Circadian studies of plasma cortisol, thyroid hormone, protein, glucose and ion concentration, liver glycogen concentration and liver and spleen weight in rainbow trout, Salmo gairdneri Richardson

1. Although there are many reports in the literature of circadian rhythms in plasma hormone and metabolite levels, the data are highly variable between research groups. The present study attempts to re-examine whether circadian rhythm in plasma cortisol, thyroid hormone, ions, glucose and protein levels and liver glycogen levels are evident in rainbow trout, Salmo gairdneri, and determine whether there is a significant correlation between any of the measured variables. 2. Significant fluctuations throughout the day were found in all measured variables; although these fluctuations appear to be a normal component in the homeostatic function of rainbow trout, their timing was neither consistent nor predictable. 3. "Circadian-like" patterns were observed in levels of plasma cortisol, glucose, Mg2+ and K+ concentrations and liver glycogen concentration. 4. Seasonal variations in these circadian-like rhythms were found in liver glycogen and plasma cortisol, Mg2+ and K+ concentrations. 5. Plasma cortisol and glucose concentrations were affected by time of feeding. 6. There were significant correlations between plasma thyroid hormone and plasma protein levels, but no other significant correlation between any of the measured variables was found.     

Diurnal and Seasonal Cortisol,Testosterone, and DHEA Rhythms in Boys and Girls during Puberty

Diurnal and seasonal rhythms of cortisol, testosterone, and DHEA were examined, as little is known about the relationship between these rhythmicities and pubertal development. Salivary samples were obtained from 60 boys and 60 girls at approximately 07∶45, 08∶00, 08∶30, 12∶00, 16∶50, and 21∶00 h. The participants' ages ranged from 8–14 yrs, and each participant was tested three times at six‐month intervals. The study was conducted at a General Clinical Research Center (GCRC) and at the homes of the participants. All hormones showed diurnal fluctuations. The acrophase (peak time) of cortisol occurred earlier than for testosterone or DHEA and showed a seasonal effect, with the acrophase occurring earlier in spring than in summer. The cortisol acrophase also occurred later in the day for boys than for girls during later puberty. Seasonal effects were found only for cortisol with higher concentrations in the spring and summer. Cortisol concentrations were relatively stable across pubertal maturation, but significantly lower concentrations were observed at pubertal stage 3 compared to the other stages. Morning cortisol levels were also higher in boys at pubertal stage 2. Testosterone concentrations were higher in boys at pubertal stages 3 and 4, and DHEA was lower at pubertal stage 1 than 3 and 4 for both boys and girls. For the total sample, there was a positive correlation between DHEA and testosterone during early puberty (stages 1–3) but not later puberty (stages 4–5). Awakening secretory activity correlated with daytime secretory activity for testosterone and DHEA, but not for cortisol. These data provide novel chronobiological information on cortisol, testosterone, and DHEA as it relates to sexual maturation and encourage further study on both normal and abnormal endocrine rhythms.     

Diurnal and seasonal cortisol, testosterone, and DHEA rhythms in boys and girls during puberty

Diurnal and seasonal rhythms of cortisol, testosterone, and DHEA were examined, as little is known about the relationship between these rhythmicities and pubertal development. Salivary samples were obtained from 60 boys and 60 girls at approximately 07:45, 08:00, 08:30, 12:00, 16:50, and 21:00 h. The participants' ages ranged from 8-14 yrs, and each participant was tested three times at six-month intervals. The study was conducted at a General Clinical Research Center (GCRC) and at the homes of the participants. All hormones showed diurnal fluctuations. The acrophase (peak time) of cortisol occurred earlier than for testosterone or DHEA and showed a seasonal effect, with the acrophase occurring earlier in spring than in summer. The cortisol acrophase also occurred later in the day for boys than for girls during later puberty. Seasonal effects were found only for cortisol with higher concentrations in the spring and summer. Cortisol concentrations were relatively stable across pubertal maturation, but significantly lower concentrations were observed at pubertal stage 3 compared to the other stages. Morning cortisol levels were also higher in boys at pubertal stage 2. Testosterone concentrations were higher in boys at pubertal stages 3 and 4, and DHEA was lower at pubertal stage 1 than 3 and 4 for both boys and girls. For the total sample, there was a positive correlation between DHEA and testosterone during early puberty (stages 1-3) but not later puberty (stages 4-5). Awakening secretory activity correlated with daytime secretory activity for testosterone and DHEA, but not for cortisol. These data provide novel chronobiological information on cortisol, testosterone, and DHEA as it relates to sexual maturation and encourage further study on both normal and abnormal endocrine rhythms.     

Photoperiodic variations in plasma concentration of testosterone in the rabbit

The photoperiodic variations of testosterone plasmatic levels in male rabbits have been studied. The animals were subjected to the influence of three circadian rhythms: 12/12, 14/10 and 10/14 h of light/darkness. The hormone assay was carried out using an enzymeimmunoassay method (Competitive ELISA). Blood samples were of two different types: seriated and non-seriated, to find if these might be any differences in the results. It is concluded that testosterone plasmatic levels are within physiologic values (0.3-10.0 ng/ml), although differences depending on the light/darkness cycle and on the type of blood extraction are remarkable; for this reason the selection of the circadian rhythm will depend on the experimentation that is to be carried out.     

A complex rhythm problem: The possibility of a lunar modulation of plant function

Abstract

The analysis of long temporal series of gas exchange of seeds in moist atmosphere or of root lengths of seedlings reveals the existence of non‐random fluctuations. Several observations allow us to envisage the presence of rhythmicities with modulated periods.

The plant material was kept in darkness at stabilised temperature and humidity. The experiments were conducted on different plant species, in various conditions of temperature and humidity in different years. The gas exchange was measured with the Warburg apparatus; the roots on seedlings after 72 h of germination on Petri glasses. We compared the rhythmicities of the biological material with some periodicities of the geophysical environment. We chose as a reference the passages of the moon and of the sun at the meridian.

An analogy is observed between several of the observed rhythmicities and the circadian and low‐frequency rhythmicities of the geophysical environment. It seems as if submultiples of those natural periods would be generated. We consider the probable existence of modulated synchronisation and we propose an hypothesis for deriving the observed periodicities from three basic circadian rhythms: solar, lunar and "circadian”;.

A model is proposed and a theoretical curve elaborated which is in reasonal concordance with, the experimental curve. We point out that appropriate mathe‐. matical methods for modulated periods and amplitudes should be useful.     

Influence of administration of pyridoxine on circadian rhythm of plasma ACTH, cortisol prolactin and somatotropin in normal subjects

The influence of vitamin B6 in a dosage of 300 mg X 2 in 24 hrs, on circadian rhythm of plasmatic ACTH, cortisol, prolactin and somatotropin have been studied in 10 normal women. After vitamin B6 24 hrs pattern of ACTH and cortisol is unchanged; prolactin levels are slightly lower, in a statistically unsignificant proportion the night peak of growth hormone is higher in a statistically significant proportion (p. 0.05). The effect of vitamin B6 is likely to me mediated by dopaminergic receptors at hypothalamic level as previous studies by other Authors appear to prove.     

Circadian rhythms of salivary cortisol content during long-term space flight

Adaptation mechanisms of adrenal function related to secretion of cortisol were studied under conditions of microgravity. Parameters of diurnal rhythms of salivary cortisol were studied by Russian cosmonauts on board orbital station Mir during long-term space flights (SF). The preflight circadian rhythms of salivary cortisol in cosmonauts were characterized by the morning maximum occurring at 9∶43 a.m., the fluctuation amplitude 6.05 nmol/1, and the daily average concentration 8.79 nmol/l. The characteristics of cortisol diurnal rhythm changed under conditions of long-term space flight. On average, the rhythm measure and amplitude decreased after two months of flight. The postflight maximum concentration of free cortisol tended to occur later in the day. Evidently, the motor activity during SF, i.e., prophylactic exercises along with other factors, significantly influenced the parameters of cortisol circadian rhythm that was revealed by the individual variability of findings during the flight. After the long-term SF, individual ratios of salivary and plasma cortisol levels increased against the background of increased plasma content of the hormone, i.e., the fraction of free, physiologically active hormone in the total pool of circulating molecules decreased.     

Changes in rhythmicities of ambulatory and drinking activities after hypophysectomy in rats.

Effects of hypophysectomy on circadian rhythms of ambulatory and drinking activities in adult male rats were automatically recorded and investigated with a Gundai-type ambulodrinkometer. The rats were maintained under LL conditions following an LD condition. When free-running rhythms had stabilized, the rats were hypophysectomized. The rhythmicities of both activities became indistinct over the 2-4 weeks following surgery, and then gradually recovered. At this time phase shifts (phase advance) were observed in the hypophysectomized rats, while these changes were not observed in sham-operated rats. All rats entrained to lighting when kept under LD conditions again. These results suggest that the pituitary does not play an essential role in maintaining circadian rhythms, but does function as an important subordinal oscillator.     

Influences of chronic administration of melatonin on hormonal rhythms in rats

Pharmacological doses of melatonin—low (0.5 mg/kg body wt.) and high (1.0 mg/kg body wt.) doses were administered chronically for 45 days to Wistar rats, and 24 h rhythms of adrenocorticotrophic hormone, cortisol, growth hormone, prolactin and melatonin were studied under semi-natural conditions. Exogenous melatonin administration caused delays in the acrophases of growth hormone and melatonin rhythm itself, whereas advances in the acrophases of adrenocorticotrophic hormone, cortisol and prolactin were observed, thus indicating that chronic administration of melatonin could alter the characteristics of endocrine rhythms. Alterations in the amplitude and mesor values of these endocrine rhythms were also observed during melatonin administration. Modulation of melatonin rhythmicity (due to exogenous administration) could influence the hormonal rhythms as a modulated internal zeitgeber and could simulate/mimic the conditions of altered photoperiod in the animal; this could be the reason for altered acrophase values in the melatonin treated groups. Significant dose-dependent effects of melatonin were absent in the present study. It remains to be proven how exogenous administration of melatonin could influence the hormonal rhythms investigated in the present study.     

Circannual rhythm of plasmatic vitamin D levels and the association with markers of psychophysical stress in a cohort of Italian professional soccer players

Adequate plasmatic Vitamin D levels are crucial to maintain calcium homeostasis and bone metabolism both in the general population and in athletes. Correct dietary supply and a regular sun exposure are fundamental for allowing the desired and effective fitness level. Past studies highlighted a scenario of Vitamin D insufficiency among professional soccer players in several countries, especially in North Europe, whilst a real deficiency in athletes is rare. The typical seasonal fluctuations of Vitamin D are wrongly described transversally in athletes belonging to teams that play at different latitudes and a chronobiologic approach studying the Vitamin D circannual rhythm in soccer players has not been described yet. Therefore, we studied plasma vitamin D, cortisol, testosterone, and creatin kinase (CK) concentrations in three different Italian professional teams training at the same latitude during a period of two consecutive competitive seasons (2013 and 2014). In this retrospective observational study, 167 professional soccer players were recruited (mean age at sampling 25.1 ± 4.7 years) and a total of 667 blood drawings were carried out to determine plasma 25(OH)D, serum cortisol, serum testosterone and CK levels. Testosterone to cortisol ratio (TC) was calculated based as a surrogate marker of overtraining and psychophysical stress and each athlete was drawn until a maximum of 5 times per season. Data extracted by a subgroup of players that underwent at least 4 sample drawings along a year (N = 45) were processed with the single and population mean cosinor tests to evaluate the presence of circannual rhythms: the amplitude (A), acrophase (Φ) and the MESOR (M) are described. In total, 55 players (32.9%) had an insufficient level of 25(OH)D during the seasons and other 15 athletes (9.0%) showed, at least once, a deficiency status of Vitamin D. The rhythmometric analyses applied to the data of Vitamin D revealed the presence of a significant circannual rhythm (p < 0.001) with the acrophase that occurred in August; the rhythms of Vitamin D levels were not different neither among the three soccer teams nor between competitive seasons. Cortisol, testosterone and TC showed significant circannual rhythms (p < 0.001): cortisol registered an acrophase during winter (February) while testosterone and TC registered their peaks in the summer months (July). On the contrary, CK did not display any seasonal fluctuations. In addition, we observed weak but significant correlations between 25(OH)D versus testosterone (r = 0.29 and p < 0.001), cortisol (r = ?0.27 and p < 0.001) and TC (r = 0.37 and p < 0.001). No correlation was detected between Vitamin D and CK. In conclusion, the correct chronobiologic approach in the study of annual variations of Vitamin D, cortisol and testosterone could be decisive in the development of more specific supplementation and injury prevention strategies by athletic trainers and physicians.     

Changes in the Diurnal Rhythms during a 45-Day Head-Down Bed Rest

In spaceflight human circadian rhythms and sleep patterns are likely subject to change, which consequently disturbs human physiology, cognitive abilities and performance efficiency. However, the influence of microgravity on sleep and circadian clock as well as the underlying mechanisms remain largely unknown. Placing volunteers in a prone position, whereby their heads rest at an angle of −6° below horizontal, mimics the microgravity environment in orbital flight. Such positioning is termed head-down bed rest (HDBR). In this work, we analysed the influence of a 45-day HDBR on physiological diurnal rhythms. We examined urinary electrolyte and hormone excretion, and the results show a dramatic elevation of cortisol levels during HDBR and recovery. Increased diuresis, melatonin and testosterone were observed at certain periods during HDBR. In addition, we investigated the changes in urination and defecation frequencies and found that the rhythmicity of urinary frequency during lights-off during and after HDBR was higher than control. The grouped defecation frequency data exhibits rhythmicity before and during HDBR but not after HDBR. Together, these data demonstrate that HDBR can alter a number of physiological processes associated with diurnal rhythms.     

Steroid-dependent ACTH-produced thymic carcinoid: regulation of POMC gene expression by cortisol via methylation of its promoter region

AIMS: Metyrapone causes a decrease in the serum cortisol level without affecting ACTH production in ectopic tumors. We report a case who presented with Cushing's syndrome due to an ectopic ACTH-producing thymic carcinoid. In the present case, it was demonstrated that metyrapone administration resulted in a significant decrease in the plasma ACTH and serum cortisol levels. We hypothesized that the steroid hormone may promote proopiomelanocortin (POMC) gene expression in the carcinoid cells. METHODS: An 11-year-old boy presented with Cushing's syndrome. Prior to the detection of a thymic tumor, metyrapone was administered to ameliorate the symptoms of Cushing's syndrome. Interestingly, plasma ACTH as well as serum cortisol levels immediately decreased after metyrapone administration. The levels of cortisol and ACTH were observed to be normal after complete surgical resection of the tumor. Biological characterization of the tumor cells was by in vitro analysis. RESULTS: Thein vitro culture of the tumor cells showed an increased expression of POMC in the presence of cortisol. A CpG methylation assay showed that the demethylation of the POMC promoter was induced by a steroid hormone. CONCLUSION: These findings suggest that the ectopic ACTH-producing tumor may partly be regulated by the elevated levels of cortisol.     

Differences of behavioral rhythms observed by flat cage and running-wheel cage in female rat

The ambulatory, wheel-running, and drinking activities were measured in Wistar-Imamichi strain female rats under 12 L:12 D condition (6:00-18:00), using Gundai type ambulo-drinkometer (for simultaneous measurements of ambulation and drinking) and wheel-drinkometer (for simultaneous measurements of wheel-running and drinking) to compare the rhythmicities of each behavioral activity. These apparatuses are able to measure the behavioral activities over a long period, successively and automatically. The circadian patterns of ambulatory activity had two large peaks at 21 or 24:00 and at 6:00 (acrophase). Contrary to the above results, the wheel-running activity exhibited clear mono-peak at 21:00 (acrophase). Thus, apparent differences of the pattern were observed between the two activities. However, ambulatory and wheel-running activities fluctuated showing 4-days rhythmicity, and both activities increased in estrus and proestrus stages, respectively. The circadian rhythms of drinking activities measured by both apparatuses showed almost same patterns with acrophases at 6:00, and 4-days rhythmicities were also observed and were characterized by remarkable decrease of activity in every proestrus stages. From these results, it is concluded that circadian pattern of ambulatory activity is different from that of wheel-running activity, but circadian patterns of drinking activities are stable regardless of different methods of the measurement. The ambulatory, wheel-running and drinking activities reflect the behavioral changes in sexual cycles.     

Age-related changes in plasma dehydroepiandrosterone sulphate, cortisol, testosterone and free testosterone circadian rhythms in adult men

The circadian rhythms of serum luteinizing hormone, follicle-stimulating hormone, testosterone (T), free testosterone (fT), sex hormone-binding globulin (SHBG), oestradiol, cortisol and dehydroepiandrosterone sulphate (DHA-s) have been investigated in 5 normal male adults and 6 elderly men. Circadian rhythms were detected statistically significant (p less than 0.05) by population mean cosinor analysis, for T, fT, cortisol and DHA-s in the young group. In the elderly population, serum cortisol showed a clear circadian rhythm, although with some phase modification, whereas DHA-s secretion lost its circadian rhythmicity. This demonstrates that ageing differently affects the two major adrenal functions, glucocorticoid and androgenic; further, the data suggest that an independent adrenal androgen-regulating system could be selectively impaired in the older subjects. In the elderly group the loss of T circadian rhythm was confirmed, but a statistically significant circadian rhythm of fT was recorded. It was characterized by a marked phase advance and not related with the SHBG modifications found in elderly men. This finding leads us to reconsider the role of fT, which appears more sensitive than total T, in studying circadian rhythm of gonadal androgen secretion.     

Daily production of human tumor necrosis factor in lipopolysaccharide (LPS)-stimulated ex vivo blood culture assays

Tumor necrosis factor (TNF) is a pleiotropic cytokine with immunological and neuroendocrine activities. A useful tool for studying TNF is the measurement of its in vitro and/or ex vivo over-expression, induced by a variety of stimuli on isolated peripheral mononuclear cells or whole blood, respectively. The capacity to over-express TNF, in ex vivo LPS-stimulated whole blood from 18 normal individuals, showed inter-individual variations ranging from high (3 ng/ml) to low (0.7 ng/ml) producers. Although at a lower level, a similar situation was observed in the spontaneous production of the cytokine. In order to detect cyclic effects in these variations, blood samples were taken at 08:00, 12:00, 16:00 and 20:00 hours, from nine healthy volunteers, and cultured in the ex vivo system. TNF and cortisol were measured by immunometric assays. Both, LPS-stimulated whole blood and plasma showed important, individual variations in TNF levels. Although cortisol levels presented a normal circadian cycle, these individual patterns in TNF production were basically conserved during the day (p > 0.05), and no correlation was observed between the levels of the hormone and those of the cytokine. When total TNF levels were determined at 20:00 hours, a moderate, temporary variation pattern of the cytokine production was found. These results suggest that cortisol does not play a predominant role in determining the ex vivo capacity of blood to produce TNF. Presumably, the variable capacity to produce the cytokine may have a strong genetic component.     

Age-dependent effect of Freund's adjuvant on 24-hour rhythms in plasma prolactin, growth hormone, thyrotropin, insulin, follicle-stimulating hormone, luteinizing hormone and testosterone in rats

The effect of Freund's adjuvant administration on 24-hour changes of plasma prolactin, growth hormone (GH), thyrotropin (TSH), insulin, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone were studied in young (2 months) and aged (18 months) male Wistar rats. Rats were injected s.c. with Freund's adjuvant or adjuvant's vehicle and, 18 days later, they were killed at 6 different time intervals throughout a 24-hour cycle to measure circulating hormone levels by specific RIAs. Young rats receiving adjuvant's vehicle exhibited significant time-of-day-dependent variations in plasma TSH, LH and testosterone, with maximal levels at 1300 h, 0100 h and 1700 h, respectively. Prolactin and insulin levels, analyzed globally in a factorial ANOVA, showed significant time-of-day changes with maximal levels at 1300 - 1700 h and 2100 h, respectively. The daily rhythms in plasma LH and testosterone found in young rats were not longer observed in Freund's adjuvant-injected rats, while as far as TSH, a second peak was observed at 0100 h after Freund's adjuvant administration. Twenty-four hour rhythms in circulating TSH, LH and testosterone were blunted in old rats receiving either Freund's adjuvant or its vehicle. Aged rats exhibited significantly higher circulating levels of prolactin, and lower levels of GH, TSH, FSH and testosterone. The results indicate that secretion of prolactin, GH, TSH, FSH and testosterone are age-dependent, as are the responses of TSH, LH and testosterone to Freund's adjuvant administration.     

Comparison between sex and age class on some physiological, thermal, and hematological indices of the cerrado's marmoset (Callithrix penicillata)

There are few papers about physiological indices in Callithrix penicillata, an increasing primate model in biomedicine. We investigated levels of plasmatic cortisol, plasmatic glucose, free fatty acids, blood cells, tympanic temperature, rectal temperature in C. penicllata, under a fast restraint. Measures of body and weight were accomplished. Males and females were not different regarding any measurements. Body measurements indicated differences between adults and juveniles. Adults showed higher hematocrit and a tendency for higher free fatty acids than juveniles. Right tympanic temperature was higher in adults than juveniles. This result suggests a higher reaction metabolism in adults than juveniles under a restraint stress. Due to the short-time of collecting the data, plasmatic cortisol did not influence physiological parameters. Therefore, we suggest that present results could be considered referential values of C. penicillata physiology.     

Absence of apparent circadian rhythms of gonadotropins and free alpha-subunit in postmenopausal women: evidence for distinct regulation relative to other hormonal rhythms

Aging is associated with a decrease in gonadotropin levels in postmenopausal women (PMW) and is also associated with alterations in a number of circadian rhythms. The goals of this study were to determine the presence of circadian rhythms of gonadotropins and glycoprotein free alpha-subunit (FAS) in young and old PMW. Healthy, euthyroid PMW, ages 45 to 55 years (n = 11) and 70 to 80 years (n = 11), were admitted in the morning to start a 24-h constant routine of light, temperature, position, and activity. Subjects remained awake and semirecumbent for the duration of the study and were fed hourly snacks, and activity was monitored continuously. Blood was sampled every 5 min for two 8-h periods corresponding to the estimated acrophase and nadir of the temperature rhythm. Luteinizing hormone (LH) and FAS were measured in all samples and follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), and cortisol in 20-min serum pools. Mean LH (p < 0.001), FSH (p < 0.002), and FAS (p < 0.002) were lower in older compared with younger PMW. Day/night differences in cortisol and TSH (p < 0.001) were present in all subjects. However, there were no day/night differences in LH in younger or older PMW or in FSH in younger or older PMW. There were no day/night differences in mean FAS in younger or older PMW or in FAS pulse frequency or amplitude. Thus, in controlled studies in which differences in cortisol and TSH were demonstrated, there were no day/night differences in LH, FSH, or FAS in PMW. These studies suggest that despite evidence of intact circadian rhythms of cortisol and TSH, gonadotropin secretion does not appear to follow a circadian pattern in PMW. Thus, the age-related decline in gonadotropin secretion in PMW is not associated with a dampening of circadian rhythmicity. The absence of day/night differences in FAS suggests that GnRH plays a more prominent role in FAS regulation than does thyrotropin-releasing hormone in PMW.     

Pulsatile ACTH secretion: variation with time of day and relationship to cortisol

It has long been known that ACTH is secreted in an episodic fashion demonstrating circadian and ultradian rhythms. High intensity venous sampling has recently revealed that in addition to these larger ultradian fluctuations in hormone levels, plasma ACTH in rats demonstrates high frequency, low amplitude oscillations which have been called "micropulses." These micropulses were not detected in previous studies due to sampling intervals of greater than 5 minutes. To investigate the presence of these ACTH micropulses in a primate species, blood samples were drawn from six chair-restrained rhesus monkeys at one-minute intervals for up to 70 minutes and plasma was assayed for immunoreactive ACTH. To assess the variation in ACTH micropulse parameters with time of day and the relationship to cortisol secretion, four of the monkeys were sampled for three 70-minute periods beginning at 0530, 1100, and 1730 hours, and plasma was assayed for immunoreactive ACTH and cortisol. Analysis of the data revealed that ACTH and cortisol are secreted in micropulses in rhesus monkeys with marked individual variation in the pattern of secretion and a concurrence of approximately 75% of ACTH and cortisol micropulses. Difference in pulse amplitude but not frequency appeared to contribute to the circadian variation in mean ACTH levels and a sampling interval of two minutes appeared to be adequate for accurately identifying micropulses of ACTH.     

Insulin counter-regulation in multiple sclerosis

Fasting hypoglycemia is frequently observed in patients with Multiple Sclerosis (S.M.) showing orthostatic hypotension and defective thermoregulation, although they never complicate in hypoglycemic coma. The aim of this study was to evaluate glucose homeostasis in S.M. patients. Both insular and counter-insular regulating mechanisms were investigated by determination of glucose, insulin, C-peptide and cortisol plasmatic levels during OGTT, and subsequently by evaluating glucagon plasmatic levels after arginine administration (30 g., i.v.). Our results suggest that the increased susceptibility of S.M. patients to undergo fasting hypoglycemia could be related to some alterations in counter-insular mechanisms, generally included among neurovegetative modifications in S.M. patients and probably due to orthosympathetic function impairment.