Biomedical subjects

J M Cottet-Emard

Publications and source records attributed to J M Cottet-Emard.

At least 19 recordsLinked to original sources

PubMed2006

Effects of increased intra-abdominal pressure on central circulation.

BACKGROUND: In an experimental model we investigated the effects of a gradual increase in intra-abdominal pressure (IAP) on the central circulation. METHODS: Seven pigs were anaesthetized, mechanically ventilated and instrumented. IAP was gradually increased by 5 mm Hg up to 30 mm Hg by abdominal banding in normovolaemic animals, and then they were made hypovolaemic after blood withdrawal. Right atrial pressure (RAP) and left ventricular end-diastolic pressure (LVEDP) at each step and aortic, femoral and inferior vena cava blood flows were measured. Left ventricular end-diastolic area (LVEDA) was determined using epicardial echocardiography. RESULTS: Cardiac output maintained at mild IAP was reduced to 76 (24)% of the initial value at 30 mm Hg IAP [mean (sd)] in normovolaemic animals, and 72 (22)% (P<0.001) in hypovolaemic animals. In normovolaemic animals the LVEDA and LVEDP were significantly increased at an IAP of 10 and 15 mm Hg by 26 (24)% and 38 (23)%, respectively. At these IAP values, the difference between the RAP and IAP was positive. When this gradient became negative, that is beyond 15 mm Hg in normovolaemia and for all IAP values in hypovolaemic animals, the LVEDA declined, reaching 78 (16)% and 62 (22)% (P<0.05) of the initial values in normovolaemic and hypovolaemic groups at the highest IAP value. CONCLUSIONS: These results showed that a gradual increase in IAP led to a redistribution of abdominal blood volume towards the thoracic compartment, at IAP lower than 15 mm Hg in normovolaemia, and at its expense at higher values of IAP. In hypovolaemia there was no thoracic compartment gain. Whereas the absolute or transmural RAPs were not informative of the direction of this blood shift, an RAP greater than IAP was associated with an intrathoracic compartment gain.

Abdomen↗

PubMed2005

Skeletal muscle HSP72 and norepinephrine response to static magnetic field in rat.

The present work was undertaken in order to investigate the noradrenergic system and skeletal muscle heat shock protein 72 (HSP72) response to static magnetic field (MF) in male rats. At thermoneutrality (25 degrees C), the exposition of rats 1 hour/day for 5 consecutive days to MF of 128 mT (m tesla) induced an increase in norepinephrine content in gastrocnemius muscle (+25%, p < 0.05) but had no effect at 67 mT (+1%, p > 0.05), indicating a stimulatory effect of sub-acute MF exposure on the noradrenergic system activity. Moreover, exposed rats to MF displayed a non-significant increase of HSP72 levels in gastrocnemius muscles (+29%, p > 0.05). The results indicate that noradrenergic systems in rat's gastrocnemius muscles are affected by MF exposure. Interestingly, sub-acute exposure insufficiency increased HSP72 levels in gastrocnemius muscles.

Animals↗

PubMed2004

Role of catecholamines in glucagon-induced thermogenesis.

The present work was undertaken in order to investigate whether the observed thermogenesis following glucagon injection requires the participation of catecholamines. Our experiments aim at studying the effects of intraperitoneal injection of glucagon on metabolic rates, plasma catecholamine and fuel metabolites in guanethidine-treated ducklings reared at thermoneutrality (25 degrees C). The chronic guanethidine treatment induced a marked decrease in catecholamines levels in peripheral tissues (heart, muscle and intestine) but not in adrenals. At thermoneutrality, intraperitoneal injection of glucagon had lower thermogenic effects in guanethidine-treated compared to control ducklings. Glucagon injection elicited a concomitant increase of plasma norepinephrine, metabolic rate and energy metabolites in control ducklings, whereas in guanethidine-treated ducklings, the plasma catecholamines and metabolic rate did not undergo any consistent change. The thermogenic action of glucagon in birds involves at least the mobilization of lipids and catecholaminergic system stimulation.

Adipose Tissue↗

PubMed2003

Sciatic nerve monoaminergic system response to cold acclimatization in Muscovy duckling.

The effect of cold acclimatization on the monoamines in duckling sciatic nerve was studied. In thermoneutral (TN) ducklings, the high dopamine (DA) to norepinephrine (NE) ratios in the right (R, 0.14) or in the left (L, 0.20) sciatic nerves at 6 weeks of age suggests the presence of non-precursor specific dopaminergic pools. DA, DOPAC (3, 4-dihydroxyphenylacetic acid) levels and the ratio DA to NE were similar in cold-acclimated (CA) and TN ducklings sciatic nerves. Moreover, serotonin and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) remained unchanged in the sciatic nerve, indicating that this system is not affected with cold exposure. The contents of NE were higher (R = +44.46%; L = +43.73%) in sciatic nerve of CA than in TN ducklings. The results indicate that noradrenergic systems in the ducklings sciatic nerve are markedly affected by cold exposure. Interestingly, chronic exposure to cold failed to alter the dopaminergic and the serotonergic system in duckling sciatic nerve.

Acclimatization↗

PubMed2003

Neurochemical development of the brainstem catecholaminergic cell groups in rat.

The postnatal development of tyrosine hydroxylase activity has been studied in the brainstem catecholaminergic cell groups (A1C1, A2C2, A5, A6, A7), involved in cardiorespiratory control. In rat, at birth and at postnatal days P3, P7, P14, P21 ant P68, we used a microdissection technique followed by in vivo measurement of the tyrosine hydroxylase (TH) activity, the rate-limiting enzyme in catecholamine synthesis. There is two successive marked increases in TH activity: at P3 in every catecholaminergic cell groups (A1C1, +225%; A2C2, +300%; A5, +190%; A6, +205% compared to birth) and during the third postnatal week with a peak of TH activity at P14 (A6, +90% above the P7 level) or at P21 (A1C1, +715%; caudal A2C2, +585%; rostral A2C2, +15%; A5, +445%; A7, +180% compared to P7). The data suggest the existence of two temporal windows during the neurochemical development of the catecholaminergic cell groups, which correspond to two metabolic transitions. The first one could be related to the intra-, extrauterine transition and the second one, to a deep energetic phase of maturation in the rat brain, closely related to the maturation of cardiorespiratory processes.

Animals↗

PubMed2002

Psychobiologic responses to 4 days of increased training and recovery in cyclists.

The psychobiologic status of cyclists after 4 days of training and the kinetics of recovery were assessed by measuring the sympatho-adrenal level, the central noradrenergic activity and the cortisol/testosterone status by non-invasive methods. For this purpose, urinary excretion of methoxyamines (metanephrine [MN], normetanephrine [NMN]), which are metabolites of circulating catecholamines, 3-methoxy-4-hydroxyphenyl glycol sulfate (MHPG-S), a metabolite of brain norepinephrine, and salivary output of cortisol and testosterone were measured in twelve national cyclists (aged 19.5 +/- 4.5 years), just before (T 1 ) and at the end of the training (T 2 ), and during the three following recovery days (R 1, R 2, R 3 ). Urinary and salivary samples were also collected during a period of relative rest, in order to get reference values (T 0 ). At T 0, T 1 and T 2, mood states, as measured by the Profile of Mood States, and rating of perceived muscle soreness were assessed. The overall mood and muscle soreness levels were not affected by the training. The load increased by 187 % as an average between the first and the fourth day of training. A significant increase in NMN levels and a decrease in T:F ratio were observed at T 2, while MHPG-S excretion remained unchanged. Persistent high urinary output of NMN and MN were observed during the post-training recovery period for 24 h (R 1 ) and 48 h (R 2 ), respectively. After 72 h of recovery (R 3 ), MN levels had returned to baseline while NMN output was lower than the control level. T:F values returned to their control levels within 48 h of recovery. The strenuous training seems to induce an alteration in peripheral neuro-endocrine parameters without modifications of central factors. The hormonal status remained altered for at least 1 day of post-training recovery and seemed to be achieved within 3 days.

Adaptation, Physiological↗

PubMed2001

Regulation of expression and enzymatic activities of tyrosine and tryptophan hydroxylases in rat brain after acute electroconvulsive shock.

Acute electroconvulsive shock (ECS) causes a significant increase of protein synthesis in depressive patients and such an increase raises the possibility that the regulation of specific proteins and enzymatic activities in the brain might be one of the mechanisms required for the induction of long-term adaptive neurochemical changes after electroconvulsive therapy. In current studies, we investigated and compared simultaneously the short- and long-term effects of an acute ECS on the expression and enzymatic activities of both tyrosine and tryptophan hydroxylases (TH and TpOH, respectively) in different rat brain areas. Our results demonstrated that an acute ECS produced: (1) a long-lasting decrease in TH and TpOH protein levels in locus ceruleus (LC), ventral tegmental area (VTA) and in TpOH protein level in the raphe centralis (RC), maximal at 72 h, with concomitant changes in mRNA levels and enzymatic activities in the LC only; (2) large increase of TpOH protein levels in the frontal cortex (Cxf) (+145%) and increase of TH protein levels in the hippocampus (Hip) (+207%), maximal at 72 h and 7 days which was not accompanied by corresponding increase of in vivo enzymatic activities. Furthermore, a second ECS increased in vivo TpOH activity in the Cxf (+19%) while decreasing K(m) value (-50%) for tetrahydrobiopterin cofactor. A stability of the observed findings on TpOH activity in the Cxf after repeated ECS might be one of the mechanisms for the antidepressant effects of electroconvulsive therapy.

5-Hydroxytryptophan↗

PubMed2001

Comparison of passive heat or exercise-induced dehydration on renal water and electrolyte excretion: the hormonal involvement.

The effects of hydromineral hormones and catecholamines on renal water and electrolyte excretion were examined during and after dehydration induced by either passive heat or exercise. Eight healthy young Caucasian subjects participated in three separate trials, each including three consecutive phases. Phases 1 and 3 involved a 90-min period at rest in a thermoneutral environment, while phase 2 involved a 120-min period designed to provide: (1) euhydration (control trial), (2) passive heat-induced dehydration of 2.8% body mass, or (3) exercise-induced dehydration of 2.8% body mass. During the two dehydration procedures, the decreases in urine flow and sodium excretion were more marked during exercise (P < 0.05). An increase in plasma catecholamines occurred only during exercise, together with a reduction in creatinine clearance and more marked increases in plasma renin and aldosterone than during passive heat exposure (P < 0.05). Although plasma vasopressin was elevated during the two dehydration procedures, urine osmolality did not change and, moreover, free water clearance increased during exercise (P < 0.05). Plasma levels of atrial natriuretic peptide increased markedly only during exercise compared to the other trials (P < 0.05). After the dehydration procedures, urine flow decreased again and urine osmolality increased markedly (P < 0.05), while plasma vasopressin remained elevated. These results suggest that sympathoadrenal activation during exercise plays a major role in the more marked reduction in diuresis and natriuresis than during passive heat exposure. Despite high plasma vasopressin concentrations during the two dehydrating events, the observed antidiuresis was not due to an increased renal concentrating ability, and the vasopressin was more effective after the dehydration procedures.

Adult↗

PubMed2001

Responsiveness of plasma catecholamines to intracerebroventricular injection of glucagon in Muscovy ducklings.

Recent investigations have demonstrated a modulatory action of glucagon on shivering via the central nervous system in ducklings. The aim of this study was to investigate the effects of intracerebroventricular injection (i.c.v.) of glucagon on metabolic rates (MR) and plasma catecholamines in control ducklings (TN) and in ducklings exhibiting nonshivering thermogenesis after chronic glucagon treatment: (GT). At thermoneutrality (25 degrees C, Ta), i.c.v. injection of glucagon had no thermogenic effects in TN and GT ducklings. At cold (+4 degrees C, Ta), i.c.v. glucagon injection elicited a concomitant decrease of plasma norepinephrine (NE) and MR in TN ducklings, whereas in GT ducklings, the plasma catecholamines and the MR remained unchanged. These results indicate that glucagon treatment rendered the catecholaminergic system of GT ducklings insensitive to cold or i.c.v. glucagon injection.

Animals↗

PubMed2001

[The diagnosis of atypical pheochromocytoma: a challenge for the biologist as well].

Biological diagnosis of pheochromocytoma is relatively easy in those cases releasing great amounts of catecholamines with strong clinical features; instead, diagnosis could be more problematic in atypical or asymptomatic familial pheochromocytoma with small tumors secreting low catecholamine amounts. Several plasma and urine adrenergic markers must be used to confirm the clinical suspicion. We have discussed the biological data of three totally asymptomatic pheochromocytomas (cases no 2, 3, 4) and one case with a very discrete clinical manifestation (no 1). Three patients had very small tumors (4, 7 and 25 g) secreting preeminently adrenaline, one patient had a 45 g adrenal incidentaloma without clinical expression. Our study shows that, in these special cases, except for an inconstant increase of adrenaline, plasma and urine catecholamines and urine VMA can be normal. The most useful markers are plasma and urine methoxyamines. However, plasma methoxyamines are the most sensitive because their increase over reference values is by far greater than in urines. Several factors may explain these findings: a low tumoral secretion, the nature of the released amine, the short half-life of catecholamines in plasma and, in some cases, the involvement of intratumoral catecholamine metabolism. Analysis of the ratio NMN/MN in plasma provides an additional diagnosis tool to reveal adrenaline secretion abnormalities.

Adrenal Gland Neoplasms↗

PubMed2001

Lack of alpha(2)-adrenergic antilipolytic effect during exercise in subcutaneous adipose tissue of trained men.

The aim of this study was to investigate the involvement of the antilipolytic alpha(2)-adrenergic receptor pathway in the regulation of lipolysis during exercise in subcutaneous abdominal adipose tissue (SCAAT). Seven trained men and 15 untrained men were studied. With the use of microdialysis, the extracellular glycerol concentration was measured in SCAAT at rest and during 60 min of exercise at 50% of maximal oxygen consumption. One microdialysis probe was perfused with Ringer solution; the other was supplemented with phentolamine (alpha(2)-adrenergic receptor antagonist). No differences in baseline extracellular or plasma glycerol concentrations were found between the two groups. The exercise-induced extracellular and plasma glycerol increase was higher in trained compared with untrained subjects (P < 0.05). Addition of phentolamine to the perfusate enhanced the exercise-induced response of extracellular glycerol in untrained subjects but not in trained subjects. The exercise-induced increase in plasma norepinephrine and epinephrine concentrations and the decrease in plasma insulin were not different in the two groups. These in vivo findings demonstrate higher exercise-induced lipolysis in trained compared with untrained subjects and show that, in trained subjects, the alpha(2)-mediated antilipolytic action is not involved in the regulation of lipolysis in SCAAT during exercise.

Adipose Tissue↗

PubMed2000

Sympathetic stimulation induced by hand cooling alters cold-induced vasodilatation in humans.

Hand cooling is a cold pressor test, which induces general sympathetic stimulation. This cooling procedure is often performed to investigate cold induced vasodilatation (CIVD) in one finger. To investigate the effects of this sympathetic stimulation on local CIVD, 12 subjects immersed either the right index finger (T1), right hand (T2) or left hand and right index finger (T3) for 30 min in water at 5 degrees C followed by 15-min recovery. Skin temperature and skin blood flow (Q(sk)) measured by laser Doppler flowmetry on the right index finger, as well as heart rate (f(c)) and mean arterial blood pressure (BP(a)), were continuously monitored during the three tests. Cutaneous vascular conductance was calculated as Q(sk)/(BP(a)). Concentrations of plasma noradrenaline (NA) and adrenaline (AD) were measured at different times during the tests. The results showed no cardiovascular change in T1, whereas f(c) and (BP(a)) increased significantly at the beginning of both T2 and T3. Similarly, sympathetic stimulation was reflected in the NA concentrations, which increased significantly (P < 0.01) during T2 and T3 after 5 min of immersion, and remained elevated until the recovery period. The AD concentration did not change during the three tests. During T2, the CIVD appeared later and slower in comparison with T1 [CIVD onset: 12.81 (SEM 2.30) min in T2 and 5.62 (SEM 0.33) min in T1]. During T3, the CIVD onset was not delayed compared to T1 [6.38 (SEM 0.67) min], but the rewarming was lower [+5.40 (SEM 0.86) degrees C in T3 and +9.10 (SEM 1.31) degrees C in T1]. These results showed that CIVD could be altered by sympathetic stimulation but it also appeared that the onset of CIVD could be influenced by local cooling, independently of the general sympathetic stimulation.

Adult↗

PubMed2000

Involvement of the catecholaminergic system in glucagon-induced thermogenesis in Muscovy ducklings (Cairina moschata).

Physiological studies have shown that glucagon is a potential mediator of nonshivering thermogenesis (NST) in birds. The present work was undertaken in order to investigate whether the observed thermogenesis results from a direct action of glucagon on avian thermoregulatory mechanisms or in fact requires the participation of other agents such as catecholamines. Our experiments were performed using cold-acclimated (CA) ducklings which developed muscle NST. A comparison was made with thermoneutral (TN) ducklings of the same age. Our principal results showed that: (1) at ambient temperature (25 degrees C), circulating norepinephrine (NE) was markedly decreased in CA ducklings (-42%), while circulating epinephrine (E) did not undergo any consistent change; (2) in CA and TN ducklings, an intraperitoneal injection of glucagon (360 microg x kg(-1)) was followed after 10 min by prominent lipolysis and a large increase in circulating NE (4- to 6-fold) and E (14- to 17-fold), which was sustained for at least 1 h. The elevation of circulating NE was less pronounced in CA ducklings. The thermogenic action of glucagon in birds is probably indirect and involves at least the mobilization of lipids and sympatho-adrenal stimulation. The changes in peripheral noradrenergic activity during cold acclimation could be associated with adaptive changes leading to NST.

Acclimatization↗

PubMed2000

Spinal cord monoaminergic system response to age and cold-acclimatization in muscovy duckling.

The effect of age and cold acclimatization on the regional distribution of monoamines in duckling spinal cord was studied. In thermoneutral controls (TN), the high dopamine (DA) to norepinephrine (NE) ratios (0.25 at 4 weeks of age and 0.15 at 6 weeks of age) suggest the presence of specific (non precursor) dopaminergic pools in cervical spinal cord. DA levels and the ratio of DA to NE were lowered by age and cold exposure in the cervical cord. In TN ducklings, serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) showed a decline with age in the spinal cord, indicating that this system is affected with development, whereas cold exposure prevents this decrease. The contents of 5-HT (+58%), 5-HIAA (+93%) and the ratio of 5-HIAA to 5-HT (+50%) are higher in the cervical spinal cord of cold acclimated than in TN ducklings. These results indicate that central monoaminergic systems are markedly affected by age and cold exposure.

3,4-Dihydroxyphenylacetic Acid↗

PubMed2000

Gender differentiation of the chemoreflex during growth at high altitude: functional and neurochemical studies.

The effect of chronic hypoxia on gender differences in physiology and neurochemistry of chemosensory pathways was studied in prepubertal and adult rats living at sea level (SL; Lyon, France) or at high altitude (HA; La Paz, Bolivia, 3,600 m). HA adult rats had higher hematocrit (Ht%), Hb concentration, resting ventilatory rate (Ve(100)), and higher tyrosine hydroxylase (TH) activity in carotid bodies (CB) than SL animals. At HA and SL, adult females had lower Ht% (46.0 +/- 0.8 vs. 50.4 +/- 0.6% at HA, P < 0.05 and 43.8 +/- 0.9 vs. 47.1 +/- 0.8% at SL, P < 0.05) and Hb (16.1 +/- 0.3 vs. 17.7 +/- 0.2 g/dl at HA, P < 0.05 and 14.5 +/- 0.3 vs. 15.6 +/- 0.1 g/dl at SL, P < 0.05) than males. Females had higher Ve(100) [170 +/- 19 vs. 109 +/- 7 ml. min(-1). 100 g(-1) at HA, P < 0.05 and 50 +/- 3 vs. 40 +/- 2 ml. min(-1). 100 g(-1) at SL, not significant (NS)] and lower CB-TH activity (1.40 +/- 0.2 vs. 3.87 +/- 0.6 pmol/20 min at HA, P < 0.05 and 0.52 +/- 0.1 vs. 0.68 +/- 0.1 pmol/20 min at SL; NS) than males at HA only. The onset of hypoxic ventilatory response during development was delayed at HA. Prepubertal HA females had higher Ve(100) than males (2 wk old, +47%) and higher CB-TH activity (3 wk old, +51%). Medullary noradrenergic groups were sex dimorphic during development at SL. Rats raised at HA had a drop of TH activity between the second and the third postnatal week in all medullary groups. In conclusion, our data support the hypothesis that the CB is the major site for sexual differentiation of the ventilatory control. Ventilatory differences appeared before puberty, and the animals bred at HA had profound alterations in the developmental process of the chemoreflex and its neural pathways. Some of these alterations are under dependence of the sex of the animal, and there is an important interaction between gender and the hypoxic environmental condition during the developmental period.

Age Factors↗

PubMed2000

Activation of alpha(2)-adrenergic receptors impairs exercise-induced lipolysis in SCAT of obese subjects.

With the use of the microdialysis method, exercise-induced lipolysis was investigated in subcutaneous adipose tissue (SCAT) in obese subjects and compared with lean ones, and the effect of blockade of alpha(2)-adrenergic receptors (ARs) on lipolysis during exercise was explored. Changes in extracellular glycerol concentrations and blood flow were measured in SCAT in a control microdialysis probe at rest and during 60-min exercise bouts (50% of heart rate reserve) and in a probe supplemented with the alpha(2)-AR antagonist phentolamine. At rest and during exercise, plasma norepinephrine and epinephrine concentrations were not different in obese compared with lean men. In the basal state, plasma and extracellular glycerol concentrations were higher, whereas blood flow was lower in SCAT of obese subjects. During exercise, the increase of plasma glycerol was higher in obese subjects (115 +/- 35 vs. 65 +/- 21 micromol/l). Oppositely, the exercise-induced increase in extracellular glycerol concentrations in SCAT was five- to sixfold lower in obese than in lean subjects (50 +/- 14 vs. 318 +/- 53 micromol/l). The exercise-induced increase in extracellular glycerol concentration was not significantly modified by phentolamine infusion in lean subjects but was strongly enhanced in the obese subjects and reached the concentrations found in lean sujects (297 +/- 46 micromol/l). These findings demonstrate that the physiological stimulation of SCAT adipocyte alpha(2)-ARs during exercice-induced sympathetic nervous system activation contributes to the blunted lipolysis noted in obese men.

Adipose Tissue↗

PubMed1999

Cardiac baroreflex during the postoperative period in patients with hypertension: effect of clonidine.

BACKGROUND: Patients with essential hypertension show altered baroreflex control of heart rate, and during the perioperative period they demonstrate increased circulatory instability. Clonidine has been shown to reduce perioperative circulatory instability. This study documents changes in measures of heart rate control after surgery in patients with essential hypertension and determines the effects of clonidine on postoperative heart rate control in these patients. METHODS: Using a randomized double-blind placebo-controlled design, 20 patients with essential hypertension (systolic pressure >160 mm Hg or diastolic pressure >95 mm Hg for > or =1 yr) were assigned to receive clonidine (or placebo), 6 microg/kg orally 120 min before anesthesia and 3 microg/kg intravenously over 60 min before the end of surgery. The spontaneous baroreflex ("sequence") technique and analysis of heart rate variability were used to quantify control of heart rate at baseline, before induction of anesthesia, and 1 and 3 h postoperatively. RESULTS: Baroreflex slope and heart rate variability were reduced postoperatively in patients given placebo but not those given clonidine. Clonidine resulted in greater postoperative baroreflex slope and power at all frequency ranges compared with placebo (4.9+/-2.9 vs. 2.2+/-2.1 ms/mm Hg for baroreflex slope, 354+/-685 vs. 30+/-37 ms2/Hz for high frequency variability). Clonidine also resulted in lower concentrations of catecholamine, decreased mean heart rate and blood pressure, and decreased perioperative tachycardia and hypertension. CONCLUSIONS: Patients with hypertension exhibit reduced heart rate control during the recovery period after elective surgery. Clonidine prevents this reduction in heart rate control. This may represent a basis for the improved circulatory stability seen with perioperative administration of clonidine.

Analgesics↗

PubMed1999

Altered daily rhythms of brain and pituitary indolamines and neuropeptides in long-term hypoxic rats.

To determine whether sustained hypoxia alters daily rhythms in brain and pituitary neurotransmitters, the daily variations in vasoactive intestinal peptide-like immunoreactivity (VIP-LI), neuropeptide Y-like immunoreactivity (NPY-LI), serotonin (5-HT), and 5-hydroxyindole-3-acetic acid (5-HIAA) content were determined in discrete brain regions, pineal gland and anterior pituitary of hypoxic (10% O(2); 14 days) and normoxic rats. Hypoxia suppressed daily variations in VIP-LI in the suprachiasmatic nuclei (SCN) and the anterior pituitary, enhanced the daily rhythmicity in serotonergic elements of the caudal part of the dorsomedial medulla oblongata (DMMc), and even induced daily variations in NPY-LI in the DMMc as well as in the ventrolateral medulla oblongata. In addition, punctual alterations in the rhythmicity of 5-HT and 5-HIAA in the pineal gland and of plasma corticosterone were observed in hypoxic rats. Thus results of this study indicate that a permanent nonphotic stimulus, such as sustained hypoxia, may affect the functioning of the internal clock located in the SCN and may alter the daily rhythmicity in neurotransmitter content of some brain nuclei and the pituitary gland.

Animals↗