Prostacyclin biosynthesis and platelet function in autonomic dysfunction

We measured urinary excretion of the principal metabolite of prostacyclin, PGI-M (2,3-dinor-6-keto-PGF1 alpha) in two patients with Shy-Drager syndrome and three with idiopathic orthostatic hypotension. All patients had a rise in blood pressure (30 +/- 6 mm Hg) after ingestion of 50 mg indomethacin. Urinary excretion of PGI-M was normal and fell 57 +/- 11% after administration of indomethacin. In two subjects, there was no evidence of any circulating inhibitor of platelet aggregation when hypotension was induced by upright posture or ingestion of a meal. Despite the efficacy of indomethacin, these patients with autonomic dysfunction did not show increased production of the vasodilator prostanoid prostacyclin.     

Distractibility with advancing age and Parkinson's disease

Focused attention can be compromised by the neurodegenerative processes associated with both healthy aging and Parkinson's disease (PD). Deficits in ignoring distractors with reflexive or overlearned response links have been attributed to impaired inhibition. The current research assessed whether similar deficits occur for distractors with recently learned arbitrary response associations, for which sensorimotor transformations are far less automatic and therefore considerably easier to resist. We used a selective attention task that evaluated distractibility and the use of distractor inhibition within the same context. The task involved stimuli that were arbitrarily assigned to responses based on a rule learned during the testing session. Performance showed that distraction increased with both healthy aging and PD. Moreover, these increases in distraction were accompanied by decreases in overt evidence of distractor inhibition, which appear to reflect at least in part a failure of reactive inhibition. Comparison of the deficits in the two groups indicates that the key difference reflects severity, rather than distinct symptoms, suggesting that they stem from neural changes associated with both aging and PD. These results demonstrate that aging- and PD-related hyper-distractibility and impaired inhibition during focused attention affect stimuli without prepotent response links, which implicates dopaminergic networks in the strategic control of arbitrary visuomotor transformations.     

Categories of manual asymmetry and their variation with advancing age

Manual asymmetries were analyzed in 18- to 63-year-old right-handers in different motor tasks. This analysis aimed at describing the asymmetry profile for each task and assessing their stability across ages. For this purpose, performance of the right and left hands were analyzed in the following aspects: simple reaction time, rate of sequential finger movements, maximum grip force, accuracy in anticipatory timing, rate of repetitive tapping, and rate of drawing movements. In addition, stability of manual preference across ages was assessed through the Edinburgh inventory (Oldfield, 1971). The results indicated different profiles of manual asymmetry, with identification of three categories across tasks: symmetric performance (asymmetry indices close to zero), inconsistent asymmetry (asymmetry indices variable in magnitude and direction), and consistent asymmetry (asymmetry indices favoring a single hand). The different profiles observed in the young adults were stable across ages with two exceptions: decreased lateral asymmetry for maximum grip force and increased asymmetry for sequential drawing in older individuals. These results indicate that manual asymmetries are task specific. Such task specificity is interpreted to be the result of different sensorimotor requirements imposed by each motor task in association with motor experiences accumulated over the lifetime. Analysis of manual preference showed that strength of preference for the right hand was greater in older individuals.     

ADP-induced platelet aggregation as a function of age in healthy humans

In 120 healthy humans (58 males and 62 females) possible differences in platelet aggregability were investigated with respect to age and sex. By using a narrow range of final ADP concentrations (0.2-1.0 microM) primary and secondary aggregation were evaluated. The rate of primary aggregation was shown to be significantly related to increasing age and this was true for both sexes. As regards secondary aggregation the same pattern was seen in the group of male subjects. Thus, among the youngest (less than 34 years) the frequency of secondary waves was only one third of that encountered among the oldest (greater than 50 years). No similar association was detectable among the female subjects. The present study calls attention to some important issues which should be considered in platelet aggregation studies; the interpretation of data obtained from such studies invariably requires a careful selection of appropriate age- as well as sex-matched control groups.     

Endothelin and platelet function

The effects of newly discovered vasoconstrictor peptide endothelin was studied on human, rabbit and canine platelet function. Endothelin (0.01 nM - lμM) did not promote platelet aggregation. In human platelets, endothelin (0.1 μM) did not significantly affect aggregation responses to ADP, collagen, epinephrine, arachidonic acid, PGH₂ or thrombin. Endothelin did not promote the mobilization of intracellular calcium in Fura2 loaded human platelets. In rabbit and canine platelets endothelin produced signficant potentiation of platelet aggregation mediated by low concentrations of ADP. Aggregation responses to higher concentration of ADP (5 μM) were unaffected by endothelin. These data reveal that under certain circumstances endothelin may potentiate rabbit and canine platelet aggregation responses to ADP, however endothelin does not produce direct effects on human platelet function.     

Effects of advancing age on peripheral nerve regeneration.

Following axotomy, the regrowth of peripheral axons takes longer in older individuals than in young ones. The present study compares the crush-induced process of degeneration and regeneration in the buccal branch of the facial motor nerve in groups of rats aged 3 months and 15 months. Observations are based on qualitative and quantitative analyses of the nerve 20 mm from the site of injury in rats 1, 2, 4, 16, 21, 28, and 56 days after crush. The buccal branch is purely motor and contains a unimodal population of about 1,600 axons commonly in a single fascicle. During the first 28 days post crush (dpc) in the 3-month animals, the progression of myelin and axon degeneration, myelin clearance, regrowth of axon sprouts, and axon maturation are relatively synchronized and uniform. In the older rats, the degeneration of myelin and axons, myelin clearance, and the appearance of axon sprouts at the site of sample are all delayed. In the younger animals, axon sprouts increase in numbers from their first appearance at 4 dpc through the 2 weeks examined following the restoration of whisking behavior. The numbers of regenerating older axons increase at a rate comparable to that in the younger animals through the time that bilaterally symmetrical whisking behavior is evident, but afterwards the number of axon sprouts decreases. At 2 months after crush the young animals have 30% more fibers in the buccal branch than control nerves, while the older animals have fewer than control numbers. In the 3-month regenerated nerve, 2 months post crush, 30% of the regenerated fibers are of very small caliber, less than 3 microns2 in cross sectional area, and typically these small axons have unusually thick myelin sheaths; the older nerves do not have such a skewed distribution of axon areas. The older regenerated axons at 2 months post crush have an unusually high density of microtubules compared to the younger regenerated ones (and controls), and the ratio of neurofilaments to microtubules is very low. The conclusions are that motor neurons in older animals regenerate damaged axons after a delay not apparent in the young; the strong regenerative response apparent initially in animals of both age groups is not maintained in the older animals; and the relationship between the numerical density of cytoskeletal elements and the axon cross-sectional area deviates from normal in the regenerated axons of the older animals.     

Impaired platelet function among platelet donors

BACKGROUND: Platelet transfusions are effective for the prevention and treatment of bleeding in patients with disorders of platelet number and/or function. In recent years plateletpheresis concentrates have outnumbered pooled platelet concentrates, albeit with significant differences between nations. Thus, the platelet quality of individual donors has become increasingly important. The aim of this study was to gain an estimate for the prevalence of impaired platelet function among platelet donors. STUDY DESIGN AND METHODS: We determined the inter-donor variability in platelet plug formation with a PFA-100 analyzer, the prevalence of impaired thromboxane formation, and effects of the density in alpha2 integrin polymorphism and density. RESULTS: (i) Collagen-epinephrine induced closure time (CEPI-CT) showed a great inter-subject variability in platelet donors and was higher than in healthy controls (p = 0.008). One-fifth of donors had abnormal CEPI-CT values and 11% exceeded >300 s (max measurable value). (ii) Decreased serum thromboxane B2 levels were found in 9% of all donors, compatible with surreptitious intake of cyclooxygenase inhibitors or with an aspirin-like defect. CEPI-CT correlated inversely with TxB2-levels in donors and controls. (iii) The density of the alpha2-integrin correlated negatively with CEPI-CT and CADP-CT values in controls, but was not responsible for the observed impaired platelet function in donors. (iv) Finally, the ABO blood group system modulates closure times. CONCLUSION: In sum, a large number of platelet donors present with prolonged closure times. Decreased thromboxane formation and frequent platelet donation partly account for this observation.     

Activation of platelet prostaglandin biosynthesis pathway during neoplastic cell-induced platelet aggregation

In a previous study we found a correlation between metastatic potential and platelet aggregating activity in sublines of a benzopyrene-induced murine fibrosarcoma (mFS6); the purpose of the present work was to elucidate the role of thromboxane biosynthesis by platelets and/or by neoplastic cells in the activation of platelets in this system. The cells of the more malignant subline induced higher aggregation and TxB₂ production than those of the non metastasizing one. The supernatants of aggregating cell suspensions contained very few TxB₂; furthermore, preincubation of platelets with ASA or Apyrase resulted in inhibition of aggregation and TxB₂ production, while preincubation of the cells was ineffective; these results suggest the platelet origin of the measured TxB₂ and indicate that platelet-derived ADP plays an important role in their activation, while the production of ADP by the cells does not seem to be relevant in this model. The involvement of platelet prostaglandin biosynthesis pathway in neoplastic cell induced platelet activation could play an important role in the development of platelet-dependent tumour metastasis.     

Cigarette smoking and platelet function

To assess the influence of cigarette smoking on platelet activation, we studied the changes in intraplatelet and platelet-released serotonin (5-HT) and plasma levels and platelet-associated production of thromboxane B2 (TXB2), in 6 non smokers and 6 habitual smokers, before and after acute exposure to smoke.Before smoking, habitual smokers showed slightly higher, albeit not significantly, 5-HT platelet concentrations and TXB2 plasma levels, as well as lower TXB2 platelet production after collagen and even more after ADP stimulation (0.59±0.27 vs 1.35±0.46 and 0.99+0.47 vs 2.08±0.51 ng/108 platelets for habitual smokers vs controls, 4 and 10 min after ADP, p<0.02). No significant differences in platelet 5-HT release were observed.Acute smoking did not induce any significant change from baseline in either 5-HT or TXB2 for controls, while significantly reduced TXB2 production from ADP-challenged platelets from habitual smokers (0.30±0.15 vs 0.59±0.27 ng/108 platelets, immediately after smoking vs baseline, p<0.01). Ninety min after the completion of the smoking, the values had returned to baseline.Immediately after smoking, significant differences were found between habitual smokers and controls for TXB2 platelet production (2.76±1.78 vs 6.42±1.60, p<0.025 and 3.01±1.90 vs 6.44±2.26 ng/108 platelets, p<0.05, for habitual smokers vs controls, 4 and 10 min after the addition of collagen; 0.30±0.15 vs 1.20±0.84 and 0.79±0.50 vs 1.70±0.74 ng/10 8 platelets, p <0.05, after ADP stimulation). Differences were no longer significant 90 min after smoking. Our data indicate that cigarette smoking is associated with platelet dysfunction, which seems due to impairment of metabolic platelet capacity rather than increased platelet activation in vivo.     

Decline in verbal memory performance with advancing age: the role of frontal lobe functioning

This study investigated the relationship between measures of frontal lobe functioning (FLF) and verbal memory performance among healthy, community-dwelling older adults (60-85 years old). All were administered measures of FLF, attention, verbal memory, and depression. After controlling for the effects of attention and depression, FLF accounted for significant amounts of the variance in verbal memory scores. Age related to the FLF measure according to the level of organization of verbal material to be recalled. Frontal lobe functioning and performance on an attention measure explained the greatest amount of the variance in the recall of unorganized verbal material, whereas age and attention abilities were the best predictors of the recall of organized verbal material. The data indicate a central role of frontal dysfunction in understanding age-related memory loss.     

Pupillometry measures of autonomic nervous system regulation with advancing age in a healthy pediatric cohort

Clinical Autonomic Research - To determine if variables of the pupillary light response mature with age and sex in a healthy pediatric cohort and the utility of pupillometry in assessment among...     

Platelet 5-hydroxytryptamine increases with platelet age in dogs.

Thrombocytopenia was induced in mongrel dogs by two mechanisms: immunologically, by intravenous injection of heterologous antiplatelet antibody, and non-immunologically, by circulating the blood through glass beads in anesthetized animals. The platelet content of 5-HT was monitored before and during the recovery of the blood platelet counts. This period is associated with the normalization of the mean platelet survival time and with a progressive increase in the mean age of the circulating platelet population. A continuous increment in platelet 5-HT closely followed the increase in platelet counts in both models of thrombocytopenia, and a strong correlation was found between the platelet age and 5-HT content. These findings support the concept that platelets accumulate 5-HT during their physiological aging process, contradicting the notion that a negative balance in 5-HT content results at the end of their physiological lifespan in circulation. These results are not in conflict with the concept that circulating platelets release and re-uptake 5-HT.     

Effect of suloctidil on platelet function in patients with shortened platelet survival time

The effect of suloctidil (600 mg/day) on platelet survival time (PST) and plasma and urine betathromboglobulin (BTG) was studied in a double-blind, placebo-controlled six-week crossover trial in 13 patients with shortened PST (less than 110 hrs, exponential model). Mean PST after suloctidil (110.6 hrs) was significantly higher than in the placebo phase (94.5 hrs) (p = 0.04). Mean plasma BTG was significantly lower during the suloctidil phase (42.8 ng/ml) compared with the placebo phase (65.8 ng/ml) (p = 0.02), but there was no significant difference in urine BTG. These results suggest that suloctidil provides a platelet protective effect and therefore may be of benefit in reducing the frequency of platelet mediated thromboembolic events.     

Measuring platelet function with platelet shape change, an early event in aggregation

Platelet shape change precedes aggregation and is sensitive to significantly less stimulant. In this study, differences in percent light transmission (%T) through stirred suspensions of spheroid or discoid platelets are exploited for studying the response of platelets to Platelet Activating Factor (PAF). Changes in %T between stirred and non-stirred suspensions of unstimulated platelets in Platelet Rich Plasma (PRP) varied with the starting concentration. Aggregation was blocked by the presence of citrate while activation by ADP was minimized by apyrase. However, phosphatidic acid formation, ATP release and minimal serotonin release occurred. A shape change parameter (SCP) was defined which varied with the concentration of PAF. Its dependence on PAF was shifted to lower concentration with washed platelets. The dose-response curves for the SCP were found to be virtually identical for both sheep and human platelets. Human platelets were then used to correlate morphology, as determined by phase contrast microscopy, with spectrophotometric data in the form of the SCP. A linear regression analysis of SCP and percent activation revealed a virtual 1:1 correspondence with a slope of 1.066 and an intercept of 0.009 with the standard error of the estimate equal to 0.053. The correlation coefficient was 0.990, making it significant at p less than 0.001. This method provides an alternative to platelet aggregation assays as a convenient, sensitive and reliable measure of platelet activation.     

Comparison between induced platelet aggregation and circulating platelet aggregates as platelet function tests in patients with transient ischemic attacks

Routine blood analysis, platelet counts, number of circulating platelet aggregates (CPA) and platelet aggregation in vitro against adenosine-diphosphate (ADP), epinephrine and collagene were studied in 45 healthy controls, in 10 hospitalized patients with other neurological diseases than stroke and in 12 patients with transient ischemic attacks (TIA) before and after prophylactive treatment with anticoagulants (AC) or anti-platelet drugs (APD).
Except for lower hemoglobin and hematocrit levels in women, sex, smoking, oral contraceptives or pregnancy did not significantly influence the routine blood parameter. Smoking females taking oral contraceptives had an increased number of CPA and the most easily induced aggregation in vitro .
Patients with TIA had no significant differences in blood or platelet findings versus the healthy controls (except smoking females on oral contraceptives) or the non-stroke patients, even though individual patients could have high numbers of CPA and an easily induced platelet aggregation in vitro . Treatment with AC did not influence platelet function, whereas APD therapy decreased the number of CPA and inhibited the secondary platelet aggregation in vitro .     

Effect of platelet age on adhesiveness to collagen and platelet surface charge.

Adhesion to collagen was investigated as a function of platelet age in rat platelets. Platelet adherence was measured using EDTA-containing platelet- rich plasma which was added to preparations of collagen fibers clamped between magnetic stirrers by recording changes in light transmission. The plot of light transmission versus logarithm of time was linear and allowed calculation of a slope factor which related to the rate of adherence. Neither the amount of collagen nor the platelet count were limiting in the test. Young platelet populations (less than or equal to 1 day old) were obtained during the recovery phase from immune induced thrombocytopenia. Old platelet populations were prepared by blocking thrombopoiesis with cyclophosphamide. Young platelets showed a moderate but statistically significant increase in adhesivity to collagen but old platelets did not differ significantly from randomly aged platelets in this function. The electrophoretic mobility of platelets was not affected by their age.