Skin Color and Severe Maternal Outcomes: Evidence from the Brazilian Network for Surveillance of Severe Maternal Morbidity.

Background: Taking into account the probable role that race/skin color may have for determining outcomes in maternal health, the objective of this study was to assess whether maternal race/skin color is a predictor of severe maternal morbidity. Methods: This is a secondary analysis of the Brazilian Network for Surveillance of Severe Maternal Morbidity, a national multicenter cross-sectional study of 27 Brazilian referral maternity hospitals. A prospective surveillance was performed to identify cases of maternal death (MD), maternal near miss (MNM) events, and potentially life-threatening conditions (PLTC), according to standard WHO definition and criteria. Among 9,555 women with severe maternal morbidity, data on race/skin color was available for 7,139 women, who were further divided into two groups: 4,108 nonwhite women (2,253 black and 1,855 from other races/skin color) and 3,031 white women. Indicators of severe maternal morbidity according to WHO definition are shown by skin color group. Adjusted Prevalence Ratios (PRadj - 95%CI) for Severe Maternal Outcome (SMO=MNM+MD) were estimated according to sociodemographic/obstetric characteristics, pregnancy outcomes, and perinatal results considering race. Results: Among 7,139 women with severe maternal morbidity evaluated, 90.5% were classified as PLTC, 8.5% as MNM, and 1.6% as MD. There was a significantly higher prevalence of MNM and MD among white women. MNMR (maternal near miss ratio) was 9.37 per thousand live births (LB). SMOR (severe maternal outcome ratio) was 11.08 per 1000 LB, and MMR (maternal mortality ratio) was 170.4 per 100,000 LB. Maternal mortality to maternal near miss ratio was 1 to 5.2, irrespective of maternal skin color. Hypertension, the main cause of maternal complications, affected mostly nonwhite women. Hemorrhage, the second more common cause of maternal complication, predominated among white women. Nonwhite skin color was associated with a reduced risk of SMO in multivariate analysis. Conclusion: Nonwhite skin color was associated with a lower risk for severe maternal outcomes. This result could be due to confounding factors linked to a high rate of Brazilian miscegenation.

Modulation of nicotine-evoked [3H]dopamine release from rat striatal synaptosomes by voltage-sensitive calcium channel ligands.

The calcium channel subtypes mediating nicotine-evoked [3H]dopamine release from rat striatal synaptosomes were probed with L-, N-, and P-type calcium channel ligands. Responses to nicotine were blocked by the peptides omega-conotoxin GVIA and omega-agatoxin IVA. The affinity constants for these compounds were consistent with their actions at N- and P-type channels, respectively. Together, these channels mediate at least 90% of the calcium-dependent response to nicotine. The L-type antagonists nifedipine, verapamil, and nicardipine were also effective blockers of nicotine-evoked release with maximal effects of 80-100% inhibition. However, these effects occurred at concentrations 2-3 orders of magnitude higher than those necessary to block L-type channels. Moreover, Bay K8644, an L-type agonist, also blocked nicotine-evoked release. Together, these findings argue strongly against the involvement of L-type channels.

Characterization of nicotinic receptors on cultured cortical neurons using anti-idiotypic antibodies and ligand binding.

Monoclonal anti-idiotypic antibodies that represent the internal image of nicotine's natural isomer, L-nicotine, were used in conjunction with L-[3H]nicotine binding to characterize nicotinic receptors on neurons cultured from fetal rat cortex. Of the antibodies tested, two (422F11 and 420G11) were found that recognized a class of high affinity [3H]nicotine binding sites present on neuronal cells, but not on glia. The binding properties and pharmacological specificity of these sites compared well with those determined previously for putative nicotinic cholinergic receptors in adult rat brain. The binding of [3H]nicotine to neuronal receptors was effectively inhibited by both antibodies. Receptor-bearing cells were identified using indirect immunofluorescence. Approximately 20 to 30% of the cells were labeled specifically by the anti-idiotypes. Labeling was blocked by L-nicotine and other nicotinic agonists, but not by antagonists or by alpha and neuronal bungarotoxins. The majority of cells which were labeled had either bipolar or pyramidal morphology. Fluorescent labeling was associated with cell bodies as well as with axonal and dendritic processes, consistent with the proposed roles of neuronal nicotinic receptors in neuromodulation and synaptic transmission. The results suggest that anti-idiotypic antibodies may provide a new tool suitable for studying the locations, structure and functional significance of high affinity neuronal nicotinic receptors at the cellular level.

Identification of putative high affinity nicotinic receptors on cultured cortical neurons.

Primary cell cultures containing predominantly neurons or glia were prepared from fetal rat cerebral cortex. The presence of nicotinic receptor sites in neuronal cultures was indicated by the specific binding of L-[3H]nicotine to cell membrane preparations. No binding was observed with membrane preparations derived from glial cell cultures. Binding to neuronal membranes was saturable, reversible and stereoselective. Scatchard analysis revealed a single class of high affinity sites with a Kd of 3 nM and an average maximum number of binding sites of 25 fmol/mg of protein. The affinity of the sites was the same as that in adult cortical tissue, but the maximum number of sites was 25% of adult levels. The time course of binding exhibited complex kinetics that were consistent with the conversion of the sites to a high affinity state. The apparent equilibrium dissociation constant calculated from the kinetic rate constants for association (0.014 min-1 nM-1) and dissociation (0.03 min-1) was 2 nM, in good agreement with the results of equilibrium binding studies. In general, the pharmacological specificity of the sites, as judged from inhibition binding studies, was similar to that in adult brain. Nicotinic agonists were the most potent competitive inhibitors of [3H]nicotine binding and antagonists were the least effective. The D-isomer of nicotine was about 30-fold less potent than the L-isomer. The results show that cortical neurons contain high affinity nicotinic binding sites and that the properties of these sites are similar to those attributed to putative nicotinic cholinergic receptors in adult rat brain tissue.

Kinetics and mechanism of L-[3H]nicotine binding to putative high affinity receptor sites in rat brain.

The properties of high affinity nicotine-binding sites in rat brain were studied by monitoring the kinetics of L-[3H]nicotine binding to whole brain membrane preparations, including both total membranes and membrane subfractions. Although nicotine appeared to bind to a single class of sites, with an apparent equilibrium dissociation constant of 2-3 nM, the binding kinetics were biphasic at all temperatures and at all nicotine concentrations tested. An initial rapid binding process, with an association rate constant of around 0.02 min-1 nM-1 at 0 degree, was followed by a slower binding process. Both the rate and the proportion of binding that occurred by the slower process were dependent on the nicotine concentration. By comparison, the kinetics of dissociation were first order at all concentrations, with a rate constant of 0.04 min-1 at 0 degree. The rates of both association and dissociation increased significantly with temperature, but there was no changed in the apparent affinity of the sites. The same results were obtained with several different membrane preparations, including whole brain membrane preparations, detergent-permeabilized membranes, P-2 fractions, and synaptosomes. The results were found to be consistent with a two-state model. Analyses based on this model indicate that the binding sites can assume two different conformations, one having a high affinity (KD = 1 nM) and the other a low affinity (KD = 150 nM) for nicotine. It was estimated that approximately 60% of the sites are in the low affinity conformation in the absence of ligand. However, the evidence suggests that nicotine binding can facilitate a shift in the conformational equilibrium, favoring the high affinity state.

The binding of L-[3H]nicotine to a single class of high affinity sites in rat brain membranes.

The binding of optically pure L-[3H]nicotine to rat brain membrane preparations was studied using a rapid filtration method. The binding properties observed depended on the method used for tissue isolation. The most consistent results were obtained with membranes prepared in the presence of protease inhibitors, without divalent cations. Binding was saturable, reversible, and stereospecific. Scatchard analysis revealed a single class of high affinity sites with an average KD of 2 nM and a Bmax of approximately 200 fmol/mg of protein. The Hill coefficient was near unity. The KD calculated from the kinetic rate constants for association (k1 = 0.012 min-1 nM-1) and dissociation (k-1 = 0.04 min-1) was around 3 nM, in good agreement with the dissociation constant determined from equilibrium binding. In competition studies, cholinergic agonists were generally the most effective in inhibiting L-[3H]nicotine binding, whereas antagonists were relatively ineffective. The D-isomer of nicotine was about 60-fold less potent than the L-isomer in inhibiting binding. The results were unaffected by temperature, with the exception that Bmax was somewhat lower at 37 degrees. The equilibrium binding properties of these sites were essentially identical in adult male and female brain. However, Bmax was lower in fetal brain tissue. The present findings are consistent with the idea that there is a single class of high affinity nicotinic binding sites in rat brain with cholinoceptive properties.