Molecular basis and species specificity of high affinity binding of vasoactive intestinal polypeptide by the rat secretin receptor

The affinity and specificity of the binding interaction between ligands and their receptors are key for appropriate hormonal regulation of target tissues. However, it is now apparent that vasoactive intestinal polypeptide (VIP) binds to the rat secretin receptor with similar affinity to that for its natural ligand, secretin (Holtmann et al., 1995). In this report, we establish that this is not a characteristic of the human secretin receptor, and use rat-human secretin receptor chimeras, site mutants and truncated receptor constructs to establish the molecular basis for this unusual binding interaction. Of note, isolated N-terminal domains of the rat secretin and the VIP receptors are capable of high affinity binding of VIP. In the recently recognized secretin family of receptors, this domain has six conserved cysteine residues and disulfide bonds that are likely important to achieve the complex conformation critical for this binding. A single acidic residue (Asp98) present in the rat secretin receptor appears to be critical, because a site-mutant changing this to the polar, but uncharged residue present in that position in the human receptor (Asn) eliminates the high affinity binding of VIP. Of interest, a previously identified critical basic residue in VIP (Lys15) provides a candidate for charge-pairing with this residue, potentially aligning the peptide ligand in a nonproductive orientation within this receptor.     

Correlation between vascular and cellular responses to atrial natriuretic peptide and to sodium nitroprusside

Atrial natriuretic peptide (ANP) and sodium nitroprusside (SNP) increase cGMP in vascular smooth muscle cells and act as vasodilators in some, but not all, blood vessels. In this present study, we attempted to correlate the ability of these two agents to dilate blood vessels with the ability to increase cGMP in cultured vascular smooth muscle cells. In the isolated guinea pig heart, SNP dose-dependently increased coronary flow while ANP was ineffective. In smooth muscle cells cultured from the coronary system, SNP increased intracellular cGMP in a dose-dependent manner while ANP had no effect on cGMP in these cells. In isolated guinea-pig thoracic aorta, precontracted with K+, both ANP and SNP produced relaxation and ANP was the more potent. In smooth muscle cells cultured from the aorta, ANP and SNP increased cGMP and the potency relationship was similar to the intact vessel. These results support the view that phenotypic properties of vascular smooth muscle cells can account for differences in the response of blood vessels to vasodilators.     

Recognition and management of catheter-induced pulmonary artery rupture

The use of PCR to amplify a specific virA gene fragment serves as a highly specific and sensitive method to detect virulent bacteria of the genus Shigella and enteroinvasive Escherichia coli. Amplification of a 215-bp DNA band was obtained by using isolated genomic DNA of Shigella, individual cells of Shigella dysenteriae, and mayonnaise contaminated with S. dysenteriae. Moreover, a multiplex PCR with specific (virA) and bacterium-restricted (16S ribosomal DNA) primers generated an amplification product of approximately 755 bp for all bacteria tested and an additional 215-bp product for Shigella and enteroinvasive E. coli.     

Clinical assessment of extrapyramidal signs in nursing home patients given antipsychotic medication

BACKGROUND: We sought to quantify the relationship between antipsychotic drug use and clinical evidence of extrapyramidal dysfunction in a large population of elderly nursing home patients. METHODS: Subjects were 251 residents (mean age, 84.1 years; range, 65 to 105 years) who were taking psychoactive drugs in 12 long-term care facilities. Patient characteristics and all medication use (both scheduled and as needed) were measured during a 1-month observation period. We then performed neuropsychological and functional testing on residents who received any psychoactive medications during the study month. The presence of rigidity, bradykinesia, or masklike facies was assessed in each patient by a research assistant who was unaware of diagnoses and medication use. RESULTS: The parkinsonian signs studied were found in 127 (50.6%) of these residents. Using logistic regression modeling to adjust for potential confounding, we found this outcome to be increased more than threefold in patients who took low-potency neuroleptics (odds ratio [OR], 3.49 for > or = 50 mg/d of chlorpromazine-type drugs; 95% confidence interval [CI], 1.28 to 9.57) and more than sixfold for use of 1 mg/d or more of haloperidol (OR, 6.42; 95% CI, 2.16 to 19.04). Age, gender, and use of nonneuroleptic psychoactive drugs were not associated with an increase in parkinsonian signs. CONCLUSIONS: Clinical evidence of extrapyramidal dysfunction is three to six times more common in institutionalized elderly patients given antipsychotic medication than in comparable patients not using such drugs. Its risk is substantially increased even in patients given low-potency chlorpromazine-type drugs, as well as those taking haloperidol. The effect is not explained by age or mental status and is not seen with other psychoactive medications. The expected frequency of parkinsonian symptoms can help to inform the balancing of risks vs therapeutic effect when the use of all drugs in this class is considered.     

External and internal calibration of the MHC class I-specific receptor Ly49A on murine natural killer cells

Expression of the H-2Dd-specific inhibitory receptor Ly49A on murine NK cells is subject to MHC class I-dependent modulation in vivo. As a result, NK cells in H-2Dd-transgenic mice express low cell surface levels of Ly49A, whereas NK cells from nontransgenic C57BL/6 (B6) mice express high levels. The purpose of this study was to assess the role of MHC class I molecules on the NK cell itself vs those on surrounding cells in this calibration and to test whether the Ly49A levels are subject to regulation in mature NK cells also. Analysis of transgenic mice with mosaic expression of an H-2Dd/Ld transgene showed that MHC class I molecules on surrounding cells (external ligands) and on the NK cell itself (internal ligands) played distinct roles in the determination of Ly49A levels. External ligands were involved in down-regulation of Ly49A levels in vivo, whereas internal ligands kept the down-regulated levels of Ly49A low upon NK cell activation in vitro. Furthermore, in an experimental system based on adoptive transfer of spleen cells, receptor down-regulation of Ly49A occurred as a rapid adaptation process in mature NK cells after interaction with the H-2Dd ligand in vivo. This suggests that Ly49 levels are not fixed but can be changed in mature NK cells when they are exposed to a changed MHC class I environment.     

Neuronal units linked to microvascular modules in cerebral cortex: response elements for imaging the brain

How neuronal activity changes cerebral blood flow is of biological and practical importance. The rodent whisker-barrel system has special merits as a model for studies of changes in local cerebral blood flow (LCBF). Stimulus-evoked changes in neural firing and 'intrinsic signals' recorded through a cranial window were used to define regions of interest for repeated flow measurements. Whisker-activated changes in flow were measured with intravascular markers at the pia. LCBF changes were always prompt and localized over the appropriate barrel. Stimulus-related changes in parenchymal flow monitored continuously with H2 electrodes recorded short latency flow changes initiated in middle cortical layers. Activation that increased flow to particular barrels often led to reduced flow to adjacent cortex. Dye was injected into single penetrating arterioles from the pia of the fixed brain and injected into arterioles in slices of cortex where barrels were evident without stains. Arteriolar and venular domains at the surface were not directly related to underlying barrels. Capillary tufts in layer IV were mainly coincident with barrels. The matching between a capillary plexus (a vascular module) and a barrel (a functional neuronal unit) is a spatial organization of neurons and blood vessels that optimizes local interactions between the two. The paths of communication probably include: neurons to neurons, neurons to glia, neurons to vessels, glia to vessels, vessels to vessels and vessels to brain. Matching a functional grouping of neurons with a vascular module is an elegant means of reducing the risk of embarrassment for energy-expensive neuronal activity (ion pumping) while minimizing energy spent for delivery of the energy (cardiac output). For imaging studies this organization sets biological limits to spatial, temporal and magnitude resolution. Reduced flow to nearby inactive cortex enhances local differences.     

Hereditary macular dystrophies

BACKGROUND: Orthostatic hypotension is a common phenomenon in the elderly. Hormonal changes during orthostatic stress have been described in elderly normotensive people and in those with essential hypertension. However, the hormonal response in elderly people who have systolic hypertension during orthostasis has not yet been quantified. METHODS: In this study we investigated 14 non-diabetic men, aged 60 to 75 years, with untreated systolic hypertension who were subjected to 45 degrees passive head-up incline on a tilt table for 15 min. Their hormonal profile and hemodynamic changes were analyzed before and after the stress. RESULTS: In the supine position, plasma levels of norepinephrine, atrial natriuretic peptide and aldosterone were in the normal range, while the plasma renin activity was low. Immediately upon tilt the systolic blood pressure fell but it reverted to baseline values after 15 min of orthostasis. At that time the cardiac output decreased while the systemic vascular resistance and the plasma norepinephrine concentration rose. The atrial natriuretic peptide appeared to fall, and the renin-aldosterone level did not change. CONCLUSION: The physiologic response to orthostatic stress in elderly people with systolic hypertension is comparable to that of elderly normotensive people and those with essential hypertension, i.e. a decrease in cardiac output and an increase in plasma norepinephrine levels. The atrial natriuretic peptide appeared to fall appropriately. The response of the renin-aldosterone system mimicked that in elderly patients with low renin essential isolated hypertension. These observations may have a bearing on the management of elderly people with systolic hypertension who also have orthostatic symptoms; they may not require a different approach from that needed for others of the same age group.     

Amygdala core nuclei volumes are decreased in recurrent major depression

Chronic myopathy is a common complication of alcoholism, but its natural history has not been well described. We, therefore, studied muscle structure and function in a 5-year study of 30 chronic alcoholics who became abstinent and 20 who relapsed, and 40 control subjects. The mean strength of the abstaining alcoholics increased from 18.6 to 23.2 kg; but, after 5 years, they were still substantially weaker than controls. In a subset who showed histological myopathy, the strength of half of the patients remained two standard deviations below that of controls. Alcoholics who relapsed tended to become progressively weaker (21.7 kg vs. 18.2 kg) and develop histological evidence of myopathy. Thus, continued alcohol abuse was generally reflected in deterioration of muscle strength and the appearance of histological injury to muscle. Importantly, almost half of the sober patients did not recover to normal levels, indicating that alcoholic myopathy is only partially reversible. We also unexpectedly found that, in some alcoholics, a substantial reduction in the amount of alcohol consumed may be as effective as complete abstinence in improving muscle strength or preventing its deterioration.