. Furthermore, the general ranking of SCT individuals is comparable to that of non-SCT individuals. Nevertheless, at the level of internationally-ranked performance, no subject with SCT only, was ranked; the one ranked subject with SCT presented an associated alpha thalassemia. We thus hypothesize that SCT may be a limiting factor for high level performance in a semi-marathon and alpha-thalassemia, an enhancing factor for subjects with SCT to succeed in long distance races.

Twenty-four-hour profiles and sleep-related variations of cortisol, thyrotropin and plasma renin activity in healthy African melanoids.

The 24-h hormone profiles have been well documented in caucasians living in a temperate climate, but they have never been examined in melanoid subjects under equatorial conditions, with a 12-h light-dark cycle in a hot climate. To establish normal data for this population, blood samples were taken at 10-min intervals over 24 h in five healthy young melanoids living in Abidjan (Ivory Coast). Cortisol and thyroid stimulating hormone (TSH) concentrations and plasma renin activity (PRA) were determined by radio-immunoassay and sleep was registered using polysomnography. Data were compared with results obtained in Strasbourg (France) from six healthy aged-matched caucasians. The 24-h profile of cortisol concentration was similar in both groups, with a 2-h phase advance in the melanoids. Nocturnal fluctuations of PRA, strongly linked to the rapid eye movement-non rapid eye movement (REM-NREM) sleep cycles, occurred in both groups, with higher levels in the caucasians in the last 2 h of sleep along with greater amounts of NREM sleep. After an evening increase in TSH, the sleep onset-related decrease seen in the caucasians was not observed in the melanoids. In both groups, increasing concentrations of TSH and cortisol occurred with awakening, decreasing concentrations being observed during slow-wave sleep. As in the caucasians studied in the temperate climates, the melanoid subjects living at the equator showed the same temporal organization of hormone rhythms within the 24-h period and the same relationships between the pulses and specific sleep stages.(ABSTRACT TRUNCATED AT 250 WORDS)