Minireview plant carbonic anhydrase.

This article reviews the literature concerning plant carbonic anhydrase. The following topics are discussed: discovery, molecular weight and structure, zinc content, amino acid composition, mechanism and kinetics of catalytic activity, and function and localization in the plant. Where deficiencies exist in the literature on plant carbonic anhydrase reference is made to articles dealing with mammalian carbonic anhydrase. The theories of carbonic anhydrase function in plants are examined critically and evaluated in the light of existing evidence.     

Minireview. Peptides and the blood-brain barrier

Most neuropeptides are known to occur both in the central nervous system and in blood. This, as well as the occurrence of central nervous peptide effects after peripheral administration, show the importance of studying the relationships between the peptides in the two compartments. For many peptides, such as the enkephalins, TRH, somatostatin and MIF-1, poor penetration of the blood-brain barrier was shown. In other cases, including beta-endorphin and angiotensin, peptides are rapidly degraded during or just after their entry into brain or cerebrospinal fluid. Some peptides, such as insulin, delta-sleep-inducing peptide, and the lipotropin-derived peptides, enter the cerebrospinal fluid to a slight or moderate extent in the intact form. Many peptide hormones, such as insulin, calcitonin and angiotensin, act directly on receptors in the circumventricular organs, where the blood-brain barrier is absent. Oxytocin, vasopressin, MSH, and an MSH-analog alter the properties of the blood-brain barrier, which may result in altered nutritient supply to the brain. In conclusion, the diffusion of most peptides across the brain vascular endothelium seems to be severely restricted. There are, however, several alternative routes for peripheral peptides to act on the central nervous system. The blood-brain barrier is a major obstacle for the development of pharmaceutically useful peptides, as in the case of synthetic enkephalin-analogs.     

Minireview: histamine receptors in brain.

The recent availability of selective pharmacological tools has allowed several classes of histamine receptors to be characterized in brain by assessment of biochemical, neurophysiological and behavioral responses as well as by radioligand binding studies. H₁-receptors might be coupled to translocation of calcium ions and H₂-receptors to an adenylate cyclase. Histamine receptors, distinct from the H₁- and H₂-receptors, might also be present as suggested by electrophysiological and binding studies. The possible involvement of cerebral histamine receptors in the sedative activity of H₁-antihistamines, in the hypotensive activity of clonidine and in the antidepressant activity of tricyclic compounds is discussed.     

Minireview. The hypothalamus and blood glucose regulation

Complex neural circuits exist in the hypothalamus for the control of metabolic hormones, enzyme activities, and substrate flux that appear to be involved with the normal adaptation to feeding and subsequent blood sugar regulation. Abnormalities within this system have been found in experimental obesity and in human diabetes, and such maladaptive changes are thought to contribute to the pathophysiology of both disorders. The present report is an attempt to present a coherent picture of the manifold factors which may be involved in the homeostatic regulation of blood glucose levels by the hypothalamus. A wide variety of evidence is touched upon here to show that this part of the ancient vertebrate forebrain mediates a neural glucoregulatory mechanism involving the endocrine pancreas, the liver, and the adrenal medulla.     

Minireview. Thyrotropin releasing hormone and CNS cholinergic neurons

The centrally mediated pharmacological effects of thyrotropin releasing hormone (TRH), their mechanistic basis and therapeutic implications, along with the possible physiological significance of extrahypothalamic TRH, have been the subject of numerous investigations for over a decade. Despite this effort a holistic perspective on these issues and considerations does not exist. However, with continued research employing multiple and diverse experimental approaches, many interactions of TRH and related peptides with central cholinergic mechanisms have been revealed. These interactions are documented in this review and it is proposed that they can account for several of the more prominent pharmacological actions of these peptides. Additionally, it is suggested that a function of endogenous YHR, throughout the neuroaxis, may be to regulate the excitability of central cholinergic neurons.     

Minireview: Clinical cryptosporidiosis

Cryptosporidium has emerged as an important cause of diarrhoeal illness worldwide, especially amongst young children and patients with immune deficiencies. Usually presenting as a gastro-enteritis-like syndrome, disease ranges in seriousness from mild to severe and signs and symptoms depend on the site of infection, nutritional and immune status of the host, and parasite-related factors. Sources and routes of transmission are multiple, involving both zoonotic and anthroponotic spread, and facilitated by the resistance of the parasite to many commonly used disinfectants. Prevention and control measures are important for the protection of vulnerable groups since treatment options are limited. This review covers the life cycle, pathogenesis, clinical presentations, diagnosis, prevention and management of cryptosporidiosis in humans.     

Minireview on Achillea millefolium Linn

Yarrow (Achillea millefolium L.) is an important medicinal plant with different pharmaceutical uses. A. millefolium has been used for centuries to treat various diseases including malaria, hepatitis and jaundice. A. millefolium is commonly prescribed to treat liver disorders. It is also used as an anti-inflammatory agent and is a hepatoprotective herb. A. millefolium is considered safe for supplemental use. It has antihepatotoxic effects also. It is prescribed as an astringent agent. It is prescribed in hemorrhoids, headache, bleeding disorders, bruises, cough, influenza, pneumonia, kidney stones, high blood pressure, menstrual disorders, fever, rheumatoid arthritis, gout, osteoarthritis, hemorrhagic disorders, chicken pox, cystitis, diabetes mellitus, indigestion, dyspepsia, eczema, psoriasis and boils.     

Arginine revisited: Minireview article

Summary. Arginine is a precursor of proteins and employed in urea synthesis. It is also the precursor of many other compounds, such as creatine, nitric oxide, polyamines, agmatine, proline. In this review, its transport and that of other basic amino acids are examined, along with its transformation into nitric oxide, agmatine and proline, and the mutual regulation of the individual pathways.     

Stress resistance induced by paramylon treatment in Artemia sp.

A study was undertaken to investigate the effectiveness of paramylon extracted from the non-photosynthetic WZSL mutant of Euglena gracilis in potentiating the resistance of the brine shrimp Artemia sp. to stress conditions resulting from poor growth medium quality and daily handling. The experimental design incorporated four different treatments: I) paramylon addition/no growth medium replacement; II) no paramylon addition/no growth medium replacement; III) paramylon addition/growth medium replacement; IV) noparamylon addition/growth medium replacement. As shown by the survival curves of Artemia sp., the addition of paramylon significantly reduced susceptibility of animals to the stressors. Paramylon effectively increased also the ability of offspring to withstand poor water quality and handling damages. Without paramylon almost all offspring died before adulthood, whereas addition of paramylon allowed the animals to moult to the adult stage. Moreover, reproductive success (higher number of living offspring) was enhanced considerably in animals treated with paramylon treated under both stress conditions. These results show that paramylon extracted from Euglena represents a promising biologically active compound for aquaculture purposes. It could be used as a purified product or as component of whole cells, since the Euglena mutant, because of the high intracellular amount of paramylon it can accumulate, could be added to the feed or to water in tanks and ponds without prior processing. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thyrotropin Releasing Hormone (TRH) suppresses stress induced eating

Thyrotropin releasing hormone (TRH) administered both intraventricularly and parenterally suppressed stress induced eating (using the mild tail pinch model) in a dose related manner. This suppression was partially reversed by intraventricular administration of the long acting synthetic enkephalin analog, D-Ala-Met-Enkephalin (p < 0.01). Preliminary data suggests that the naturally occurring metabolic breakdown product of TRH, histidyl-proline-diketopiperazine, may be the active substance with TRH acting as a pro-hormone. The TRH effect was present in hypophysectomized animals showing that the TRH-induced decrease in food ingestion was not secondary to an increase in thyrotropin or thyroid hormones. TRH did not alter blood glucose levels. Our data is compatible with a possible physiological role for TRH, as a peptidergic mediator of satiety acting as a direct antagonist of the lateral hypothalamic of satiety acting as a direct antagonist of the lateral hypothalamic enkephalin-mediated feeding center.     

Minireview. Evidence that dopamine is a neurotransmitter in peripheral tissues

In the CNS, dopamine (DA) is a recognized neurotransmitter as well as a precursor for norepinephrine (NE) and epinephrine (EPI). In contrast to the CNS, DA has been assumed to be only a precursor in peripheral tissues. There is now, however, considerable evidence to support the hypothesis that it may function as a neurotransmitter and/or cotransmitter in peripheral tissues in addition to being a precursor. In this minireview we summarize evidence supporting the view that DA plays a role of its own in peripheral neurotransmission.     

Stress induced changes in testis function

The mechanism through which chronic stress inhibits the hypothalamic-pituitary-testicular axis has been investigated. Chronic restraint stress decreases testosterone secretion, an effect that is associated with a decrease in plasma gonadotropin levels. In chronically stressed rats there was a decrease in hypothalamic luteinizing hormone-releasing hormone (LHRH) content and the response on plasma gonadotropins to LHRH administration was enhanced. Thus the inhibitory effect of chronic stress on plasma LH and FSH levels seems not to be due to a reduction in pituitary responsiveness to LHRH, but rather to a modification in LHRH secretion. It has been suggested that beta-endorphin might interfere with hypothalamic LHRH secretion during stress. Chronic immobilization did not modify hypothalamic beta-endorphin, while an increase in pituitary beta-endorphin secretion was observed. Since we cannot exclude that changes in beta-endorphin secreted by the pituitary or other opioids may play some role in the stress-induced decrease in LHRH secretion, the effect of naltrexone administration on plasma gonadotropin was studied in chronically stressed rats. Naltrexone treatment did not modify the decrease in plasma concentrations of LH or FSH. These findings suggest that the inhibitory effect of restraint on the testicular axis is exerted at hypothalamic level by some mechanism other than opioids.     

Minireview on pancreatic lipase and colipase

By hydrolyzing the dietary triacylglycerols, pancreatic lipase causes catalysis in heterogeneous medium. In vivo, lipase action cannot take place without colipase due to the presence of bile salts. The cofactor enables lipase anchoring to the water-lipid interface. The lipase-colipase system furnishes an excellent example of specific interactions (protein-protein and protein-lipid). The studies of lipase catalytic properties brought to light the importance of certain parameters related to the 'quality of the interface'. The structure-function relationship analyses revealed a certain number of functional amino acid residues in lipase and colipase involved either in the catalytic site of the enzyme or in the recognition sites (lipase-colipase and protein-interface). Comparisons of the sequences of lipases derived from different sources display interesting similarities in certain cases.     

Minireview: Multiple MU opiate receptors

In addition to morphine-selective mu₂ and enkephalin-preferring delta sites, recent evidence supports the presence within the central nervous system of a common site with very high affinity for both enkephalins and opiates termed tht mu₁ site. This concept of a common, very high affinity site for multiple neurotransmitters is a unique concept in neuropharmacology, differing from classical transmitter systems which possess multiple receptor classes for a single transmitter. This review will address both the biochemical and pharmacological evidence supporting the existence of this site.