Development of gastric sensitivity to histamine in the rat

Sensitivity of the developing rat stomach to histamine (HA) was examined on isolated gastric mucosae of rats of various ages from the fetal to adult periods. Spontaneous acid secretion in mu eq/h.cm2 occurred at all the ages studied, at a basal rate of 0.45 +/- 0.07 in fetuses to 0.22 +/- 0.03 (day 5), 0.11 +/- 0.04 (day 10), 0.12 +/- 0.04 (day 12), 0.22 +/- 0.08 (day 16) and 0.33 +/- 0.04 (adults). In the fetal rats as in the adults, marked responses to respectively 10(-5) and 10(-4) M HA were demonstrated. The H2-receptor antagonist cimetidine diminished HA-induced secretion by 66 and 57% in fetuses and adults respectively. Between these two stages (from days 5 to 12), basal secretion and the response to HA dropped significantly. On day 21 of gestation, as well as on the critical days 5 and 12 after parturition, db-cAMP (10(-4) M) caused maximal stimulation of acid secretion. These results indicate that the development of responsiveness to HA in the rat is biphasic. They suggest that after birth, the H2-receptor adenylate cyclase system undergoes major modifications which might lead to the complete lack of responsiveness to HA by day 12.     

Genes for the biosynthesis of spinosyns: applications for yield improvement in Saccharopolyspora spinosa

Spinosyns A and D are the active ingredients in an insect control agent produced by fermentation of Saccharopolyspora spinosa. Spinosyns are macrolides with a 21-carbon, tetracyclic lactone backbone to which the deoxysugars forosamine and tri-O-methylrhamnose are attached. The spinosyn biosynthesis genes, except for the rhamnose genes, are located in a cluster that spans 74 kb of the S. spinosa genome. DNA sequence analysis, targeted gene disruptions and bioconversion studies identified five large genes encoding type I polyketide synthase subunits, and 14 genes involved in sugar biosynthesis, sugar attachment to the polyketide or cross-bridging of the polyketide. Four rhamnose biosynthetic genes, two of which are also necessary for forosamine biosynthesis, are located outside the spinosyn gene cluster. Duplication of the spinosyn genes linked to the polyketide synthase genes stimulated the final step in the biosynthesis — the conversion of the forosamine-less pseudoaglycones to endproducts. Duplication of genes involved in the early steps of deoxysugar biosynthesis increased spinosyn yield significantly. Journal of Industrial Microbiology & Biotechnology (2001) 27, 399–402. Received 31 May 2001/ Accepted in revised form 09 July 2001     

Heart rate and respiratory patterns in mild hypoxia in unanaesthetized newborn mammals

The heart rate and respiratory patterns in hypoxia are not well documented in unanaesthetized intact newborn animals. We studied heart rate and respiratory patterns during quiet sleep in 17% inspired O2 in 31 unanaesthetized newborns of five species: lamb, piglet, puppy, kitten, and rabbit. There was no significant change in mean heart rate and respiratory rate with hypoxia for any species. Brief apneas greater than 5 s were frequent (5-8/h), both in 21 and 17% O2 only in lambs and puppies. No sustained periodic breathing was induced by hypoxia. Thus, mild hypoxia has little steady-state effect on heart rate and respiratory rate and pattern in these unanaesthetized newborns. These findings are compatible with depressed chemoreceptor threshold, but indicate a remarkably mature respiratory pattern in full-term newborns of these species.     

Levels of genetic polymorphism: marker loci versus quantitative traits.

Species are the units used to measure ecological diversity and alleles are the units of genetic diversity. Genetic variation within and among species has been documented most extensively using allozyme electrophoresis. This reveals wide differences in genetic variability within, and genetic distances among, species, demonstrating that species are not equivalent units of diversity. The extent to which the pattern observed for allozymes can be used to infer patterns of genetic variation in quantitative traits depends on the forces generating and maintaining variability. Allozyme variation is probably not strictly neutral but, nevertheless, heterozygosity is expected to be influenced by population size and genetic distance will be affected by time since divergence. The same is true for quantitative traits influenced by many genes and under weak stabilizing selection. However, the limited data available suggest that allozyme variability is a poor predictor of genetic variation in quantitative traits within populations. It is a better predictor of general phenotypic divergence and of postzygotic isolation between populations or species, but is only weakly correlated with prezygotic isolation. Studies of grasshopper and planthopper mating signal variation and assortative mating illustrate how these characters evolve independently of general genetic and morphological variation. The role of such traits in prezygotic isolation, and hence speciation, means that they will contribute significantly to the diversity of levels of genetic variation within and among species.     

Peanut (Arachis hypogaea) lectin recognizes α-linked galactose, but not N-acetyl lactosamine in N-linked oligosaccharide terminals

Peanut (Arachis hypogaea) agglutinin (PNA) is extensively used as tumour marker as it strongly recognises the cancer specific T antigen (Galβ1→3GalNAc-), but not its sialylated version. However, an additional specificity towards Galβ1→4GlcNAc (LacNAc), which is not tumour specific, had been attributed to PNA. For correct interpretation of lectin histochemical results we examined PNA sugar specificity using naturally occurring or semi-synthetic glycoproteins, matrix-immobilised galactosides and lectin-binding tissue glycoproteins, rather than mono- or disaccharides as ligands. Dot-blots, transfer blots or polystyrene plate coatings of the soluble glycoconjugates were probed with horse-radish peroxidase (HRP) conjugates of PNA and other lectins of known specificity. Modifications of PNA-binding glycoproteins, including selective removal of O-linked oligosaccharides and treatment with glycosidases revealed that Galβ1→4GlcNAc (LacNAc) was ineffective while terminal α-linked galactose (TAG) as well as exposed T antigen (Galβ1→3 GalNAc-) was excellent as sugar moiety in glycoproteins for their recognition by PNA. When immobilised, melibiose was superior to lactose in PNA binding. Results were confirmed using TAG-specific human serum anti-α-galactoside antibody.