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Biomedical subjects

L P Yao

Publications and source records attributed to L P Yao.

8 recordsLinked to original sources
PubMed2006

Heterogeneous diazo-transfer reaction: a facile unmasking of azide groups on amine-functionalized insoluble supports for solid-phase synthesis.

Solid-supported azides are commonly generated through direct nucleophilic displacement of appropriately activated supports by the azide ion. This reaction usually proceeds rather sluggishly under harsh conditions. Here, we report that triflyl azide rapidly reacts with a series of amine-functionalized solid supports to generate azide-coated supports under mild conditions. Further, we demonstrate that the "azide coat" allows facile loading of alkyne-functionalized leader nucleoside monomers by click chemistry. Finally, we show that the nucleoside-functionalized supports are suitable for solid-phase oligonucleotide synthetic applications. The approach herein described extends the scope of the amine-azide conversion reaction and may be adaptable for the introduction of azide to diverse amine-terminated solid supports that are not easily accessible by the conventional nucleophilic displacement method.

Amines↗
PubMed1998

Dopamine D1 receptor and protein kinase C isoforms in spontaneously hypertensive rats.

-Dopamine, via D1-like receptors, stimulates the activity of both protein kinase A (PKA) and protein kinase C (PKC), which results in inhibition of renal sodium transport. Since D1-like receptors differentially regulate sodium transport in normotensive and hypertensive rats, they may also differentially regulate PKC expression in these rat strains. Thus, 2 different D1-like agonists (fenoldopam or SKF 38393) were infused into the renal artery of anesthetized normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) (n=5 to 6/drug/strain). Ten or 60 minutes after starting the D1-like agonist infusion, both the infused kidney and the noninfused kidney that served as control were prepared for analysis. The D1-like agonists produced a greater diuresis and natriuresis and inhibited Na+,K+-ATPase activity in proximal tubule (PT) and medullary thick ascending limb (mTAL) to a greater extent in WKY (Delta20+/-1%) than in SHR (Delta7+/-1%, P<0.001). D1-like agonists had no effect on PKC-alpha or PKC-lambda expression in either membrane or cytosol but increased PKC-theta expression in PT in both WKY and SHR at 10 minutes but not at 60 minutes. However, membranous PKC-delta expression in PT and mTAL decreased in WKY but increased in SHR with either 10 or 60 minutes of D1-like agonist infusion. D1-like agonists also decreased membranous PKC-zeta expression in PT and mTAL in WKY but increased it in PT but not in mTAL in SHR. We conclude that there is differential regulation of PKC isoform expression by D1-like agonists that inhibits membranous PKC-delta and PKC-zeta in WKY but stimulates them in SHR; this effect in SHR is similar to the stimulatory effect of norepinephrine and angiotensin II and may be a mechanism for their differential effects on sodium transport.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1995

Developmental renal hemodynamics.

Renal blood flow, which is lower in the immature than in the mature animal, achieves adult values in human subjects by 1-2 years of age. The age-related increase in renal blood flow cannot be completely explained by increases in kidney size, since nephrogenesis is complete by 36 weeks' gestation in humans. Thus, other factors, especially changes in renal hemodynamics, are likely to be responsible for the increase in renal blood flow. The increase in renal blood flow appears to be directly related to the decrease in renal vascular resistance during the postnatal period. Decreases in the effect of renal vasoconstrictors, increases in the effect of renal vasodilators, or a combination of the two, may be responsible. Many mediators of vasoconstriction have been studied, including adenosine, catecholamines, endothelin, endogenous digitalis-like peptide, and the renin-angiotensin system. Mediators of vasodilation include endothelium-derived relaxing factor (e.g., nitric oxide), prostaglandins, atrial natriuretic peptide, dopamine, and kinins. However, the decrease in renal vascular resistance with age is most likely related to decreases in activity of the renin-angiotensin system and responsiveness to catecholamines; these effects are modulated by nitric oxide. Other mediators may also be important in determining the age-related decrease in renal vascular resistance, but their exact roles remain to be defined.

Aging↗
PubMed1992

Effect of 33% xenon inhalation on whole-brain blood flow and metabolism in awake and fentanyl-anesthetized monkeys.

BACKGROUND AND PURPOSE: Despite the documented diagnostic value of local cerebral blood flow maps by xenon-enhanced computed tomography, reports of cerebral blood flow activation by inhaled 33% Xe raised concerns about the method's safety and accuracy. We evaluated the effect of 33% Xe inhalation on cerebral blood flow and cerebral metabolic rates for oxygen and glucose in four awake and six fentanyl-anesthetized rhesus monkeys. METHODS: Platinum microelectrodes and catheters in the torcular Herophili were used to measure cerebral blood flow by hydrogen clearance, and oxygen and glucose concentrations. Cerebral variables were measured after 5 and 35 minutes of exposure to room air followed randomly by 67% O2 in 33% N2 or Xe. Five- and 35-minute measurements were combined because the duration of exposure had no effect. RESULTS: In awake monkeys, 33% Xe compared with 33% N2 reduced (p less than 0.05) cerebral blood flow from 75 +/- 12 to 66 +/- 9 (mean +/- SD) ml.100 g-1.min-1 and oxygen consumption from 6.1 +/- 0.7 to 5.1 +/- 0.6 ml.100 g-1.min-1. In fentanyl-anesthetized monkeys, cerebral variables during 33% N2 versus 33% Xe were cerebral blood flow, 84 +/- 26 versus 79 +/- 23 ml.100 g-1.min-1; oxygen consumption, 5.0 +/- 0.7 versus 4.9 +/- 0.5 ml.100 g-1.min-1; and glucose consumption, 8.4 +/- 1.9 versus 7.9 +/- 2.0 mg.100 g-1.min-1. CONCLUSIONS: In awake monkeys, 33% Xe reduced rather than activated cerebral blood flow and oxygen consumption by 12% and 16%, respectively; it had no effect in fentanyl-anesthetized monkeys.

Administration, Inhalation↗
PubMed1990

CGS-19755, a competitive NMDA receptor antagonist, reduces calcium-calmodulin binding and improves outcome after global cerebral ischemia.

We evaluated several doses of cis-4-(phosphonomethyl)-2-piperidine-carboxylic acid (CGS-19755), a potent competitive N-methyl-D-aspartate (NMDA) receptor antagonist, systemically administered either before or after 20 to 30 minutes of global ischemia in rats. We measured outcome by mortality, histological damage by light microscopy, and learning ability on an eight-arm maze, and determined the drug's mechanism of action by an immunohistochemical assay of calcium-calmodulin binding. High-dose treatment begun prior to ischemia resulted in reduced cellular damage in severely ischemic hippocampal tissue, but also caused high mortality due to respiratory depression. Treatment begun 30 minutes after ischemia resulted in little histological protection but significantly improved learning ability when tested 1 month after ischemia, and did not increase mortality. Furthermore, CGS-19755, 10 mg/kg intraperitoneally, begun either before or after ischemia substantially reduced calcium influx into ischemic neurons as evidenced by reduced calcium-calmodulin binding. We conclude that CGS-19755 prevents calcium entry into ischemic neurons and may be effective therapy for very acute cerebral ischemia.

Animals↗
PubMed1990

Effect of nicardipine on somatosensory evoked potentials in patients with acute cerebral infarction.

We evaluated the effect of nicardipine, a calcium channel blocker, on somatosensory evoked potentials (SEP) in 26 patients with acute cerebral infarction. Post treatment, 58% (15/26) of the N20 and P25 latencies were prolonged in the affected hemispheres; 8% (2/26) were shortened; and 35% (9/26) did not change. The mean N20 and P25 latencies were significantly prolonged two hours post treatment in the affected hemisphere (N20, P less than 0.01, P25 P less than 0.01). Nicardipine (Ni) had no effect on SEP components in the intact hemispheres. Seventy five per cent of the 12 patients with hypertension had a decrease in blood pressure (BP) after taking nicardipine, but there were no undesirable side effects or worsening of neurological signs. Our study demonstrates that nicardipine prolongs the latencies of short-latency components of SEP in the affected hemisphere after acute ischaemic stroke and also decreases BP. These observations suggest that nicardipine therapy might impair neuronal function in the ischaemic zone.

Administration, Oral↗
PubMed1990

Neuronal protection correlates with prevention of calcium-calmodulin binding in rats.

We correlated the efficacy of several clinically relevant pharmacotherapies with their ability to prevent calcium influx into neurons and subsequent binding to calmodulin. We studied the administration of CGS 19755, nimodipine, nicardipine, and combinations of these drugs before or immediately after ischemia in globally ischemic rats. Calcium-calmodulin binding was graded by an immunohistochemical assay after 2 and 24 hours of reperfusion (n = 5-6 at each time period), and histologic damage was graded by light microscopy after 72 hours of reperfusion (n = 6). Calcium-calmodulin binding correlated with the severity of delayed histologic damage in various brain regions. In untreated ischemic control rats, marked calcium-calmodulin binding was seen in CA1 and CA3 after 24 hours of reperfusion (p less than or equal to 0.01). Administered before ischemia, CGS 19755 prevented calcium-calmodulin binding across all brain regions after 2 and 24 hours of reperfusion compared with controls (p less than or equal to 0.05). This effect was most prominent in CA3 and CA1, where the drug also reduced delayed neuronal damage (p less than or equal to 0.05). Lower doses or postischemic administration of CGS 19755, nimodipine, nicardipine, and a combination of postischemic CGS 19755 and nicardipine had a more limited effect on calcium-calmodulin binding and did not protect against delayed neuronal damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗