Interaction of heavy metal toxicants with brain constitutive nitric oxide synthase.

This study was designed to evaluate the in vitro effects of transition heavy metal cations on activity of constitutive isoform of nitric oxide synthase (cNOS) in rat brain. NOS activity was determined in the cytosolic fractions of rat cerebral hemispheres by conversion of 3H-L-arginine to 3H-L-citrulline. Different concentrations of mercury (Hg2+), nickel (Ni2+), manganese (Mn2+), zinc (Zn2+), cadmium (Cd2+), lead (Pd2+) and calcium (Ca2+) were tested on NOS activity. While all the cations caused inhibition, there were differences in the apparent inhibition constants (Ki) among the cations. With the exception of calcium ion no other cation required preincubation with the enzyme preparation. These results indicate that while calcium ion modulate cNOS activity at regulatory site(s), inhibitory influence of toxic heavy metal cations may be exerted on the catalytic site(s) either by direct binding to it or by interfering with the electron transfer during catalysis.

Effects of acute and continuous administration of morphine on the cyclic AMP response induced by norepinephrine in rat brain slices.

Pre-incubated cortical brain slices from adult male Sprague Dawley rats when challenged by exogenous norepinephrine (NE) exhibited a dose-dependent increase in the level of endogenous cyclic 3',5' adenosine monophosphate (cyclic AMP), with the maximal response elicited at 50 microM NE concentration. The administration of 50 mg/kg sub-cutaneous (Sub-Q) morphine 5 minutes before sacrifice significantly increased the responsiveness of the brain slices to the NE-induced cyclic AMP response at 0.5, 5.0, and 50.0 microM NE. Sustained administration of morphine from the subcutaneously implanted morphine pellet (75 mg morphine base) attenuated the potentiated cyclic AMP response to NE in the brain slices of the rats exposed to a single challenge dose of 50 mg/kg (Sub-Q) morphine 5 minutes before sacrifice. This tolerance or attenuated response is first observed 24 hours after morphine pellet implantation with maximal tolerance observed at 48 hours after the pellet implantation. A complete reversal of attenuated NE-induced cyclic AMP response was observed when the 3 day morphine implanted rats were injected with a challenge dose of naloxone (4 mg/kg, Sub-Q) at 10 minutes prior to the acute administration of 50 mg/kg Sub-Q injection of morphine 5 minutes before sacrifice. These results suggest that both acute and prolonged administration of morphine alters NE-induced cyclic AMP response of the brain slices, and that naloxone, an opioid antagonist, reverses this response. This is perhaps due to morphine-induced alterations in the availability of NE in the CNS.

Preparation and evaluation of a sustained morphine delivery system in rats.

A new drug delivery system to induce physical dependence to morphine in rats is described. The device consists of a silicone polymer containing a water soluble "carrier" material, sodium alginate, which swells on contact with moisture to release the drug. The silicone or silastic pellets formulated to contain morphine sulfate are very easily prepared and the advantages over existing methods to induce physical dependence to morphine are discussed. In addition, a comparison of the percent of drug released and withdrawal intensities in rats was made with a silastic-morphine sulfate pellet, silastic-morphine base pellet and a microcrystalline cellulose-morphine base pellet.

Sustained release of alcohol: subcutaneous silastic implants in mice.

A sustained-release device for use in ethanol dependence studies in mice is described. The Silastic device, dubbed SERT (sustained ethanol release tube), holds 0.35 milliliter of 95 percent ethanol (by volume) and is implanted under the skin of the back where it releases ethanol for up to 12 hours, with no observable tissue damage. The device may be adaptable to the release of other volatile liquids or drugs, in other animals.

Chronic administration of cyanide: urinary excretion of thiocyanate in male and female rats.

The urinary elimination of thiocyanate was investigated in male and female rats following the chronic administration of potassium cyanide. Female rats dosed at the level of 5 mg KCN/kg once a week and twice a week respectively, displayed no significant difference in the excretion of thiocyanate in urine after periods of up to eight weeks of study. Similarly, male rats that were administered 5 mg/KCN/kg twice weekly showed no significant difference in the amount of thiocyanate excreted. The elimination patterns of thiocyanate in male and female rats showed no significant differences. The results suggest that a substrate saturation phenomenon is not operative with cyanide metabolism at the dosage level of potassium cyanide employed in this study. This is contrary to a previously published study which reported that the urinary excretion of thiocyanate decreased after chronic potassium cyanide administration.