J. Throck Watson

Effects of Caffeine on Plasma Renin Activity, Catecholamines and Blood Pressure

Using a double-blind, randomized, cross-over protocol, we studied the effect of a single dose of oral caffeine on plasma renin activity, catecholamines and cardiovascular control in nine healthy, young, non-coffee drinkers maintained in sodium balance throughout the study period. Caffeine (250 mg) or placebo was administered in a methylxanthine-free beverage to overnight-fasted supine subjects who had had no coffee, tea or cola in the previous three weeks. Caffeine increased plasma renin activity by 57 per cent, plasma norepinephrine by 75 per cent and plasma epinephrine by 207 per cent. Urinary normetanephrine and metanephrine were increased 52 per cent and 100 per cent respectively. Mean blood pressure rose 14/10 mm Hg one hour after caffeine ingestion. There was a slight fall and then a rise in heart rate. Plasma caffeine levels were usually maximal one hour after ingestion but there was considerable individual variation. A 20 per cent increase in respiratory rate correlated well with plasma caffeine levels. Under the conditions of study caffeine was a potent stimulator of plasma renin activity and adrenomedullary secretion. Whether habitual ingestion has similar effects remains to be determined.

Relation between plasma concentration of indomethacin and its effect on prostaglandin synthesis and platelet aggregation in man.

The dose and plasma levels of indomethacin correlated with inhibition of prostaglandin synthesis as measured both by urinary excretion of the major metabolite of prostaglandin E2 (PGE‐M) and by the release of prostaglandin E drom thrombin‐stimulated platelets. Considerable intersubject variability was observed in the suppression of PGE‐M excretion. In some patients 37.5 mg indomethacin daily, usually considered subtherapeutic, caused suppression. Maximal suppression (>90%) occurred in some after a daily dose of 75 mg, whereas 150 mg was required to achieve this level of inhibition in others. Suppression of the excretion of PGE‐M by 60% occurred when the end of the dosage interval plasma levels of indomethacin were in the range 0.05 to 0.3 µg/ml, which implies that a somewhat higher average steady‐state concentration during the dosage interval was required to achieve this effect. A similar degree of inhibition of the release of PGE2 on thrombin‐stimulated platelets was associated with the same range of plasma levels. Upon discontinuation of the drug, the levels of indomethacin in plasma decreased exponentially; inhibition of the release of PGE2 from platelets by indomethacin declined linearly with time and in parallel with the logarithm of the diminishing plasma levels.

Metabolism of linoleic and arachidonic acids in VX2 carcinoma tissue: Identification of monohydroxy octadecadienoic acids and monohydroxy eicosatetraenoic acids

The metabolism of arachidonic and linoleic acids by VX2 carcinoma tissue in vitro was determined. Prostaglandin E2 was the major metabolic product of arachidonic acid in the neoplastic tissue. Minor products accounting for 3- 8% of arachidonic acid metabolism were II-hydroxy-5, 8, 12, 14-eicosatetraenoic acid (II-HETE) and 15-hydroxy-5, 8, 11, 13-eicosatetraenoic acid (15-HETE). Linoleic acid was converted to a mixture of 9-hydroxy-10, 12-octadecadienoic acid (9-HODD) and 13-hydroxy-9, 11-octadecadienoic acid (13-HODD). The conversion of linoleic acid to monohydroxy C-18 fatty acids varied from 40-80% 9-HODD and 20-60% 13-HODD in tumor tissue harvested from different animals. The quantity of monohydroxy C-18 fatty acids biosynthesized by VX2 carcinoma tissue from endogenous linoleic acid equals or exceeds that of prostaglandin E2 biosynthesis from endogenous arachidonic acid. The presence of a hydroxyl group adjacent to a conjugated diene suggest that the monohydroxy C-18 and monohydroxy C-20 fatty acids were formed via the action of lipoxygenase-like enzymes. These lipoxygenase-like reactions are inhibited by indomethacin in a concentration-dependent fashion similar to the inhibition of prostaglandin E2 biosynthesis. The enzymes catalyzing the lipoxygenase-like reactions of linoleic and arachidonic acids are localized in the microsomal fraction of VX2 carcinoma tissue. These data suggest that the lipoxygenase-like reactions are catalyzed by fatty acid cyclooxygenase and that there are two major pathways of fatty acid cyclooxygenase metabolism of polyenoic fatty acids in the neoplastic tissue. One pathway involves the formation of prostaglandin E2 via cyclic endoperoxy intermediates. The second pathway involves the formation of monohydroxy C-18 fatty acids from linoleic acid via lipoxygenase-like reactions.

Biomedical Applications of Selected Ion Monitoring

Abstract In 1961 Henneberg [1] employed selected ion monitoring (SIM) to study hydrocarbons eluting from a gas chromatographic column, and in 1966 the first biological application was reported by Sweeley, Elliott, Fries, and Ryhage [2]. Since these efforts and the early impetus given by Hammar, Holmstedt, and co-workers [3–6], SIM has found widespread application in biological, medicinal, and environmental research. Recent review articles have described ion monitoring work with magnetic sector instruments [7,8,8a,8b], quadrupole instruments [9], and time-of-flight instruments [19]. These articles provide comprehensive coverage of applications through 1972. This review emphasizes medicinal and biological applications through 1973 and attempts to evaluate current methods and recent developments.

Quantitative determination of prostaglandins A, B and E in the sub-nanogram range☆

Abstract Conversion of prostaglandin E(PGE) into the methyl ester, 15-trimethylsilyl ether of either PGA or PGB, makes possible the estimation of PGE in the sub-nanogram range, using vapor-phase analysis. PGE methyl ester can be efficiently converted at sub-nanogram levels to the TMS derivative of PGA by treatment with N,O,- bis -trimethylsilylacetamide in pyridine. The well-known, base-catalysed dehydration and rearrangement of PGE to PGB can similarly be achieved using sub-nanogram levels of prostaglandin. The methyl ester, trimethylsilyl ethers of PGA or PGB are shown to possess excellent properties for vapor-phase analysis, presenting minimal difficulties due to adsorption or thermal degradation, and have mass spectra characterized by only one or two predominant ions, facilitating their quantification into the sub-nanogram range, using mass spectrometry. Quantitative determination, with improved sensitivity into the sub-nanogram range of the derivative of PGB, has also been achieved using the electron capture detector. The same system can be applied to the estimation of PGA in the low nanogram range. These derivatives and analytical methods have the potential to provide quantitative estimation, with excellent sensitivity and specificity, of 9-keto-prostaglandins at low levels in biological samples.

Effects of a False Neurotransmitter, p-Hydroxynorephedrine, on the Function of Adrenergic Neurons in Hypertensive Patients

Previous studies have shown that amphetamine and p-hydroxyamphetamine impair adrenergic transmission, and it has been suggested that this effect is mediated by an active metabolite, p-hydroxynorephedrine (PHN). Studies in experimental animals have shown that PHN can deplete and substitute for norepinephrine (NE) in the transmitter pool, thus meeting the criteria of a false neurotransmitter. The pharmacologic effects of PHN on adrenergic function and NE synthesis were studied in eight hypertensive patients and compared with placebo. Mean erect and supine blood pressure (BP) decreased 22/14 and 9/6 mm Hg, respectively, during PHN 600 mg daily. The post-Valsalva diastolic overshoot was abolished. The pressor sensitivity to tyramine decreased whereas the pressor response to NE was enhanced. A mild natriuresis occurred. The 24 h urinary excretion of catecholamines and catecholamine metabolites during the administration of PHN compared with placebo changed as follows: vanillylmandelic acid (VMA), 42% decrease; NE. 42% decrease; normetanephrine (NM), 400% increase: metanephrine, unchanged; dopamine, 40% decrease; while homovanillic acid was unchanged. The sum of VMA, NE, and NM decreased 23%. The posttreatment urinary excretion of PHN was biexponential with first and second phase half-lives of 13 and 55 h. respectively. The time of the second phase closely approximated the recovery of the changes in BP and excretion of VMA. No effects of PHN on the central nervous system were observed. These studies show that PHN acts peripherally to interfere with adrenergic function and NE synthesis in hypertensive patients with a resultant decrease in BP.

Mass spectrometric methods of isotope determination

Although there are several analytical techniques for determining the isotopic composition of a sample, combined gas chromatography—mass spectrometry (GC—MS) is often the most suitable for analysis of samples of biological origin (Watson, 1976). For example, biological samples are rarely pure (even after extensive sample processing) and the biologically active component may represent only a trace constituent of the total sample. The combination of a separation technique with an identification technique in GC—MS permits a complex mixture to be separated in the time domain so that characteristic mass spectra can be obtained from picomole to nanomole quantities of sample depending on the mode of instrument operation.