No abstract

(S)-alpha-Chlorohydrin and 3-chloro-1-hydroxyacetone inhibited the oxidative metabolism of fructose by boar spermatozoa only after a period of incubation in which they presumably underwent conversion to (S)-3-chlorolactaldehyde, an inhibitor of sperm glyceraldehyde 3-phosphate dehydrogenase. With glycerol as substrate, 3-chloro-1-hydroxyacetone had a similar effect, (S)-alpha-chlorohydrin was ineffective while (R,S)-3-chlorolactaldehyde was immediately effective with either substrate. All three compounds caused the accumulation of fructose 1,6-bisphosphate and dihydroxyacetone phosphate from fructose but not from glycerol which led to the conclusion that inhibition of triosephosphate isomerase was also associated with the anti-glycolytic action of (S)-3-chlorolactaldehyde. (S)-3-Chlorolactaldehyde caused the depletion of ATP in incubates of boar spermatozoa metabolizing fructose but not glycerol. This suggests that futile substrate cycling may play an important function in the anti-glycolytic action of (S)-3-chlorolactaldehyde and/or that boar spermatozoa can synthesize ATP from glycerol by a mechanism not involving the glycolytic pathway.

No abstract

We examined DNA synthesis in non-enzymatically isolated neonatal rat pancreatic islets sub-cultured to eliminate fibroblast contamination, which was excluded both by demonstrating no effect of fibroblast growth factor (FGF) on 3H-thymidine incorporation and by immunofluorescence of attached islets using a mouse anti-fibroblast monoclonal antibody. 3H-thymidine incorporation in islets increased with increasing glucose up to a concentration of 21.1 mM in both free-floating islets (11,789 cpm/micrograms DNA +/- 1,610 SEM) and islets attached to fibronectin coated plastic (43,043 cpm/micrograms DNA +/- 9,203 SEM). These values were significantly higher when compared to 3H-thymidine incorporation in medium containing 11.1 mM glucose (p < 0.007, and p < 0.0001 for free-floating and attached islets respectively). 3H-thymidine incorporation was significantly higher in attached islets than in free-floating islets at all glucose concentrations tested (p < 0.005 at 11.1 mM, 16.1 mM, and 21.1 mM; and p < 0.01 at 26.1 mM). 5-bromo-2'-deoxyuridine (BrDU) staining of islets showed an increased number of positive nuclei in cells localised within attached islets (37.6 nuclei per islet +/- 5.1 SEM) compared to free-floating islets (7.62 nuclei per islet +/- 1.04 SEM, p < 0.001), indicating that attachment influenced proliferation of islet cells not physically in contact with the matrix. No difference in glucose-stimulated insulin release was observed between attached and free-floating islets. In conclusion, a fibroblast free islet culture was used to document the stimulatory effect of islet attachment on DNA synthesis, which was greater than the stimulation exerted by glucose alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Approximately 75% of the PAF present in saliva is recovered on extraction of whole saliva (0.8 vol) with chloroform/methanol/water (2:2:1, v/v/v). PAF levels, determined by our recently developed radioimmunoassay, in saliva extracts ranged from 0.5-21 ng/mL with 59% between 2-6 ng/mL. These figures, for apparently healthy subjects, are higher than previously reported levels obtained by platelet assays. The validity of our radioimmunoassay results was checked by isolating and quantitating the PAF fraction from whole saliva. In addition, when we examined our saliva samples by platelet aggregation, low levels of PAF, comparable with the values found in the literature, were detected. Investigations revealed the presence of a substance(s) which inhibited PAF-induced platelet aggregation but which did not affect the radioimmunoassay.