Search

AIM:: To describe plasma retinol values according to age, gender and pubertal maturation. TYPE OF STUDY:: Comparative, transverse and descriptive. PLACE:: Medellín, Colombia. SUBJECTS AND METHODS:: Plasma retinol values were determined in 588 boys and 531 girls aged between 6 and 18?y. For this, we used spectrophotometry by UV oxidation of retinol, results below 0.87?mmol/l were confirmed by high-performance liquid chromatography. RESULTS:: Mean retinol plasma concentrations were slightly higher in girls under 10?y. However, above this age, values are generally higher in boys. Plasma retinol concentrations increased with pubertal maturation in both boys and girls in a statistically significant manner. The highest values were observed in girls with mammary development grades 3 and 4 (P<0.05) and in boys with external genitalia development grades 1 and 2 (P<0.05). Vitamin A deficiency based on plasma retinol concentration (<0.70?mmol/l), was observed in 3.6% of all individuals regardless of gender. CONCLUSIONS:: Plasma retinol concentration is correlated to pubertal maturation in both boys and girls. Vitamin A deficiency in school children and adolescents of Medellín is not a major health problem.European Journal of Clinical Nutrition (2004) 58, 456-461. doi:10.1038/sj.ejcn.1601828 [ABSTRACT FROM AUTHOR]

Computerized information systems have become an in-dispensable source of quality improvement data in the healthcare field. The degree to which we are successful in using these systems is limited only by our ability to ask the right questions. In this study, computerized patient records were used to evaluate the uniformity in the prescribing patterns for oral corticosteroids among house staff and attending physicians as a measure of the adequacy of resident supervision in the outpatient setting. Retrospective analysis of the records of 771 outpatients receiving prescriptions for oral corticosteroid preparations over 1 year in a large tertiary-care university-affiliated Department of Veterans Affairs Medical Center indicated different prescribing patterns for attending physicians and house staff. Additionally, it was noted that house staff tended to manage more complex patients than did attending physicians. We further evaluated the clinical outcomes of these patients to assess the quality, appropriateness, and comparability of care within cohorts of patients and to determine the degree to which resident supervision may have affected outcomes. The study results suggest that there is an opportunity to improve the management of patients treated with oral corticosteroid therapy by increasing staff physician involvement either through direct care of the most complex cases or through enhanced resident supervision. [ABSTRACT FROM PUBLISHER]

A previous study has shown bidirectional saturable transport of LHRH across the blood-brain barrier. Here, the effects of the steroids progesterone and beta-estradiol and the pituitary glycoproteins luteinizing hormone (LH) and follicle stimulating hormone (FSH) on the bidirectional transport rate were determined. No statistically significant difference in brain to blood transport of 125I-LHRH was found in mice given ICV progesterone (1 and 100 pmol/mouse), beta-estradiol (1 and 100 pmol/mouse), FSH (10 and 1000 pmol/mouse) or LH (100 and 1000 pmol/mouse). Blood to brain transport of 125I-LHRH, tested in rats with a carotid artery perfusion method, was not affected by inclusion of progesterone (100 nmol/ml), beta-estradiol (100 nmol/ml), LH (2 and 10 nmol/ml), or FSH (10 nmol/ml) in the perfusate. We conclude, therefore, that unlike its release from the hypothalamus, the exchange of LHRH between the CNS and blood is unlikely to be influenced by reproductive hormones.

beta-Amyloid and related peptides are components of the neurofibrillary tangles found in the brains of patients with Alzheimer's disease and have been suggested to be directly involved in the pathophysiology of that condition. It is unclear whether the amyloid deposited in the brain arises from the peripheral circulation, which would require passage across the blood-brain barrier (BBB), or whether it is produced within the brain itself. We examined the ability of beta-amyloid1-28 (beta Am), a commercially available, biologically active fragment, radioactively labeled with 125I (I-beta Am), to cross the BBB. After IV injection of I-beta Am, radioactivity entered the brain slowly, but to a greater extent than could be attributed to its being trapped in the vascular space of the brain. Entry was not inhibited by an excess of unlabeled beta Am or by pretreatment with aluminum, indicating that entry was by the nonsaturable mechanism of transmembrane diffusion. After intraventricular injection of I-beta Am, radioactivity was cleared slowly from the brain and was not affected by excess unlabeled beta Am or by pretreatment with aluminum, indicating that clearance probably occurred with reabsorption of cerebrospinal fluid. The excess beta Am did not alter the brain/blood ratio or the clearance rate of radioactively labeled albumin, indicating that under the conditions of this experiment beta Am did not have measurable effects on BBB integrity or on the rate of reabsorption of cerebrospinal fluid. High performance liquid chromatography (HPLC) showed that I-beta Am was rapidly degraded, especially by the brain, to smaller peptide fragments.(ABSTRACT TRUNCATED AT 250 WORDS)

Peptides have been shown to cross the blood-brain barrier (BBB) as intact molecules so that they can influence the central nervous system. Peptides cross by saturable and nonsaturable mechanisms in the direction of both brain to blood and blood to brain. Passage of peptides, especially by saturable transport, has been shown to be influenced by pharmacological agents and physiological events. These findings support the view that peptides or their analogues could be useful as therapeutic agents for disorders of the central nervous system. They also suggest strategies in approaching therapeutic goals, including manipulating transport rates, targeting diseases due to altered BBB-peptide interactions, and designing analogues capable of taking advantage of such mechanisms of passage as paracellular transmembrane diffusion and brain-to-blood transport.

The role of bromocriptine as primary therapy for prolactin-producing tumors is currently well accepted in the literature. Bromocriptine decreases the concentration of serum prolactin and this decrease precludes tumor shrinkage, despite the lack of correlation between amount of decrease in tumor size and baseline serum prolactin. We submit the case of a patient on chronic bromocriptine therapy followed by measuring baseline and thyrotropin-releasing hormone (TRH)-stimulated serum prolactins. Bromocriptine affects both release and storage of prolactin. The literature has suggested that the effects of bromocriptine on storage and synthesis may be responsible for its effects on tumor size. It was felt that TRH stimulation would more accurately reflect storage and synthesis, and thus correlate better with tumor size. The pituitary was initially debulked via a right frontal approach; then the patient was placed on bromocriptine therapy and postoperatively followed with baseline and TRH-stimulated serum prolactins. The size of the pituitary was measured by computed tomography. Baseline serum prolactin levels rapidly decreased, but despite the slow decrease in TRH-stimulated prolactins no change was noted in tumor size. Because of the time difference between the baseline and TRH-stimulated prolactin levels, we conclude that clinically bromocriptine affects primarily secretion of prolactin and secondarily storage and synthesis. We also show that TRH-stimulated prolactin does not correlate with size of prolactin-secreting pituitary tumors and therefore tumor size should be independently measured. The literature has shown that prolactinomas do not respond well to TRH stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Previous studies have suggested that peptide transport system-1 (PTS-1), the saturable system that transports Tyr-MIF-1, the enkephalins, and related peptides out of the central nervous system (CNS), exhibits stereospecificity. In the present studies, we showed that 125I-L-Tyr-MIF-1, but not 131I-D-Tyr-MIF-1, was cleared from the CNS more rapidly than could be accounted for by nonspecific mechanisms. Such clearance was inhibited by a 1.0 nmol dose of L-Tyr-MIF-1, but not by D-Tyr-MIF-1. Neither L- nor D-Tyr-MIF-1 altered the much lower clearance of I-D-Tyr-MIF-1 from the brain. Radioactivity recovered from the vascular space after the injection of 125I-Tyr-MIF-1 into the lateral ventricle of the brain eluted by HPLC primarily as intact peptide, demonstrating that most of the Tyr-MIF-1 was not degraded during transport. By contrast, the nonsaturable unidirectional influx of Tyr-MIF-1 into the CNS did not distinguish between the isomers. These studies confirm and extend the observations that Tyr-MIF-1 is transported out of the CNS by a saturable, stereospecific transport system as an intact peptide while the influx into the CNS is by a nonsaturable mechanism that does not distinguish between the isomers.

Previous studies have demonstrated that elevated levels of serum uric acid or caffeine are associated with increased locomotor activity in rats and humans. Since uric acid and caffeine are structurally similar, it was hypothesized that these compounds alter locomotor activity through a common neural mechanism, specifically by acting as receptor antagonists at adenosine A1 binding sites. In vitro competition of caffeine and uric acid against the A1 agonist, [3H] cyclohexyladenosine ([3H]CHA), was conducted using homogenates of adult rat forebrain. Caffeine effectively competed for the A1 binding site as previously reported (IC50 = 107 microM), but uric acid failed to compete with [3H]CHA binding at concentrations within a relevant physiological range. Nevertheless, in vivo experiments indicated that chronic elevation of uric acid following allantoxanamide treatment of male rats on days 4-27 of life significantly decreased A1 receptor binding in the striatum, a region traditionally implicated in mammalian locomotion. In contrast, chronic caffeine treatment on days 4-27 of life caused an increase in A1 receptor binding in the cortex similar to increases reported previously in whole brain. These changes in A1 receptor binding following chronic elevation of uric acid or caffeine did not persist in rats that had been withdrawn from allantoxanamide or caffeine treatment for 14 days. Results from in vitro and in vivo experiments indicate that despite a similar molecular structure uric acid does not act by the same mechanism as caffeine to increase locomotor activity in rats.

Although iron is involved in brain function, very little is known about the regulation of its concentrations in the central nervous system. We quantitatively measured the entry and exit rates of iron, transferrin (its major transport protein), and albumin in mice. The blood to brain transport of iron greater than transferrin greater than albumin and the brain to blood transport of transferrin greater than albumin greater than iron. The results suggest that iron and transferrin have slow, bidirectional, probably saturable, and to some degree independent transport systems, although iron introduced directly into the brain is not readily available for brain to blood transport.

This research was motivated by the previous finding that serum uric acid levels correlate with symptoms of hyperactivity in normal children. We attempted, therefore, to investigate this relationship in an animal model. Dose and time relationships between allantoxanamide-induced heightened serum uric acid and locomotor activity were investigated. A dose- and time-dependent relationship was shown between serum uric acid levels and allantoxanamide. Those doses of allantoxanamide which elevated serum uric acid produced time-dependent changes in locomotor activity. In the first two hours following injection, activity increased relative to controls, in the next two-hour block activity decreased, only to rise again above control levels in the third two-hour period. The possible role of uric acid and allantoxanamide are discussed in relation to these complex changes in activity.

It is becoming increasingly evident that peptides can cross the blood-brain barrier. The entry into the central nervous system of a commercially available analog of Peptide T, an octapeptide derived from the human immunodeficiency virus envelope glycoprotein 120, was studied in several experiments. It was found that 125I-Peptide T analog given intravenously in the periphery entered the brain in an intact form, as confirmed by HPLC, to a greater extent than did the labeled albumin control. This entry occurred despite the very low lipid solubility, measured by the octanol/buffer partition coefficient, for the iodinated analog. The rate of entry was decreased by unlabeled Peptide T analog, but not by iodo-tyrosine. Saturable transport out of the brain was not observed after intraventricular administration. Thus, results with 125I-Peptide T analog indicate that saturable systems can transport peptides from the blood into the central nervous system.

Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) has been shown to be transported from the brain to blood by a saturable system shared with Met-enkephalin and a few other substances. It is not known whether a similar system exists in the opposite direction. Accordingly, the entry rate of 125I-Tyr-MIF-1 from blood to brain was measured by a method involving perfusion of the test substances into the common carotid artery. The rate of entry was obtained from the slope of the line determined by brain to blood ratios at multiple points of time. Penetration of 125I-Tyr-MIF-1 across the blood-brain barrier was found to be 4.444 x 10(-3) ml/g/min, an entry rate significantly higher than that of the vascular marker 125I-albumin. Competition with Tyr-MIF-1 or nonradioactively labeled 127I-Tyr-MIF-1 showed no difference in rate of entry, indicating that the penetration of 125I-tyr-MIF-1 was not saturable. Met-enkephalin and Leu-enkephalin also failed to affect entry of 125I-Tyr-MIF-1. The results indicate that Tyr-MIF-1 can enter the brain from the blood to a greater extent than does albumin, but that this penetration does not involve a saturable system.