Mapping of genetic determinants of the sympathoneural response to stress

Activation of the sympathoadrenal system (SAS, comprising the sympathetic nervous system and the adrenal medulla) in response to stressful stimuli is an important defense mechanism as well as a contributor to several cardiovascular diseases. There is variability in the SAS response to stress, although the extent to which this is genetically regulated is unclear. Some rodent models, including the hereditary hypertriglyceridemic (hHTg) rat, are hyperresponsive to stress. We investigated whether quantitative trait loci (QTLs) that affect sympathoadrenal response to stress could be identified. Second filial generation rats ( n = 189) derived from a cross of the hHTg rat and the Brown Norway rat had plasma norepinephrine (NE) and epinephrine (Epi) levels, indices of activation of the sympathoneural and adrenal medulla components, respectively, measured in the resting state and in response to an immobilization stress. Responses were assessed early (20 min) and late (120 min) after the application of the stress. A genome scan was conducted using 153 microsatellite markers. Two QTLs (maximum peak LOD scores of 4.17 and 3.52, respectively) influencing both the early and late plasma NE response to stress were found on chromosome 10. Together, the QTLs accounted for ∼20% of the total variation in both the early and late NE responses in the F2rats. Interestingly, the QTLs had no effect on plasma Epi response to stress. These findings provide evidence for a genetic determination of the response of a specific component of the SAS response to stress. Genetically determined variation in sympathetic nervous system response to stress may contribute to cardiovascular diseases.

Effect of in ovo leptin administration on the development of Japanese quail

Potential changes in the activity of endocrine axes related to growth as a result of leptin administration during embryonic development of birds were evaluated in the Japanese quail as a model bird with fast growth and development. On day 5 of incubation, 0.1 microg or 1 microg of recombinant mice leptin in 50 microl of phosphate buffered saline were injected into the albumen of eggs. Animals from each group were killed by decapitation on day 0, 2, 5, 7, 14, 21, 28, 35, 42, 49 and 56 of life. Plasma concentrations of triiodothyronine (T(3)), thyroxin (T(4)), corticosterone, testosterone, total lipids, triacylglycerols, cholesterol, glucose and alkaline phosphatase activity were measured. Quail treated by leptin hatched earlier (5-24 hours) and had a higher body weight than the control group (P<0.05-0.001). Mean body weight across the whole observed period was higher in both treated groups as compared to the control group (P<0.05). Leptin in ovo administration was accompanied by changes of endocrine and metabolic parameters during postembryonic development. The most prominent changes appeared immediately after hatching (T(3), T(4), total lipids, triacylglycerols) and before sexual maturity. It is suggested that leptin acts as a general signal of low energy status to neuroendocrine systems in birds which improves utilization of nutrients.

Hypothalamo-pituitary-adrenocortical axis function and hedonic behavior in adult male and female rats prenatally stressed by maternal food restriction

Neuroendocrine activation during stress is affected by many factors contributing to the variability of the stress response. The present study was aimed at evaluating long-term changes in hypothalamo-pituitary-adrenocortical (HPA) axis function and in hedonic behavior in adult offspring prenatally stressed by maternal food restriction, with attention on possible gender differences. Adult offspring were blood sampled via a tail artery cannula. Prenatally stressed females had significantly higher adrenal weights compared to males. Plasma ACTH levels, which rose in response to acute stress induced by handling, were significantly higher in females compared to those in males. A similar pattern was found in plasma corticosterone. The rise in ACTH levels was more pronounced in prenatally stressed rats though the rise in corticosterone failed to be modified. Corticotropin releasing hormone (CRH) and proopiomelanocortin mRNA levels in the hypothalamic paraventricular nucleus and anterior pituitary, respectively, were found to be unchanged. The present experiments failed to reveal a decrease in hedonic behavior in prenatally stressed rats. In contrast, in male offspring a tendency to a higher sucrose preference was observed. These data together with observed changes in hormone and CRH mRNA levels indicate that the gestational stress used did not result in a depression-like state in adult offspring.

Nitric oxide synthase mRNA levels correlate with gene expression of angiotensin II type-1 but not type-2 receptors, renin or angiotensin converting enzyme in selected brain areas

Recent data suggest that there is interaction between peripheral angiotensin II and nitric oxide. However, sparse information is available on the mutual interaction of these two compounds in the brain. The potential intercourse of nitric oxide with brain neuropeptides needs to be substantiated by assessing its local production and gene expression of the synthesizing enzymes involved. The aim of the present study was to evaluate whether the gene expression of brain nitric oxide synthase (bNOS) is related to the sites of gene expression of different components of the rat brain renin angiotensin system (renin, angiotensin converting enzyme (ACE) or angiotensin receptors of AT1 and AT2 subtypes). The levels of corresponding mRNAs were measured and correlated in nine structures of adult rat brain (hippocampus, amygdala, septum, thalamus, hypothalamus, cortex, pons, medulla and cerebellum). As was expected, positive correlation was observed between renin and angiotensin-converting enzyme mRNAs. Moreover, a significant correlation was found between brain NO synthase and AT1 receptor mRNAs, but not with mRNA of the AT2 receptor, ACE and renin. Parallel distribution of mRNAs coding for bNOS and AT1 receptors in several rat brain structures suggests a possible interaction between brain angiotensin 11 and nitric oxide, which remains to be definitely demonstrated by other approaches.

Gene expression of NMDA receptor subunits in rat adrenals under basal and stress conditions

In addition to the central nervous system, glutamate receptors have been recently identified in a number of peripheral tissues, including adrenals. Pharmacological evidence indicates that adrenal glutamate receptors may be involved in stress response, particularly in catecholamine release. However, possible stress-induced changes at the level of local receptors themselves have not been evaluated yet. This study was aimed to investigate gene expression of N-methyl-D-aspartate (NMDA) receptor subunits (NR1, NR2A, NR2B) in rat adrenal gland under basal and stress conditions, using RT-PCR. NR1 mRNA was found to be present in the adrenal gland, while mRNAs coding for NR2-type subunits failed to be detected in adrenal tissue. The distribution of NR1 mRNA in rat adrenals showed higher concentrations in the adrenal medulla (228%) compared to those in the cortex. Single stress stimulus (immobilization) induced a significant increase of NR1 gene expression in both medullar (by 25%) and cortical (by 66%) regions of the adrenal gland at 24 h, while no changes were observed at 3 h after the stress exposure. It is possible that delayed rise in adrenal NR1 gene expression following stress exposure represents one of the factors by which stress exerts long-term effects on adrenal function at the molecular level.

Elevated AT1 receptor protein but lower angiotensin II-binding in adipose tissue of rats with monosodium glutamate-induced obesity

Age-related hypertrophy of adipose tissue has been associated with a significant decrease in the number of angiotensin II receptors. The aim of this study was to investigate the characteristics of angiotensin II receptors in hypertrophic adipose tissue in animal obesity model using rats postnatally treated with monosodium glutamate. Angiotensin II is known to induce hypertrophy in several tissues of the cardiovascular system and might do the same in fat tissue. The expression and binding properties of angiotensin II AT(1) receptors in epididymal fat tissue of adult rats were studied using membrane-binding, RT-PCR, and immunoblotting. The amount of AT(1) receptor mRNA did not differ significantly between obese and control rats. Despite that glutamate-treated rats displayed approximately 4-times more AT(1) receptor immunoreactive protein content in fat tissue cell membranes than the controls did. In contrast, binding experiments showed a significant (40.3 +/- 6.2 %) decrease of (125)I-Sar(1)-Ile(8)-angiotensin II-binding to fat tissue cell membranes in obese rats compared to controls. In conclusion, the present study provides evidence for the low binding properties associated with an accumulation of AT(1) receptor protein in cell membranes of the fat tissue of rats with glutamate-induced obesity. Discrepancies among angiotensin II-binding, AT(1) receptor protein, and AT(1) receptor mRNA levels indicate a possible defect in the receptor protein, which remains to be identified. The results obtained support a role of angiotensin II and AT(1) receptors in the pathogenesis of obesity.

Altered function of peripheral organ systems in rats exposed to chronic mild stress model of depression

1. In depression, psychiatric symptoms are frequently associated with impaired cardiovascular function and perhaps also increased risk for cancer diseases. Pathophysiological basis of this comorbidity is not clearly understood. Molecular events involved, particularly factors modified by chronic stress exposure, may only be evaluated in animal models of depression. 2. Present experiments were aimed to study parameters related to cardiovascular system (tyrosine hydroxylase (TH) gene expression in adrenal glands) and carcinogenesis (retinoic acid receptors in the liver) in the chronic mild stress model of depression. 3. Chronic mild stress induced a rise in adrenal TH gene expression in both male and female rats. Gender dependent changes were found in retinoic acid receptor binding with stress-induced activation in females but not males. Ovariectomized animals exhibited higher retinoic acid receptor binding. slightly elevated TH mRNA levels and failed to respond to chronic mild stress exposure with further increase in TH mRNA levels. Similarly, chronic mild stress induced an anhedonic state manifested by decreased sucrose preference in control but not ovariectomized rats. 4. Presented data document that central neurochemical and behavioral changes in animals exposed to chronic mild stress model of depression are associated with changes in adrenal TH gene expression and with gender dependent changes in retinoic acid receptor status in the liver. Such alterations may participate in the development of pathological changes and could participate on increased risk for cardiovascular and oncologic comorbidity in depressive patients.

[Glutamate receptors and transporters in the brain and peripheral tissues]

Functional diversity of glutamate receptors in the central nervous system (CNS) is a consequence of their considerable molecular diversity. The family of glutamate receptors including their subunits consists of more than 25 proteins. It is the result of gene expression as well as extensive post-transcriptional modifications. Evidence is increasing that glutamate receptors are localised not only in the CNS, but also in the peripheral tissues. Whereas characteristics and physiological significance of peripheral glutamate receptors are little understood, there are studies indicating their role in hormone secretion, neuromuscular functions, sensory transmission and paracrine signalization. In addition, peripheral glutamate receptors may participate in mediating of excitatory amino acids toxicity. A special attention is paid to glutamate receptors localised in the heart and adrenals, as these receptors may be involved in the maintenance of homeostatic mechanisms under pathological or stress conditions.

Effect of nitric oxide inhibition on blood pressure and corticosterone responses in adult rats neonatally treated with glutamate

The role of nitric oxide (NO) in the regulation of blood pressure and hypothalamic-pituitary-adrenal function of adult rats treated with monosodium glutamate (MSG) during the neonatal period was investigated. Blood pressure and the heart rate were registered by a computerized system of direct blood pressure measurement through an indwelling cannula in the femoral artery. The inhibition of the activity of NO synthase by acute injection of Nomega-nitro-L-argininemethylester (L-NAME, 30 mg/kg, i.v.) to control rats produced a rise of blood pressure and a fall of heart rate. Both responses were reduced in MSG-treated rats. Repeated administration of L-NAME (50 mg/kg, i.p, two times daily for 4 days) increased BP in both groups of animals. Corticosterone concentrations in the plasma were significantly increased in response to repeated L-NAME administration in MSG-treated rats, while ACTH levels were similar in both groups of animals. These data suggest that some of the cardiovascular and endocrine changes in rats treated with MSG may be due to the abnormal function of the NO system.

Corticotropin-releasing hormone mRNA levels in response to chronic mild stress rise in male but not in female rats while tyrosine hydroxylase mRNA levels decrease in both sexes

Corticotropin-releasing hormone (CRH) and catecholamines are suggested to play a significant role in the pathophysiology of depression. In the present study we investigated gene expression of CRH in the hypothalamic paraventricular nucleus (PVN) and tyrosine hydroxylase (TH) in the locus coeruleus (LC) in an experimental model of depression. A chronic mild stress model was applied in rats of both genders for a three-week period. Anhedonic behaviour, a typical sign of depression-like state, was measured by a sucrose preference test. The chronic mild stress induced a decrease in sucrose preference in both genders. The body weight gain was reduced in males only. The total activity in the open field test was unchanged, however, male rats exposed to chronic mild stress showed enhanced locomotor activity during the first minute of the session, suggesting increased anxiety. Basal plasma corticosterone levels, thymus and adrenal weights measured on the third day after cessation of the stress regimen, were not affected by the stress procedure. Evaluation of CRH mRNA levels in the PVN by in situ hybridisation revealed a significant rise in response to chronic mild stress in males. In females, the basal CRH mRNA levels were higher compared to those in males, but the stress-induced rise was absent. Chronic mild stress resulted in a decrease in TH mRNA levels in the LC. These data demonstrate that chronic mild stress model of depression induces a specific stress response with a reduction of TH gene expression in the LC and clear gender differences in gain of body weight, anxiety-like behaviour, and CRH mRNA levels in the PVN.

Daily profiles of arginine vasopressin mRNA in the suprachiasmatic, supraoptic and paraventricular nuclei of the rat hypothalamus under various photoperiods

Daily rhythm of arginine vasopressin (AVP) mRNA levels in the suprachiasmatic nucleus (SCN) of rats maintained under a short, LD 8:16 photoperiod differed from that of rats maintained under a long, LD 16:8 photoperiod: under the short photoperiod the morning AVP rise occurred significantly later than under the long one. Daily profiles of AVP mRNA in the supraoptic and paraventricular nuclei were not rhythmic and AVP mRNA levels under LD 8:16 did not differ from those under LD 16:8. The data indicate that photoperiod affects selectively the clock driven AVP gene expression in the SCN.

Quinolinic acid enhances permeability of rat brain microvessels to plasma albumin

Several studies have established that increased cerebrospinal fluid (CSF) levels of quinolinic acid (QUIN), a macrophage/microglia-derived excitotoxin with N-methyl-D-aspartate (NMDA)-receptor affinity, may reflect abnormal blood-brain barrier (BBB) function in patients with acquired immunodeficiency syndrome (AIDS) dementia complex, exhibiting a relationship to their clinical and neurological status. This study was aimed to evaluate whether QUIN (250 nmol/0.25 microl/ventricle) infused into both lateral cerebral ventricles permeates adult rat brain microvessels to plasma albumin. Possible BBB dysfunction was examined 4 days after the intracerebroventricular (i.c.v.) infusion of QUIN by measuring plasma albumin extravasation using rocket immunoelectrophoresis. The i.c.v. infusion of QUIN failed to increase the extracellular tissue concentration of albumin in the entorhinal cortex, but significantly higher levels were found in the hippocampus proper (but not in the subiculum region and dentate gyrus) and in the striatum. To evaluate the possible relationship between plasma protein extravasation and QUIN-induced tissue necrosis, we quantified neuronal death in the rat hippocampal formation (subiculum, CA1/CA3 areas of the hippocampus proper, dentate gyrus). We found significantly higher tissue levels of plasma albumin in the hippocampus proper, in which the CA1 area exhibited the highest neuronal loss while the low rate of neuronal death was not accompanied by significant albumin extravasation in the dentate gyrus. However, in case of the subiculum, in which the neuronal loss reached comparable values to those in the CA1 area, we did not find significant enhancement of plasma albumin leakage into this area. The regional differences in brain microvascular permeability may depend on the density of NMDA receptors in the multicellular capillary barrier, but the differences in neuronal death may also reflect an involvement of NMDA receptors in neuronal membranes. We conclude that increased CSF QUIN levels evoke a dysfunction of the BBB that may only partially be related to sites with pronounced neuronal damage in the rat brain regions susceptible to NMDA-receptor mediated toxicity.

Gene expression of two glutamate receptor subunits in response to repeated stress exposure in rat hippocampus

1. Glutamatergic mechanisms are thought to be involved in stress-induced alterations of brain function, especially in the hippocampus. We have hypothesized that repeated stress exposure may evoke changes of hippocampal glutamate receptors at the level of gene expression. 2. The study was designed to analyze the levels of mRNA coding for NMDAR1, the essential subunit of the N-methyl-D-aspartate (NMDA) receptor subtype, and for GluR1, an AMPA glutamate receptor subunit, after repeated immobilization stress in rat hippocampus. Toward this aim, we applied a competitive RT-PCR technique which allowed precise and reliable quantification of the transcripts. 3. We found that repeated immobilization stress for 7 days significantly increased GluR1 mRNA levels, by 27% (P<0.01), as measured 24 hr after the last stress exposure. Levels of mRNA coding for NMDAR1 were slightly elevated, but the difference failed to be significant. 4. These results demonstrate selective changes in the gene expression of glutamate receptor subunits, which are likely to take part in the mechanisms leading to enhanced excitability and vulnerability of hippocampal neurons and to potential damage during repeated or chronic stress exposure.

Neonatal stress alters habituation of exploratory behavior in adult male but not female rats

The effect of monosodium-L-glutamate (MSG) administration in the neonatal period on habituation of exploratory behavior related to gender differences was investigated. Rats of both sexes were intraperitoneally treated with MSG (4 mg/g) or hypertonic saline (10% NaCl) on postnatal days 2, 4, 6, 8, and 10. On postnatal day 65, the animals were tested in an open-field test during 4 consecutive days, once daily in 6-min sessions. The rapidity of habituation of exploratory behavior during repeated exposure to the open field (interrupted habituation) and over individual sessions (uninterrupted habituation) was evaluated by using the method of linear regression. Compared to intact controls, there were no significant differences found in interrupted habituation, neither in males nor in females. Uninterrupted habituation in neonatally treated males was slowed down in the first 2 days of testing. No differences in adult behavior between treated groups (MSG and hypertonic saline) were observed, i.e., there were no late effects specific for neonatal MSG administration. In females, uninterrupted habituation was not affected. Males proved to be more sensitive to neonatal stress associated with injections of MSG or hypertonic saline than females, and showed feminine-like habituation in the new environment.

Corticotropin-releasing hormone synthesizing neurons in the hypothalamic paraventricular nucleus of rats neonatally treated with monosodium glutamate can respond to different stress paradigms

Neonatal administration of monosodium glutamate (MSG) produces pathological lesions in many brain regions. There are indications that MSG treatment could also influence the neurons of the hypothalamic paraventricular nucleus (PVN). The goal of this study was to find out whether MSG treatment could alter the activity of the corticotropin-releasing hormone synthesizing neurons, i.e. the principal regulators of the corticotropin hormone secretion, located in the medial posterior subdivision of the PVN. The activity of CRH neurons was assessed by changes in CRH mRNA levels in response to both stimulatory and inhibitory conditions induced by immobilization and water deprivation, respectively. In addition, effect of the circulating glucocorticoid deficit induced by bilateral adrenalectomy was investigated. The obtained data show that in MSG-treated animals the rise in CRH mRNA in response to immobilization stress and adrenalectomy as well as the decrease after water deprivation were similar to the changes seen in controls. In addition POMC mRNA changes in MSG-treated animals indicate an uninterrupted capability of CRH neurons to transform different signals to corticotropin cells. It can be concluded that CRH neurons of the PVN are not functionally altered, in spite of the widespread neurotoxic effect of MSG treatment.

Dissociation of changes in hypothalamic corticotropin-releasing hormone and pituitary proopiomelanocortin mRNA levels after prolonged stress exposure

Repeated immobilization stress for 7 days caused marked increase in corticotropin-releasing hormone (CRH) mRNA in the paraventricular nucleus (PVN, 90% above the control) and proopiomelanocortin (POMC) mRNA in the anterior pituitary (73% above the control) in rats. Prolongation of the stress exposure to 42 days led to a decline of CRH mRNA response (42% above the control) in comparison with that after 7 days, while POMC mRNA persisted at the same level. Observed adaptation of CRH but not POMC responses suggests that other factor(s) next to CRH participate in sustained rise in POMC expression during long-term stress.

Plasma catecholamines and renin activity in wrestlers following vigorous swimming

Cardiovascular and neuroendocrine responses to exercise in a physically fit and an untrained group of young healthy subjects were compared to study the significance of physical fitness for performance in a discipline for which the athletes were not trained. Ten wrestlers of national rank prepared for an international competition (age 18 years) and 9 untrained healthy males (age 21 years). Exercise consisted of 27-min swimming, freestyle, in water of 29 degrees C, with last 3 min increased to maximal effort. The blood pressure, heart rate and sublingual temperature were measured and blood samples were withdrawn before exercise, immediately after and after a 30 min period of rest. Catecholamines were analyzed by radioenzymatic method and plasma renin activity (PRA) using commercial kits. Systolic blood pressure and heart rate after swimming were increased comparably in the two groups, diastolic pressure was unchanged in the controls and decreased in the wrestlers. Plasma cortisol remained unchanged. Plasma glucose tended to increase in the controls and so decrease in wrestlers, with a significant difference between them after swimming (p < 0.05). However, plasma adrenaline was concomitantly increased in both groups (p < 0.01). Noradrenaline and PRA were increased after swimming in both the control and trained group. The increments of noradrenaline and PRA in wrestlers were significantly reduced compared to the control group (p < 0.01, p < 0.05, respectively). Higher physical fitness in athletes significantly reduced plasma noradrenaline and angiotensin responses to maximal exercise demanding special skill in work performance which had not been included in their training program. Training of wrestlers did not cause an exaggerated plasma adrenaline response to exercise.

Four-week ethanol intake decreases food intake and body weight but does not affect plasma leptin, corticosterone, and insulin levels in pubertal rats

Long-term intake of ethanol decreases food intake and inhibits growth in experimental rats. The aim of this study was to determine the effect of 4-week oral ethanol ingestion on plasma leptin and adrenal function. Male 45-day-old Wistar rats were divided into three groups: absolute control (AC), ethanol (E) administered 10% (wt/vol) ethanol instead of tap water, and pair-fed (PF) given an amount of food corresponding to the food intake of E animals. E rats consumed less pelleted diet (74% cumulative total intake); however, this caloric deficit was compensated by ethanol ingestion. Net water intake in E animals was 76% of that in the control groups. The body growth of both E and PF rats was stunted compared with AC animals, but E rats were heavier than PF rats. The plasma leptin level was similar in E and AC and decreased in PF animals. There were no differences in plasma osmolality or glycemia among the three groups. Plasma insulin was decreased in PF compared with both AC and E rats. Plasma corticosterone was not affected by ethanol, but was increased in the food-restricted (PF) group. Although there were no differences in basal adrenal corticosterone production in vitro, there was a slightly higher response to corticotropin (ACTH) in E rats. We conclude that drinking 10% ethanol decreased the dietary intake and body growth. These changes were not mediated by plasma leptin changes. Although alcohol ingestion and its energy content theoretically normalized the total energy intake and prevented the decrease of plasma leptin, the growth of young rats was inhibited. Drinking 10% ethanol instead of tap water for 4 weeks did not stimulate basal adrenal activity.

The hypothalamic-pituitary response in SLE. Regulation of prolactin, growth hormone and cortisol release

It has been suggested that neuroendocrine regulation plays an important role in the pathogenesis and activation of autoimmune diseases. The aim of this investigation was to clarify the hypothalamic-pituitary response to a well-defined stimulus under standardised conditions in patients with SLE. Plasma concentrations of prolactin (PRL), growth hormone (GH) and cortisol were determined in venous blood drawn through an indwelling cannula during insulin-induced hypoglycaemia (0.1 U/kg b.w., i.v.) in ten patients and in 12 age-, gender- and weight-matched healthy subjects. Basal PRL concentrations were higher in patients vs healthy controls (12 vs 6 ng/ml, P < 0.01), though still within the physiological range. Insulin-induced plasma PRL and GH were significantly increased both in patients and healthy subjects; however, the increments or areas under the curves were not different in the two groups. Plasma cortisol response showed moderate attenuation in patients. Sensitivity of pituitary lactotrothrops to thyrotropin-releasing hormone (TRH) administration (200 microg, i.v.) was the same in patients and control subjects. In SLE patients with low activity of the disease the sensitivity of pituitary PRL release to TRH administration remained unchanged. The hypothalamic response to stress stimulus (hypoglycaemia) was comparable in patients and healthy subjects.

Treatment of neonatal rats with monosodium glutamate attenuates the cardiovascular reactivity to phenylephrine and angiotensin II

In rats, neonatal administration of monosodium glutamate (MSG) causes serious damage in some hypothalamic and circumventricular areas. The resulting loss of appropriate neurons important for the regulation of blood pressure (BP) may modulate cardiovascular system receptivity in these animals. In the present study, the reactivity of the cardiovascular system to intravenous injection of alpha1-adrenergic receptor agonist phenylephrine (200 microg/kg/ml) and angiotensin II (500 ng/kg in 0.6 ml for 2 min) was investigated in adult rats which had been neonatally treated with MSG or vehicle. BP parameters measured directly in conscious cannulated rats were continuously registered using a computerized system. Under basal conditions, MSG-treated rats had slightly lower systolic, diastolic and mean BP with significant differences in pulse pressure (systolic - diastolic BP). In MSG-treated animals, the maximal increase of mean arterial BP after phenylephrine and the duration of BP elevation after both agents were significantly reduced. Slopes of the linear portion of baroreceptor function curves in control and MSG-treated rats did not differ significantly, indicating that baroreflex efficacy was unchanged. The results obtained by perfusion of the hindlimb vascular bed in situ showed that the pressure responses to increasing doses of noradrenaline in MSG-treated rats were reduced. These findings demonstrate that neonatal treatment of rats with MSG lowers the responsiveness of the cardiovascular system, particularly in response to alpha-adrenergic stimulation. It is suggested that the attenuation of cardiovascular reactivity in MSG-treated rats is, at least partly, caused by diminished vascular responsiveness.

Stress and colchicine do not induce the release of galanin from the external zone of the median eminence

The aim of the present study was to verify the hypothesis that stress exposure modifies the content and release of galanin in the hypothalamic paraventricular nucleus and the median eminence. Colchicine and immobilization served as stress stimuli, and the changes in galanin immunoreactivity were compared with those in corticotropin-releasing hormone and vasopressin. In control animals, a limited number of galanin perikarya were identified in the paraventricular nucleus. The high dose (75 microg) of colchicine enhanced galanin in both parvicellular and magnocellular subdivisions, as analysed 72 h later. In the median eminence, galanin accumulated only in the external zone. High-dose colchicine did not affect galanin, while corticotropin-releasing hormone and vasopressin were depleted from the median eminence. Immobilization (120 min) neither alone nor in combination with colchicine influenced galanin immunoreactivity in the external zone. The low dose of colchicine induced an unexpected accumulation of galanin in the internal zone of the median eminence, which was further increased by subsequent immobilization. In the external zone, low-dose colchicine induced a complete disappearance of vasopressin, substantial depletion of corticotropin-releasing hormone and no changes in galanin immunoreactivity. The present studies demonstrate that galanin in the external zone of the median eminence is not influenced by colchicine or by immobilization stress.

Enhanced neuroendocrine response to insulin tolerance test performed under increased ambient temperature

The hypothesis that an increase in ambient temperature modulates neuroendocrine response in clinically used provocative pituitary function tests was verified. Healthy male volunteers were subjected to insulin tolerance tests in two randomized trials. In the first trial hypoglycemia was induced by a bolus injection of insulin (0.1 U per kg of BW, i.v.) at room temperature. In the second trial, the subjects were exposed to increased ambient temperature for 45 min before insulin injection and for 45 min thereafter. The environmental temperature was selected to increase body temperature less than 1C. Under conditions of increased temperature basal hormone levels as measured in antecubital venous blood samples failed to be modified and the hypoglycemia was less severe. Nevertheless, the responses of most (beta-endorphin, ACTH, prolactin, catecholamines), but not all (growth hormone, cortisol), hormones to hypoglycemia were exaggerated. The remarkable increase in ACTH and beta-endorphin release was not accompanied by concomitant increase of plasma cortisol response. The sympathetic-adrenomedullary system was significantly activated, which was manifested particularly by enhanced norepinephrine release. Growth hormone response to hypoglycemia was not modified, while that of prolactin was enhanced. Thus during evaluation of neuroendocrine function under clinical conditions, changes in ambient and body temperature should not be underestimated.

Neurotoxic lesions induced by monosodium glutamate result in increased adenopituitary proopiomelanocortin gene expression and decreased corticosterone clearance in rats

Hypothalamic-pituitary-adrenocortical function in rats with brain lesions induced by neonatal monosodium glutamate (MSG) treatment (4 mg/g, 5 administrations, i.p.) was evaluated in the present study. Using in situ hybridization we found increased proopiomelanocortin (POMC) mRNA levels in the adenopituitary and normal corticotropin-releasing hormone mRNA levels in the hypothalamic paraventricular nucleus in MSG-treated rats. The total content of pituitary adrenocorticotropin (ACTH) was not changed, while pituitary ACTH concentration was higher in MSG-treated compared to control rats. The number of ACTH-immunostained cells per a constant area of adenohypophysial section, as measured by immunohistochemistry, was unchanged indicating that no significant condensation of corticotropes occurred. Basal plasma ACTH concentrations were not different, whereas morning corticosterone levels were elevated in rats with MSG treatment. While ACTH response to stress stimuli was similar in both groups of rats, corticosterone response to exogenous ACTH (500 ng/kg, i.v., Synacthen), short-lasting handling and immobilization was of the same magnitude but prolonged in MSG-treated rats. Based on the decline of [3H] corticosterone in plasma, a decreased corticosterone clearance rate was found in MSG-treated rats. These findings suggest that MSG treatment results in increased POMC gene expression per corticotrope of the atrophic pituitary resulting in maintenance of normal pituitary ACTH stores and plasma ACTH levels. Elevated basal levels of corticosterone in plasma as well as prolonged corticosterone responses to stimulations in rats treated with MSG seem to be due to a decreased clearance rate of corticosterone.

[The syndrome of inappropriate secretion of antidiuretic hormone in hypophyseal tumors]

70-year old man was admitted to the hospital due to the sudden change in his behaviour with the production of unusual echolalic word connections. Arginin-vasopressin (AVP) level (1.16 pg/ml) was found inappropriately higher in relation to the severe serum hypoosmolality (261 mmol/kg) and hyponatraemia (117 mmol/l) with relatively high urinary osmolality (590 mmol/kg) and natriuria (684 mmol/24 h). Diagnosis of the syndrome of inappropriate secretion of antidiuretic hormone (SIADH-type C) was confirmed during the water load test. Magnetic resonance imaging and CT scans revealed in the region of hypophysis intrasellar tumour (diameter of 16 mm) and the stabilized finding of temporal cyst. Substitution of sodium losses with the restricted fluid intake resulted in the correction of water-electrolyte balance and the restoration of normal clinical state.

Stress-induced increase in blood-brain barrier permeability in control and monosodium glutamate-treated rats

Glutamate administration in neonatal rats causes reversible changes in blood-brain barrier (BBB) permeability and known neurotoxic lesions. This study was aimed to evaluate whether glutamate administered to neonatal rats influences properties of the developing BBB with consequences on adult BBB function. The vulnerability of the BBB was examined after short-lasting stress exposure by measurement of plasma albumin extravasation using immunoelectrophoresis. In control rats, 30 min of immobilization stress resulted in increased endogenous albumin extravasation in the hypothalamus, hippocampus, brain stem and cerebellum, but not in the cortex and striatum. Basal levels of albumin in adult glutamate-treated rats (4 mg monosodium glutamate/g BW, IP, five times during neonatal period) were significantly lower in the hypothalamus compared to that in controls. Stress-induced increase in albumin levels was lower in the brain stem, higher in the hypothalamus, and similar in other brain regions studied in glutamate-treated rats in comparison with controls. It is concluded that short-lasting immobilization stress increased BBB permeability in some but not all brain regions studied. Glutamate treatment of neonatal rats resulted in low basal albumin levels in the hypothalamus but did not exert a pronounced influence on adult BBB function. BBB vulnerability in glutamate-treated rats during stress exposure was increased in the hypothalamus and decreased in the brain stem.

Relationship between endocrine, immune, and clinical variables in patients with systemic lupus erythematosus

OBJECTIVE

To assess the frequency of increased plasma prolactin (PRL) in patients with systemic lupus erythematosus (SLE) and to evaluate its relationship to other hormonal and immune variables.

METHODS

Thirty-five patients with SLE with various levels of disease activity were studied. Plasma PRL, cortisol, growth hormone (GH) were determined by radioimmunoassay and interleukin 6 (IL-6) by ELISA: SLE activity was evaluated using the European Consensus Lupus Activity Measurement (ECLAM).

RESULTS

Increased plasma PRL concentration (> 20 ng/ml) was recorded in 11 patients (31%). No correlation was found between plasma PRL and GH, IL-6, cortisol, or C-reactive protein, nor was any significant correlation observed between plasma PRL and the ECLAM score. Patients with hyperprolactinemia were, however, found to have been treated with higher doses of prednisone therapy than patients with normal plasma PRL. Further analysis of the relationship of plasma PRL and therapy showed that patients with SLE selected by the attending physician for prednisone therapy in doses > or = 10 mg/day were more frequently hyperprolactinemic.

CONCLUSION

Our findings that patients with SLE with a more active form of the disease and who are less responsive to therapy had increased plasma PRL levels more frequently may be indicative of a potential relationship of hyperprolactinemia to severity of disease.

Chronic blockade of nitric oxide synthesis elevates plasma levels of catecholamines and their metabolites at rest and during stress in rats

Formation of nitric oxide, and endothelium-derived relaxing factor, can be inhibited by administration of N-nitro-L-arginine methylesther (L-NAME). In the present study, the activity of the sympathoadrenal system in rats with blood pressure (BP) elevation induced by L-NAME was investigated. L-NAME was administered in a dose of 50 mg/kg, i.p. every 12 h for 4 days. Blood samples were collected via chronically inserted arterial catheters in conscious, freely moving rats at rest and during immobilization stress. Plasma epinephrine (EPI), norepinephrine (NE), and dopamine (DA), as well as catecholamine metabolites dihydroxyphenylglycol (DHPG) and dihydroxyphenylacetic acid (DOPAC) were measured by HPLC method. In L-NAME treated animals, which slowed a significant increase in BP, plasma EPI levels were markedly elevated both before and during stress. Plasma NE levels were not significantly increased, however, DHPG levels, which indicate NE turnover and reuptake, were highly elevated. Plasma DA levels were not changed after L-NAME administration but DA metabolite DOPAC showed a significant elevation both under basal conditions and during stress. Thus, the present results indicate that the prolonged blockade of nitric oxide synthesis that causes arterial hypertension is associated with an activation of the sympathoadrenal system.

Effect of central administration of the non-NMDA receptor antagonist DNQX on ACTH and corticosterone release before and during immobilization stress

The purpose of the present study was to evaluate the role of central alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA)/kainate type of glutamate receptors in the control of ACTH and corticosterone release under basal and stress conditions. AMPA/ kainate competitive receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX), which does not penetrate the blood-brain barrier, was administered intracerebroventricularly (i.c.v.). A modified method for i.c.v. drug administration in conscious freely moving rats was employed. DNQX or artificial cerebrospinal fluid (aCSF) was injected into lateral ventricle through a thin polyethylene cannula with a steel needle on the end which was inserted and moved via large polyethylene cannula to the guide stainless steel cannula. This procedure was performed out of the cage. ACTH and corticosterone release under basal conditions and during immobilization stress were investigated. Intracerebroventricular administration of DNQX resulted in an increase of ACTH and corticosterone in plasma reaching maximal values at 15 min after drug injection. During immobilization stress, i.c.v. DNQX induced a mild reduction in plasma ACTH levels compared to those in aCSF pretreated rats. Corticosterone secretion was high throughout the whole period of stress exposure. These findings indicate that endogenous excitatory amino acids (EAA) acting at AMPA/kainate receptors may interfere with the control of ACTH release under both basal and stress conditions, but the mechanisms involved remain to be elucidated.

Presence of atriopeptin-like immunoreactivity in human and rat milk

Maternal milk is a significant source of hormones and other bioactive substances. They might be involved either in the control of mammary gland function or in the regulation of growth and development of the neonate. Atriopeptin (atrial natriuretic factor, ANF) is a peptide with strong diuretic, natriuretic and vasorelaxant actions, and it has been suggested to play an important role in the circulatory adaptation to extrauterine life. The aim of this study was to determine whether ANF is present in maternal milk, using radioimmunological analysis. The levels of ANF-like substance in human milk were found to be in the range of 0.3-3.0 pg/ml, those in rat milk between 37-117 pg/ml. The measured concentrations of ANF were proportional to the volume of the extracted milk. Serial dilutions of the extracts yielded curves which were not totally parallel to the human alpha-ANF standard curve. Our data indicate that, during the first days after delivery, ANF levels in human milk are higher than those in later periods of lactation. This pilot study provides the first description of the presence of atriopeptin in milk. Though a detailed characterization of milk ANF-like immunoreactivity is needed, a biological significance of present findings seems possible.

[Activation of the neuroendocrine system during changes in homeostasis during stress conditions]

Neuroendocrine response to stress stimuli is aimed to maintain body homeostasis. The activation of the neuroendocrine system is accomplished mainly by two ways: by feedback regulation based on the recognition of altered metabolic homeostasis by appropriate receptors sending the signal into the CNS, and by forward regulation involving a direct stimulation of the neuroendocrine system by a central command coming from an activated brain regulatory center. With regard to mechanisms of neuroendocrine activation, the signal specificity and site of its origin are of particular importance. The significance of the signal in neuroendocrine responses has been evaluated in three different stress conditions: hypoglycemia, surgical trauma and dynamic physical exercise. The stimulus inducing neuroendocrine response during hypoglycemia is the glucopenia. The signal for the activation of the neuroendocrine response is generated in glucosensitive cells which are not located in a single brain structure (hypothetical glucostat). The signal for growth hormone, vasopressin and oxytocin release is produced in brain structures protected by the blood-brain barrier, that for ACTH release in regions both protected and unprotected by the barrier, while the signal for prolactin release is generated in tissues lacking the blood-brain barrier. The neuroendocrine response during surgical trauma is activated by a signal formed in the damaged tissue reaching the CNS by neural pathways. Moreover, cytokins may participate on endocrine stimulation in those surgical interventions in which a large amount of bacterial endotoxins is released. During a complicated surgery, e.g. during a bypass other signals and modifying factors, such as hypothermia, dilution of blood, hypoperfusion of organs, rewarming of the body and hormone degradation in the oxygenator are important. On the On the other hand, during a short-term dynamic exercise, a forward regulation by a central signal from the activated CNS motor center comes into play with the consequent release of catecholamines, growth hormone, etc. In the control of some other hormones (beta-endorphin, partly ACTH) and especially during a long term exercise, neural signals from working muscles (feedback) are also involved. During a static exercise mainly catecholamines triggered by signals from working muscle cells are activated. The understanding of the signal and mechanisms of neuroendocrine activation during stress is indispensable for selective modulation of physiological and pathological responses.

Head-up tilt and lower body suction: comparison of hormone responses in healthy men

The purpose of this study was to compare, in the same subjects, hormonal responses to 30-min head-up tilt (HUT) and lower body suction (LBNP) of different intensity (24 degrees and 70 degrees, and 15 and 35 mm Hg, respectively). Basal pooled individual data from -10 min (n = 32) were within normal reference limits: norepinephrine (NE) averaged 318 +/- 23 pg/ml; epinephrine, 34.0 +/- 5.5 pg/ml; plasma renin activity (PRA), 0.72 +/- 0.08 ng ATII/ml/h; aldosterone, 164 +/- 20 pg/ml; atrial natriuretic peptide (ANP), 29.9 +/- 2.0 pg/ml; cGMP, 6.29 +/- 0.59 mmol/l; cortisol, 95.7 +/- 5.8 ng/ml; and ACTH, 50.3 +/- 2.6 pg/ml. The low-level stimuli failed to induce consistent changes in hormone levels. From the onset of the stimulus (minute 0) to its termination (minute 30), norepinephrine (NE) increased by 101% with LBNP-35, and by 70% with HUT70, respectively. The NE increase with LBNP-35 was higher (p < 0.05) than with HUT70. Epinephrine rose with HUT70 (by 162%) only. PRA increased by 157% with LBNP-35, and by 119% with HUT70, respectively; these responses were not significantly different. Aldosterone rose equally (by 85 and 89%) with LBNP-35 and HUT70 but not with the low-level stimuli. No consistent changes were observed in ANP, c-GMP or ACTH concentrations. Cortisol values fell during the LBNP and HUT24 situations but rose transiently after HUT70. We conclude that the hormones investigated respond differently to head-up posture and lower body suction and in a specific manner. Greater effects of high-level stimuli (HUT70, LBNP-35) were noted as compared to low-level stimuli (HUT24, LBNP-15). The application of combined sets of models stimulating the cardiovascular system may aid in the analysis of responses of hormonal systems in man.

Neuroendocrine response during stress with relation to gender differences

Neuroendocrine activation belongs to the main characteristics of the stress response. This response is not uniform but depends on the stress stimulus involved and on many other factors including the gender of the individual. In rats, corticosterone and ACTH levels as well as functional activity of the hypothalamo-pituitary-adrenocortical axis are higher in females compared to males under both basal and stress conditions. Marked sex differences were observed in stress-induced changes posterior pituitary hormone release. In male rats, release of vasopressin is not stimulated during stress conditions without an osmotic component while in female rats a rise in plasma vasopressin levels was observed even after short immobilization. Oxytocin release is enhanced in response to the majority of stress stimuli and it was found to be greater in females than in males. Mentioned gender differences are attributed to the effect of sex steroids, particularly those of estrogens. Not enough information is available on gender differences in the neuroendocrine response during stress in humans. We observed a greater neuroendocrine activation in women than in men in response to heat exposure in sauna with pronounced differences in ACTH and prolactin release and partly also after a cold-pressor test. Understanding of gender differences in neuroendocrine response during stress might contribute to the explanation of the development of some emotional and other disorders with higher incidence in women.

Low ambient temperature and neuroendocrine response to hypoglycemia in men

Nutritional factors, such as an excess or a deficiency of glucose, play an important role in neuroendocrine regulations. Hormonal and metabolic responses to hypoglycemia were examined in healthy non-obese volunteers under conditions of low ambient temperature. Hypoglycemia was induced by intravenous injection of insulin in two randomized trials performed at room temperature and at 4 degrees C. At room temperature, the typical neuroendocrine response to hypoglycemia was established. The increases of ACTH, beta-endorphin, growth hormone and cortisol in response to insulin hypoglycemia failed to be modified by low ambient temperature. Acute cold exposure significantly reduced epinephrine and totally inhibited prolactin response to insulin-induced hypoglycemia. In spite of significant changes in epinephrine response to hypoglycemia at low ambient temperature, no striking differences in plasma glucose levels compared to those measured at room temperature were observed. However, under conditions of low temperature the reestablishment of normoglycemia was delayed. No changes in free fatty acids were found under our experimental conditions. The presented data show that low ambient temperature exerts selective effects on some neuroendocrine and metabolic parameters.

Ion transport in rat antral mucosa in vitro: general characteristics

Although numerous studies have shown the existence of various types of ion conductance in antral part of gastric fundus mucosa epithelia of amphibian, practically no data are available on ion conductance in higher animal species. Present experiments were undertaken to check the possible existence of ion conductance in rat gastric antral mucosa and to investigate its general electrophysiological characteristics. Antral epithelia were isolated from adult Sprague Dawley rats. The tissues were mounted to a modified Ussing-type chamber and continually perfused with identical Krebs-Henseleit bicarbonate buffer on both sides. Antrum generated a transepithelial electrical potential difference (Vt = -10 +/- 2.6 mV) and short-circuit current (Isc = 76 +/- 15 microA.cm-2) with a transepithelial electrical resistance (Rt = 135 +/- 16.8 Ohm.cm2). Ion replacement experiments showed that it is mainly Na+ transport that contributes to Vt and Isc as evidenced by a) Na+ and/or Cl- removal, b) the effects of amiloride a sodium channel blocker, on the apical (secretory) surface, c) the effects of the Na(+)-K(+)-ATPase inhibitor ouabain on the basolateral (nutrient) side of the epithelium. Microelectrode experiments confirmed the existence of Na+ and/or Cl- conductance of the apical cell membrane. Antral mucosa also showed a gradual and time-dependent increase in sensitivity to amiloride (10(-5) mol/l). Maximum inhibition of Vt and Isc by amiloride in dose-dependent manner was detected after 1-2 h. This amiloride-sensitive sodium transport (maximal level 31.5 +/- 5.9 microA.cm-2) represented approximately 50% of the whole transepithelial ion conductance. Results of experiments with ouabain (10(-4 mol/l) suggest the presence of functional Na(+)-K(+)-ATPase and/or Na(+)-ATPase in the basolateral cell membranes. Which signals trigger this epithelial ion transport, which hormones are responsible for its regulation and what is the physiological significance of this ion conductance remains to be elucidated.

[Glutamate neurotransmission, stress and hormone secretion]

Glutamate neurotransmission has been investigated in relation to several physiological processes (learning, memory) as well as to neurodegenerative and other disorders. Little attention has been paid to its involvement in neuroendocrine response during stress. Penetration of excitatory amino acids from blood to the brain is limited by the blood-brain barrier. As a consequence, several toxic effects but also bioavailability for therapeutic purposes are reduced. A free access to circulating glutamate is possible only in brain structures lacking the blood-brain barrier or under conditions of its increased permeability. Excitatory amino acids were shown to stimulate the pituitary hormone release, though the mechanism of their action is still not fully understood. Stress exposure in experimental animals induced specific changes in mRNA levels coding the glutamate receptor subunits in the hippocampus and hypothalamus. The results obtained with the use of glutamate receptor antagonists indicate that a number of specific receptor subtypes contribute to the stimulation of ACTH release during stress. The authors provided also data on the role of NMDA receptors in the control of catecholamine release, particularly in stress-induced secretion of epinephrine. These results were the first piece of evidence on the involvement of endogenous excitatory amino acids in neuroendocrine activation during stress. Neurotoxic effects of glutamate in animals are well described, especially after its administration in the neonatal period. In men, glutamate toxicity and its use as a food additive are a continuous subject of discussions. The authors found an increase in plasma cortisol and norepinephrine, but not epinephrine and prolactin, in response to the administration of a high dose of glutamate. It cannot be excluded that these effects might be induced even by lower doses in situations with increased vulnerability to glutamate action (age, individual variability). (Tab. 1, Fig. 6, Ref. 44.).

Endogenous excitatory amino acids are involved in stress-induced adrenocorticotropin and catecholamine release

The effect of N-methyl-D-aspartic acid (NMDA) receptor blockade on adrenocorticotropin (ACTH) and catecholamine activation during stress was investigated in conscious rats with indwelling catheters for both blood sampling and drug treatment. Secretion of ACTH in response to immobilization stress (20 min) was inhibited by pretreatment (20 min before stress exposure) with the centrally acting noncompetitive antagonist of NMDA receptors MK-801 (dizocilpine, the racemic form, 1 mg/kg i.p.) but not by 3-[(+/-)-2-carboxypiperazin-4-yl]propyl-1-phosphonic acid (CPP; 10 mg/kg i.p.), a competitive NMDA receptor antagonist. Administration of MK-801 (1 mg/kg i.p.) inhibited norepinephrine and totally prevented epinephrine response during acute immobilization stress. Pretreatment with a low dose of MK-801 (0.1 mg/kg i.p.) failed to modify basal or stress-induced ACTH and catecholamine release. The stress-induced rise in plasma epinephrine was found to be attenuated by the peripherally injected competitive antagonist CPP (10 mg/kg i.p.) suggesting that modulation not only of central but also of peripheral NMDA receptors may come into play. Our results indicate the involvement of endogenous excitatory amino acids in the control of ACTH and particularly of epinephrine secretion during stress.

Central stimulation of hormone release and the proliferative response of lymphocytes in humans

The central nervous system (CNS) may communicate with the immune system by direct innervation of lymphoid organs and/or by neurotransmitters and changes in neuroendocrine functioning and hormone release. The consequences of selective transient changes in circulating hormones on immune functioning in humans have not yet been studied. To address this problem, the authors evaluated the lymphoproliferative responses to optimal and suboptimal concentrations of phytohemagglutinin (PHA) and pokeweek mitogen (PWM) under selective enhancement of circulating growth hormone, prolactin, or norepinephrine. The authors failed to demonstrate any effect of elevated growth hormone levels after clonidine challenge on the lymphoproliferative response to mitogens. Similarly, the results did not show any effect of elevated prolactin concentrations induced by domperidone administration on the immune test. Exposure of volunteers to cold resulted in elevation of plasma norepinephrine levels without changes in growth hormone, epinephrine, or cortisol secretion. Cold exposure induced elevation of plasma norepinephrine and reduction of the lymphoproliferative response to the suboptimal dosage of PHA. The reduction was significant 180 and 240 min after exposure. These results are indicative of a relationship between norepinephrine and immunity.

Studies on the physiological role of ANF in ACTH regulation

To investigate the impact of changes in the level of the endogenous atrial natriuretic factor (ANF) on pituitary-adrenocortical activity, the secretion of corticotropin (ACTH) and corticosterone was studied under the conditions of enhanced and decreased circulating ANF levels in rats. Volume expansion (intravenous infusion of 5 ml of saline within 2 min) induced significant elevation in ANF levels 5 min after the infusion, whereas ACTH levels remained unchanged during the first 20 min and were elevated only at 40 min, i.e. at the time when ANF levels were again normal. Water deprivation for 48 h resulted in decreased ANF levels and increased corticosterone concentrations. ANF concentrations in peripheral blood obtained under thiopental anesthesia were lower than those in blood sampled in the same rats in conscious state. However, such changes were not observed in water deprived animals. In addition, ANF was found to be present in the hypophysial portal blood of anesthetized rats. In conscious sheep, portal ANF levels were significantly higher than those in peripheral blood. Our results support the suggestion of an inhibitory role of ANF in the control of ACTH release and indicate that this role of ANF is physiologically relevant.

Angiotensin II induces reduced oxytocin but normal corticotropin release in rats with lesions of the subfornical organ

The subfornical organ (SFO) was suggested to be the site of the central nervous system which mediates the stimulatory effect of angiotensin II (AII) on corticotropin (ACTH) release. To verify this hypothesis, ACTH response to peripherally administered AII was measured in rats with electrolytic lesion of the SFO. Increase in ACTH levels in response to AII (0.5 micrograms/kg or 2.0 micrograms/kg i.v. within 2 min) in conscious cannulated rats was dose-related and it was not affected by SFO lesion. The short infusion of AII (2.0 micrograms/kg) was enough to induce an elevation in plasma oxytocin. Oxytocin response to AII was reduced while that of aldosterone and blood pressure was not modified by SFO lesion. Our data show that an intact SFO is needed for a full response of oxytocin but not of ACTH release to peripherally injected AII.

Influence of salmon melanin concentrating hormone on vasopressin analogue (dDAVP) activity and sodium transport in frog skin

Salmon melanin-concentrating hormone (sMCH) is a peptide known to regulate skin pigmentation both in fish and tetrapod (frog and lizard). To evaluate the influence of sMCH on ionic transport in frog skin, standard voltage-clamp technique for the measurement of transepithelial short-circuit current (ISC) reflecting net sodium transport was used. It was found that sMCH alone applied at concentrations of 0.5; 5 or 10 mumol/l failed to influence ISC. The application of 5 mumol/l of sMCH, however, inhibited ISC across the skin stimulated by a synthetic analogue of vasopressin (dDAVP), whereas no influence on natriferic effect of 1 mumol/l forskolin by the studied peptide was observed. The results indicate that cAMP was presumably not involved in the mediation of sMCH action in frog skin. We assume that the interaction of sMCH with the basolateral membrane could lead either (1) to changes of membrane structure including organization of its lipid surrounding or (2) to modification of AVP/dDAVP receptor activity and binding capacity. The nature of these interactions and change(s) in cell membrane and signal(s) which trigger processes responsible for the inhibitory effect of sMCH on dDAVP-stimulated frog skin sodium transport remains to be elucidated.

Sex differences in endocrine response to hyperthermia in sauna

Neuroendocrine response was investigated during and after a single 20 min bath in sauna (80 degrees C) in a group of 8 healthy men and 8 healthy women. In an additional group of 8 young men, the dynamics of plasma ACTH and cortisol levels were studied during a 30 min sauna exposure (90 degrees C). This dynamic study showed a biphasic response of plasma cortisol which decreased during the initial phase of sauna bath (15 min) and increased thereafter, reaching its maximum 15 min after the end of bathing. Maximal increase in plasma ACTH levels occurred 15 min earlier. In the first sauna exposed group the increase in body temperature was the same (about 2 degrees C) in both sexes. Nevertheless, the elevation in plasma ACTH concentration was significantly more pronounced in women than in men. In the plasma collected at the end of sauna bath inside the sauna room, a significant rise in both adrenaline and noradrenaline levels was found. Though the catecholamine responses were similar in both groups, the increase in heart rate during sauna bath was significantly higher in women. Sauna-induced prolactin release was also more pronounced in women compared with men. Thus hyperthermia induced by sauna exposure resulted in a more pronounced neuroendocrine activation in women compared with men. Moreover, it is evident that repeated blood sampling is necessary to reveal the sauna-induced activation of some hormonal systems.

Albumin content in the developing rat brain in relation to the blood-brain barrier

The problem of functional development of the blood-brain barrier (BBB) has been the subject of intensive discussion for many years. Some morphological data indicate that the cerebral endothelium becomes impermeable to macromolecules already before birth. On the other hand, specific features in transport of macromolecular markers in fetuses and neonates were described supporting the hypothesis of an immature BBB. Part of the confusion seems to result from inadequately designed experiments, concerning frequently the administration of markers. In our study we decided not to use an exogenous marker and to follow up to changes of endogenous albumin content in selected brain regions of rats from the neonatal period to adulthood. Shortly after birth, the concentrations of albumin in all brain regions studied (hypothalamus, hippocampus, cortex, striatum, brainstem, cerebellum) were significantly higher compared to those of adult animals. Moreover, the distribution of albumin within these structures in newborns differed from that in adults. Several factors may contribute to the accumulation of albumin in the developing rat brain, including increased permeability of the BBB.

Effect of a low salt diet on blood pressure and vasoactive hormones in the hereditary hypertriglyceridemic rat

In hereditary HTG rats, basal systolic blood pressure using tail-cuff sphygmomanometry was significantly higher (122.1 +/- 2.1 mm Hg; n = 16) than that in NTG animals (107.1 +/- 1.52; n = 16). A low salt diet did not influence blood pressure in NTG rats during the consecutive 4 weekly periods. However, in the second week blood pressure in HTG rats rose significantly in both the control rats on a normal salt diet and those on a low salt diet (132.5 +/- 1.89, n = 8, and 132.6 +/- 1.93, n = 8). No further changes were registered in the third and fourth week in control HTG rats. On the other hand, blood pressure fell significantly in HTG rats on a low salt diet in the third week in comparison with the second week (119.5 +/- 3.2, n = 8), and it increased again in the fourth week (123.0 +/- 2.35, n = 8). Hormones in plasma were determined at the end of the experiment. Plasma levels of norepinephrine were not influenced by differences in salt intake and were significantly higher by about 45% in HTG than in NTG animals. The lowest concentration of corticosterone in plasma was found in control HTG rats (1.2 +/- 0.2 vs 4.6 +/- 0.8 micrograms/100 ml in control NTG rats). Nevertheless, corticosterone concentration increased in HTG rats on a low salt diet at comparable values found in NTG rats on a low salt diet (3.1 +/- 0.8 vs 4.3 +/- 1.5). Plasma renin activity and plasma aldosterone concentrations were not different in the NTG and HTG groups and were uninfluenced by the diets (Table 1). We conclude that the elevated blood pressure in HTG rats and its variations during the experiment may reflect more pronounced sympathetic activity in HTG rats rather than blood pressure dependency on different salt intake.

Paraventricular and supraoptic nuclei of the hypothalamus are not equally important for oxytocin release during stress

The relative importance of the paraventricular (PVN) and the supraoptic nuclei (SON) for the secretion of oxytocin was evaluated by comparison of stress-induced oxytocin release under normal conditions, in the absence of vasopressin and/or corticoliberin (CRF). We introduced an incomplete anterolateral cut (iALC) around the mediobasal hypothalamus designed to leave intact the SON-neurohypophysial connections but to inflict damage to the nerve fibers from the PVN. The studies were performed in conscious cannulated rats using immobilization as the stress stimulus. Stress-induced oxytocin release was found in heterozygous Brattleboro rats as well as in homozygous animals lacking vasopressin, yet in the latter it was less pronounced and in both cases it was prevented by iALC. In Wistar rats, stress-induced oxytocin release was markedly reduced after iALC and absent after PVN lesion. Both hypothalamic interventions failed to influence basal oxytocin levels and resulted in a similar reduction of ACTH release. It is concluded that a functional diversity exists between the hypothalamic magnocellular nuclei. At least in relation to immobilization stress, the PVN is essential for stress-induced oxytocin release and it is evident that the SON without the PVN cannot preserve oxytocin secretion during stress.

Effect of space flight on the development of endocrine functions in rats

The effects of the exposure to space flights on plasma hormone levels were studied in adult male rats, in pregnant females and in their progeny. An increase of plasma corticosterone (CS) and insulin (I) levels was found in male rats after space flights for a period of 7, 15, 18 and 20 days. Plasma levels of growth hormone (GH) were decreased and those of epinephrine (E) and norepinephrine (NE) were elevated in rats exposed to longer space flights (18 or 20 days). In pregnant female rats no significant changes of plasma concentrations of CS, GH, I, E and NE were noted after short term space flight (5 days). However, the plasma prolactin levels were elevated. In young animals exposed to space flight during fetal development no changes of plasma I and prolactin levels were noted during the period of postnatal growth. However, the plasma CS levels were elevated in these rats and no gradual increase of CS plasma concentration was observed during the postnatal period. The plasma GH levels were reduced in rats exposed to space flight and the levels of catecholamines in plasma and in adrenal glands were elevated in 30 and 100 day old rats exposed to microgravity during the fetal development. These results demonstrated: 1. that exposure of rats to space flight is followed by changes in I and CS plasma levels, but the sympathetic-adrenomedullary system is only slightly activated by longer space flights; 2. that a short term space flight is only a mild stressor for pregnant rats and slightly affects the activity of adrenocortical and sympathetic-adrenomedullary systems during the development of their offsprings.

Specificity of the effect of repeated handling on sympathetic-adrenomedullary and pituitary-adrenocortical activity in rats

The response of the pituitary-adrenocortical and sympathetic-adrenomedullary system to single and repeated handling was studied in rats. After repeated handling (14 days, 3 x 1 min daily or 1 day, 6 x 1 min at 30 min intervals) a reduction of plasma epinephrine and ACTH level was observed, while norepinephrine levels increased to the same extent as after the first handling. When repeatedly handled rats were handled by a different person, hormonal responses were altered: The reduction in the ACTH and epinephrine response was no longer apparent, whereas the norepinephrine response was potentiated. In the case of repeated handling over a short time period (3 hr) the last handling by a different person did not alter the reduced hormonal response. Behavioral habituation to repeated handling paralleled adaptation of plasma ACTH and epinephrine levels. The observed dissociation of plasma epinephrine and norepinephrine response suggests that different pathways control the response of the adrenal medulla and the peripheral sympathetic nervous system.

N-methyl-D-aspartic acid injected peripherally stimulates oxytocin and vasopressin release

The effects of N-methyl-D-aspartic acid (NMDA), injected s.c. or i.p. in the dose range of 2.5-10 mg/kg, on oxytocin and vasopressin levels were assessed in conscious rats. NMDA administration was found to induce a dose-related increase in oxytocin concentration with a peak response at 7.5 min. Plasma vasopressin was elevated only after injection of the highest dose used (10 mg/kg). Thus, though at different thresholds, the release of both posterior pituitary hormones was stimulated after NMDA administration.