Hepatic removal of two fractions of indocyanine green after bolus injection in anesthetized pigs

In the anesthetized pig, we studied the kinetics after intravenous bolus injection of two fractions of indocyanine green (ICG): the genuine ICGg (95-99% of total) and a degradation product, ICGdp (1-5%). Plasma concentrations were followed in the carotid artery and a hepatic vein. ICGg disappearance curves (n = 7) were biexponential with rate constants alpha = 0.189 +/- 0.021 min-1 and beta = 0.0356 +/- 0.0061 min-1. The hepatic extraction fraction was constant with time. A detailed mathematical analysis showed this to be in disagreement with the conventional assumption that the biexponential plasma disappearance curve is a result of backflux from the liver storage to plasma. In contrast, our observations were predicted by an alternative model assuming temporary extrahepatic, extravasal redistribution during first-order, one-way hepatic uptake. Nevertheless, when a large bolus of sulfobromophthalein (BSP) was injected 20 min after ICG, a net backflux of ICG could be demonstrated, presumably due to countertransport. Thus a sufficient description of ICGg kinetics must include the complex kinetic behavior of the hepatic membrane carrier involved. Mass spectrometry suggested that ICGdp is formed by two ICGg molecules. Plasma elimination of ICGdp was slower (alpha = 0.0094 +/- 0.0007 min-1). Analysis of the bile after bolus injection (n = 2) of ICGdp revealed two possible metabolites of ICGdp that were not found in urine. Since BSP injection did not alter the ICGdp disappearance curve, ICGdp is probably not taken up by the same hepatic membrane carrier as ICGg.

Fate of circulating amino-terminal propeptide of type III procollagen in conscious pigs

The amino-terminal propeptide of type III procollagen (PIIINP, M(r) 42,000) is a promising marker for the formation of type III collagen of granulation tissue in experimental and clinical studies. The disposal kinetics of circulating PIIINP is, however, almost unknown. In conscious pigs with a thoracic duct-venous shunt, 125I-labeled PIIINP was injected intravenously. The initial distribution volume was 2.2 liters, which was 1.7 times the plasma volume (P < 0.01). The disappearance curve was three-phased, with an initial steep decline (t1/2 58 min), followed by two slower phases (t1/2 239 min and 289 h). Consecutive gel filtrations showed that the initial slope of the plasma disappearance curve corresponded to the plasma clearance of the intact PIIINP. The initial plasma clearance was 26.5 ml plasma/min, whereas the urinary clearance was 8.7 ml plasma/min (P < 0.01). The other components of the plasma disappearance curve originated from the formation and disappearance of a high and a low molecular weight (MW) fraction as part of the degradation of PIIINP. The high MW fraction (approximately M(r) 90,000) was similar to a previously described, but not further characterized, PIIINP immunoreactive component. The existence of the low MW fraction (approximately M(r) 20,000) has not been reported before. The lymphatic recirculation of intact PIIINP was rapid, and the lymph-serum ratio was almost constant within 1 h of injection. We conclude that the t1/2 of circulating PIIINP is 58 min, that PIIINP escapes the circulation very quickly, and that the degradation of PIIINP includes at least two intermediary steps.

Disposal and distribution of rT3 in humans: a new double-tracer kinetic study

A satisfactory definition of reverse 3,3',5'-triiodothyronine (rT3) kinetics in humans cannot be obtained if the plasma disappearance curve of the injected labeled hormone is the only experimental data available; most of the kinetic parameters can only be bounded within ranges showing unacceptable variabilities. To gain additional experimental data a double-tracer approach is proposed. After simultaneous injection of [125I]rT3 and 131I the following three experimental curves were determined in plasma: 1) the disappearance of [125I]rT3, 2) the disappearance of 131I, and 3) the appearance of 125I generated in vivo from labeled rT3 degradation. Combined analysis of these three curves, based on a complex six-compartment model, was developed and applied to data obtained in a group of normal subjects. Through this new analysis, fractional disposal rates and fractional exchange rates between the plasma compartment and the periphery are uniquely determined. The main physiologically interesting information on the degradation of the hormone that emerges from these studies are 1) all degradative pathways of rT3 generate iodide, being in all cases the [125I]rT3 dose completely recovered as 125I in plasma; and 2) most rT3 is degraded (65–90%) in peripheral tissues rapidly exchanging with the plasma pool. The extended experimental base is not yet sufficient to compute unique values for production rate (PR) and body mass (Qt); the validity of estimates of PR and Qt is based on the assumption that injected [125I]rT3 is able to trace all rT3 peripherally produced (from thyroxine). The new approach yields ranges for PR and Qt (1.12–2.15 micrograms/h and 2.88–8.24 micrograms) much narrower than those computable from the [125I]rT3 disappearance curve only (1.12–5.07 micrograms/h for PR and 2.88-23.7 micrograms for Qt).

Clinical pharmacology of a novel diarylsulfonylurea anticancer agent.

LY186641 (diarylsulfonylurea, [DSU]) is a novel anticancer agent because of its unique diarylsulfonylurea chemical structure, broad-spectrum antisolid-tumor activity in preclinical models, presumed novel mechanism of action and preclinical toxicities of methemoglobinemia (Met Hgb) and decreased red blood cell (RBC) survival. In this study, the in vitro drug sensitivity of human tumors as well as clinical pharmacology and toxicology of DSU in patients with cancer were examined. DSU was administered orally, daily for 7 days with a 3-week treatment cycle. Dose-limiting toxicities were Met Hgb and RBC hemolysis. The maximum-tolerated dose was found to be 1,200 mg/m2/d for 7 days. In pharmacokinetic studies, DSU was found to have a prolonged serum half-life (approximately 30 hours) and a large area under the plasma disappearance curve (8,883.3 micrograms.hr/mL at 1,200 mg/m2/d). A partial remission was observed in one patient with refractory ovarian cancer. In conclusion, DSU can be safely administered to cancer patients and does display antitumor activity. Potential means of obviating the toxicities of this compound are discussed.

Hepatic clearance of rat plasma intestinal alkaline phosphatase

The mechanism and route of clearance of intestinal alkaline phosphatase from plasma have been studied in rats to define the magnitude of hepatic extraction and biliary excretion of the enzyme. Plasma clearance, tissue distribution, and biliary excretion of enzyme were followed after intravenous administration of physiological amounts of 125I-labeled rat intestinal alkaline phosphatase. The plasma disappearance curve was biphasic; the initial phase was rapid, during which 50% of injected enzyme was selectively extracted by the liver over 5 min. Less than 4% of total hepatic radioactivity was excreted into bile over 80 min; this was shown by chromatographic analysis to be degraded enzyme only. Rapid clearance of enzyme could be significantly slowed by injection of large amounts of mannan or N-acetylglucosamine-bovine serum albumin, but not by desialylated fetuin, demonstrating that clearance was probably mediated by mannose/N-acetylglucosamine-specific receptors. It is concluded that, under physiological conditions, rat plasma intestinal alkaline phosphatase is rapidly cleared from the circulation by the liver. However, biliary excretion of undergraded enzyme is negligible, and a physiologically significant enterohepatic circulation seems most unlikely.

Clearance and Non-Invasive Determination of the Hepatic Extraction of Indocyanine Green in Baboons and Man

1. The disposition of an intravenous bolus of indocyanine green (ICG) has been studied in healthy man and baboons using a novel analysis of a two compartment pharmacokinetic model. 2. This analysis enabled the hepatic extraction ratio (ER) of dye to be determined solely from the plasma disappearance curve, and the ER determined did not differ from that measured by hepatic vein catheterization. 3. When compared with clearance measured at steady state, the two compartment model gave a significantly more accurate determination of plasma clearance than did the conventional one compartment model. 4. It is concluded that, in health, liver blood flow may be calculated accurately and noninvasively after a single intravenous injection of ICG.

Effects of a Meal on Plasma Clearance of [14C]Glycocholic Acid and Indocyanine Green in Man

1. The fasting plasma disappearance curve of [14C]glycocholic acid after intravenous injection was compared in nine normal subjects with that obtained 100 min after a standard liquid test meal. 2. Plasma disappearance curves of indocyanine green were determined in 13 normal subjects under the same conditions. 3. Plasma clearances were significantly increased after the meal for both [14C]glycocholic acid (median 455 ml min−1 m−2, range 376–672 increased to 704, 528–1968; P < 0.01) and indocyanine green (359, 227–473 increased to 435, 358–985; P < 0.01). 4. Median initial volume of distribution was unaltered, but in four subjects it was greatly increased after the meal, although no alteration in plasma volume, measured with Evans blue dye, was observed. 5. The increased postprandial plasma clearance of glycocholic acid is probably due to an increase in liver blood flow, and suggests that in health this part of the enterohepatic circulation of bile acids also varies with meals.

OXYTOCIN DETERMINATION BY RADIOIMMUNOASSAY IN CATTLE

ABSTRACT A radioimmunoassay for oxytocin in cow plasma is described. Antisera were raised in rabbits against synthetic oxytocin coupled to bovine thyroglobulin. Iodinated oxytocin free of unlabelled oxytocin and most likely also free of diiodo-oxytocin was used as radioactive tracer. The tracer showed a high degree of purity, and was stable on storage. It could be used in the assay for 2–3 months. The assay showed very little crossreactivity with vasopressin. Acetone was used for the extraction of oxytocin from plasma as well as from standards made of synthetic oxytocin in pooled cow plasma. Inhibition curves obtained with plasma collected from cows at parturition were parallel to those obtained with the oxytocin standard preparation. The mean recovery of oxytocin added to cow plasma was 106 % (sd = 14). The within-assay coefficient of variation (CV) varied from 5.2 to 10.9 %, and the between-assay CV was in the order of 13 %. The assay sensitivity was 1 pg (0.5 μU) per tube, corresponding to 3 pg/ml plasma. Around the time of milking the plasma oxytocin profile showed a strong response to the preparation for milking, and a further effect releated to the attachment of the teat cups of the milking machine. Peak concentrations were in the range of 15–50 pg/ml. During parturition there was a peak of oxytocin (65 pg/ml) coinciding with the expulsion phase. After this peak levels decreased but remained measurably elevated until the expulsion of the placenta. The plasma disappearance curve for immunoreactive oxytocin after the infusion of 100 IU oxytocin over a period of 1 h showed two components with apparent half-lives of 7–9 and 25 min, respectively.

Compartment analysis of metabolism of chromium(III) in rats of various ages.

The metabolism of chromium(III) was studied in groups of female Wistar rats of various ages (35, 60, and 120 days) after a single intravenous injection of 51CrCl3 in trace amounts. In all the animals, the plasma disappearance curve could be adequately described by a sum of three exponential terms between 0 and 265 h postinjection. A three-compartment mammillary model is proposed that permits the description of Cr(III) metabolism in quantitative terms. The model defines compartment volumes, clearances by exchange, and clearances by excretion. The total excretory clearance is the sum of three components: urinary clearance (fu), fecal clearance (fd), and a residual clearance (fs), corresponding to an apparently irreversible deposition of chromium into long term body reservoirs. The parameters of the model are reported for each age group; when their values are expressed per 100 g of body wt, all the components of the excretory clearance decrease with age. In all cases elimination takes place primarily via the urine and fs accounts for 31-41% of the total excretory clearance. Consistent with the model, 51Cr was found to accumulate with time in several organs such as bone, kidney, spleen, and liver after a single intravenous injection of 51CrCl3.