The pharmacokinetics and effects of a long-acting preparation of superoxide dismutase (PC-SOD) in man.

AIM: To study the pharmacokinetics (PK), safety and tolerability of single rising doses up to 80 mg of superoxide dismutase covalently linked to lecithin (PC-SOD) in healthy White volunteers. METHODS: This double-blind, placebo-controlled, four-period cross-over study was performed in eight healthy volunteers (four male/four female). Three doses of PC-SOD (20, 40 and 80 mg) and placebo were administered intravenously in randomized order. Serum and urinary PC-SOD concentrations were measured predose and up to 96 h after dosing. In addition to standard safety measurements, the urinary excretion of N-acetyl-beta-glucosaminidase, alpha-glutathione S-transferase (alpha-GST) and pi-GST was measured to evaluate renal function. The PK of PC-SOD was analysed using noncompartmental and compartmental methods. RESULTS: All treatments were well tolerated, and no obvious relationship between adverse events and treatment was observed. No effects of PC-SOD on renal function could be detected. Dose normalized C(max) and AUC were not different between the different dosages, indicating linearity of plasma concentrations with dose. Estimated PC-SOD clearance was 2.54 ml min(-1)[95% confidence interval (CI) 2.07, 2.83]. The terminal half-life was estimated to be 1.54 days (95% CI 0.93, 2.15). SOD activity was elevated above baseline for 19 +/- 6 h after the 80-mg dose. CONCLUSIONS: Single intravenous administrations of PC-SOD in doses up to 80 mg were well tolerated in healthy White male and female volunteers. With the doses used, SOD activity was linearly related to the dose; after the 80-mg dose it was present for an appreciable period. These findings suggest that it is worthwhile to investigate PC-SOD in clinical conditions characterized by a high radical overload.

Plasma amino acid ratios related to brain serotonin synthesis in response to food intake in bulimia nervosa.

Fifteen bulimic women (BN) and 19 healthy female controls (CO) were studied. The subjects were cross-over treated with either fluoxetine (FXT) or placebo during 4 days. They received, in randomized order, a breakfast containing pure carbohydrate (CHO) or a protein-rich (PROT) breakfast following day 3 and 4 of each treatment period. Twenty-nine different food items were offered for lunch. The fasting serum glucose and insulin concentrations and the fasting plasma tryptophan (Trp)/large neutral amino acid (LNAA) ratio were slightly higher in BN. The changes of these metabolic parameters in response to a CHO or PROT breakfast were similar in both groups. Across breakfast type, the plasma (Trp)/(LNAA) ratio at 120 min after breakfast was higher in BN. Total caloric intake at lunchtime was less in BN. In CO, less carbohydrate was selected at lunchtime following the CHO breakfast, an effect that was abolished by FXT. Breakfast type or FXT did not have any apparent effect on food intake at lunchtime in BN. This might indicate that bulimic subjects are less sensitive to serotoninergic stimuli than control subjects.

Grapefruit juice and cimetidine inhibit stereoselective metabolism of nitrendipine in humans.

The effects of grapefruit juice (150 ml at -15, -10, -1/4, +5, and +10 hours) and cimetidine (200 mg at the same times) on the stereoselective pharmacokinetics and effects of 20 mg oral racemic nitrendipine were investigated in a placebo-controlled crossover study in nine healthy men. In all subjects the AUC of racemic nitrendipine was increased by grapefruit juice (mean increase 106%; 95% confidence interval 64% to 158%) and cimetidine treatment (+154%; 95% confidence interval 77% to 265%). Comparable results were obtained for the peak plasma drug concentration and for both parameters of (S)- and (R)-nitrendipine. There were highly significant differences in the area under the concentration-time curve and peak plasma drug concentration between enantiomers within all treatments. Grapefruit juice had no effect on this stereoselectivity, but cimetidine increased the mean S/R ratio of areas under the curve (2.25) by 20% (95% confidence interval 12% to 29%) compared with placebo treatment (1.89). Half-lives and time to reach peak concentration of the enantiomers were not different within and between treatments. There were no consistent effects on blood pressure with all treatments, but in most subjects there was a small temporary increase in heart rate after intake of nitrendipine. Grapefruit juice and cimetidine did not affect these hemodynamic parameters and did not cause additional adverse effects.

A comparison of the sensitivities of adaptive tracking, eye movement analysis and visual analog lines to the effects of incremental doses of temazepam in healthy volunteers.

The effects of single oral doses of 5, 10, and 20 mg temazepam were evaluated with the adaptive tracking test, analysis of smooth-pursuit and saccadic eye movements, and visual analog lines in a placebo-controlled, double-blind, crossover experiment with 12 healthy volunteers. Pharmacodynamic testing was performed until 10 hours and pharmacokinetics were evaluated until 24 hours. Temazepam, 20 mg, caused effects in all tests, with peak effects occurring at 30 minutes. The 10 mg dose caused effects on saccadic eye movements and subjective scores of alertness, whereas 5 mg temazepam was detected only by analysis of saccadic eye movements. Linear relationships between plasma concentrations and effects were found in nine subjects for saccadic peak velocity and eight subjects for subjective scores of alertness. The results of this study demonstrate manifest differences in the sensitivities of performance tests and stress the importance of validation of methods when effects of drugs on human performance are studied.

Effects of temazepam on saccadic eye movements: concentration-effect relationships in individual volunteers.

Saccadic eye movements were analyzed after single oral doses of 20 mg temazepam and placebo in a randomized, double-blind crossover study in eight healthy volunteers. For an optimal evaluation of concentration-effect relationships, 18 blood samples and 43 effect measures were obtained over 33 1/2 hours. After placebo, saccadic peak velocity decreased within the first hour, with average values remaining 6.2% to 12.1% below baseline up to 15 hours after intake. After temazepam, significant changes in peak velocity occurred for 5 hours, with maximum decreases averaging 29.2% (95% confidence interval, 10.0 to 37.2). The apparent duration of effects ranged from 3 to 9 hours in individual subjects. Linear concentration-effect relationships were demonstrated for peak velocity, with individual slopes ranging from -0.11 to -0.46 deg/sec.(ng/ml)-1 (average r = -0.82, all p < 0.01). Differences in protein binding of temazepam did not account for the approximate fourfold variability in individual sensitivities to temazepam. By increasing the frequency of measurements, the accuracy of pharmacodynamic evaluations was clearly enhanced in this study.

Effects of intravenous temazepam. I. Saccadic eye movements and electroencephalogram after fast and slow infusion to pseudo steady state.

OBJECTIVE: To study the pharmacodynamic effects of intravenous temazepam after different infusion rates to pseudo steady-state concentrations. METHODS: This was a randomized, double-blind, placebo-controlled crossover study in an academic department of clinical pharmacology. Subjects were nine healthy volunteers. A computerized infusion pump was used to obtain target plasma concentrations of temazepam after 30 or 120 minutes and to maintain these levels for 2 hours. A vehicle infusion, similar to the 30-minute (fast) infusion was used as a placebo control. Infusion schedules were based on data obtained from individual subjects after infusion of 0.4 mg/kg temazepam in 30 minutes. Target plasma concentrations were chosen to induce subhypnotic effects and averaged (+/- SD) 597 +/- 123 ng/ml. Venous plasma concentrations of temazepam were measured by HPLC. Free fractions of temazepam were assessed at the start of the pseudo steady-state concentration intervals. Electroencephalogram alpha and beta amplitudes, saccadic peak velocity, and saccadic latency were used as pharmacodynamic parameters. RESULTS: The rate of change of plasma concentrations averaged 21 +/- 4 ng/ml.min-1 during fast infusion and 5 +/- 1 ng/ml.min-1 during slow infusion of temazepam. Average pseudo steady-state concentrations were 639 +/- 132 ng/ml after fast infusion and 629 +/- 133 ng/ml after slow infusion. At the onset of pseudo steady-state concentration intervals the average free fractions of temazepam were 44% (95% confidence interval, 19% to 61%) lower for slow than for fast infusions. Compared with the slow infusion, electroencephalogram beta amplitudes were significantly larger during the first 30 minutes of pseudo steady-state concentration after fast infusion of temazepam. No significant differences were found for the other parameters. There was a slight decline of temazepam effects during the pseudo steady-state concentration intervals for all parameters after the fast infusion and for saccadic peak velocity and saccadic latency after the slow infusion. CONCLUSIONS: The pharmacodynamic effects of intravenous temazepam may depend partly on the rate of administration. Differences in pharmacodynamic effects after fast and slow infusions could be caused by changes in protein binding over time.

Effects of intravenous temazepam. II. A study of the long-term reproducibility of pharmacokinetics, pharmacodynamics, and concentration-effect parameters.

OBJECTIVE: To evaluate the long-term reproducibility of pharmacokinetic, pharmacodynamic, and concentration-effect parameters after intravenous administration of temazepam. METHODS: Nine healthy volunteers were studied. Temazepam, 0.4 mg/kg, was infused intravenously for 30 minutes on two occasions 6 months apart. Venous plasma concentrations of temazepam were measured by HPLC in samples obtained between 0 and 24 hours. Pharmacodynamic effects were evaluated up to 8 hours for saccadic peak velocity and electroencephalogram (EEG) beta amplitudes. Subjects' state and trait anxiety were assessed by use of the Spielberger anxiety inventory. RESULTS: Significant correlations between occasions were found for area under the plasma concentration-time curve (AUC) values (r = 0.91; p < 0.01) but not for maximum concentration and half-life. Significant correlations were also found for area under the effect-time curve (AUEC) values of peak velocity (r = 0.88; p < 0.01) but not for peak velocity (r = 0.48; p > 0.05). Significant differences between the slopes of concentration effect plots on different occasions were observed in two subjects for EEG beta and in three subjects for peak velocity, with one subject showing a similar change for both parameters. Trait anxiety scores were higher on the first occasion (33 +/- 7) than on the second occasion (29 +/- 7; p < 0.01). A negative correlation was found between trait anxiety scores and the slopes of concentration-effect plots for peak velocity (r = -0.63; p < 0.01). CONCLUSIONS: For AUC and AUEC values the results indicate a reasonable long-term reproducibility of differences between subjects in the pharmacokinetics and pharmacodynamics of temazepam. However, there were limitations to the predictive value of derived concentration-effect parameters.

Effect of isotretinoin on endogenous tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor 1 (PAI-1) in humans.

The effect of isotretinoin on fibrinolysis was investigated in 10 healthy, male volunteers in a randomized, double-blind, crossover-designed study. Isotretinoin (40 mg) was administered in the morning and in the evening for 5 days. t-PA, u-PA and PAI-1 antigen and activity in plasma were measured every morning at 9 a.m. on days 1 to 4 and every 3 hours over 24 hours on day 5. Isotretinoin treatment had no significant stimulatory effect on endogenous t-PA antigen and activity in morning plasma samples nor on their circadian variation. Also, u-PA antigen levels did not change after isotretinoin treatment. Mean PAI-1 antigen and PAI activity in 9 a.m. plasma samples were non-significantly higher during isotretinoin than during placebo treatment. After treatment with isotretinoin a significant rise of fasting triglyceride plasma levels was observed as compared to placebo. The study shows that isotretinoin has no clinically significant effect on endogenous fibrinolysis.

Pronounced effects of the combination of a new thromboxane antagonist (GR32191) and heparin on bleeding time in man.

Potential pharmacokinetic and pharmacodynamic interactions between two oral doses of GR32191 (40 and 80 mg), a new thromboxane antagonist, and heparin (5,000 IU bolus + 1,000 IU/h for 3 h) were studied in eighteen healthy male volunteers using two separate double-blind, randomised, placebo-controlled, cross-over studies. Mean (range) bleeding time values were 8.4 min (7.5-9.7) during heparin/placebo, 12.1 min (9.2-18.6) (GR32191/placebo) and 16.3 min (11.5-21.4) (GR32191/heparin) in the 40 mg study, while these values were 8.7 min (5.5-15.5), 16.0 min (9.3 - greater than 36.0) and 23.8 min (10.7 - greater than 36.0), respectively in the 80 mg study. Compared to screening values, the combination of 80 mg of GR32191 and heparin had a greater effect on the bleeding time than the sum of the prolongations after the separate treatments (p = 0.05). In the 40 mg study this was not the case. Pharmacokinetics of heparin (as assessed by plasma anti-Xa and antithrombin activity) and GR32191 were unaltered during co-administration of the two drugs. GR32191 did not influence the effects of heparin on APTT. Heparin slightly diminished the inhibition of collagen induced platelet aggregation by 80 mg of GR32191 and the U-46619 (thromboxane A2-mimetic) induced platelet aggregation remained unchanged. Overall fibrinolytic activity (as evaluated by the fibrin plate test) was similar during all three treatments in the study with 80 mg. The combination of 80 mg of GR32191 and heparin caused a prolongation of the bleeding time which was more than expected on the basis of their individual effects.

Diurnal rhythm in anticoagulant effect of heparin during a low dose constant rate infusion. A study in healthy volunteers.

The objective of the study was to investigate possible diurnal rhythms in coagulation tests during a continuous intravenous infusion of unfractionated heparin. Six volunteers participated in the study, which was divided in a treatment (500 U heparin/h for 30 h) and a control experiment. Under basal conditions, no rhythm was found in coagulation tests. During heparin treatment, APTT, thrombin clotting time and anti-Xa activity showed a greater anticoagulant effect at night, with a striking decrease in the morning. In a search for the explanation of this phenomenon we looked for diurnal variations in the urinary excretion of heparin, in the plasma concentrations of antithrombin III and platelet factor 4, and in the effect of heparin added to the plasma samples in vitro. None of these studies provided the explanation.

Liver blood flow as a major determinant of the clearance of recombinant human tissue-type plasminogen activator.

The influence of changes in liver blood flow on the clearance of rt-PA was studied both in healthy subjects and in a perfused rat liver model. Liver blood flow in healthy subjects was documented indirectly by the clearance of indocyanine green (ICG). Exercise reduced liver blood flow on average by 57% with a 95% confidence interval (95% CI) ranging from 51% to 62% (n = 5) and increased plasma levels of rt-PA activity (after an i.v. infusion of 18 mg of rt-PA over 120 min) by 119% (95% CI, 58%-203%) and rt-PA antigen by 91% (95% CI, 30%-140%). In the perfused rat liver model it was shown that halving or doubling of the physiological flow rate of a perfusate, containing rt-PA caused a proportional change in the clearance of rt-PA, while the extraction of rt-PA by the liver remained similar. In conclusion, liver blood flow is a major determinant of the clearance of rt-PA. This may have important implications for dosage of rt-PA in patients with myocardial infarction.

Dose-related effects of motilin on proximal gastrointestinal motility.

AIM: To assess non-invasively the dose-response relations for the effects of exogenous motilin on antrum contraction frequency, gall-bladder volume and gastric myoelectrical activity. METHODS: In a double-blind, randomized, placebo-controlled, five-way crossover study, 10 fasted healthy volunteers were infused intravenously with synthetic human motilin (0.5, 1, 2 and 4 pmol x min/kg) or placebo for 60 min. Gall-bladder volume and antrum contractions were assessed by ultrasonography and gastric myoelectrical activity by electrogastrography. Motilin concentrations were measured using a radioimmunoassay. RESULTS: Baseline plasma motilin levels (60 pmol/L) were similar for all treatments. Motilin levels increased upon the start of infusion and rapidly returned to baseline after cessation of the infusion. At motilin doses of 2 and 4 pmol.min/kg, the antrum contraction frequency was significantly augmented, with maximum differences of two contractions per 2-min interval compared to placebo, while no changes in gastric myoelectrical activity were observed. Changes in gall-bladder volume were not significantly different for any of the motilin doses compared to placebo. CONCLUSIONS: Motilin increased antrum contraction frequency, whereas no effect on gastric myoelectrical activity was observed. Antrum contraction frequency appears to be a useful biomarker for motilin efficacy, and motilin doses of 2 and 4 pmol x min/kg were equally effective.

Pharmacodynamic interactions of diazepam and intravenous alcohol at pseudo steady state.

Pharmacodynamic interactions of low doses of diazepam and alcohol were investigated in a double blind, randomised, 2 x 2 factorial, cross-over study in eight healthy volunteers. Alcohol or glucose 5% were administered intravenously at rates calculated to maintain breath alcohol levels of 0.5 g/l from 1.5 to 5.5 h after starting the alcohol infusion. Diazepam 5 mg or placebo were administered orally at 1.5 h. Evaluation of pharmacodynamic interactions was performed for the average results of tests performed at 2, 3.5 and 5 h. Plasma concentrations of (desmethyl-) diazepam and breath alcohol levels were measured for pharmacokinetic analysis. Breath alcohol reached pseudo steady state levels of 0.38 g/l (range: 0.24-0.57) after alcohol alone and 0.37 g/l (range: 0.27-0.52) in combination with diazepam. Alcohol effects were demonstrated for latency of saccadic eye movements, smooth pursuit eye movements and subjective drug effects. Diazepam impaired smooth pursuit and saccadic eye movements, adaptive tracking, digit symbol substitution and body sway. The effects of combined alcohol and diazepam were mostly additive without significant synergistic interactions. However, in two subjects large supra-additive effects occurred at 3.5 h following alcohol+diazepam, which were not explained by increased drug levels. The design and methods used in this study proved advantageous in evaluating low dose pharmacodynamic interactions. Despite the absence of significant synergistic interactions, unanticipated impairment of performance may occur in susceptible individuals when taking combined low doses of alcohol and diazepam.

Intraindividual variability in nifedipine pharmacokinetics and effects in healthy subjects.

The intraindividual variability in pharmacokinetics and effects of oral nifedipine (10 mg), administered with 1 week intervals, was investigated in twelve young healthy subjects. The population estimate of the coefficient of intraindividual variability (CVw) in AUC of nifedipine (13%) was much smaller than the pure between-subject variability (CVb 54%). The long-term (1 1/2 year) intraindividual variability was much larger than the short-term variability. Maximum changes from baseline-values of mean blood pressure (SBP -5%, DBP -4%) and mean heart rate (HR +21%) were small. Individual maximum changes in systolic blood pressure, diastolic blood pressure, and heart rate (SBP, DBP, and HR) and areas under effect curves were highly variable (CVw 34-250%, CVb 8-88%). For most subjects a significant positive linear relation was observed between nifedipine plasma concentration and the change in HR (mean r = 0.63). The CVw in slope (106%) and intercept (685%) were even larger than the high CVb in these parameters (38% and 252%). Changes in blood pressure were not significantly related to nifedipine plasma concentrations within these healthy subjects. The small intraindividual variability in nifedipine pharmacokinetics allows crossover studies to detect pharmacokinetic relationships between nifedipine and other dihydropyridine calcium entry blockers.

The effects of clonazepam and vigabatrin in hyperekplexia.

Hyperekplexia is an autosomal dominant disorder caused by a point mutation in the alpha1 subunit of the glycine receptor, characterized by excessive startle responses followed by temporary generalized stiffness. Clonazepam, effective in open case studies, potentiates, through unknown mechanisms, the neurotransmitter gamma-aminobutyric acid (GABA). Vigabatrin increases GABA by inhibition of the GABA catabolic enzyme GABA-transaminase. Effects of clonazepam (1 mg for 1 day) and vigabatrin (1000 mg per day for 5 days) were investigated in a double-blind placebo-controlled cross-over study in 4 patients with hyperekplexia. The pharmacodynamic parameters were startle reflexes, studied 3 times during the day. At each time, 2 trains of 10 auditive stimuli (113 dB) were given at intervals of 10 and 60 s. Startle movements were quantified with summed areas of EMG-bursts of the orbicularis oculi, sternocleidomastoid, biceps and thenar muscles. The degrees of stiffness and drowsiness were quantified with visual analogue scores (VAS) 10 times during the day, by both the patient and the observer. Clonazepam, but not vigabatrin, reduced startle activity significantly in both paradigms. The degree of stiffness and drowsiness was not significantly influenced by either drug.

The Neurotoxicity Scale: the validity of a patient-based scale, assessing neurotoxicity.

The validity of a patient-based scale, presumably measuring adverse effects of drugs on cognitive function, was examined in a normal volunteer study. Thirty subjects were randomly assigned to placebo or one of two doses of a benzodiazepine, temazepam (10 mg and 20 mg), in a double-blind placebo-controlled parallel group design. Plasma samples were taken before the scale was completed and up to 8 hours post-dose. After administration of the medication the subjects were asked to maintain their normal daily routine as much as possible (reading, studying, conversations). The inventory was administered twice, at 50 minutes and 2 hours post-dose (peak level). The overall score was different between the three groups, only for the second assessment, 2 h post-dose (ANOVA, P < 0.02). Multiple t-testing between the three groups revealed statistically significant differences between placebo and the 10 mg temazepam group (P = 0.02) and between placebo and the 20 mg temazepam group (P = 0.006). No significant difference was found between the two temazepam groups. Analysis of the separate questions showed least sensitivity for questions related to the domain of 'hyperexcitability' and most sensitivity for 'fatigue' and 'slowing.' The overall score appeared to be sensitive already for the lower toxicity range suggesting an 'all or nothing effect'. The subjective reports, collected by using this scale, may therefore be used for the detection of gross overall changes in cognitive functioning.

Quantitated fetal heart rhythm at 20, 32 and 38 weeks of gestation and dependence on rest-activity patterns.

Quantitative parameters of fetal heart rate (FHR) were automatically analysed at 20, 32 and 38 weeks of pregnancy. FHR was obtained both by the fetal ECG method and by wide range Doppler ultrasound with autocorrelation. At 32 and 38 weeks, FHR was studied in relation to fetal rest-activity according to the fetal behavioural state concept (coincidence 1F and 2F). Basal fetal heart rate was significantly higher at 20 weeks of gestation than at 32 and 38 weeks. The number of accelerations increased significantly from 20 weeks to 32 and 38 weeks for C2F periods. Parameters of FHR variability, i.e. ID, ABB, LTI indices and bandwidth, were higher during periods C2F compared to periods C1F. Lowest values of all four parameters were found at 20 weeks gestation. The ID index, which is a measure of short-term variability increased significantly between 32 to 38 (C2F). The absolute values of ID, ABB and LTI were lower for ultrasound recordings than for the fetal ECG.

Coincidence of behavioural state parameters in the human fetus at three gestational ages.

The fetal behavioural state concept was used to study fetal rest-activity cycles in normal pregnancies at gestational ages of 32 and 38 weeks. In addition, it was investigated if clustering of fetal movements was already present in recordings obtained at 20 weeks. At 20 weeks, 17 periods lasting longer than 3 min were found in which fetal body movements were absent. The mean duration of these periods was 4.0 +/- 0.8 min. On the basis of random scattering of movements on a time axis, it appeared unlikely that these periods of inactivity occurred by chance alone. At 32 and 38 weeks, data on body movements were combined with data on eye movements and the FHR pattern. At 32 weeks, true fetal behavioural states were not found. The average coincidence of 1F to 4F was 58%, while only 23% was to be expected if state parameters had fulfilled state criteria purely by chance. At 38 weeks, coincidence of 1F to 4F had increased to 80% (P less than 0.001). Expected coincidence purely by chance was 30%. True fetal behavioural states were found in 17 out of 35 recordings. For transitions from 1F into 2F, the FHR changed relatively early, i.e. as first or second parameter, while for the reverse transitions it changed relatively late (P less than 0.05). There was no clearly preferred sequence for body and eye movements within transitions.

Assessment of changes in liver blood flow after food intake--comparison of ICG clearance and echo-Doppler.

Echo-Doppler measurements of portal venous blood flow in intrahepatic branches and indocyanine green (ICG) clearance after continuous i.v. infusion as measure for liver blood flow were compared to evaluate the increase in splanchnic blood flow after food intake. It was shown that both methods assessed the changes in flow in a similar manner. Changes in blood flow in intrahepatic portal vein branches measured with echo-Doppler adequately predicted the change in ICG concentrations. Hence, echo-Doppler measurements of hepatic portal blood flow in intrahepatic branches can be used to estimate changes in total liver blood flow.

Pharmaco-dynamics of human menopausal gonadotrophin (HMG) and follicle-stimulating hormone (FSH). The importance of the FSH concentration in initiating follicular growth in polycystic ovary-like disease.

Using a randomized double-blind cross-over design, the pharmaco-dynamic and pharmaco-kinetic properties of 'pure' follicle-stimulating hormone (FSH) (Metrodin) and human menopausal gonadotrophin (HMG) (Pergonal) were studied in 24 women with polycystic ovary-like disease (PCOD) during induction of ovulation. Fifty-six cycles were stimulated with FSH and 60 cycles with HMG, according to a standard protocol. Gonadotrophins were administered i.v. in a pulsatile fashion using pulse frequencies of either 30 or 120 min. The cycles stimulated with either 30 or 120 min pulse intervals showed no differences among themselves. During the stimulation phase, the FSH and HMG stimulated cycles showed equal and dose dependent FSH concentrations (mean +/- SD). The luteinizing hormone (LH) concentrations (mean +/- SD) were also equal but unchanged compared to the mean basal concentration. The LH, FSH, total urinary oestrogen excretion, and testosterone profiles (mean +/- SD) obtained from cycle days -10 to 0 as well as the pregnanediol profiles obtained from cycle days 0 to +14 showed no differences either. The occurrence of an endogenous preovulatory LH surge was significantly more frequent in the cycles stimulated with a pulse interval of 30 min compared to the cycles stimulated with a pulse interval of 120 min. The addition of LH as provided in HMG did not influence the FSH threshold concentration above which initiation of follicular growth occurred, since no differences were found in the FSH 'stable' concentrations between FSH and HMG stimulated cycles. However, intra- and inter-individual variation in the FSH 'stable' concentration at which follicular growth was initiated became obvious.(ABSTRACT TRUNCATED AT 250 WORDS)