Overexpression of a constitutively active form of phosphatidylinositol 3-kinase is sufficient to promote Glut 4 translocation in adipocytes

Insulin stimulates glucose transport in its target cells by recruiting the glucose transporter Glut 4 from an intracellular compartment to the cell surface. Previous studies have indicated that phosphatidylinositol 3-kinase (PI 3-kinase) is a necessary step in this insulin action. We have investigated whether PI 3-kinase activation is sufficient to promote Glut 4 translocation in transiently transfected adipocytes. Rat adipose cells were cotransfected with expression vectors that allowed transient expression of epitope-tagged Glut 4 and a constitutively active form of PI 3-kinase (p110*). The expression of p110* induced the appearance of epitope-tagged Glut 4 at the cell surface at a level similar to that obtained after insulin treatment, whereas a kinase-dead version of p110* had no effect. The p110* effect was observed over a wide range of the transfected cDNA. When subcellular fractionation of adipocytes was performed, p110* was found, similar to the endogenous PI 3-kinase, enriched in the low density microsomal compartment, which also contains the Glut 4 vesicles. This could suggest that a specific localization of PI 3-kinase in this compartment is required for the action on Glut 4. The observations made with PI 3-kinase are in contrast with those seen with the MAP kinase cascade. Indeed, a constitutively active form of MAP kinase kinase had no effect on Glut 4 translocation in basal conditions. At the highest degree of expression, the constitutively active form of MAP kinase kinase slightly inhibited the insulin stimulation of Glut 4 translocation. Taken together, our results indicate that Glut 4 translocation can be efficiently promoted by an active form of PI 3-kinase but not by the activation of the MAP kinase pathway.     

Japanese encephalitis on Saipan: a survey of suspected mosquito vectors

An outbreak of Japanese encephalitis (JE) occurred on Saipan, Commonwealth of Northern Mariana Islands, in October 1990. Adult and larval mosquitoes were collected during September-October 1991 to retrospectively determine the probable mosquito vector(s). Virus was not isolated from 119 mosquito pools composed of 7,250 adult specimens as follows: Aedes vexans nocturnis (14%), Culex tritaeniorhynchus (39%), Cx. sitiens group (11%), Culex (Culex) species (35%), and < 1% each of Ae. albopictus, Ae. oakleyi, Aedes saipanensis, Cx. annulirostris marianae, and Cx. fuscanus. Three additional species were collected only as larvae: Anopheles indefinitus, Ae. neopandani, and Cx. quinquefasciatus. Among the vectors of JE incriminated in other areas, Cx. tritaeniorhynchus was the predominant species in our collections and the principal species feeding on swine. This is the first published record of the occurrence of this species on Saipan. Culex tritaeniorhynchus is abundant and widely distributed on the southern half of Saipan where human JE cases occurred in 1990, and where swine seroconversions were detected. Although the identity of the mosquito vector(s) responsible for the 1990 outbreak cannot be established with certainty, our results suggest that Cx. tritaeniorhychus was probably involved.     

Pharmacological effects of propylthiouracil on corticosterone secretion in male rats

BACKGROUND: We investigated the direct effects of propylthiouracil (PTU) on corticosterone secretion both in vivo and in vitro. METHODS: Male rats were divided into 4 groups and then injected subcutaneously with saline, PTU, PTU plus thyroxine (T4), or T4 once daily for 2 weeks. After 2 weeks, rats were decapitated or received adrenocorticotropic hormone (ACTH), intravenously. Zona fasciculata-reticularis (ZFR) cells from normal, saline-, PTU-, PTU plus T4-, or T4-treated rats were incubated with ACTH, forskolin, 8-Br-cAMP, deoxycorticosterone (DOC) +/- PTU (1, 2, or 5 mg/mL) at 37 degrees C for 2 hours. Corticosterone concentrations in plasma and cell media, and 3':5'-cyclic adenosine monophosphate (cAMP) production in ZFR cells were determined by radioimmunoassay. The effects of PTU on the activities of steroidogenic enzymes in ZFR cells were measured by the amounts of intermediate steroidal products separated by thin-layer chromatography. RESULTS: The basal and ACTH-stimulated levels of plasma corticosterone in PTU-treated rats were lower as compared to saline-treated animals. Both basal and ACTH-stimulated corticosterone secretion were inhibited by PTU > 2 mg/mL in rat ZFR cells. The cAMP production induced by forskolin was lower in PTU, PTU plus T4, or T4-treated rats than in saline-treated animals. Chronic administration of PTU or PTU plus T4 inhibited the 3 beta-hydroxysteroid dehydrogenase, 21 beta-hydroxylase, and 11 beta-hydroxylase activities. Administration of PTU (1, 2, and 5 mg/mL) suppressed the basal, ACTH, 8-Br-cAMP, forskolin, and DOC-stimulated corticosterone secretion in rat ZFR cells. Likewise, PTU > 2 mg/mL inhibited the ACTH and 8-Br-cAMP-stimulated levels of intracellular cAMP in rat ZFR cells. CONCLUSIONS: These results suggest that PTU counteracts both basal and ACTH-induced adrenal steroidogenesis through their attenuation of the activity of 11 beta-hydroxylase and cAMP production in rat ZFR cells.     

Macular pigment densities derived from central and peripheral spectral sensitivity differences

Estimates of the density spectrum of the macular pigment (Wyszecki G, Stiles WS. Color Science: Concepts and Methods. Quantitative Data and Formulas. 1st ed. New York: Wiley, 1967); (Vos JJ. Literature review of human macular absorption in the visible and its consequences for the cone receptor primaries. Institute for Perception. Soesterberg, The Netherlands, 1972) are partially based on the difference between central and peripheral spectral sensitivities, measured under conditions chosen to isolate a single cone class (Stiles WS. Madrid: Union Internationale de Physique Pure et Appliquée, 1953;1:65-103). Such derivations assume that the isolated spectral sensitivity is the same at both retinal locations, save for the intervening macular pigment. If this is true, then the type of cone class mediating detection should not influence the calculated difference spectrum. To test this assumption, we measured central and peripheral spectral sensitivities in a deuteranope, a protanope and a normal trichromat observer: (a) for short-wave sensitive (S-) cone detection; and (b) for long-wave sensitive (L-) cone detection (deuteranope), for middle-wave sensitive (M-) cone detection (protanope) or for both L- and M-cone detection (normal trichromat). The difference spectra determined for L- or M-cone detection deviate significantly from those measured for S-cone detection, at wavelengths below 450 nm. A theoretical analysis suggests that the discrepancies are owing, in part, to regional variation in the optical density of the cone pigments; and that such receptor variation cannot be ignored when deriving the standard density spectrum of the macular pigment.     

Testing the indeterminacy of linear color mechanisms from color discrimination data

It have previously been reported that, for some choices of the fixed spatial and temporal characteristics of test stimuli, it was possible to estimate the spectral sensitivities of chromatic mechanisms from chromatic discrimination data alone. If mechanism sensitivities could be reliably estimated for any choice of test stimuli characteristics, the influence of spatial and temporal factors on chromatic discrimination performance could be directly measured. Previous studies, using test stimuli with other spatio-temporal characteristics, have found equi-discrimination contours whose ellipsoidal shapes seem to preclude estimation of mechanisms. Since there is no commonly-accepted method for testing the adequacy of ellipsoidal fits of chromatic equi-discrimination contours, it is possible that alternative psychophysical procedures combined with more powerful statistical tests could detect the pattern of deviations from ellipticality reported previously. In this paper, we described psychophysical tests and statistical analyses that, taken together, provide a more powerful test of the indeterminacy of mechanisms than previous methods. We develop a method based on analysis of residuals for detecting the pattern of deviations from ellipticality. We apply these tests under fixed experimental conditions similar to those in which other researchers have found ellipsoidal equi-discrimination contours. For these conditions, for any of the tests performed, we do not reject the hypothesis that equi-discrimination surfaces are ellipsoidal.     

Supplemental dietary biotin for prevention of lesions associated with aseptic subclinical laminitis (pododermatitis aseptica diffusa) in primiparous cows

OBJECTIVE: To evaluate, in primiparous cows, the effect of dietary biotin supplementation on severity of lesions of aseptic subclinical laminitis. ANIMALS: 100 primiparous cows in a 800-cow commercial dairy herd. PROCEDURE: Cows were assigned after calving to a biotin-supplemented (20 mg/head/d) or control group on an alternating basis. Digits 3 and 4 of the left forelimb and right hind limb were examined at a mean of 25, 108, and 293 days after parturition. Toe length, hoof angle, and heel depth were measured, and hooves were examined for solear hemorrhage, yellow solear discoloration, separation of the white line, and heel erosion. Serum and milk biotin concentrations were also measured. RESULTS: Serum biotin concentrations were significantly higher for supplemented than for control cows. During the second examination, prevalence of separation of the white line of digits 3 and 4 of the hind limb and digit 4 of the forelimb was lower for supplemented than for control cows. Mean decrease in heel depth between the first and third examinations was approximately twice as great for digit 4 of the forelimb and 4 times as great for digit 3 of the forelimb in supplemented, versus control, cows. Other differences were not found. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that supplemental dietary biotin may have a beneficial effect on hoof health in intensively managed primiparous dairy cows.     

Effects of photoisomers of cyclodiene insecticides on liver and microsomal cytochrome P450 in rats

The effects of seasonality and other temporal patterns on the occurrence of rotavirus diarrhoea were studied among hospitalised cases at Pune, India from July 1992 to June 1996. The well-accepted Box-Jenkins methodology based on modelling was employed for the analysis. This is the first presentation of such analysis for rotavirus diarrhoea. The model suggests strong influence of climatic changes on the incidence of the disease. Further study of weather parameters not only confirms that daily minimum temperature is the principal factor but also reveals that easterly wave, a characteristic feature of tropical weather, is useful in predicting the peak of hospital admissions and the geographical sequence of outbreaks of the disease in tropical India.     

Stable isotope breath tests

To assess the association of polymorphisms at the sulphonylurea receptor (SUR1) gene with the development of Type 2 diabetes mellitus, 456 subjects, 236 with Type 2 diabetes and 220 non-diabetic controls, were analysed for variants at exon 7, exon 22 and intron 24 of the SUR1 gene by the polymerase chain reaction and restriction fragment length polymorphism. The T761T substitution in exon 22 of the SUR1 gene was not found in either diabetic patients or non-diabetic controls. Both the exon 7 variant and the intron 24 variant were present in both groups at similar frequencies. No significant association was seen between either variant and obesity. Diabetic patients homozygous for the -3C allele of intron 24 had a higher ratio of positive family history than patients homozygous for the -3T allele (p = 0.03). We conclude that these polymorphisms are not major determinants of diabetes and obesity in the Japanese population.