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R V Smith

Publications and source records attributed to R V Smith.

At least 127 records · Page 7Linked to original sources
PubMed1971

Nitrogenase activity in cell-free extracts of the blue-green alga, Anabaena cylindrica.

Cell-free extracts with high nitrogenase activity were prepared by sonic oscillation and French press treatment from the blue-gree alga Anabaena cylindrica. Extracts were prepared from cells grown on a 95% N(2)-5% CO(2) gas mixture followed by a period of nitrogen starvation under an atmosphere of 95% argon-5% CO(2). No increase in the specific activity of extracts was achieved by breaking heterocysts. Activity (assayed by acetylene reduction) was found to be dependent on adenosine triphosphate (ATP), an ATP-generating system, and a low-potential reductant. Na(2)S(2)O(2) employed as reductant supports higher rates of nitrogenase activity than reduced ferredoxin. The activity is associated with a small-particle fraction that can be sedimented by ultracentrifugation. In contrast to the particulate nitrogenase of Azotobacter, which is stable in air, the A. cylindrica nitrogenase is an oxygen sensitive as nitrogenase prepared from anaerobic bacteria.

Acetylene↗
PubMed1969

Metabolic hydroxylations of trans-stilbene.

1. A study was made of the hydroxylation of trans-stilbene in rabbits, guinea pigs and mice, as well as by rabbit liver microsomes. 2. In the rabbit in vivo, trans-stilbene is converted into 4-hydroxy-,4,4'-dihydroxy-,3-hydroxy-4-methoxy-and 4-hydroxy-3-methoxy-stilbene, and hydroxylation plays a more significant role in the metabolism of trans-stilbene than has previously been reported. 3. Investigation of the hydroxylation of 4-hydroxystilbene in the rabbit in vivo demonstrated its ready conversion into 4,4'-dihydroxystilbene and established its intermediacy in the formation of this compound and the methylated analogues of 3,4-dihydroxystilbene. 4. Hydroxylation of trans-stilbene in the guinea pig was found to follow a pattern similar, both qualitatively and quantitatively, to that in the rabbit. 5. Studies in the mouse revealed only limited yields of 4,4'-dihydroxystilbene. 6. Studies of the hydroxylation of trans-stilbene and 4-hydroxystilbene by rabbit liver microsomes located two of the reactions that occur with these compounds in vivo. 7. Work with a solubilized liver-microsomal preparation provided evidence that ;stilbene hydroxylase' activity is not completely lost on solubilization, thus allowing for future microsomal enzyme-isolation studies.

Animals↗
PubMedDate not supplied

Pharmacokinetics of furosemide after three different single oral doses.

Furosemide solution was orally administered to 21 healthy adult males to determine dose proportionality over the dose range used and the reproducibility of disposition following a repeated dose. Furosemide solution was given in doses of 20, 40, and 80 mg, with the 40 mg dose repeated once. Blood was collected for 12 hours post-dose and urine for 24 hours. The maximum plasma concentrations resulting from 20, 40, and 80 mg doses were significantly different (p less than 0.05). Dose normalized maximum concentrations for the 20 and 80 mg doses were significantly different (p less than 0.05). Mean time to Cpmax was 50 minutes, with no differences observed among doses. Plasma AUCs were significantly different (p less than 0.05) for 20, 40, and 80 mg. Dose normalized AUCs were not significantly different. Mean amounts of furosemide in urine (Xu) were 9.62, 16.7, and 32.0 mg for the 20, 40, and 80 mg doses, respectively. These amounts were significantly different (p less than 0.05); dose normalized amounts were not significantly different. Renal clearances of furosemide following the three doses were not significantly different. Regressions of Cpmax, AUC and Xu on dose were significant. There were no significant differences in Cpmax, tmax, AUC or Xu for 40 mg given on two separate days. Renal clearance of furosemide was statistically different for 40 mg given on two separate days, but the difference was not clinically significant. The pharmacokinetics of furosemide are linear over the dosage range studied. Furosemide 40 mg given on two separate days results in similar disposition parameters.

Administration, Oral↗
PubMedDate not supplied

Comparative bioavailability of furosemide from solution and 40 mg tablets with different dissolution characteristics following oral administration in normal men.

Furosemide tablets, with markedly different dissolution characteristics, and solution were orally administered to 21 healthy adult males to determine the effect of in vitro dissolution rate on in vivo bioavailability profiles. Furosemide 40 mg was given as Tablet A (fast dissolution characteristics), Tablet B (slow dissolution characteristics), and an aqueous solution. Both batches of tablets had identical formulae and were produced by a common process. The dissolution rate of the slower Tablet B was probably retarded by extension of the wet granulation time. Blood was collected for 12 h postdose and urine for 24 h. Peak plasma furosemide concentrations after the solution were significantly greater than after the tablets; there was no significant difference between the tablets. The time to peak occurred significantly earlier with the solution, with no significant difference between the tablets. Relative bioavailabilities of Tablet A and B were 89 per cent and 101 per cent, respectively, as determined by AUC, and 79 per cent and 84 per cent, respectively, as determined by urine recovery. These differences are not statistically significant. These results indicate that dissolution rate profiles of furosemide tablets may not be predictive of in vivo bioavailability.

Administration, Oral↗