Discovery of 505-million-year old chitin in the basal demosponge Vauxia gracilenta.

Sponges are probably the earliest branching animals, and their fossil record dates back to the Precambrian. Identifying their skeletal structure and composition is thus a crucial step in improving our understanding of the early evolution of metazoans. Here, we present the discovery of 505-million-year-old chitin, found in exceptionally well preserved Vauxia gracilenta sponges from the Middle Cambrian Burgess Shale. Our new findings indicate that, given the right fossilization conditions, chitin is stable for much longer than previously suspected. The preservation of chitin in these fossils opens new avenues for research into other ancient fossil groups.

Defining the role of COX-2 inhibitors in inflammatory and other diseases.

The well-established side effects of drug treatments for inflammatory disease, in particular those of the nonsteroidal antiinflammatory drugs (NSAIDs)--principally gastrointestinal (GI) toxicity--, have become an acute problem. There is now considerable experience with the COX-2 selective NSAIDs, which offer an improved GI side-effect profile. The William Harvey Research Conference held in Porto, Portugal, October 23, 2000, reviewed the history of the use of NSAIDs and discussed the pathological and physiological significance of the COX-2 enzyme while covering topics ranging from assays to measure the COX-2:COX-1 ratio, the structural basis for COX-2 selectivity, potential mechanisms of NSAID-induced gastrointestinal toxicity, preclinical studies, effects of COX-2 inhibitors on the kidney and vascular systems, to the latest clinical results, as well as the potential implication of COX-2 in cancer and Alzheimer's disease.

Nonsteroidal antiinflammatory agents.

Since the synthesis of aspirin in 1897, aspirin-like or nonsteroidal antiinflammatory drugs (NSAIDs) have been the mainstay of therapy for rheumatoid arthritis. Although of diverse chemical structure, these drugs not only exhibit the same antipyretic, analgesic and antiinflammatory therapeutic actions, but they also manifest identical toxic actions on the gastric mucosa and the kidney. This indicated that a single pharmacological effect was responsible for the properties of NSAIDs, a theory that was confirmed by the epochal discovery by Vane in 1971, that inhibition of the enzyme-producing prostanoids (cyclooxygenase [COX]) produced both the therapeutic and side effects of aspirin-like drugs. However, at equivalent antiinflammatory doses, different NSAIDs exhibited different degrees of toxicity. The reason for this was resolved by the discovery that prostaglandins at sites of tissue damage were synthesized by an inducible COX (COX-2) formed by a gene distinct from that producing the constitutive enzyme (COX-1), responsible for the formation of prostaglandins that serve an essential physiological function. Modification of the structure of drugs showing a moderately selective effect on COX-2, and the elucidation of the crystal structure of both enzymes, has paved the way for the synthesis of NSAIDs that are highly selective for the inducible enzyme and which are, therefore, antiinflammatory without the typical side effects of the classical NSAIDs. The focus on COX-2 has also expanded our knowledge of the pathophysiological significance of prostanoids and raised the possibility of new uses for selective COX-2 inhibitors, for example, in colon cancer, premature labor and possibly Alzheimer's disease. However, the clinical effects of chronic administration of potent, selective COX-2 inhibitors must await the results of ongoing clinical trials.

Relationship between gender difference in intravascular aggregation of platelets and the fibrinolytic pathway in the rat.

Intravascular aggregation of platelets was evaluated in relation to the fibrinolytic system in order to assess the possibility of a "cause-effect" relationship. The spontaneous fibrinolytic activities of the plasma of male rats and of female rats at the various stages of the oestrous cycle were determined. Male rats had higher euglobulin clot lysis time (54.5 +/- 5.3 vs 29.2 +/- 3.1 min; P less than 0.05), higher fibrinogen levels (330.0 +/- 15.8 vs 231.0 +/- 31.1 mg/dl; P less than 0.025) and higher plasminogen activity (8.1 +/- 1.2 vs 6.1 +/- 1.6 plasmin units/ml; P less than 0.05) than female rats. Female rats had higher fibrinolytic index (8.8 +/- 0.8 vs 6.3 +/- 0.3 mg/dl; P less than 0.05) and plasminogen activator activity (99.1 +/- 6.0 vs 76.5 +/- 7.7 Plough units/ml; P less than 0.05) than male rats. The antiplasmin activities were the same in both sexes. During the oestrous cycle in female rats, euglobulin clot lysis time was not significantly different though it was highest during met-oestrous (34.2 +/- 3.6 min). However, pro-oestrous rats had lower fibrinogen (122.9 +/- 5.3 mg/dl; P less than 0.005), higher fibrinolytic index (10.6 +/- 0.8 mg/dl/min; P less than 0.001) and higher plasminogen activator activity (109.4 +/- 7.8 Plough units/ml; P less than 0.05) than rats from the other stages of the oestrous cycle. There were no significant differences in plasminogen content and antiplasmin activity. Using native rats, aggregatory responses to submaximal doses of adenosine diphosphate (20 micrograms/kg) were determined and correlated with the fibrinolytic data in age- and weight-matched rats (of both sexes). Aggregatory responses in all the groups of rats used correlated positively with fibrinogen levels (r = 0.8316; P less than 0.001) and negatively with plasminogen activator activity (r = -0.7839; P less than 0.05). Streptokinase (250-1000 Plough units/kg/hr) and urokinase (1000-4000 Plough units/kg/hr) produced dose-related reductions in intravascular aggregation induced by adenosine diphosphate. The streptokinase effect (but not urokinase effect) was reversed by epsilon-aminocaproic acid. Following the cessation of infusion of streptokinase and urokinase, there was a recovery of the platelets to aggregate to adenosine diphosphate. These observations suggest fibrinolytic pathway-specific effects. However, on its own, epsilon-amino-caproic acid did not affect the aggregatory responses of platelets from pro-oestrous rats. These results suggest that changes in fibrinolytic mechanisms may account for differences observed in intravascular aggregation of platelets of male and female rats and of female rats during the oestrous cycle.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenaline inhibits adenosine diphosphate induced intravascular aggregation of rat platelets through stimulation of alpha 2 adrenoceptors.

STUDY OBJECTIVE: The aim was to determine the receptors involved in the antiaggregatory effects of adrenaline in the rat. DESIGN: The 111indium oxine technique was used to evaluate ADP induced pulmonary accumulation of 111In labelled platelets in adrenalectomised rats (ie, no endogenous adrenaline) in the absence of anticoagulants. Adrenaline was infused (10, 20 and 40 micrograms.kg-1.h-1) and ADP aggregation measured. Adrenoceptor agonists, isoprenaline, methoxamine, and BHT 933, were given to evaluate whether they mimic the adrenaline effects. Adrenoceptor antagonists, yohimbine, propranolol, prazosin, and WY 26392, were given to assess whether they block the adrenaline effects. MEASUREMENTS AND MAIN RESULTS: In all cases, pulmonary accumulation of platelets was measured in response to ADP. Adrenaline dose dependently inhibited platelet aggregation. BHT 933 (1.5 micrograms.kg-1.min-1) mimicked, while phentolamine (1 mg.kg-1), yohimbine (2.5 mg.kg-1), and WY 26392 (0.1, 1.0, 5.0 mg.kg-1) blocked, the adrenaline effects. Methoxamine (3.3 micrograms.kg-1.min-1) produced a relatively weak non-specific inhibition of ADP aggregation. Isoprenaline (33 ng.kg-1.min-1) did not mimic the effects of adrenaline, neither did propranolol (1 mg.kg-1) affect the adrenaline inhibition of the aggregatory responses to ADP. Indomethacin (3 mg.kg-1) blocked the inhibitory effects of adrenaline. CONCLUSIONS: Adrenaline stimulates alpha receptors on platelets but inhibits platelet aggregation. There is no evidence to suggest that beta receptors participated in the effects produced by adrenaline. There is a role for cyclo-oxygenase products in the inhibitory effects of adrenaline on aggregation.

Pharmacodynamic interaction between oestradiol and adrenaline on intravascular aggregation induced by adenosine diphosphate in the rat.

Physiological levels of oestradiol and adrenaline inhibit intravascular aggregation of platelets, and effect dependent on the presence of an adrenal gland secretion (possibly adrenaline) and oestrogens, respectively. This infers a "mutual dependence" phenomenon. Acute adrenalectomy had a biphasic effect on intravascular aggregation: enhancing platelet aggregation when levels of oestradiol are high, e.g. in pro-oestrous rat, and reducing platelet aggregation when levels of oestradiol are nil or very low, i.e., in ovariectomized or di-oestrous rats, respectively. Ovariectomy also had a biphasic effect on platelet aggregation reducing aggregation in the absence of adrenaline and enhancing aggregation in its presence. Removal of endogenous oestradiol (by ovariectomy) and its replacement fully corroborates the "mutual dependence" hypothesis, whereas the removal of endogenous adrenaline (by acute adrenalectomy) and its replacement only partially supports it. It is concluded that, though both oestradiol and adrenaline have inhibitory effects on intravascular aggregation at physiological doses, each seems to need the full compliment of the other to achieve the effect.

Inhibition of intravascular platelet aggregation in the rat by adrenaline.

Intravascular platelet aggregation to adenosine diphosphate (ADP) was measured in anesthetized rats using 111indium-labelled platelets. Acute adrenalectomy increased the aggregatory effect of ADP in vivo, whereas infusions of low concentrations of adrenaline into adrenalectomized rats suppressed ADP-induced platelet aggregation. Similar antiaggregatory effects were seen with the alpha 2 agonist B-HT 933 and the alpha 1 agonist methoxamine, but not with isoprenaline. The effect of adrenaline was inhibited by phentolamine, yohimbine, the selective alpha 2 adrenoceptor antagonist WY 26392 and by indomethacin, but not by propranolol or prazosin. Adrenaline thus inhibits ADP-induced aggregation in vivo by a mechanism that may involve stimulation of an alpha 2 adrenoreceptor and may be dependent on activation of cyclooxygenase enzyme.

Indium-111 oxine technique of studying platelet aggregation in vivo. Some physiological considerations.

Intravascular aggregation in response to ADP, thrombin, arachidonate and collagen has been studied in the rat with a view to throwing more light on the validity, the reproducibility and physiology of the model. The radioisotopic technique of labelling platelets with indium-111 oxine was employed. The model is minimally invasive and involves collecting blood from donor rats, separating and labelling their platelets with indium-111 oxine and assessing the accumulation of platelets in the lungs of recipient rats following the intravascular administration of aggregating agents. Of the parameters evaluated, percentage peak increase in radio-labelled platelet count and area under the curve are good parameters of expressing aggregatory responses. Of the visceral organs evaluated, the lung is the most important organ for assessing platelet accumulation. Of the vascular routes examined, no aggregatory response occurred in the lungs when ADP was injected via any of the intra-arterial routes, and of the intravenous routes, injection via the tail vein gave the highest response. The results of this investigation provide some more detailed technical information to take note of when studying platelet aggregation in vivo by this model. The results also highlight the physiological phenomenon involved.

The influence of adrenaline on gender difference in adenosine diphosphate-induced aggregation of platelets in the rat.

The role of adrenaline on the inhibitory effects of physiological levels of oestradiol on ADP-induced intravascular aggregation has been studied. Platelets from pro-oestrous female rats aggregated less than those from dioestrous and male rats. Following adrenalectomy, there was no longer any difference(s) in the aggregability of the platelets to ADP in any of the rats. Adrenaline infusion (20 mg kg-1 hr-1) restored platelet aggregation to preadrenalectomy levels in pro-oestrous rate. Measurement of spontaneous fibrinolytic activity of the plasma showed highest value in pro-oestrous rats. Adrenalectomy reduced, while adrenaline infusion increased the fibrinolytic activity. The results suggest that the inhibitory effects of oestradiol on intravascular aggregation are dependent on endogenous adrenaline possibly working through the fibrinolytic pathway.

Cryptolepine inhibits platelet aggregation in vitro and in vivo and stimulates fibrinolysis ex vivo.

1. Cryptolepine--the methylquindolanol alkaloid of Cryptolepsis sanguinolenta was evaluated for its antiplatelet and fibrinolytic effects. 2. It exhibited antiplatelet effects in vitro in human, rabbit and rat PRP with EC50 values ranging between 8.1 x 10(-8) M and 1.7 x 10(-7) M for ADP, AA and thrombin. 3. In the rat, it inhibited ADP-aggregation in vivo with delayed onset and prolonged action. 4. In vitro, cryptolepine disaggregated (dose-dependently) platelets aggregated by ADP, AA and thrombin. 5. In addition, it exhibited an indirect fibrinolytic action in the rat possibly by causing the release of plasminogen activators from the vascular endothelium.

The involvement of platelet activating factor in endotoxin-induced pulmonary platelet recruitment in the guinea-pig.

1 Exposure of conscious guinea-pigs to an aerosol of endotoxin (25-100 micrograms ml-1) resulted in a dose-related, progressive accumulation of platelets in the thoracic region. Accumulation of 111indium oxine labelled erythrocytes was not observed following exposure to an aerosol of endotoxin (50 micrograms ml-1). 2 Pretreatment of guinea-pigs with the selective platelet activating factor (Paf)-antagonists. CV-3988 or brotizolam resulted in a dose-related inhibition of endotoxin-induced pulmonary platelet recruitment. Pretreatment of guinea-pigs with the selective Paf-antagonist BN 52021 resulted in significant inhibition of endotoxin-induced pulmonary platelet recruitment, although the effects of BN 52021 were not dose-related. 3 Pretreatment of guinea-pigs with indomethacin at doses known to inhibit cyclo-oxygenase did not inhibit endotoxin-induced pulmonary platelet recruitment, whereas higher doses of indomethacin produced a reduction in platelet recruitment in the lung. 4 Pretreatment of guinea-pigs with the anticoagulant heparin and the prostacyclin analogue ZK 36374 inhibited endotoxin-induced platelet recruitment. 5 These observations suggest that endotoxin-induced pulmonary platelet recruitment in the guinea-pig is secondary to the release of platelet activating factor, but not to cyclo-oxygenase products of arachidonic acid and may also involve activation of the coagulation cascade.