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Biomedical subjects

R M Perkins

Publications and source records attributed to R M Perkins.

At least 19 recordsLinked to original sources
PubMed2000

The use of buck and ram extenders and two packaging systems to cryopreserve aoudad (Ammotragus lervia) spermatozoa.

Because the aoudad has been hunted to near extinction, cryopreservation of their semen would be useful for DNA conservation and for the possible re-establishment of captive bred animals to their former ranges. This study was conducted to investigate the effectiveness of cryopreserving aoudad spermatozoa. Semen samples from four post-pubertal animals were collected using electro-ejaculation. Microscopic analysis was performed to assess the percentages of progressively and non-progressively motile spermatozoa as well as intact acrosomes in samples prior to freezing and post-thaw. Extended samples (0.2 mL) were frozen using 2 different extenders and packaging systems and stored in LN2 Post-thaw data were arcsine-transformed and analyzed using ANOVA, 2 x 2 factorial. Samples that were processed using the ram/straw method had a significantly higher percentage (P < 0.05) of spermatozoa with intact acrosomes than did any other system. In addition, samples that were processed with the buck/pellet system had significantly greater percentages (P < 0.05) of progressive and non-progressively motile spermatozoa than the samples processed using either extender and packaged in straws. This study illustrates that some aoudad spermatozoa may be cryopreserved using the extender/processing systems developed for the domestic buck and ram.

Animals↗
PubMed1993

Novel acyclonucleotides: synthesis and antiviral activity of alkenylphosphonic acid derivatives of purines and a pyrimidine.

A series of phosphonoalkenyl and (phosphonoalkenyl)oxy derivatives of purines and a pyrimidine were synthesized. These compounds are the first reported acyclonucleotides which incorporate the alpha,beta-unsaturated phosphonic acid moiety as the phosphate mimic and include compounds in which the acyclic substituent is attached to N-9 of a purine or N-1 of a pyrimidine by either a nitrogen-carbon or a nitrogen-oxygen bond. The phosphonoalkenyl-substituted compounds 7a-c, 8a-c, 9, 10, and 12 were prepared either by Mitsunobu coupling of alcohols with purine or pyrimidine derivatives or by alternative alkylations of the heterocyclic bases. The (phosphonoalkenyl) oxy derivatives 7d-g, 8d-g, and 11 were synthesized by coupling of alcohols with 9-hydroxypurines or a 1-hydroxypyrimidine under Mitsunobu conditions. The novel acyclonucleotides were tested for activity against herpes simplex types 1 and 2 (HSV-1 and HSV-2), varicella zoster virus (VZV), cytomegalovirus (CMV), visna virus, and human immunodeficiency virus type 1 (HIV-1). Guanine derivatives were moderately to extremely cytotoxic, but the adenines were less toxic to cells. At the concentrations tested, (Z)-isomers in the unbranched series had no activity against herpes viruses or HIV-1. (E)-9-[(4-Phosphonobut-3-enyl) oxy]adenine (7d) displayed selective activity against HIV-1, (E)-2,6-diamino-9-(4-phosphonobut-3-enyl) purine (9) showed selective antiretrovirus activity, and (E)-9-[2-(hydroxymethyl)-4-phosphonobut-3-enyl]adenine (7c) showed selective antiherpesvirus (VZV and CMV) activity.

Antiviral Agents↗
PubMed1992

Mode of antiviral action of penciclovir in MRC-5 cells infected with herpes simplex virus type 1 (HSV-1), HSV-2, and varicella-zoster virus.

The metabolism and mode of action of penciclovir [9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine; BRL 39123] were studied and compared with those of acyclovir. In uninfected MRC-5 cells, low concentrations of the triphosphates of penciclovir and acyclovir were occasionally just detectable, the limit of detection being about 1 pmol/10(6) cells. In contrast, in cells infected with either herpes simplex virus type 2 (HSV-2) or varicella-zoster virus (VZV), penciclovir was phosphorylated quickly to give high concentrations of the triphosphate ester. Following the removal of penciclovir from the culture medium, penciclovir-triphosphate remained trapped within the cells for a long time (half-lives, 20 and 7 h in HSV-2- and VZV-infected cells, respectively). In HSV-2-infected cells, acyclovir was phosphorylated to a lesser extent and the half-life of the triphosphate ester was only 1 h. We were unable to detect any phosphates of acyclovir in VZV-infected cells. (S)-Penciclovir-triphosphate inhibited HSV-1 and HSV-2 DNA polymerase competitively with dGTP, the Ki values being 8.5 and 5.8 microM, respectively, whereas for acyclovir-triphosphate, the Ki value was 0.07 microM for the two enzymes. Both compounds had relatively low levels of activity against the cellular DNA polymerase alpha, with Ki values of 175 and 3.8 microM, respectively. (S)-Penciclovir-triphosphate did inhibit DNA synthesis by HSV-2 DNA polymerase with a defined template-primer, although it was not an obligate chain terminator like acyclovir-triphosphate. These results provide a biochemical rationale for the highly selective and effective inhibition of HSV-2 and VZV DNA synthesis by penciclovir and for the greater activity of penciclovir than that of acyclovir when HSV-2-infected cells were treated for a short time.

Acyclovir↗
PubMed1990

Effect of paraxanthine on FFA mobilization after intravenous caffeine administration in humans.

Because it has previously been shown that it takes much more caffeine to cause fat mobilization in vitro than in vivo, it has been suggested that there may be an active metabolite working with caffeine causing an increase in lipolysis in vivo. To determine the relationship between the appearance of paraxanthine (caffeine's major dimethylxanthine metabolite) and free fatty acid (FFA) mobilization after intravenous caffeine administration, 10 men were studied at rest after receiving a dose of 4 mg/kg lean body mass. Venous blood samples were obtained before dosing and at minutes 5, 10, 15, 30, 45, 60, 90, 120, 150, and 180. Serum levels of FFA, glycerol, caffeine, and paraxanthine were determined in duplicate. Concentrations of FFA and glycerol were corrected for plasma volume changes. A high negative correlation was seen between decreases in caffeine and increases in FFA (r = -0.90) and a high positive correlation was seen between the appearance of paraxanthine and FFA (r = 0.93). It was concluded that paraxanthine may play a role in increased lipolysis after caffeine administration in humans.

Adult↗
PubMed1989

Mode of action of 9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine (BRL 39123) against herpes simplex virus in MRC-5 cells.

The metabolism and mode of action of 9-(4-hydroxy-3-hydroxymethylbut-1-yl)guanine (BRL 39123) were studied in herpes simplex virus type 1 (HSV-1)-infected and uninfected MRC-5 cells and compared with those of acyclovir. In uninfected cells incubated with 10 microM acyclonucleoside for 4 h, no phosphorylation of either BRL 39123 or acyclovir was detected. In contrast, in HSV-1-infected cells, both BRL 39123 and acyclovir were phosphorylated up to the triphosphate esters. Phosphorylation of BRL 39123 occurred much more rapidly and proceeded to a greater extent than did that of acyclovir. Furthermore, following the removal of acyclonucleoside from the culture medium, the intracellular triphosphate ester of BRL 39123 was much more stable than was that of acyclovir, the half-lives being about 10 and 0.7 h, respectively. BRL 39123 treatment effectively inhibited the formation of HSV-1 DNA in infected MRC-5 cells, 50% inhibitory concentrations of BRL 39123 and acyclovir being 0.04 microgram/ml (0.16 microM) and 0.15 microgram/ml (0.67 microM), respectively. In addition, BRL 39123 was shown to be more effective than acyclovir at inhibiting viral DNA synthesis following short treatment times, presumably reflecting the greater stability of BRL 39123 triphosphate. Neither BRL 39123 nor acyclovir inhibited cellular DNA synthesis in uninfected cells at concentrations of up to 100 micrograms/ml.

Acyclovir↗
PubMed1987

The effects of obesity and exercise on the pharmacokinetics of caffeine in lean and obese volunteers.

The effects of obesity, exercise, and the interaction of obesity and exercise were examined in 6 caffeine naive, untrained, nonsmoking, college males (3 lean (LV), 3 obese (OV]. Each subject received caffeine (oral, 5.83 mg X kg-1 lean body weight) or placebo (50 mg citrate) prior to 3 h of seated rest and prior to 90 min of treadmill walking (40% of their maximal aerobic power) followed by 90 min of seated recovery. Serum samples were collected at various times and analyzed for caffeine by HPLC. Pharmacokinetic analysis indicated that at rest, OV had a significantly higher absorption rate constant (Ka 0.0757 vs. 0.0397 min-1), lower elimination rate constant (Ke 0.0027 vs. 0.0045 min-1), and longer serum half-life (t1/2 4.37 vs. 2.59 h) in comparison to LV. In exercise, as well as at rest LV and OV had a large difference in the volume of distribution (43.2 vs. 101.1) (rest, 54.1 vs. 103.1). Exercise consistently resulted in a decrease in the maximal serum concentration of caffeine and the area under the curve in OV while having no consistent effect on LV. The interactive effects of obesity and exercise could not be dissociated. However, these results demonstrate that both obesity and exercise have modified the pharmacokinetics of caffeine.

Adult↗
PubMed1986

Effect of simple short term dietary control on urine electrolyte excretion in normal men.

Normal diet and a simple short term prescribed diet were compared with respect to mean excretion of urine electrolytes and the variability in these responses in 12 healthy male subjects. Urine was collected from 7 to 15 h (overnight) and 15 to 25 h (daytime) after the start of dietary control. Differences in mean responses were slight. For sodium and potassium excretion, however, there were tendencies for responses in subjects with high excretion on normal diet to decrease and for responses in those with low excretion on normal diet to increase towards the overall mean during the prescribed diet. The prescribed diet reduced markedly the variability in electrolyte responses and for log transformed data reductions in variability were statistically significant in the daytime urine collections. The results of this study have confirmed quantitatively the benefit of a short period of simple dietary control. The marked reduction in the variability of sodium and potassium excretion improves considerably the precision and sensitivity of studies of urine electrolyte composition.

Adult↗
PubMed1986

Variants of BALB/c 3T3 cells lacking complex gangliosides retain a fibronectin matrix and spread normally on fibronectin-coated substrates.

Evidence has accumulated that di- and trisialogangliosides are involved in the interaction of cells with fibronectin. We have therefore tested the ability of variants of BALB/c 3T3 deficient in such gangliosides to organize a fibronectin matrix and to spread on fibronectin-coated substrates. Whereas BALB/c 3T3 cells contained gangliosides GM3, GM1, and GD1a, direct chemical analysis showed that five out of six variants isolated contained no detectable GD1a. By the overlaying of thin layer chromatograms of cellular gangliosides with 125I-cholera toxin, these variants were also found to lack ganglioside GM1. In contrast, the sialogalactoprotein profile of these cells, analyzed using an 125I-ricin/SDS polyacrylamide gel overlay technique, was similar to that of the parent cell line. All variants organized an extensive fibronectin matrix comparable to that of BALB/c 3T3, as shown using either immunofluorescence or lactoperoxidase-catalyzed iodination. The variants could also spread on fibronectin-coated substrates and adopt a morphology similar to that of BALB/c 3T3 cells, with little or no difference in the concentration of fibronectin required for 50% cell spreading. Cell spreading of the variants was accompanied by the formation of focal contacts and microfilament bundles, in a manner closely resembling that seen with BALB/c 3T3 cells. Treatment of BALB/c 3T3 cells with neuraminidase, which converts much of the cellular GD1a to GM1, did not affect cell spreading on fibronectin. The results clearly demonstrate that complex gangliosides are not essential for retention of a fibronectin matrix or for spreading on fibronectin-coated substrates.

Actin Cytoskeleton↗
PubMed1986

Relationships of aerobic capacity and percent body fat with plasma free fatty acid following walking.

We investigated relationships of peak VO2 and percent body fat with postexercise plasma free fatty acid (FFA) and glycerol concentrations in 14 men using multiple-regression techniques. During 1 h of walking (36% of peak VO2), no significant differences in plasma-FFA response were attributed to either peak VO2 or percent body fat. However, individuals with higher peak VO2S tended to have greater elevations in plasma-glycerol concentration during exercise (p = 0.074). They also had greater peak FFA concentrations and FFA X glycerol(-1)-molar ratios immediately after exercise and faster subsequent clearing of excess FFA from the blood (p less than 0.05). Percent fat was not related to postexercise plasma glycerol, FFA, FFA X glycerol-1 responses. Differing postexercise FFA responses, as related to peak VO2, were due, not to varying rates of lipolysis but rather to different rates of FFA mobilization and utilization.

Adipose Tissue↗
PubMed1984

Relative potency of prorenoate potassium and spironolactone in attenuating diuretic induced hypokalaemia.

The plasma potassium responses to the aldosterone antagonists prorenoate K (10 mg/day and 40 mg/day) and spironolactone (25 mg/day and 100 mg/day) were compared following treatment for 11 days in combination with the diuretic metolazone (2.5 mg/day) in a double-blind crossover study in twelve healthy men. The best estimate of the potency of prorenoate K relative to spironolactone in attenuating metolazone induced hypokalaemia was 5.6 with 95% confidence limits 2.4-35.2. The method employed allowed a statistically valid quantitative comparison of the potassium sparing properties of the mineralocorticoid antagonists after repeated doses and may be useful in the preclinical evaluation of these drugs.

Adult↗
PubMed1983

Use of a bioassay in healthy men to evaluate diuretic-spironolactone combinations.

The plasma potassium responses to 1 week's treatment with metolazone 0.625 mg, 1.25 mg and 2.5 mg in combination with spironolactone 50 mg, and metolazone 2.5 alone were examined in a double-blind, crossover study in twelve healthy subjects. Spironolactone attenuated the hypokalaemia induced by metolazone--addition of spironolactone 50 mg to metolazone 2.5 mg raised plasma potassium by 0.18 mmol/l (P less than 0.025). In the presence of spironolactone, a linear log metolazone dose-plasma potassium response relationship (P less than 0.01) was demonstrated. Spironolactone was unable to compensate fully for metolazone's hypokalaemic effect although in combination with metolazone 0.625 mg and 1.25 mg, plasma potassium concentration was maintained close to pretreatment levels. The human bioassay employed provided conveniently quantitative information which allows the rational development of a fixed dose diuretic-spironolactone combination tablet.

Adult↗
PubMed1982

Lack of correlation between metastasis of human rectal carcinoma and the absence of stromal fibronectin.

In a retrospective study we have used an immunoperoxidase procedure to localize the glycoprotein fibronectin in human rectal carcinomas, concentrating on tumour invading thick-walled extramural veins. Fibronectin was present in 29 out of 38 cases, in connective tissue stroma, and was not in direct association with the tumour cells, except in areas of necrosis. We found no correlation between the presence or absence of stromal fibronectin and (1) the degree of cellular differentiation within the tumour, (2) tumour progression (Dukes' classification) (3) the subsequent development of metastases and (4) patient longevity. OUr results do not support the conclusions from in vitro studies (Smith et al., 1979) that the metastatic potential of carcinomas may be partly determined by the ability of tumour cells to synthesize pericellular fibronectin.

Adenocarcinoma↗
PubMed1982

Dose-response relationships for spironolactone at steady state.

The overnight urine electrolyte and plasma potassium responses to spironolactone (25, 50, 100, and 200 mg daily) at steady state were investigated in 11 healthy subjects after fludrocortisone challenge. For sodium excretion and urine log10 10 Na/K, log dose-response relationships were defined (P less than 0.001 in each case), but there was little evidence of dose-related influences on potassium excretion or plasma potassium. The findings confirm the limitations of the fludrocortisone model in evaluating the potassium-sparing properties of aldosterone antagonists at steady state and of the urine sodium; potassium ratio as an overall index of renal antimineralocorticoid activity.

Adult↗
PubMed1982

Comparison of prorenoate potassium and spironolactone after repeated doses and steady state plasma levels of active metabolites.

1 After repeated single daily doses, the aldosterone antagonists prorenoate potassium and spironolactone were compared with regard to renal antimineralocorticoid activity, plasma potassium concentration and steady state plasma levels of their active metabolites, prorenone and canrenone respectively, in a balanced crossover study of twelve healthy subjects. 2 Following challenge with the mineralocorticoid, fludrocortisone, best estimates of the potency of prorenoate potassium relative to spironolactone were 3.6 (95% confidence limits 1.6-10.4) for urinary sodium excretion and 3.4 (95% confidence limits 2.0-6.5) for urinary log10 10Na/K. Estimates with respect to urinary potassium excretion and plasma potassium concentration were imprecise, confirming the limitations of the fludrocortisone model in the evaluation of aldosterone antagonists at steady state. 3 Both compounds exhibited directly proportional relationships between daily dose and steady state plasma levels of active metabolites. The approximate mean terminal elimination half-life of prorenone at steady state was 32.6 h (range 18-80 h).

Adolescent↗
PubMed1982

Relative potency and structure activity relationships of aldosterone antagonists in healthy man: correlation with animal experience.

1 The renal antimineralocorticoid potency of single doses of thirteen compounds with properties in animals compatible with competitive aldosterone antagonism was compared to that of spironolactone in healthy men. 2 Twelve compounds showed significant activity when compared to placebo but only one, prorenoate potassium, was significantly more potent than spironolactone on a weight basis. 3 The results allowed ranking of the compounds in order of potency relative to spironolactone and general observations on structure activity relationships in man. 4 Animal bioassays and in vitro aldosterone binding studies are unreliable predictors of the human activity of competitive mineralocorticoid antagonists.

Animals↗
PubMed1982

Spironolactone dose-response relationships in healthy subjects.

1 The effect of single oral doses of spironolactone 25 mg, 50 mg, 100 mg, 200 mg, 400 mg, and placebo in reversing the urinary electrolyte changes induced by fludrocortisone between 2-10 h and 12-16 h after treatment was examined in healthy subjects. 2 In the two collection periods, there were statistically significant log linear dose-response relationships for sodium excretion (P less than 0.001), potassium excretion (P less than 0.001 and P less than 0.025 respectively) and log10 10 Na/K (P less than 0.001). 3 However, there was evidence that the log spironolactone dose-urinary sodium responses did not increase monotonically, while the relationship for urinary potassium appeared to enter the lower 'plateau' at doses between 100 mg and 200 mg, and when compared to placebo values, potassium excretion was not significantly depressed 12-16 h after treatment (P greater than 0.1). Thus, sodium and potassium responses were dissociated in dose producing maximal effect and in duration of activity, reinforcing the view that functions or the urinary sodium/potassium ratio alone cannot be considered an adequate description of renal antimineralocorticoid activity. 4 Dose-response relationships for all urinary electrolyte variables seem consistently steep and linear between 25 mg and 100 mg of spironolactone, suggesting that, in studies employing this model, the doses of spironolactone should be restricted to this range.

Adult↗