Nondestructive Measurement of Retinal Glucose Transport and Consumption In Vivo Using NMR Spectroscopy

Abstract: The cellular events underlying various retinopathies are poorly understood but likely involve perturbation of retinal glucose metabolism. Current methods for assessing this metabolism are destructive, thus limiting longitudinal studies. We hypothesize that following an intravitreous injection, the clearance rate of a glucose analogue will be a nondestructive index of retinal glucose transport and metabolism in vivo. First, radiolabeled glucose analogues were injected into the vitreous. After 40 min, the dominant clearance path was posterior via the retina and was consistent with a facilitated transport mechanism. Next, either [6,6-²H₂]glucose or 3-deoxy-3-fluoro- d -glucose was injected into the vitreous of rabbit eyes, and the clearance rate of each analogue was determined over 40 min using, respectively, ²H or ¹⁹F NMR. These rates were interpreted as a function of the retinal glucose transport and consumption. From the NMR data, the rate of retinal glucose consumption was ∼16 times slower than the transport of glucose. These data demonstrate that NMR measurements of glucose analogue clearance rate from the vitreous can provide a nondestructive index of retinal glucose transport and consumption in vivo.     

A prospective randomised controlled clinical trial comparing somatostatin and vasopressin in controlling acute variceal haemorrhage.

Twenty two patients were entered into a randomised controlled clinical trial comparing the efficacy of somatostatin and vasopressin in controlling acute variceal haemorrhage. Somatostatin was significantly more successful in controlling acute variceal haemorrhage than vasopressin (p = 0.003). Furthermore, no complications were observed during treatment with somatostatin.     

Changing semantic factors in case selection: Russian evidence from the last two centuries

We present a corpus-based study of variation in case assignment of the direct object of negated verbs in Russian over the past 200 years. Superficially the system of case forms available over this relatively short period has remained largely the same, but the way in which certain cases are used has been radically altered. This is particularly apparent in the treatment of the direct object of negated verbs. We argue that various semantic factors have been involved in bringing about this change, and that the role and significance of these factors has been changing over the period under investigation. This has implications for our understanding of the role of semantics in case assignment.     

Partial amino acid sequence of a somatostatin receptor isolated from GH4C1 pituitary cells.

A somatostatin receptor isolated from GH4C1 rat pituitary tumor-derived cells was cleaved with cyanogen bromide or cyanogen bromide+trypsin to obtain sequenceable fragments. Five unique amino acid sequences ranging from 6 to 27 amino acid residues were obtained. The sequence was identical to sequence recently reported for one of two somatostatin receptors cloned from human pancreas [Yamada et al., (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 251-255] except for a single valine to isoleucine substitution. This is the first report of amino acid sequence from a purified somatostatin receptor.     

Separation of multiple forms of protein-bound metabolites of the carcinogenic hydrocarbons 3-methylcholanthrene and 7,12-dimethylbenz[a]anthracene from several rodent species

Our findings demonstrate that the carcinogenic hydrocarbons 7,12-dimethylbenz[a] anthracene (DMBA) and 3-methylcholanthrene (3-MCA) bind in multiple forms to the proteins of skin and lung tissue. These metabolites are freed from the proteins by treatment with Raney nickel, thus, the metabolites are most likely bound through cysteine or homocysteine. The numbers and the relative quantities of the bound metabolites vary greatly among the Fischer rat, the Syrian golden hamster, and 3 mouse strains. It is possible that the metabolites (which indicate a particular pathway of metabolic activation) correlate with species susceptibility to hydrocarbon carcinogenesis.     

The scopoletin assay for hydrogen peroxide. A review and a better method

Scopoletin, 7-hydroxy-6-methoxy-2H-1-benzopyran-2-one, a naturally occurring component in cotton leaf and citrus peel is a fluorescent substrate for peroxidase which has been used by many investigators for the determination of hydrogen peroxide concentration. The technical details of these investigations are application-specific and rather critical, making it difficult to apply the scopoletin assay to alternative systems without extensive modification. Although such factors as interfering substances and optimum conditions have been discussed in many publications, these discussions tend to be application-specific. The present paper attempts to provide a technical review of scopoletin applications, add a few new experimental observations, and discuss general parameters which must be carefully controlled for reliable results.     

Hydroxamic acids from the reaction of active acetaldehyde with aromatic nitroso compounds

α-Hydroxyethylthiamine (4) reacts with nitrosobenzene (5) to produce N-phenylacetohydroxamic acid (7). A mechanism for this reaction is proposed. The possibility that similar reactions can occur in vivo with the production of carcinogenic hydroxamic acids is discussed.