Pre- and Postjunctional Effects of Diadenosine Polyphosphates in the Guinea-pig Vas Deferens

The pre- and postjunctional activities of a number of diadenosine polyphosphates were examined in the guinea-pig isolated vas deferens at the level of the membrane-potential, using a modified sucrose-gap technique. P¹,P³-Di(adenosine 5′)triphosphate (Ap₃A), P¹,P⁴-di(adenosine 5′)tetraphosphate (Ap₄A) and P¹,P⁵-di(adenosine 5′)pentaphosphate (Ap₅ A) all caused concentration-dependent depolarization of the smooth muscle membrane. The potency order was: Ap₅A > Ap₄A. Ap₃A. P¹, P²-Di(adenosine 5′)pyrophosphate (Ap₂A) did not evoke depolarization even at the highest concentration tested (1 mM). All the dinucleotides caused a reduction in the amplitude of evoked excitatory junction potentials (e.j.ps). The potency order was: Ap₅A = Ap₄A > Ap₃A > Ap₂A. The depolarizations evoked by the dinucleotides were markedly reduced by the selective P_2X-purinoceptor antagonist, pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS, 10 μM), as was the amplitude of the fully facilitated e.j.p. The inhibition of the e.j.p. evoked by Ap₃A and Ap₂A was reduced by the P₁-purinoceptor antagonist, 8-p-sulphophenyltheophylline (8-pSPT, 50 μM), but that evoked by Ap₅A and Ap₄A was not. Thus, Ap₃A, Ap₄A and Ap₅ A evoke depolarization of the guinea-pig vas deferens via P_2X-purinoceptors, and additionally Ap₂A and Ap₃A exert a prejunctional effect via P₁-purinoceptors. The prejunctional activity of Ap₄A and Ap₅A is mediated via an undefined purinoceptor, which is neither P₁ nor P_2X.     

Intrastriatal grafts of rat colonic smooth muscle lacking myenteric ganglia stimulate axonal sprouting and regeneration

Grafts of living or freeze-killed freshly dissected colonic smooth muscle from young inbred Fischer rats were implanted into the corpus striatum of adult Fischer rats. Sections of brain were examined electron microscopically 3 and 6 wk after implantation. At both times, living grafts were vascularised and contained healthy differentiated smooth muscle cells, fibroblasts, interstitial cells of Cajal and some macrophages. Large bundles of small nonmyelinated axons, identified as CNS axonal sprouts, could be observed in the brain at and near the interface between the living smooth muscle and the CNS tissue. Bundles of regenerating CNS axons, often associated with astrocyte processes, had grown into the grafts. Some axons within the grafts had matured, enlarged and become myelinated by oligodendrocyte processes or Schwann cells. In some cases, smooth muscle cells were observed in close and intricate association with axons. In contrast to the living grafts, grafts of freeze-killed smooth muscle, examined 3 and 6 wk after implantation, contained macrophages, fibroblasts, collagen and large amounts of cellular debris, but no living muscle cells, astrocytes or Schwann cells. The striatal neuropil around freeze-killed grafts did not contain large bundles of CNS axonal sprouts and bundles of axons were not observed within the freeze-killed graft. This study demonstrates that cells from the smooth muscle layers of the colon, in the absence of myenteric ganglia, can stimulate a vigorous regenerative response from CNS axons when implanted into the corpus striatum of adult rats.     

Stereospecific effects of tryptophan on gastric emptying and hunger in humans

The amino acid tryptophan (tryp) is a potent inhibitor of gastric emptying in both animals and humans. Animal studies suggest that this effect may be specific for the L-enantiomer. The effects of _D- and _L-tryptophan on gastric emptying, intragastric distribution and appetite in humans were evaluated. Ten volunteers ingested 300 mL of either _L-tryp (50 mmol/L), _D-tryp (50 mmol/L) or normal saline labelled with ^99mTc sulfur colloid on three occasions, separated by between 3 and 7 days. Hunger and fullness were measured with a visual analogue scale at -2, 15, 30 and 60 min after ingestion of each drink. Saline emptied faster from the stomach than both _L-tryp and _D-tryp (P <0.05) and _D-tryp emptied faster than _L-tryp (P <0.005). Emptying from the proximal stomach was fastest for saline (P <0.05) and faster for _D-tryp than _L-tryp (P <0.005). Emptying from the distal stomach was faster for saline than both _D- and _L-tryp (P <0.05). A reduction in hunger (P <0.05) and a non-significant trend for an increase in fullness were observed after all three drinks. At 60 min, fullness was greater after _L-tryp than after ingestion of _D-tryp (P <0.01). These observations indicate that the effect of tryptophan on gastric emptying in humans is stereospecific, consistent with the concept that stereospecific receptors for tryptophan exist in the human small intestine.     

Follow-up of Gambian children recruited to a pilot safety and immunogenicity study of the malaria vaccine SPf66

A pilot safety and immunogenicity trial of the malaria vaccine SPf66 was undertaken in The Gambia in 1993. One hundred and fifty infants aged 6–11 months were immunized with either 0.5 mg or 1.0 mg of SPf66 produced either in Colombia or in the USA or with a control vaccine. Children who received SPf66 experienced more clinical attacks of malaria than did children in the control group during the first period of surveillance and the difference in incidence between children who had received high dose Colombian vaccine and the control children was statistically significant at the 5% level. During the 1995 malaria transmission season, 127 children from the original cohort of 150 were observed. During 18 weeks of intensive surveillance, the incidence of clinical malaria was again higher among children who had received SPf66 than among children who had received inactivated polio vaccine (6.23 vs 4.89 clinical attacks per 1000 days at risk), the effect being most marked among children who were in the high dose groups, but differences between groups were now no longer statistically significant .     

Chilled Foods

Chilling provides the Food Technologist with a valuable means of extending the shelf life of food products, and the chilled food market has seen exceptional growth as ownership of domestic refrigerators has grown. Recent media attention has highlighted that chilling cannot be effective as a food safety mechanism unless used in association with high standards of hygiene, or in combination with other traditional preservative techniques. Many microbiological and quality aspects of chilled foods are considered in the following report which help to put into context recent and future legislation requirements for chilled foods control.