The food mutagen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline: a conformational analysis of its major DNA adduct and comparison with the 2-amino-3-methylimidazo[4,5-f]quinoline adduct.

The heterocyclic amine 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) is one of a group of heterocyclic amine carcinogens that exists in cooked meat and fish. It causes mutations in bacterial and mammalian assays and induces tumors in mammals. MeIQx is converted within cells to a reactive derivative which forms a major covalent adduct at carbon-8 of guanine in DNA. This adduct may alter the DNA conformation at critical stages of the replicative process, and cause mutations which initiate the carcinogenic process. Atomic resolution structures of the MeIQx-damaged DNA are not yet available experimentally. We have carried out an extensive molecular mechanics/energy minimization search to locate feasible structures for the major MeIQx adduct in DNA, using the sequence d(5'-C1-G2-C3-G4[IQ]-C5-G6-C7-3').d(5'-G8-C9-G10-C11-G12-C13-G14-3') with MeIQx modification at G4. We have created 1152 starting conformations which uniformly sampled each of the three flexible torsion angles that govern the MeIQx-DNA orientation at 15 degrees intervals, and minimized their energy. A mixture of conformations was generated, which were separated into families according to the position of the ring system of the carcinogenic amine: major groove, minor groove, and base-displaced-intercalated. While a generally similar mixture had been generated previously for the related carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) [Wu, X., et al. (1999) Chem. Res. Toxicol. 12, 895-905], differences were found which could be rationalized in terms of the additional methyl group in the MeIQx.

Nitric oxide diminishes apoptosis and p53 gene expression after renal ischemia and reperfusion injury.

BACKGROUND: The role of nitric oxide in the ischemic injury of the kidney is still controversial. The aim of this study was to reevaluate the beneficial effect of exogenous nitric oxide and define its effects as regulator of gene p53 expression and apoptosis in the ischemic renal injury. METHODS: Sprague-Dawley rats were subjected to 75 min of renal warm ischemia and contralateral nephrectomy. The animals were divided into six groups (n=6 per group): Two sham groups at 4 and 24 hr, two ischemic control (IC) at same times and two treated groups (Na-NP), studied at same intervals, where sodium nitroprusside (5 mg/kg) was given 15 min before reperfusion. The parameters evaluated included: serum creatinine, blood urea nitrogen, neutrophil infiltration determined by myeloperoxidase, gene p53 expression determined by reverse transcriptase polymerase chain reaction, apoptosis determined by peroxidase in situ technique and light histology. RESULTS: There were significant improvements in serum creatinine and blood urea nitrogen at 24 hr in the NA-NP group when compared with the IC group (P<0.05). Myeloperoxidase levels were higher in the IC when evaluated against the Na-NP groups. Na-NP exhibited a downregulating effect in the expression of gene p53 when compared to the IC group. Apoptosis was more evident in the IC group and had moderately increased histological damage when compared to the Na-NP group. CONCLUSIONS: Nitric oxide demonstrated a protective effect in the ischemic injury of the kidney and exerted an antiapoptotic action dowregulating the expression of gene p53.

Increase of aldosterone secretion in adrenal cortex suspensions derived from pregnant rats.

Plasma aldosterone levels increase markedly during pregnancy, but not in proportion to the rise in plasma renin activity (PRA). We have developed a reliable in vitro method to investigate aldosterone secretion during pregnancy. With this method, we have assessed the potency and effectiveness of ACTH and potassium to stimulate this secretion during pregnancy. Adrenal capsules from pregnant and nonpregnant rats were incubated in 1 ml of culture medium within wells of tissues culture plates. The cortex was transferred every 20 min to another well containing fresh medium with or without ACTH or potassium. Basal and stimulated aldosterone secretions were not significantly affected by time under our experimental conditions. The glands remained responsive to stimulants throughout the study period (360 min). Plasma aldosterone levels and PRA were increased during pregnancy. Basal aldosterone secretion in adrenal cortex suspensions from pregnant rats showed a 1.6-fold increment (P < 0.001) in comparison with nonpregnant controls. The dose-response curves of ACTH were not significantly different between pregnant and nonpregnant animals. However, sensitivity to potassium was significantly reduced during pregnancy, as demonstrated by an elevated ED50 (4.01 +/- 0.08 vs 4.71 +/- 0.07 mM for nonpregnant versus pregnant rats respectively, P < 0.001). These data indicate that adrenal cortex suspensions are a reliable and reproducible way to study aldosterone secretion during pregnancy. They reveal that, during pregnancy, sensitivity of potassium to stimulate aldosterone secretion is decreased while the response to ACTH is not affected.

Cocaine downregulates beta-adrenergic receptors in pregnant sheep myometrium.

Cocaine abuse is associated with premature labor. Although cocaine is known to competitively inhibit beta-adrenergic receptor binding, cocaine's effect on receptor downregulation is uncertain. This study was designed to determine the in vitro effect of cocaine on downregulation of beta-adrenergic receptors in pregnant myometrium. Pregnant sheep myometrium was incubated with either cocaine, isoproterenol, or a cocaine metabolite, benzoylecgonine. Membrane fractions were assayed for beta-adrenergic receptors using (125I)-cyanopindolol and the beta 2-adrenergic antagonist ICI 118,551. We found that cocaine (10(-6) to 10(-4) mol/L), but not benzoylecgonine, downregulated both beta 1- and beta 2-adrenergic receptors, but did not further augment receptor downregulation by isoproterenol. The 46% decrease in beta-adrenergic receptors seen after exposure to cocaine was similar to the 53% decrease seen after isoproterenol. We hypothesize downregulation of beta-adrenergic receptors by cocaine may play a role in the association of cocaine abuse with premature labor.

Phase calibration and applications of a liquid-crystal spatial light modulator.

A simple phase-characterization method for spatial light modulators is proposed. The low-cost method permits high-precision measurement and provides data for the setting of the spatial-light-modulator operating point in the phase-modulation mode. The dynamic phase response is used to perform efficient kinoform recording. In order to record the kinoform, we modify the global iterative coding to compute phase holograms. Finally, modified phase-phase correlation is introduced. The phase-phase correlator permits sharper correlation peaks, better energy transmission, and higher discrimination than an amplitude-phase correlation. Optical experimental results are presented.

Inhibition of adhesion reformation in the rabbit model by meclofenamate: an inhibitor of both prostaglandin and leukotriene production.

OBJECTIVE: To determine the relative ability of meclofenamate sodium, a water-soluble inhibitor of both prostaglandin and leukotriene synthesis, to inhibit adhesion reformation. DESIGN: Prospective, randomized study in a rabbit model. INTERVENTIONS: Laparotomies were performed on mature New Zealand White rabbits, and each uterine horn was devascularized and traumatized with unipolar electrocautery. One week later, adhesions were microsurgically lysed. Each rabbit was randomly assigned to one of five different groups, and different solutions or an adhesion barrier were placed into the peritoneal cavities before closure: [1] control, 40 mL of normal saline (n = 8); [2] meclofenamate, 1.75 mg/mL in 40 mL of normal saline (n = 7); [3] Hyskon, 40 mL of 32% dextran-70 (n = 6); [4] meclofenamate 1.75 mg/mL in 40 mL of 32% dextran-70 (n = 6); and [5] TC-7, 40 mL of normal saline plus oxidized regenerated cellulose fabric, Interceed, placed over the site of adhesion lysis (n = 6). Two weeks later, adhesion reformation was scored according to percent involvement of each uterine horn (0 to 4), and adhesion density (0 to 1) and compared using a one-factor analysis of variance. RESULTS: Adhesion reformation was greatest in the control group (mean score +/- SEM, 3.7 +/- 0.4) and was decreased, but not significantly, in the Hyskon group (2.7 +/- 0.4). Compared with the control group, reformation was significantly decreased in the meclofenamate group (2.3 +/- 0.2), the TC-7 group (2.0 +/- 0.5), and the meclofenamate/Hyskon group (1.1 +/- 0.3). This last group was also decreased compared with the meclofenamate and Hyskon groups. CONCLUSION: Meclofenamate significantly inhibits adhesion reformation in the rabbit model, especially when used in combination with a 32% dextran-70 solution.

Cocaine selectively inhibits beta-adrenergic receptor binding in pregnant human myometrium.

OBJECTIVE: This study evaluated the in vitro effects of cocaine on the binding characteristics of alpha- and beta-adrenergic receptors from pregnant human myometrium. STUDY DESIGN: By means of membrane fractions from myometrium obtained from 26 women at term undergoing cesarean section, equilibrium binding assays were performed with tritiated dihydroergocryptine for alpha-adrenergic receptors and iodine 125-cyanopindolol for beta-adrenergic receptors. Equilibrium competition curves were determined with and without cocaine. Results were compared by one-way analysis of variance. RESULTS: Cocaine inhibited beta-adrenergic receptor binding (inhibition constant = 132 mumol/L) but had little effect on alpha-adrenergic receptor binding (inhibition constant = 1.63 mmol/L). Benzoylecgonine, a stable metabolite of cocaine, had no effect on binding to either receptor. CONCLUSION: Cocaine selectively inhibits myometrial beta-adrenergic receptor binding. This may alter the contractile equilibrium of the pregnant uterus and could explain, in part, the association of cocaine abuse with premature delivery.

Etiology of closure-related adhesion formation after wedge resection of the rabbit ovary.

Adhesion formation after closure after ovarian wedge resection of the rabbit ovary may be related to the use of polyglactin suture rather than to the closure itself.

The effect of cocaine on sperm motility characteristics and bovine cervical mucus penetration.

OBJECTIVES: To determine the in vitro effects of cocaine on sperm motility and bovine mucus penetration because cocaine abuse is associated with decreased sperm motility, and related compounds, such as procaine, are known to decrease sperm motility. DESIGN: Human semen samples were exposed to a range of cocaine concentrations and the effects quantified using computer-assisted sperm analysis and the bovine mucus penetration test. SETTING: University research laboratory. PATIENTS, PARTICIPANTS: Samples were obtained from 18 healthy volunteers. INTERVENTIONS: Normal semen samples were exposed to concentrations of cocaine ranging from 10(-11) to 10(-4) M. Motility characteristics were evaluated after 2 hours, and bovine mucus penetration was evaluated after 30 minutes, 1 hour, and 2 hours. Mucus penetration by washed sperm was also evaluated. MAIN OUTCOME MEASURES: Motility characteristics were evaluated using computer-assisted sperm analysis, and functional sperm motility was evaluated using the bovine mucus penetration test. RESULTS: Cocaine exposure decreased the percentage of motile sperm in a concentration-dependent manner with a maximum decrease of 23% at 10(-4) M but had no effect on other motility characteristics. Cocaine decreased bovine mucus penetration by 12% at high cocaine concentrations (10(-4) M), but increased penetration by 69% at low concentrations (10(-9) M). Washing sperm before cocaine exposure attenuated the increased sperm penetration. CONCLUSION: The ability of cocaine to decrease the percentage of motile sperm at high concentrations may explain the decreased sperm motility associated with cocaine use. Cocaine's ability to augment sperm penetration at low concentrations suggests an interaction of cocaine with the sperm adrenergic system.

Cocaine blocks extraneuronal uptake of norepinephrine by the pregnant human uterus.

Premature labor is one of the most common complications associated with cocaine abuse during pregnancy. Still, the effect of cocaine on the pregnant uterus is largely unknown. Although inhibition of neuronal uptake is the most important effect of cocaine in most tissues, after mid-pregnancy, the uterus has few functioning adrenergic nerve endings. To determine whether cocaine has any effect on uptake during pregnancy, we evaluated the ability of the term pregnant human uterus to take up [3H]-norepinephrine (9 x 10(-8) mol/L) and the ability of cocaine (10(-6)-10(-8) mol/L) to block this uptake. Because d-propranolol has been shown to block the direct effects of cocaine on the pregnant rabbit uterus, we also evaluated the ability of d-propranolol (2 x 10(-6) mol/L) to block the effect of cocaine on catecholamine uptake. The ability of the Uptake 2 inhibitor hydrocortisone (2 x 10(-5) mol/L) to block catecholamine uptake was also studied. We found that [3H]-norepinephrine was taken up by both the pregnant myometrium and endometrium, and that cocaine blocked this uptake by up to 55% at concentrations as low as 10(-7) mol/L. D-propranolol had no effect on the ability of cocaine to block catecholamine uptake. Hydrocortisone blocked uptake by the endometrium by 15% but did not block uptake by the myometrium. We conclude that the pregnant human uterus at term retains the ability to take up catecholamines and that cocaine blocks this extraneuronal uptake. This may explain, in part, the association of cocaine use with premature labor.

Abdominal wall characterization with magnetic resonance imaging and computed tomography. The effect of obesity on the laparoscopic approach.

Laparoscopic complications are most often related to insertion of the Veress cannula or primary trocar. We evaluated the midline abdominal walls of 33 women using magnetic resonance imaging (MRI) or computed tomography to determine if the location and angle of placement of the Veress cannula and primary trocar should be chosen according to the patient's weight to minimize the risk of both preperitoneal placement and retroperitoneal vessel injury. The anterior abdominal wall thickness was measured for three standard approaches used for placement of laparoscopic instruments through the umbilicus at both 45 degrees and 90 degrees from the horizontal. In addition, the distance from the base of the umbilicus to the retroperitoneal vessels was measured. We found that in the nonobese patient, both the Veress cannula and primary trocar can be inserted at 45 degrees, at either the lower margin or base of the umbilicus, with little risk of preperitoneal placement or major vessel injury. In the overweight patient the cannula and trocar can still be inserted at 45 degrees, but placement through the base of the umbilicus rather than the lower margin will minimize the chance of preperitoneal placement. In the majority of obese patients it is only by placing both the Veress cannula and sharp trocar through the base of the umbilicus at or near 90 degrees that preperitoneal placement can be avoided. Alternatively, an open laparoscopic technique can be considered in such high-risk patients to decrease the risk of major vessel injury.