Disposition kinetics of human epidermal growth factor (hEGF1-53) and its truncated fragment (hEGF1-48) in rats.

Clearance of human epidermal growth factor (hEGF1-53) has been proposed to be mediated by a receptor pathway involving a typical cascade of ligand-receptor endocytosis and lysosomal degradation. Deletion of the C-terminal pentapeptide from hEGF1-53, which yields hEGF1-48, is known to be associated with a marked reduction in receptor binding. We defined the intravenous (iv)-bolus (acute exposure) and the iv-infusion (prolonged exposure) pharmacokinetics of hEGF1-53 and hEGF1-48 in rats to investigate the impact of the deletion of C-terminal pentapeptide on the EGF clearance using a validated, sensitive ELISA method for quantitation of the peptides in plasma. Both peptides at the low iv bolus dose of 10 micrograms/kg were cleared from plasma with unusually high clearances (CLtot: 128 +/- 31 ml/min/kg for hEGF1-53 and 168 +/- 47 ml/min/kg for hEGF1-48), which are virtually complete within 4-min postdose, and the difference in the overall pharmacokinetics is of minor significance. A 10-fold increase in bolus dose to 100 micrograms/kg decreased clearances 3- to 6-fold, indicating a nonlinear kinetics for both peptides; however, hEGF1-48 was cleared (52 +/- 11 ml/min/kg) 2.5-fold faster than hEGF1-53. A similar nonlinear kinetics was also noticed for both peptides when they were administered by a 2-hr iv infusion at 30 and 300 micrograms/kg doses. hEGF1-48 at the low and high infusion doses was cleared at 126 +/- 16 and 33.7 +/- 14.5 ml/min/kg, respectively, which are 4-fold greater than the corresponding clearance rates of hEGF1-53. These observations suggest that a) deletion of C-terminal pentapeptide is associated with a faster clearance of the growth factor and b) the receptor clearance pathway may be more sensitive to saturation with hEGF1-53 than with hEGF1-48 at low microgram dose levels. hEGF1-53 at the low infusion dose of 30 micrograms/kg was cleared (32.1 +/- 6.2 ml/min/kg) 4-fold slower in comparison with the low bolus dose of 10 micrograms/kg, indicating a remarkable injection mode-dependent disposition kinetics for hEGF1-53, which does not exist for hEGF1-48. The overall results suggest that deletion of C-terminal pentapeptide leads to faster clearance of the growth factor, and the degree of the impact of deletion of C-terminal pentapeptide on the global pharmacokinetics is also dependent on the length of exposure of the receptor to the ligand. The negative relationship between receptor binding and plasma clearance for the two peptides remains to be elucidated at the molecular and receptor levels.

Salivary estriol as an index to fetal wellbeing.

We adapted two commercially available kits for measuring serum estriol to use in assaying salivary estriol in the third trimester of pregnancy. Salivary estriol increases during gestation, as does unconjugated estriol in serum. With a meticulous collection protocol, fetal wellbeing can be monitored as successfully with saliva samples as with serum. A fetal demise was charted similarly by the salivary and the serum estriol assay. Inter- and intra-assay reproducibility (CV) of the saliva assay was 6.2%. Day-to-day CV, based on a fasting sample before breakfast but obtained 1 to 3 h after rising, was 14.8% (SD 5.8%). Values for salivary estriol obtained immediately after ingestion of food or drink dropped by 19.0% (SD 17.9%) and 32.1% (SD 21.9%), respectively, as compared with values determined immediately before intake of food or water.

Plasma estriol in the evaluation of third-trimester gestational age.

This study attempts to confirm previous reports of a clinically useful serum unconjugated estriol surge at 36 weeks' gestation. Although an apparently physiologic estriol surge occurred at 36 +/- 2.1 weeks in 25 of 32 patients, clinical reality makes weekly plasma sampling difficult. In individual cases, use of the "surge point" predicted gestational age within a 4-week range with only 66% accuracy, and potentially serious errors in dating occurred. Other biochemical (lecithin:sphingomyelin, phosphatidylglycerol) and sonographic methods are superior in resolving problems with dating gestational age in the third trimester.

Diurnal variations in unconjugated and total plasma estriol levels in late normal pregnancy.

Diurnal variations in plasma unconjugated and total estriol were assessed in 11 third-trimester subjects with uncomplicated pregnancies. Commercially available 125I-labeled radioimmunoassay kits were used. Total plasma estriols reach a nadir during the hours of sleep (400 and 700 hours) which exceeds the episodic fluctuations seen from day to day or during a given 90-minute period. Plasma unconjugated estriol fluctuations over 24 hours did not significantly exceed our previously reported episodic fluctuation of 15.6 +/- 8.2%. The data are interpreted as showing no circadian rhythm, but reflecting, in the case of total plasma estriols, an effect of improved renal clearance during hours of rest. Plasma unconjugated estriol emerges as the test of choice in the monitoring of high-risk pregnancies.

Plasma estriol vs. estrogen assays in 24-h urines as an index to fetal status.

Conventionally, urinary estrogens are measured to monitor fetal well-being in the third trimester of pregnancy. There are many theoretical and practical advantages to the use of recently introduced plasma estriol assays; consequently, we undertook to compare the results of a spectrophotometric assay for total urinary estrogen with values for plasma total and free (unconjugated) estriol obtained by radioimmunoassay with commercially available kits. The data correlate well, r = 0.70 for plasma total estriol with urinary estrogen (expressed as milligrams of estrogens per gram of creatinine [E/C]), r = 0.79 for plasma free estriol with E/C, and r = 0.71 between the two plasma values. Minute-to-minute fluctuations during 90 min and day-to-day fluctuations followed during five days suggest that fluctuations of up to +/- 45% are within the normal range (means +/- SD of the day-to-day fluctuations were 16.9 +/- 7.7% and 15.6+/- 8.2%). Turn-around time is a minimum of 29 h for the urinary estrogen assay, 4.5 h for the plasma total estriol, and 3 h for the plasma free estriol.

Evaluation of serum ionic calcium measurement in a general hospital population.

Direct measurement of ionic calcium was evaluated in light of conflicting reports concerning the correlation of ionic calcium with total calcium and ionic calcium as predicted from total calcium and serum protein. Ionic calcium in the sera of normo- hypo-, and hypercalcemic adult hospitalized patients was measured anaerobically using an Orion model 98-20 calcium flow-thorugh electrode. Good correlation (r = .77) was found with the calculated ionic calcium value derived from total protein and total calcium, using the McLean-Hastings nomogram. Good correlation was also present between the measured ionic and total calcium (r = .80). In view of these correlations, the introduction of serum ionic calcium measurements into the general hospital laboratory repertoire is of questionable value.