Effects of prolonged adrenaline infusion and of mental stress on plasma minerals and parathyroid hormone

The diagnostic utility of hypophosphatemia for differentiating generalized tonic-clonic seizures from syncope in dogs: A case control study

Transient hypophosphatemia is often detected in humans following generalized tonic-clonic seizures (GTCS), and serum phosphorus concentration (sPi) serves as a marker to differentiate GTCS from syncope. The objective of this retrospective study was to assess the usefulness of hypophosphatemia as a diagnostic marker for GTCS in dogs. Eighty-seven and 26 client-owned dogs with GTCS or syncope, respectively, were enrolled. Dogs were included if the episode occurred ≤ 3 h from presentation, and if sPi and serum creatinine (sCr) were measured. Dogs were excluded if aged < 1 year or if sCr exceeded 176.8 μmol/L. There were no group differences in sCr. Hypophosphatemia (sPi ≤ 0.97 mmol/L) occurred in 28 dogs (32%) in the seizure group, and in no dogs in the syncope group. Median sPi was significantly (P < 0.001) lower in the seizure group (1 mmol/L, [range, 0.31-2.87 mmol/L]) compared to the syncope group (1.35 mmol/L [range, 0.97-2.71 mmol/L]). Furthermore, in dogs presented while seizing (n = 24/87; 28%) median sPi was significantly lower compared to those that were not (0.9 mmol/L [range, 0.3-1.74 mmol/L] vs. 1 mmol/L [range, 0.33-2.18 mmol/L], P = 0.050). ROC analysis of sPi as a marker of GTCS yielded an AUC of 0.757 (95% confidence interval 0.667-0.847), with an optimum cutoff point of 0.97 mmol/L, corresponding to specificity and sensitivity levels of 100% and 44%, respectively. In conclusion, sPi may, in certain cases, serve as an additional diagnostic tool to differentiate GTCS from syncope in dogs. Hypophosphatemia, especially with sPi < 0.97 mmol/L, may be useful in clinical practice to rule in GTCS.

Physical Activity-Dependent Regulation of Parathyroid Hormone and Calcium-Phosphorous Metabolism

Exercise perturbs homeostasis, alters the levels of circulating mediators and hormones, and increases the demand by skeletal muscles and other vital organs for energy substrates. Exercise also affects bone and mineral metabolism, particularly calcium and phosphate, both of which are essential for muscle contraction, neuromuscular signaling, biosynthesis of adenosine triphosphate (ATP), and other energy substrates. Parathyroid hormone (PTH) is involved in the regulation of calcium and phosphate homeostasis. Understanding the effects of exercise on PTH secretion is fundamental for appreciating how the body adapts to exercise. Altered PTH metabolism underlies hyperparathyroidism and hypoparathyroidism, the complications of which affect the organs involved in calcium and phosphorous metabolism (bone and kidney) and other body systems as well. Exercise affects PTH expression and secretion by altering the circulating levels of calcium and phosphate. In turn, PTH responds directly to exercise and exercise-induced myokines. Here, we review the main concepts of the regulation of PTH expression and secretion under physiological conditions, in acute and chronic exercise, and in relation to PTH-related disorders.

Vitamin D alleviates oxidative stress in adipose tissue and mesenteric vessels from obese patients with subclinical inflammation

Obesity is an age-independent, lifestyle-triggered, pandemic disease associated with both endothelial and visceral adipose tissue (VAT) dysfunction leading to cardiometabolic complications mediated via increased oxidative stress and persistent chronic inflammation. The purpose of the present study was to assess the oxidative stress in VAT and vascular samples and the effect of in vitro administration of vitamin D. VAT and mesenteric artery branches were harvested during abdominal surgery performed on patients referred for general surgery (n = 30) that were randomized into two subgroups: nonobese and obese. Serum levels of C-reactive protein (CRP) and vitamin D were measured. Tissue samples were treated or not with the active form of vitamin D: 1,25(OH)₂D₃ (100 nmol/L, 12 h). The main findings are that in obese patients, (i) a low vitamin D status was associated with increased inflammatory markers and reactive oxygen species generation in VAT and vascular samples and (ii) in vitro incubation with vitamin D alleviated oxidative stress in VAT and vascular preparations and also improved the vascular function. We report here that the serum level of vitamin D is inversely correlated with the magnitude of oxidative stress in the adipose tissue. Ex vivo treatment with active vitamin D mitigated obesity-related oxidative stress.

Maintenance of Serum Ionized Calcium During Exercise Attenuates Parathyroid Hormone and Bone Resorption Responses

Exercise can cause a decrease in serum ionized calcium (iCa) and increases in parathyroid hormone (PTH) and bone resorption. We used a novel intravenous iCa clamp technique to determine whether preventing a decline in serum iCa during exercise prevents increases in PTH and carboxy-terminal collagen crosslinks (CTX). Eleven cycling-trained men (aged 18 to 45 years) underwent two identical 60-min cycling bouts with infusion of Ca gluconate or saline. Blood sampling for iCa, total calcium (tCa), PTH, CTX, and procollagen type 1 amino-terminal propeptide (P1NP) occurred before, during, and for 4 hours after exercise; results are presented as unadjusted and adjusted for plasma volume shifts (denoted with subscript ADJ). iCa decreased during exercise with saline infusion (p = 0.01 at 60 min) and this was prevented by Ca infusion (interaction, p < 0.007); there were abrupt decreases in Ca content (iCa_ADJ and tCa_ADJ ) in the first 15 min of exercise under both conditions. PTH and CTX were increased at the end of exercise (both p < 0.01) on the saline day, and markedly attenuated (-65% and -71%; both p < 0.001) by Ca. CTX remained elevated for 4 hours after exercise on the saline day (p < 0.001), despite the return of PTH to baseline by 1 hour after exercise. P1NP increased in response to exercise (p < 0.001), with no difference between conditions, but the increase in P1NP_ADJ was not significant. Results for PTH_ADJ and CTX_ADJ were similar to unadjusted results. These findings demonstrate that bone resorption is stimulated early in exercise to defend serum iCa. Vascular Ca content decreased early in exercise, but neither the reason why this occurred, nor the fate of Ca, are known. The results suggest that the exercise-induced increase in PTH had an acute catabolic effect on bone. Future research should determine whether the increase in PTH generates an anabolic response that occurs more than 4 hours after exercise. © 2018 American Society for Bone and Mineral Research.

Hypophosphatemia after nontraumatic intracranial hemorrhage

BACKGROUND

The aim of this study was to assess the incidence and contributing factors of hypophosphatemia and the association with poor long-term outcome after nontraumatic intracranial hemorrhage.

METHODS

This was a prospective, observational study of patients with nontraumatic intracranial hemorrhage (i.e., aneurysmal or perimesencephalic subarachnoid hemorrhage, or spontaneous intracerebral or intraventricular hemorrhage) treated in the intensive care unit (ICU) at our university hospital. Plasma phosphate concentrations were measured serially in 2-day sections during the 6 day study period. The ICU mortality was recorded, 3-month and 1-year outcomes were assessed using the Glasgow Outcome Scale.

RESULTS

One hundred patients were enrolled. The frequency of hypophosphatemia (Pi ≤ 0.65 mmol/l) was 70%. Chronic hypertension, acute hydrocephalus, and diffuse brain edema were more common in patients with hypophosphatemia compared with normophosphatemics (44% vs. 21%, P = 0.021; 59% vs. 33%, P = 0.021; and 43% vs. 13%, P = 0.004, respectively). Hypophosphatemic patients had higher maximum SOFA scores [10 (7-11) vs. 7.5 (5.75-10), P = 0.024]. Initial phosphate concentration correlated inversely with APACHE II score on admission (ρ = -0.304, P = 0.002) and SOFA score on the first ICU day (ρ = -0.269, P = 0.008). There was no difference in outcome between hypophosphatemic and normophosphatemic patients. In all five patients with severe hypophosphatemia (Pi < 0.32 mmol/l) the functional outcome was good.

CONCLUSION

Hypophosphatemia was common in this patient population. The outcome was similar between hypophosphatemic and normophosphatemic patients. Chronic hypertension, acute hydrocephalus, diffuse brain edema and higher SOFA scores were more common in patients with hypophosphatemia.

Maintaining normal levels of ionized calcium during citrate-based renal replacement therapy is associated with stable parathyroid hormone levels

BACKGROUND/AIMS

Citrate is an effective anticoagulant during continuous renal replacement therapy (CRRT). Previous studies showed raised parathyroid hormone (PTH) levels when aiming for serum ionized calcium [Cai] between 0.8 and 1.1 mmol/l. Our objective was to assess whether citrate-based CRRT with physiologic target systemic [Ca(i)] between 1.12 and 1.20 mmol/l could maintain stable PTH levels.

METHODS

Measurement of intact PTH (PTHi) in 30 consecutive critically ill patients treated with citrate-based CRRT.

RESULTS

Thirty patients [mean age: 70.4 (SD 11.3) years; 56.7% males] were enrolled. Mean serum [Ca(i)] was 1.16 mmol/l (SD 0.09), 1.13 mmol/l (SD 0.09), 1.17 mmol/l (SD 0.05) and 1.16 mmol/l (SD 0.04) at baseline, 12, 24 and 48 h, respectively (p = 0.29). Median PTHi levels (interquartile range) at baseline, 12, 24 and 48 h were 66.5 (43-111), 109 (59.5-151.5), 88.5 (47-133) and 85 pg/ml (53-140), respectively. The differences between baseline and 12 h and across all time points were statistically not significant (p = 0.16 and p = 0.49, respectively). In a mixed-effects model, each 0.1 mmol/l increase in serum [Ca(i)] was associated with a 31.2% decrease in PTHi (p < 0.001). Results were unchanged after adjustment for age, gender, magnesium, phosphate, arterial pH and time spent on CRRT.

CONCLUSIONS

Maintaining systemic [Ca(i)] within the physiologic range was associated with stable PTHi levels.

Calcium regulating hormones and serum calcium and magnesium concentrations in septic and critically ill foals and their association with survival

BACKGROUND

Disorders of calcium regulation are frequently found in humans with critical illness, yet limited information exists in foals with similar conditions including septicemia. The purpose of this study was to determine whether disorders of calcium exist in septic foals, and to determine any association with survival.

HYPOTHESIS

Blood concentrations of ionized calcium (Ca(2+)) and magnesium (Mg(2+)) will be lower in septic foals with concomitant increases in parathyroid hormone (PTH), calcitonin (CT), and parathyroid-related peptide (PTHrP) compared with healthy foals. The magnitude of these differences will be negatively associated with survival.

ANIMALS

Eighty-two septic, 40 sick nonseptic, and 24 healthy foals of <or=7 days were included.

METHODS

Prospective, observational study. Blood was collected at initial examination for analysis. Foals with positive blood culture or sepsis score >or=14 were considered septic. Foals with disease other than sepsis and healthy foals were used as controls. Hormone concentrations were measured with validated immunoassays.

RESULTS

Septic foals had decreased Ca(2+) (5.6 versus 6.1 mg/dL, P < .01) and increased serum PTH (16.2 versus 3.2 pmol/L, P < .05), and phosphorus concentrations (7.1 versus 6.3 mg/dL, P < .01). No differences in serum Mg(2+), PTHrP, and CT concentrations were found. Nonsurviving septic foals (n = 42/82) had higher PTH concentrations (41.1 versus 10.7 pmol/L, P < .01) than survivors (n = 40/82).

CONCLUSIONS AND CLINICAL IMPORTANCE

Septic foals were more likely to have disorders of calcium regulation compared with healthy foals, where hyperparathyroidemia was associated with nonsurvival.

Regulation of cation channels in cardiac and smooth muscle cells by intracellular magnesium

Magnesium regulates various ion channels in many tissues, including those of the cardiovascular system. General mechanisms by which intracellular Mg(2+) (Mg(i)(2+)) regulates channels are presented. These involve either a direct interaction with the channel, or an indirect modification of channel function via other proteins, such as enzymes or G proteins, or via membrane surface charges and phospholipids. To provide an insight into the role of Mg(i)(2+) in the cardiovascular system, effects of Mg(i)(2+) on major channels in cardiac and smooth muscle cells and the underlying mechanisms are then reviewed. Although Mg(i)(2+) concentrations are known to be stable, conditions under which they may change exist, such as following stimulation of beta-adrenergic receptors and of insulin receptors, or during pathophysiological conditions such as ischemia, heart failure or hypertension. Modifications of cardiovascular electrical or mechanical function, possibly resulting in arrhythmias or hypertension, may result from such changes of Mg(i)(2+) and their effects on cation channels.

Stuttering in adults: the acoustic startle response, temperamental traits, and biological factors

The purpose of this study was to investigate the relation between stuttering and a range of variables of possible relevance, with the main focus on neuromuscular reactivity, and anxiety. The explorative analysis also included temperament, biochemical variables, heredity, preonset lesions, and altered auditory feedback (AAF). An increased level of neuromuscular reactivity in stuttering adults has previously been reported by [Guitar, B. (2003). Acoustic startle responses and temperament in individuals who stutter. Journal of Speech Language and Hearing Research, 46, 233-240], also indicating a link to anxiety and temperament. The present study included a large number of variables in order to enable analysis of subgroups and relations between variables. Totally 32 stuttering adults were compared with nonstuttering controls. The acoustic startle eyeblink response was used as a measure of neuromuscular reactivity. No significant group difference was found regarding startle, and startle was not significantly correlated with trait anxiety, stuttering severity, or AAF. Startle was mainly related to calcium and prolactin. The stuttering group had significantly higher scores for anxiety and childhood ADHD. Two subgroups of stuttering were found, with high versus low traits of childhood ADHD, characterized by indications of preonset lesions versus heredity for stuttering. The study does not support the view that excessive reactivity is a typical characteristic of stuttering. The increased anxiety is suggested to mainly be an effect of experiences of stuttering.

LEARNING OUTCOMES

As a result of reading this article, the reader will be able to: (a) critically discuss the literature regarding stuttering in relation to acoustic startle, anxiety, and temperament; (b) describe the effect of calcium on neuromuscular reactivity; (c) discuss findings supporting the importance of early neurological incidents in some cases of stuttering, and the relation between such incidents and traits of ADHD or ADD; and (d) discuss the role of genetics in stuttering.

Parathyroid hormone response to tracheal intubation in hyperparathyroid patients and normal subjects

The stress of direct laryngoscopy and passing an endotracheal tube through the vocal cords elicits haemodynamic, metabolic and hormonal changes such as raising blood catecholamine levels. Catecholamines are known stimulants of PTH secretion. The effect of tracheal intubation on plasma parathyroid hormone levels has not yet been investigated. We monitored changes in plasma parathyroid hormone levels before and after tracheal intubation in 72 hyperparathyroid patients undergoing elective parathyroidectomy for primary and secondary hyperparathyroidism. These findings were compared to data collected from 20 subjects who underwent elective surgery (thyroidectomy or laparoscopic cholecystectomy) under general anesthesia. In the control group, tracheal intubation significantly increased plasma parathyroid hormone levels from 59 +/- 31 pg/ml to 91 +/- 40 pg/ml (mean +/- SD) (p<0.0003). In primary hyperparathyroid patients, the identical procedure increased plasma parathyroid hormone levels from 206 +/- 104 pg/ml to 217 +/- 113 pg/ml (p = 0.12) and from 898 +/- 495 pg/ml to 1162 +/- 613 pg/ml (p = 0.07) in secondary hyperparathyroidism patients. We concluded that tracheal intubation raises plasma parathyroid hormone levels. The mechanism underlying this response requires further investigation.

Drug-induced hypomagnesaemia : scope and management

Nearly 50 medications have been implicated as inducing hypomagnesaemia, sometimes based on insufficient data regarding clinical significance and frequency of occurrence. In fact, clinical effects attributed to hypomagnaesemia have been reported in only 17 of these drugs. A considerable amount of literature relating to individual drugs has been published, yet a comprehensive overview of this issue is not available and the hypomagnesaemic effect of a drug could be either overemphasised or under-rated. In addition, there are neither guidelines regarding treatment, prevention and monitoring of drug-induced hypomagnesaemia nor agreement as to what serum level of magnesium may actually be defined as 'hypomagnesaemia'. By compiling data from published papers, electronic databases, textbooks and product information leaflets, we attempted to assess the clinical significance of hypomagnesaemia induced by each drug. A practical approach for managing drug-induced hypomagnesaemia, incorporating both published literature and personal experience of the physician, is proposed. When drugs classified as inducing 'significant' hypomagnesaemia (cisplatin, amphotericin B, ciclosporin) are administered, routine magnesium monitoring is warranted, preventive treatment should be considered and treatment of hypomagnesaemia should be initiated with or without overt clinical manifestations. In drugs belonging to the 'potentially significant' category, among which are amikacin, gentamicin, laxatives, pentamidine, tobramycin, tacrolimus and carboplatin, magnesium monitoring is justified when either of the following occurs: clinical manifestations are apparent; persistent hypokalaemia, hypocalcaemia or alkalosis are present; other precipitating factors for hypomagnesaemia coexist; or treatment is with more than one potentially hypomagnesaemic drug. No preventive treatment is required and treatment should be initiated only if hypomagnesaemia is accompanied by symptoms or clinically significant relevant laboratory findings. In those drugs whose hypomagnesaemic effect is labelled as 'questionable', including furosemide and hydrochlorothiazide, routine monitoring and treatment are not required.

Insulin-induced hypoglycemia suppresses plasma parathyroid hormone levels in patients with adrenal insufficiency

Hypoglycemia has been reported to cause suppression of parathyroid hormone (PTH) levels in serum in normal subjects. It is possible that increasing cortisol levels in response to hypoglycemia was responsible. To examine this possibility the acute PTH response to insulin administration and resulting hypoglycemia was examined in patients with adrenal insufficiency. The possible acute impact of insulin-induced hypoglycemia on bone formation and bone resorption in the absence of an endogenous cortisol response was also examined. A prospective open study was undertaken to examine the acute effects of insulin and resulting hypoglycemia on PTH levels, on bone formation as indicated by serum levels of aminoterminal propeptide of type 1 procollagen (PINP), and on bone resorption as indicated by serum levels of beta carboxy terminal telopeptide of type 1 collagen (beta-CTx). Seven patients with adrenal insufficiency participated. These patients were studied on 3 occasions under different conditions: (1) when insulin was administered to induce hypoglycemia while the patients received their routine glucocorticoid replacement; (2) when the patients received their routine glucocorticoid replacement, but were not rendered hypoglycemic; and (3) when they did not receive glucocorticoid replacement and were not rendered hypoglycemic, ie, untreated. This facilitated isolation of the PTH response to insulin and hypoglycemia from the effects of the normal increase in endogenous cortisol levels in response to hypoglycemia. Blood samples were taken at baseline and after 3 hours while the subjects continued fasting for measurement of plasma glucose, serum ionized calcium (Cai), magnesium, phosphate, PINP, PTH, and beta-CTx. Insulin 0.075 IU/kg body weight was given intravenously after the first blood sample. The usual morning glucocorticoid replacement dose was given 20 minutes after the baseline blood sample was obtained. After the administration of insulin, plasma glucose decreased from 4.8 +/- 0.5 to 2.7 +/- 0.5 mmol/L, mean +/- SD (P < .0001). PTH was not influenced by time or glucocorticoid treatment, but decreased in response to insulin-induced hypoglycemia (P < .05). Serum levels of PINP and beta-CTx decreased when untreated between 9 AM and 12 PM (P < .05), but were not independently influenced by insulin-induced hypoglycemia or glucocorticoid treatment. Serum levels of Cai increased and serum phosphate levels decreased in response to insulin-induced hypoglycemia, while serum phosphate levels were also independently influenced by time decreasing between 9 AM and 12 PM (P < .05). There was no effect of time, insulin-induced hypoglycemia, or glucocorticoid treatment on serum levels of magnesium. Possible mechanisms involved in the acute decrease in serum PTH observed include a direct effect of insulin or hypoglycemia or an indirect effect, eg, increased sympathomimetic activity on PTH secretion or on calcium or phosphate intercompartmental shifts.

Hypocalcemic syndromes

Hypocalcemia is common in the ICU and is a marker of poor prognosis. The mechanisms behind the low calcium levels include extravasation, increased chelation, intracellular overload of calcium, and an altered parathyroid hormone (PTH) secretion. Hypocalcemia and an altered PTH secretion seem to be related to systemic inflammation, but it is not known today if this response is appropriate or not. Therefore, a general supplementation with calcium in these patients cannot be recommended at this stage.

Parathyroid hormone and ionized calcium levels are related to the severity of illness and survival in critically ill patients

BACKGROUND

The present study explores serum parathyroid hormone (PTH) and blood ionized calcium (Ca2+) levels in relation to the severity of disease and mortality in the intensive care unit (ICU).

METHODS

In a pilot study, 37 consecutive critically ill patients admitted to the ICU were studied with determinations of serum PTH and total serum calcium within the first 24 h. In a following prospective study, patients suffering from sepsis (n = 13) or subjected to major surgery (n = 13) were investigated daily for 1 week with determinations of serum PTH and ionized calcium (Ca2+). Severity of disease was assessed by the APACHE II score and hospital mortality was recorded.

RESULTS

In the pilot study, serum PTH levels were elevated (> 55 ng L-1) in 38% of the patients and were not related to serum calcium but showed a significant relationship to the APACHE II score (r = 0.39, P < 0.05). In the prospective study, serum PTH was elevated in 69% of the patients in both groups at inclusion, and 6 days later 87% of the septic and 37% of the surgery patients still showed elevated levels. Hypocalcaemia was more commonly seen in the septic patients [mean Ca2+ 1.03 +/- 0.08 (SD) mmol L-1] than in the surgical patients (1.14 +/- 0.06 mmol L-1) at inclusion. Both PTH and Ca2+ levels were significantly related to the APACHE II score (r = 0.46, P < 0.03, and r = -0.54, P < 0.009, respectively). Furthermore, PTH levels were significantly increased in non-survivors (n = 5) compared with survivors (mean 161 +/- 51 vs. 79 +/- 51 ng L-1, P < 0.005).

CONCLUSION

Hypocalcaemia and increased levels of PTH were common findings in critically ill patients. These alterations in calcium homeostasis were related to the severity of disease and increased PTH levels were associated with a poor outcome.

Hypophosphataemia. Pathophysiology, effects and management on the intensive care unit

Routine detection and treatment of hypophosphataemia on the intensive care unit is commonplace. Hypophosphataemia has been associated with a multitude of clinical effects and there are many associations between correction of hypophosphataemia and improvement in symptoms. However, there is no evidence at present to support the routine correction of hypophosphataemia in the absence of clinical symptoms or signs.

Correlation between serum and urinary calcium levels and psychopathology in patients with affective disorders. Short communication

To examine whether serum and urinary calcium levels were related to the psychopathology index (i.e. average score in clinically relevant scales of Minnesota Multiphasic Personality Inventory), 24 women aged 35.6 +/- 2.5 years and 20 men aged 34.3 +/- 2.1 years, suffering from affective disorders, were studied. A non-parametric bivariate correlation analysis revealed a negative correlation between PI and serum calcium (r = -0.256, p < 0.01), while urinary calcium levels correlated positively with PI (r = 0.236, p < 0.02). A positive correlation occurred between serum and urinary calcium (r = 0.968, p < 0.0001). When the data were analyzed by categorical classification of patients with normal or abnormal PI scores, serum calcium levels were smaller, and urinary calcium levels higher, in patients with abnormal PI (p < 0.01). The results support to the concept that alterations of calcium homeostasis occur in psychopathology.

The influence of cervical sympathetic neurons on parathyroid hormone and calcitonin release in the rat: independence of pineal mediation

The objective of this study was to evaluate the involvement of the pineal gland in modulation of parathyroid hormone (PTH) and calcitonin release found in rats after changes in activity of cervical sympathetic nerves. The response of serum PTH to a hypocalcemia produced by EDTA injection, and of serum calcitonin to a hypercalcemia produced by administering calcium chloride, were studied in rats at the time of the wallerian degeneration of regional sympathetic nerves (i.e., 16 hr after superior cervical ganglionectomy, SCGx). Rats received a pinealectomy or its sham-operation 4 days before SCGx. During wallerian degeneration of nerves after SCGx, a higher hypocalcemia and a lower PTH response were found as compared to sham-SCGx rats, regardless of whether the pineal gland was present or not. When the response of calcitonin to a bolus injection of calcium chloride was assessed, rats subjected to SCGx 16 hr earlier showed a depressed calcitonin release, which was also unaffected after pinealectomy. To a similar extent in pinealectomized and sham-pinealectomized rats, a mild stress given by the subcutaneous injection of turpentine oil brought about a greater hypocalcemia after EDTA, concomitantly with a higher PTH secretory response. In turpentine oil-injected rats, the rise of serum calcitonin was significantly greater than that of vehicle-treated rats, regardless of pineal presence. The results further indicate that cervical autonomic nerves constitute a pathway through which the brain modulates calcium homeostasis and do not support the participation of the pineal gland in short term changes of PTH or calcitonin release.

Alcohol consumption inhibits bone growth and development in young actively growing rats

Adolescence is an age of widespread alcohol abuse, but the effect of alcohol consumption on bone formation has not been studied in the young population. This study addresses the effect of alcohol on the early phases of bone growth and development in an animal model. Four-week-old, female Sprague-Dawley rats were divided into three groups. Alcohol-treated animals were fed a modified Lieber-DeCarli diet ad libitum containing 35% ethanol-derived calories, whereas the pair-fed animals (weight-matched to ethanol rats) received an isocaloric liquid diet in which maltose-dextrin substituted calories supplied by ethanol. Chow animals were fed a standard rat chow ad libitum. Proximal tibiae (primarily cancellous bone) and femora (primarily cortical bone) were removed for analysis after 2, 4, 6, or 8 weeks on the diets. Serum was collected for analysis of calcium levels, osteocalcin, corticosterone, growth hormone, parathyroid hormone, and 25-hydroxyvitamin D. The most rapid weight gain occurred between 6 and 8 weeks of age, it was significantly delayed in alcohol and pair-fed animals. Almost all morphological parameters of bone were lower in the alcohol groups. No significant difference in serum calcium levels, osteocalcin, or growth hormone levels were found, and small difference in calciotropic hormone levels was found between groups. The results indicated that chronic alcohol consumption during the age of bone development reduces bone density and peak bone mass in both cortical and cancellous bone. The mechanism whereby this effect occurs is not fully understood, but, our results suggest that the negative impact of alcohol on growing bone is not due to the secondary effects of altered bone mineral regulating hormones.

Differential regulation of circulating Mg2+ in the rat by beta 1- and beta 2-adrenergic receptor stimulation

Extracellular Mg2+ homeostasis was studied in vivo in the anesthetized rat. Animals were infused with isoproterenol (ISO) for 10 minutes, and serum Mg2+ was measured after the infusion and then 10 and 20 minutes later. A dose-dependent increase in circulating Mg2+ was observed in animals infused with ISO at a rate of 0.1 microgram.kg-1.min-1 or higher. The time course of the effect demonstrated that circulating Mg2+ continued to increase 20 minutes after the end of the ISO infusion. A predicted maximal increase in serum Mg2+ concentration of 19.3% was derived with a predicted EC50 of 0.08 microgram.kg-1.min-1. The maximal percent increase corresponded to a net increase of 6.7 mumol/300 g body wt. Because infusion of ISO resulted in changes in hemodynamic parameters, most notably a drop in blood pressure, a group of animals was infused with nitroprusside to mimic the hypotensive response via a nonadrenergic mechanism. Under these conditions, there was a transient increase in circulating Mg2+ that was largely inhibited by propranolol, indicating that hypotension per se was not responsible for the mobilization of Mg2+. Infusion of salbutamol, but not prenalterol, also induced an increase in circulating Mg2+. Pretreatment with butoxamine, ICI-118551, or propranolol prevented the ISO-induced increase in serum Mg2+. Pretreatment with atenolol minimally affected the ISO-induced changes in circulating Mg2+. Pretreatment with CGP-20271A actually enhanced the ISO-induced increase in circulating Mg2+. This evidence demonstrates the existence of a pool of Mg2+ that is mobilized into the circulation in response to selective beta 2-adrenergic stimulation.

Changes of ionized magnesium and free fatty acids in serum after acute myocardial infarction

The most feared early complications after an acute myocardial infarction are ventricular arrhythmias. These may be initiated by changed concentrations of catecholamines and electrolytes. The present study shows a reduction of total serum magnesium after acute myocardial infarction which is normalized within a few days. Further, it could be shown that a more significant decrease of ionized Mg2+ (iMg2+) takes place at the day of acute myocardial infarction in the total group of myocardial infarction patients (n = 36). A closer investigation reveals that iMg2+ was considerably decreased in one third of the patients, whereas two thirds showed minor changes of iMg2+ in both directions. The pronounced decrease of iMg2+ in the first sub-group can be explained by the time course of free fatty acids in serum. On the day of the myocardial infarction free fatty acids in serum were increased. This is probably caused by beta-adrenergic-induced lipolysis due to catecholamines released by the stressful situation of an acute myocardial infarction. The increased free fatty acids in serum bind Mg2+, thus reducing iMg2+. As long as a beneficial effect of a general Mg infusion in all acute myocardial infarction patients is controversial, iMg2+ should be measured and Mg infusion therapy should be applied only in patients with low iMg2+.

The effect of entacapone on the disposition and hemodynamic effects of intravenous isoproterenol and epinephrine

BACKGROUND

Entacapone is a potent, selective catechol-O-methyltransferase (COMT) inhibitor. Entacapone could potentiate the hemodynamic effects of exogenously administered catecholamines, which are substrates of the COMT enzyme.

DESIGN AND METHODS

Originally, the study was to follow a placebo-controlled, randomized crossover design. Because of two cases of ventricular arrhythmia, a decision was made to terminate the study before its completion. Six subjects went through the isoproterenol and epinephrine infusions while taking placebo and five other subjects while taking entacapone. The actual design was thus one with two parallel groups with random allocation and double-blind drug administration. The subjects were given either a single dose of 400 mg entacapone or placebo 30 minutes before the start of isoproterenol or epinephrine infusions. Four dosages of epinephrine (1.5, 3, 6, or 12 micrograms/min) and isoproterenol (0.5, 1, 1.5, or 2 micrograms/min) were infused (5 minutes for each level). Heart rate and blood pressure were measured and ECG was monitored. The concentrations of isoproterenol and epinephrine in plasma were determined by HPLC.

RESULTS

The maximal increase in heart rate during isoproterenol infusion after entacapone administration (40 +/- 11 beats/min, mean +/- SD) was statistically greater (p = 0.0496) than after placebo administration (27 +/- 7 beats/min). The increase in heart rate during epinephrine infusion was 25 +/- 13 beats/min after entacapone administration and 14 +/- 9 beats/min after placebo administration (p = 0.127). There were no statistically significant differences between entacapone and placebo in blood pressure or in plasma concentrations of isoproterenol and epinephrine.

CONCLUSION

We conclude that entacapone may potentiate the chronotropic and arrhythmogenic effects of exogenously administered isoproterenol and epinephrine.

Secondary hyperparathyroidism, vitamin D deficiency and hip fracture: importance of sampling times after fracture

There is controversy about how often elevated parathyroid hormone (PTH) levels are found in hip fracture patients. The aim of this study was to determine whether changes in PTH levels after fracture and surgery could explain some of the variation in published data. Blood samples were obtained from 24 elderly patients with hip fracture before surgery, immediately after surgery and at 2 weeks and 3 months after fracture. PTH levels were elevated (> 5.5 pmol) in 33% initially and then fell significantly at 2 weeks in virtually all subjects (P < 0.001) and remained significantly lower after 3 months (n = 17). Although 25-hydroxyvitamin D levels were low (< 30 nmol) in 44% of the patients, the fall in PTH was not explained by alterations in vitamin D metabolites or other measured parameters. The cause of the variation in PTH levels is unknown but measurements immediately after fracture could overestimate the incidence of secondary hyperparathyroidism. Vitamin D deficiency is common in our hip fracture population and is not influenced by hospitalisation.

Drug- and nutrition-induced hypophosphatemia: mechanisms and relevance in the critically ill

OBJECTIVE

To provide an outline of the drugs and nutritional therapy that could contribute to the development of hypophosphatemia in the critically ill patient.

DATA SOURCES

Computerized abstracting services, references to primary literature articles, and review publications were screened for references to drug- or nutrition-related hypophosphatemia.

STUDY SELECTION

Studies primarily describing responses in adults were selected. Animal research is described that illustrates findings in humans.

DATA EXTRACTION

Information was abstracted from the findings of individual case reports and clinical trials.

DATA SYNTHESIS

Data are organized by mechanism of possible effect on serum phosphate concentration. No reference is made to drugs that do not have an effect on phosphate metabolism.

CONCLUSIONS

Hypophosphatemia can have significant effects that would hinder recovery of the critically ill patient. Antacids, catecholamines, beta-adrenergic agonists, sodium bicarbonate, and acetazolamide are commonly used therapeutic agents that could contribute significantly to the development of hypophosphatemia. Provision of nutrition to the chronically malnourished individual or chronic administration of phosphate-depleted parenteral nutrition could produce symptoms associated with hypophosphatemia. Other drugs could have a mild effect on lowering serum phosphate concentrations, but would be unlikely to produce symptoms unless combined with other etiologies of hypophosphatemia.

On the relationships between mineral metabolism, obesity and fat distribution

Alterations in calcium metabolism have been associated with cardiovascular risk factors. An altered binding of calcium to plasma proteins and raised levels of parathyroid hormone (PTH) have been described in morbid obesity. In the present study, indices of mineral metabolism were related to obesity (body mass index, BMI) and fat distribution (waist to hip ratio, w/h) in 194 subjects with a wide range of BMI and w/h. The ratio of total serum calcium to plasma ionized calcium (Ca2+) was found to be significantly correlated to both BMI (r = 0.20, P < 0.02) and w/h (r = 0.22, P < 0.005). Serum phosphate was also correlated to both of the indices of obesity in an inverse way (r = -0.24, P < 0.0008 for BMI and r = -0.33, P < 0.0001 for w/h). These relationships were still significant when the influences of age, sex and serum creatinine were included in the multiple regression analysis. This kind of analysis also disclosed that w/h was superior to BMI as a determinant of serum phosphate and the total calcium/Ca2+ ratio in serum. PTH was not significantly correlated to any of the indices of obesity. In conclusion, fat distribution rather than obesity per se was found to be associated with an altered mineral metabolism.

Plasma catecholamines--analytical challenges and physiological limitations

Catecholamines in plasma may be measured to assess sympathoadrenal activity. Numerous assay methodologies have been published, illustrating the fact that there are many analytical problems. Different methodologies are discussed briefly. A plea for better validation, especially with regard to specificity (which should not be confused with sensitivity or reproducibility), is made. Plasma NA is a frequently used marker for sympathetic nerve activity in humans, but the data obtained are often misinterpreted due to lack of appreciation of the physiological determinants of the NA concentration measured. NA overflow from an organ gives a good reflection of nerve activity in that organ. However, sympathetic nerve activity is highly differentiated, particularly during stress, and conventional plasma NA levels (usually forearm venous samples) cannot be taken as an indication of 'sympathetic tone' in the whole individual. NA is rapidly removed from plasma, resulting in meaningless net veno-arterial concentration differences over organs unless its removal from arterial plasma is taken into account. In the forearm, for example, 40-50% of catecholamines are removed during one passage; about half of the NA in a venous sample is derived from the arm and half from the rest of the body. Therefore, conventional venous sampling overemphasizes local (mainly skeletal muscle) nerve activity. Whole-body sympathetic nerve activity may be monitored in arterial or mixed venous (i.e. pulmonary arterial) samples, which reflect NA overflow from all organs in the body. NA levels are determined both by overflow to plasma and clearance from plasma. NA turnover studies with 3H-NA infusions may be needed to assess clearance, but the simpler concentration measurements usually yield adequate information if the sampling site is relevant. NA overflow from an organ can be assessed (using 3H-NA or ADR as a marker for NA extraction in the organ) and provides valuable information on local sympathetic activity. Mental stress elicits marked circulatory responses, with mainly cardiorenal sympathetic activation and minor elevations of conventional venous plasma NA levels, thus illustrating the differentiated firing pattern of the sympathetic nerves. Circulating ADR is less important than neurogenic mechanisms in the responses to stress. Concentration-effect studies for infused catecholamines may be used for receptor sensitivity studies in vivo, but reflexogenic contributions to responses need to be determined. However, prejunctional mechanisms cannot be assessed without knowledge of the nerve activity present; for example, ADR infusion leads to increased nerve activity. When correctly sampled, measured and interpreted, plasma catecholamines can yield very valuable information on sympathoadrenal activity.

Lipids in psychological research: the last decade

We review the recent literature examining lipid changes during stressful experiences, and the psychological and constitutional differences that influence lipid levels at rest and that may modulate lipid response to stress. Mild forms of chronic or episodic stress are apparently not associated with alterations in lipids and lipoproteins, but severe forms of real or perceived stress do appear to alter lipid levels. Acute laboratory stress is frequently associated with short-term alterations in lipids and lipoproteins, but the significance of these changes is unclear. Several individual characteristics, such as heightened neuroendocrine or autonomic reactivity to stressors, Type A component behavior, and other aspects of personality, appear to be associated with an atherogenic lipid profile. Stress may influence lipid concentrations and metabolism through a variety of physiological and behavioral mechanisms, but none have been clearly elucidated. Future research should concentrate on understanding these mechanisms.

Lower serum magnesium level after exposure to cold in women with primary Raynaud's phenomenon

Serum levels of magnesium (s-Mg), calcium (s-Ca), potassium (s-K) and sodium (s-Na) were measured in 80 women with primary Raynaud's phenomenon (RP) and in 24 age-matched female controls recruited from a population survey. The blood samples were taken after a 40-min standardized whole body cooling test. The mean s-Mg level in the group with RP was significantly lower than in the controls (0.81 +/- 0.05 vs. 0.86 +/- 0.07 mmol l-1, P less than 0.05). One year later, 66 members of the RP group and 22 members of the control group were investigated further, but without any exposure to cold. No differences in mean s-Mg values were found between the groups. The mean s-Mg level was significantly higher in the blood samples taken later without cold exposure than at the initial examinations after exposure to cold in the RP group, but not in the controls. The s-Mg level was lower after exposure to cold in 82% of the women with RP, compared to 45% of the controls (P less than 0.001). No differences in the other electrolytes were found. It is concluded that exposure to cold under standardized conditions may decrease the s-Mg level in women with primary RP. Further studies of the role of magnesium in patients with RP are required.

Platelet and plasma catecholamines in relation to plasma minerals and parathyroid hormone following acute myocardial infarction

Epinephrine has been shown to lower the plasma concentrations of several minerals and elevate those of parathyroid hormone (PTH). In order to evaluate the possible clinical importance of such experimental observations, 34 patients with acute myocardial infarction (AMI) were studied with daily determinations of plasma catecholamines, minerals, and PTH during the first week after AMI and at follow-up one month later. In addition, platelet catecholamines were determined as they fluctuate more slowly than plasma catecholamines. After infarction initial platelet epinephrine and norepinephrine levels were higher (p less than 0.05 for both) in nonsurvivors than survivors during a one year follow-up. Results suggested that activation of the sympathoadrenal system influences calcium homeostasis following AMI, but that the impact of sympathoadrenal activation on mineral metabolism is of minor clinical significance in the average AMI patient. High platelet catecholamine levels may predict a poor outcome after AMI.