David P. Hanlon

The interaction of divalent metal ions with tris buffer in dilute solution

Abstract The interaction of 2-amino-2-(hydroxymethyl)-1,3-propanediol (tris) with eight divalent metal ions has been investigated under conditions commonly employed in biochemical studies. Formation constants have been calculated, where possible from pH titration data. Hg ++ and Cu ++ interact strongly with tris, and Co ++ , Zn ++ , Cd ++ much less so. The interaction of tris with Mg ++ and Mn ++ is too weak to be detected under the conditions used. Above pH 7.5 further reaction of the metal complexes with added hydroxyl ion complicates the calculation of formation constants for higher complexes of divalent metal ions and Tris.

Embryotoxicity and dose-response relationships of selenium in hamsters

Pregnant hamsters were treated with selenite, selenate, and selenomethionine during the critical stages of embryogenesis. The dosing regimens were oral, intravenous, and osmotic minipump infusion. Malformations, mainly encephaloceles, were noted with oral and intravenous selenite and selenate but were associated with maternal toxicity manifested by inanition and weight loss. Fetal body weights and lengths were reduced in a dose-dependent manner with the inorganic forms. Single oral doses of selenomethionine above 77 mumol/kg induced similar malformations but not when the dose was delivered orally over four days nor by minipump over several days. Fetal body weights and lengths were decreased by selenomethionine in a dose-dependent manner. Maternal toxicity was pronounced with the higher doses of selenomethionine. Assigning a specific teratogenic effect to selenium is confounded by maternal toxicity.

The distribution of arginase and urease in marine invertebrates.

Abstract 1. 1. Arginase and urease activities of the same tissue extracts were measured on the same day in 15 species of marine invertebrate from 5 phyla. 2. 2. Highest arginase activities were found in the Crustacea, in particular, the digestive gland of Carcinus maenas. Two gastropods, Busycon canaliculatum and Littorina litorrea showed the greatest urease activities. 3. 3. High arginase levels in Crustacea were coupled with low urease activities. The reverse was true for most bivalve and gastropod molluscs examined. 4. 4. Arginase from the hepatopancreas of Carcinus maenas was found to have an apparent Michaelis constant of 40 mM and substrate inhibition at 50 mM and greater. 5. 5. Animals known to excrete little or no urea had high urease activities and those in which urea excretion is known to occur generally had very low urease activities.

The chemical status of cadmium ion in the placenta.

Abstract The chemical status of cadmium ion in the chorioallantoic and yolk sac placentas of SWV strain mice during the critical phase of embryonic organogenesis was investigated. Twenty-four hours after a single teratogenic dose of cadmium ion, both placentas contained significant amounts of a macromolecular chelator. Gel filtration data and disc electrophoresis data suggest that the cadmium-binding macromolecule of the chorioallantois (which binds 61% of the cadmium ion content of the tissue) is a metallothionein dimer.

Constant rate exposure of pregnant hamsters to arsenate during early gestation

We have examined the teratogenic and embryotoxic effects of constant-rate exposure of pregnant hamsters to arsenate by means of subcutaneous implants of osmotic minipumps. Different total exposure regimens were established by varying the duration of minipump implants and by varying the concentration of arsenate in the minipumps. Dams were killed on Day 13 of pregnancy, 5 days after the critical stage of organogenesis. Numbers of resorptions, dead fetuses, and living fetuses were obtained. Fetal weights, crown-rump lengths, and the incidence of malformations were recorded. Control animals were treated identically with minipumps containing demineralized water. The percentage of malformations per litter, a direct measure of teratogenesis, was dependent only upon the concentration of arsenate in the minipumps. The minimum teratogenic response was achieved with a dose of 70 mumol/kg dam/24 hr during the critical stages of organogenesis. The embryotoxic (fetotoxic) indicators, fetal weight and crown-rump length, decreased with increases in exposure time and with increased concentrations of arsenate. The resorption rate also depended directly upon duration of exposure and concentration of arsenate in the minipump.

The permeability of the Syrian hamster placenta to mercury

Abstract Three mercury compounds; mercuric acetate, mercuric nitrate and phenylmercuric acetate, labeled with 203 Hg, were administered to pregnant hamsters early on the 8th gestation day. Mercury levels of selected tissues were measured 24 and 96 hours after injection. Significant concentrations of mercury were found in maternal tissues, placentae, and embryos. The results are discussed in relation to other reports on the placental transfer of radiolabeled cadmium, manganese, mercury, and zinc.

Arsenate-Induced Neural Tube Defects Not Influenced by Constant Rate Administration of Folic Acid

ABSTRACT. Serious suggestions have been made that dietary supplementation with folic acid (FA) and perhaps other vitamins during pregnancy may reduce the incidence of neural tube defect (NTD) in human newborns. The purpose of these experiments was to evaluate the effect of continuous infusion of FA on the incidence of NTDs induced by arsenate. This teratogen induces NTDs in up to 90% of golden hamster fetuses when administered acutely during critical stages of embryogenesis. FA was administered by subcutaneously implanted osmotic minipumps beginning on the 6th day of gestation, 48 h before an acutely administered dose of sodium arsenate. The protective effect of FA was examined at three teratogenic dose levels of arsenate: optimal, with 90% NTDs, intermediate, with 38% NTDs, and low, with 20% NTDs. Fetuses were recovered at day 13 of gestation and examined for NTDs and other malformations. Maternal red cell folate levels were determined on day 8, 48 h after implantation of the pumps. The results show that the maternal red blood cell level of FA can be significantly increased within 48 h by chronic infusion to levels which are almost two times (550 ng/ml) control levels. There was no significant protection against arsenate-induced NTDs following FA supplementation at any of three levels of this teratogen.

Neuroaudiological effects in a case of fatal dimethylmercury poisoning.

OBJECTIVE The audiological examination of this patient was to determine the degree and type of hearing loss that was incurred from apparent dimethylmercury poisoning. DESIGN This was a single subject case study design. Audiologic tests were selected to help determine sensory from neural and/or central auditory system dysfunction. RESULTS This patient demonstrated an inability to understand speech, both in formal and informal assessments, yet relatively good hearing sensitivity for pure tones bilaterally. Distortion product otoacoustic emissions showed only minimal deficits in each ear. The auditory brain stem response was abnormal bilaterally, indicating neural and/or central involvement. CONCLUSION Dimethylmercury poisoning, in this case, resulted in compromise of the auditory neural system with little effect on the sensory (cochlea) mechanism.

Metal-Induced Congenital Malformations

Certain heavy metals induce specific patterns of developmental malformations in the hamster model. These metals are indium, cadmium, mercury, copper and arsenic (as arsenate) listed in order of increasing dose required to provoke a teratogenic response. The hamster model is well suited to teratogenic investigations by reason of its short gestation period and remarkably condensed period of organogenesis in addition to the fact that maternal toxicity is not a problem at teratogenic doses. Each of the metal teratogens causes a characteristic response in the form of a particular pattern of fetal abnormalities. These characteristic responses can be modified by the presence of certain other metals or genetic and environmental factors. Non-teratogenic metals cross the hamster placenta with ease. In contrast, heavy metal teratogens concentrate in the placenta and only small amounts are deposited in the embryo. These data imply the presence of a placental barrier to heavy metals; further studies with cadmium have suggested that this barrier is a cadmium-binding protein. Future studies on heavy metal teratogenesis should focus on the potential effect of chronic low-level exposure to these metals, genetic factors influencing teratogenic response, and identification of possible environmental factors which can modify heavy metal teratogens.

Inhibition of brain dopamine-β-hydroxylase activity by methimazole

Abstract Rat brain dopamine-β-hydroxylase (DβH) activity was estimated using graded doses of 3 H-dopamine injected intracistermally. Animals treated acutely with methimazole, 5 to 50 mg/kg (.044 to .44 millimole/kg), displayed a dose-related decrease in the levels of 3 H-norepinephrine formed from 3 H-dopamine. The ID 50 of methimazole was 10 mg/kg (.088 millimole/kg). The duration of DβH inhibition, which was accompanied by a decrease in endogenous norepinephrine concentration, was between 6 and 12 hours following a single acute 10 mg/kg dose of methimazole. Methimazoles effect on DβH is thought to be mediated via its ability to chelate copper.