Heavy metals in Jamaican surface soils.

A regional survey of Jamaican surface soils has been conducted in which more than 200 samples were collected at a sample density of 1 per 64 km(2) across the island and analysed for total concentrations of 31 elements by instrumental neutron activation analysis (INAA), energy dispersive X-ray fluorescence (EDXRF) analysis and atomic absorption spectrophotometry (AAS). The aim of the survey was to begin the construction of a high-precision geochemical database to provide information on elemental levels in soils for application to environmental studies, agriculture, and human and animal health. Results on the regional scale are presented for As, Cd, Cu, Hg and Pb. Although Jamaican surface soils are enriched in several heavy metals compared with world soil means and crustal abundances, lead is of particular importance at this stage because of its occurrence in residential areas. Except for Cu, the distribution maps of these elements are highly correlated with bauxite which in Jamaica is associated with white limestone geology and residualterra rossa soils.

Elemental concentrations in Jamaican peat.

The peat of the Negril Morass in Western Jamaica was sampled at depths down to 7 m in directions parallel and perpendicular to the seashore, and the samples were analysed for Al, As, B, Br, Ca, Ce, Cl, Co, Cr, Cs, Dy, Eu, Fe, Hf, I, La, Mg, Mn, Na, Sb, Sc, Sm, Sr, Ti, U and V by instrumental neutron activation analysis and by spectrophotometry. The peat is high in ash content, but the concentrations of most elements are below crustal abundances and therefore provide no evidence of nearby mineralisation. The elemental concentrations indicate that no particular environmental hazards are to expected from the use of this peat in electricity generation.

Capsaicin effects on muscularis mucosa of opossum esophagus: substance P release from afferent nerves?

The effects of capsaicin on the function and structure of muscularis mucosa of opossum esophagus were studied. In this tissue there are numerous nerves containing a substance P-like immunoreactive substance (SPLS), and electrical field stimulation (EFS) leads to a phasic response that appears to be due to release of acetylcholine, followed by a tonic response at higher frequencies of stimulation that appears to be due to release of a SPLS. The acetylcholine released by EFS and exogenous muscarinic agonists inhibits release of this SPLS (8). In the present study capsaicin (5 X 10(-5) M) was shown to cause a tonic submaximal contraction in most cases. This was prevented by substance P tachyphylaxis and by pretreatment with the partial agonist [D-Pro2, D-Trp7,9]substance P, the antagonist [D-Arg1, D-Trp7, Leu11]substance P, and tetrodotoxin. This response to capsaicin could not be repeated even after 2 h. Capsaicin also abolished the tonic response to high-frequency EFS without affecting phasic responses and reduced markedly the enhanced tonic response after atropine had abolished the phasic response. This occurred with or without a preliminary contraction to capsaicin. This tonic response to high-frequency EFS recovered completely 1-2 h after washing out capsaicin. Then, a further administration of capsaicin had no direct effect but again abolished tonic responses to EFS. Capsaicin reduced responses to exogenous substance P or carbachol only partially. When tissues were fixed and studied after capsaicin had abolished tonic responses to EFS, specific damage to nerve varicosities or synaptic vesicles in nerve varicosities could not be demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Muscarinic inhibition of canine small intestinal motility in vivo.

The quiescent canine gastrointestinal tract responsed to close intraarterial acetylcholine with an atropine-sensitive, hexamethonium, and tetrodotoxin-insensitive contraction, thus suggesting acetylcholine interacts with a muscarinic receptor located on the muscle. When the gut is actively contracting (spontaneously, in response to field stimulation or to motilin), acetylcholine caused a contraction followed by prolonged inhibition of contractions. No such inhibition was apparent after tetrodotoxin; therefore, the receptor for acetylcholine-induced inhibition was apparently on nerves. Neither the acetylcholine-induced excitation nor the inhibition was altered by hexamethonium or reserpine treatment. Both inhibitory and excitatory responses were greatly reduced by atropine, suggesting that both receptors were muscarinic in nature. McNeil A343 produced inhibition but no excitation. Tetrodotoxin, hexamethonium, reserpine, and pirenzepine all increased the concentration of McNeil A343 required for production of 50% inhibition, suggesting it acts via multiple mechanisms. Furthermore, pirenzepine reduced both the inhibitory and excitatory response to acetylcholine, suggesting that it is nonselective in its action on the neural inhibitory or muscular excitatory receptors. We suggest that the presynaptic muscarinic receptor responsible for inhibitory effects of acetylcholine is on the postganglionic cholinergic neuron itself and constitutes an important negative-feedback loop to reduce excessive cholinergic output. Although such a mechanism has been found in vitro previously, this is the first report in vivo in canine small intestine.

The mechanism of motilin excitation of the canine small intestine.

Close intraarterial injections of motilin to the small intestine of the anaesthetized dog produce prolonged phasic contractions. Tetrodotoxin infused intraarterially blocked field stimulated contractions and abolished the response to motilin as did treatment with a combination of hexamethonium and atropine. Atropine alone increased the dose of motilin required to induce responses. Hexamethonium alone similarly increased the dose of motilin required in the jejunum, but not for the ileum. These results suggest that motilin acts to contract small intestine by stimulation of intrinsic excitatory nerves, some of which are post-ganglionic cholinergic and some of which are not, but are activated by a pathway with a nicotinic synapse. The ED50 for ileal contractions was greater than that for the jejunum and the time to reach maximum contractions longer suggesting a decreased responsiveness of the lower small intestine to motilin as compared to the upper gastrointestinal tract. These results and the lesser quantity of immunoreactive motilin in the ileum than in the jejunum may explain the lack of relationship of the activity front of the migrating motor complex in the lower small intestine to venous motilin concentrations.