Pharmacokinetics of naloxone in rats and in man: basis for its potency and short duration of action

Using a specific and sensitive radioimmunoassay, naloxone concentrations in the brains and sera of rats were measured at intervals for four hours following iv injection (5 mg/kg). Decrement curves of naloxone were compared with those after iv injection of morphine (5 mg/kg). Serum concentration of naloxone at 5 minutes was 1.45 +/- 0.1 mug/ml (mean +/- SE) and that of morphine was 1.0 +/- 0.08 mug/ml. Their serum half-lives from one to four hours were approximately the same, 30-40 minutes. With naloxone, the brain-serum concentration ratios ranged from 2.7 to 4.6. Concentration of naloxone in the brain declined parallel to that in the serum. However, with morphine the initial brain concentration was approximately one tenth that in the serum (0.096 +/- 0.04 mug/ml). The brain morphine concentration was sustained for one hour, while serum morphine concentrations declined from 1.0 to 0.19 mug/ml during this period. Two minutes after iv injection of naloxone HCl (0.4 mg) in nine healthy volunteers, the serum drug concentration was 0.01 +/- .001 mug/ml. At 5 minutes, 97 per cent of the administered dose was no longer found in the serum, the serum concentration being 0.004 +/- .0003 mug/ml. From 20 minutes to two hours after injection, the calculated mean serum half-life of naloxone was 64 minutes. These results suggest that the rapid penetrance of naloxone into the brain and the high brain-serum concentration ratio contribute to its rapid onset of action and potency as a narcotic antagonist. The rapid decline of naloxone concentration in the brain found in the animal model, in contrast to that of morphine, could be the basis for its relatively short duration of action.

Metabolic Conversion of l-Ascorbic Acid to Oxalic Acid in Oxalate-accumulating Plants

l-Ascorbic acid-1-(14)C and its oxidation product, dehydro-l-ascorbic acid, produced labeled oxalic acid in oxalate-accumulating plants such as spinach seedlings (Spinacia oleracea) and the detached leaves of woodsorrel (Oxalis stricta and O. oregana), shamrock (Oxalis adenopylla), and begonia (Begonia evansiana). In O. oregana, conversion occurred equally well in the presence or absence of light. This relationship between l-ascorbic acid metabolism and oxalic acid formation must be given careful consideration in attempts to explain oxalic accumulation in plants.

Stereoisomeric Characterization of Tartaric Acid Produced during l-Ascorbic Acid Metabolism in Plants

Labeled tartaric acids from Pelargonium crispum apices which had been fed l-ascorbic acid-6-(14)C and Vitis labrusca and Parthenocissus inserta tissues which had been fed l-ascorbic acid-1-(14)C were examined by chemical means to determine chiral configuration. In each instance, label was associated with (+)-tartaric acid.Similar experiments with labeled tartaric acid from P. crispum which had been labeled with d-glucose-1-(14)C or -6-(14)C led to the same result. No evidence was obtained for formation of labeled meso-tartaric acid in experiments described above. The recent suggestion of H. Ruffner and D. Rast (Z. Pflanzenphysiol. 73: 45-55, 1974) that conversion of l-ascorbic acid to tartaric acid in plants is a nonenzymatic process is re-examined in the light of present findings.

The diposi tion of morphine in surgical patients

The disposition of serum morphine following administration of 10 mg/70 kg was determined by a sensitive and specific radioimmunoassay in 31 anethetized surgical patients ranging in age from 23 to 75 yr. Following iv injection, 93 per cent of the morphine disappeared from the serum within 5 min. The early serum levels of the drug (2 min) correlated directly with the patients' ages (r equal to 0.63, p smaller than 0.01). Patient 23 to 50 yr of age averaged 0.29 mug/ml, whereas patients 51 to 75 ur of age averaged 70 percent higher, 0.49 mug/ml. The serum half-life between 10 and 240 min was independent of age and averaged about 2 hr after either iv or im administration. Following im admininstration, morphine was rapidly absorbed, with peak levels occurring within 10 to 20 min. The decline in morphine serum levels paralleled the decline in morphine analgesia and was coincident with the apperance of morphine glucuronide in the serum. These studies demonstrate the applicability and specificity of the radioimmunoassay for morphine and suggest that serum levels of morphine may be a useful and objective indicator of its pharmacologic activity.

Acupunctural analgesia? Evaluation by signal detection theory

Pain responses to noxious thermal stimulation decreased in the acupunctured arm of subjects as compared to the arm not treated with acupuncture; this result suggested that effective analgesia had been induced. However, sensory decision theory analysis of the data revealed no difference in discriminability. This failure to find a sensory (physiological) change strongly suggests that analgesia had not been induced. The sole effect of acupuncture was to cause the subjects to raise their pain criterion in response to the expectation that acture works.