Myocardial β-adrenergic reactivity in volume overload-induced cardiac hypertrophy in the rat

Summary— The purpose of this study was to evaluate the changes in myocardial β-adrenergic reactivity in animals undergoing a 4 week cardiac volume overload. Aortocaval shunt (ACS) or sham operation (sham) were performed in male Wistar rats, and 4 weeks later, isoproterenol dose-effects (chronotropic, inotropic and lusitropic properties) were studied after pithing. Noradrenaline (NA) and adrenaline (A) concentrations and NA turn-over index were evaluated in plasma and heart ventricles, while β-adrenoceptor characteristics in ventricle homogenates and slices with [¹²⁵I]iodocyanopindolol, and the β(1)/β(2)-adrenoceptor ratio were estimated. Four weeks of cardiac volume overload resulted in a 55% increase in ventricle weight/body weight ratio (from 2.5 ± 0.1 to 3.9 ± 0.1 mg/g in sham and ACS rats, respectively) and a 20% increase in protein contents (from 11.3 ± 0.7 to 13.8 ± 1.1 mg/100 mg ventricles in sham and ACS rats, respectively). Furthermore, NA and A concentrations and NA turn-over index were increased in ACS rats (14, 40 and 80% versus sham, respectively). A shift to the right of the responses in heart rate, left ventricular systolic pressure, +d P /d t _max and -d/ P /d t _max responses following increasing doses of isoproterenol was observed, without change in the dose inducing maximum effect. Total β-adrenoceptor characteristics and β(1)/β(2) ratio were unchanged. However, β(1)-adrenoceptor density increased in epicardium while decreasing in endocardium of left ventricle from ACS rats. Rightward shift at lower doses of isoproterenol-induced cardiac responses in volume-overloaded rats are not likely due to overall β-adrenoceptor density changes.     

β-Adrenoceptor density in patients with left-sided valvular regurgitation

Summary— Aortic regurgitation differs from mitral regurgitation in that it is a result of combined volume and pressure overload, while the latter represents an almost pure volume overload. In this study, we tested the possibility that these two forms of left ventricular volume overload exert different effects on β-adrenoceptor density. Lymphocyte (n = 33) and myocardial (n = 22) β-adrenoceptor densities were evaluated by [¹²⁵I]-iodocyanopindolol binding in volume-overloaded patients with left heart valvular disease, compared with 31 healthy donor blood and 15 donor heart controls, made available as a result of failing to get matching recipient. The total lymphocyte (LC) β-adrenoceptor density decreased from 43.4 ± 5.5 fmol mg^?1 protein in controls to 9.2 ± 2.7 fmol (P < 0.001) in heart valvular patients. In the myocardial controls, the left ventricular (LV)-receptor density was 126.7 ± 19.5 fmol; right ventricular (RV), 123.1 ± 14.6 fmol; left atrial (LA), 81.6 ± 10.5 fmol; and right atrial (RA), 108.1 ± 14.5 fmol mg^?1 protein. Compared to this group, the total LV-receptor density of the patients decreased by 63%, RV by 54%, LA by 31% and RA by 34%. The decrease in receptor density exhibited a positive correlation with increasing ejection fractions in both the left (r = 0.38) and right (r = 0.44) ventricles, indicating that the former was dependent on the extent of the disease. These changes were accompanied by a 44% increase in plasma epinephrine, 13% in norepinephrine and a 27% decrease in dopamine levels. Based on the predominant left ventricular volume overload classified as aortic regurgitation (AVR), mitral regurgitation (MVR) and mixed aortic and mitral regurgitation (MOL), the attenuation in myocardial-receptor densities showed the following trend: MOL > MVR > AVR. The results show a global reduction in myocardial and LC β-adrenoceptor density, which depends on the origin and the gravity of the LV volume overload.     

Turnover in humans of β2-microglobulin: the constant chain of HLA-antigens

Abstract The turnover of β₂-microglobulin, the common subunit of the HLA antigens, has been examined in normal subjects and in some patients with kidney disorders, multiple myeloma and rheumatoid arthritis. All patients displayed elevated serum levels of β₂-microglobulin. The plasma disappearance curve of ¹²⁵I-β₂-microglobulin demonstrated that the protein has a rapid turnover (11/2 = 21 h; range 1 1–2–8 h) in normal persons and in patients with a normal glomerular filtration rate. In patients with kidney disorders the impaired renal filtration prolonged the turnover time and led to elevated serum levels of β₂-microglobulin.
Simultaneous measurements of ¹²⁵-β₂-microglobulin in serum and urine allowed estimations of the β₂-microglobulin net reabsorption in the renal tubuli. Two patients with renal disease reabsorbed 84% and 89%, respectively, of the β₂-microglobulin filtered in the glomeruli. In normal persons the net reabsorption is close to 100%.
In patients with normal kidney function increased serum levels of β₂-microglobulin seem to be due to an increased synthetic rate of the protein as the elimination rate is normal. HLA antigen heavy chains in serum are present in smaller amounts than β₂-microglobulin. The present data, therefore, suggest an imba-lanced synthesis of the two chains.     

β-adrenergic priming of rats in vivo modulates the effect of β-agonist in vitro on surfactant phospholipid metabolism of isolated lungs

Abstract. To evaluate the effects of multiple β -adrenergic stimulations on pulmonary surfactant phospholipids, perfused lungs from β -adrenergic primed and non-primed rats were challenged with the β -agonist terbutaline in vitro . Cell-free lung lavage, lavagable alveolar cells and lung tissue were analysed for phospholipid content and incorporation of precursors. In lung lavage, terbutaline in vitro doubled the incorporation of ¹⁴C-choline and ³H-palmitate into total phosphatidylcholine (PC) and of ³H-palmitate into phosphatidylglycerol (PG). β -adrenergic priming in vivo prior to terbutaline in vitro lowered the increase of precursor incorporation. For lavagable cells, terbutaline in vitro increased the incorporation of ³H-palmitate into PC. Priming in vivo reduced this effect and diminished the specific ³H-choline incorporation into lavagable cell PC below control level. For lung tissue, priming increased the amounts of PC and disaturated PC (DSPC) whereas terbutaline in vitro decreased DSPC in both primed and non-primed lungs. Terbutaline in vitro slightly increased the incorporation of ¹⁴C-choline and ³H-palmitate into PC and DSPC in non-primed but not in primed lungs. β -adrenergic blockade by ICI 118.551 prevented all effects but generally increased ³H-palmitate incorporation into the phospholipids and, in lavagable cells, the amount of PC. We conclude that long-term β -adrenergic treatment may alter the metabolism of pulmonary surfactant phospholipids by increasing tissue PC and DSPC and by decreasing the secretion of newly-synthesized PC.     

Cytoplasmic regions of the β3 subunit of integrin αIIbβ3 involved in platelet adhesion on fibrinogen under flow conditions

Summary.  Platelet adhesion to surface-bound fibrinogen depends on integrin α_IIbβ₃. In the present study, we investigated the role of the regions ⁷⁴⁹EATSTFT⁷⁵⁶N and ⁷⁵⁵TNITYRG⁷⁶²T of the β₃ cytoplasmic tail in the regulation of platelet adhesion under flow conditions, by introducing peptide mimetics in platelets. Introduction of peptide EATSTFTN (E–N) increased surface coverage by 35%, an effect caused by 25% more adhesion. In contrast, peptide TNITYRGT (T–T) decreased surface coverage by 16%, as a result of 25% less adhesion. An S→P substitution in the E–N peptide, thereby mimicking a mutation in Glanzmann's thrombasthenia, abolished the effect of E–N. A suboptimal concentration of cytochalasin D is known to enhance ligand binding to α_IIbβ₃ in platelet suspensions. Under flow, cytochalasin D (1 µmol L⁻¹) induced 50% more platelet adhesion, with a strong reduction in platelet spreading. Both peptides opposed the increase in adhesion by cytochalasin D and partly (E–N) and completely (T–T) restored platelet spreading. Thus, the ⁷⁴⁹EATSTFT⁷⁵⁶N and ⁷⁵⁵TNITYRG⁷⁶²T regions of β₃ contribute to the regulation of αIIbβ3 anchorage to the cytoskeleton and platelet spreading to an adhesive surface.     

Tritium and 14C isotope effects using tracers of leucine and alpha-ketoisocaproate

Abstract. To test if different leucine tracers behave in an indistinguishable manner and, by implication, that their metabolism is identical to that of natural leucine, we measured whole body leucine turnover in dogs and humans and fibrinogen synthesis in dogs by simultaneously infusing either [1–¹⁴C]leucine or [4,5–³H]leucine or [I-¹⁴C]α-ketoisocaproate (KIC) and [4,5–³H]KIC. Whole body leucine fluxes calculated from the plasma specific activity of the transaminated product of the infused tracer (reciprocal pool model) were lower (dogs by 5.7%; humans by 6.4%, both P<0.02) when the plasma 'H specific activity compared to ¹⁴C specific activity were used with leucine tracers and were also lower (dogs by 4.4%, P<0.02; humans by 86%, P<0.06 ) using the KIC tracers. Using leucine or KIC tracers in dogs, the fractional rate of fibrinogen synthesis was 6.7% or 9.4% lower, respectively, (P<0.02) using the ³H versus the ¹⁴C tracer. The apparently lower incorporation of ³H into protein was only in part accounted for by detritiation (2.1%, P = 0.05) of [³H]leucine during acid hydrolysis of proteins. These results suggest that in vivo and/or in vitro differential isotope effects are small (˜5%), but should be considered when dual isotopes infusions are employed to partition amino acid metabolism.     

Alzheimer amyloid β-peptides exhibit ionophore-like properties in human erythrocytes

Abstract. There is growing evidence that the amyloid β-peptide (β₁_₄₀) is involved in the aetiology of Alzheimer's disease also implicating an altered calcium homeostasis of affected cells. Beta₁_₄₀ has been proposed to form calcium channels in synthetic bilayer membranes [1]. We wanted to investigate in the present study whether β₁-₄₀ (or fragments thereof) could act as ionophores in a biological membrane like the one in human erythrocytes. Incubation of the cells for 2h and 4h at 37°C together with 6μmolL^-1 of β₁-₄₀ or of fragments β₁_₂₈and β₂₅-₃₅, resulted in a significantly decreased energy charge qualitatively similar to the one obtained by a known calcium ionophore (A 23187, 0.05μmolL^-1). Moreover, β₁_₄₀ and its two fragments induced a significant alteration of ⁴⁵Ca permeability in human red blood cells of the same type as the one achieved by the calcium ionophore. The ionophoric action of β₁_₄₀ and its two fragments may lead to an increase of the intracellular calcium ion concentration, in turn resulting in enhanced Ca²⁺-ATPase activity and a decrease in energy charge. This may be valid also for neuronal plasma membranes and could, therefore, be a possible aetiological mechanism in Alzheimer's disease.     

Platelet Alpha2-Adrenoceptor Binding in Migraine

SYNOPSIS
Platelet alpha 2 -adrenoceptor binding was determined in ten migraine patients and sixteen healthy controls using (³H)-yohimbine as radioligand. The mean value of maximum binding (^Bmax ) in the migraine patients was 133 ±55 binding sites/ platelet which is significantly lower than that of 217 ± 76 binding sites/platelet in controls (p<0.01). There was also a significant difference in the mean dissociation constant (K_D ); 2.05 ± 0.44 nM in migraineurs and 2.98 ± 1.15 nM in controls (p<0.05). Platelet alpha 2 -adrenoceptors may constitute valid models for certain characteristics of alpha 2 -adrenoceptors in the brain. An alteration in platelet alpha₂ -adrenoceptor binding may thus reflect similar alterations in central alpha₂ -adrenoceptors. It is also discussed whether the alpha₂ -adrenoceptor abberrations are intrinsic to migraine or a result of endogenous and/or pharmacologically induced modulation.     

Hemicranial Disorder of Vasomotor Adrenoceptors in Migraine and Cluster Headache

SYNOPSIS
Regional cerebral blood flow (rCBF) and cerebral vasomotor responses to 5% CO₂ inhalation were measured before and after pharmacologic μ- or β-adrenoceptor manipulation in Migraine (M) and Cluster headaches (C). Responses of 77 vascular headache patients (M =66 and C = 11) were compared to those of 15 Muscle contraction headache (MCH) and 64 normal volunteers. Oral drugs were: Peripheral μ-adrenoceptor stimulator:isometheptene (Midrin(r)), peripheral μ-blocker:dihydroergotoxin (Hydergine(r)), centrally acting μ-blocker:clonidine (Catapres(r)), peripheral β-blocker:propranolol (Inderal(r)), peripheral β-stimulator:isoproterenol (Isuprel(r)). Peripheral μ stimulation markedly reduced rCBF during headache but effect lessened after headache subsided in M and C. Peripheral μ-blockade and β-stimulation increased CBF in M and C. Peripheral β-blockade markedly decreased CBF during headache in M but caused only small CBF reductions when headache-free. Peripheral adrenoceptor effects on rCBF in M and C were greatest on most recent headache side. Central effects of clonidine were opposite (greatest on non-headache side). Excessive CO₂ responses were greatest on side of headache. After peripheral μ-stimulation, peripheral μ-blockade, peripheral β-stimulation or blockade, CO₂ responses were restored toward normal but not after central μ-blockade. In MCH. contrary to M and C, μ-stimulation had no effect on CBF or CO₂ responses. There appears to be an asymmetrical adrenoceptor disorder in M and C possibly due to sympathetic denervation-hypersensitivity.     

Comparative Absorption of Ferri-Haemoglobin-59Fe/Ferro-Haemoglobin-59Fe and 59Fe3+/59Fe2+ in Humans with Normal and Depleted Iron Stores*

Abstract. The intestinal ⁵⁹Fe absorption from ferri- and ferro-haemogIobin-⁵⁹Fe and ⁵⁹Fe³⁺ and ⁵⁹Fe⁺ was calculated from whole body-⁵⁹Fe-retention measurements in subjects with normal and depleted iron stores. A ferri-haemoglobin-⁵⁹Fe/ferro-haemoglobin-⁵⁹Fe absorption ratio of 1.03 ±0.11 was observed for the absorption of ferri-haemoglobin-⁵⁹Fe (8.6± 0.77%) and ferro-haemogIobin-⁵⁹Fe (8.7±0.94%) in persons with normal iron stores. Depletion of iron stores caused a slight but significant higher rise of ferri-haemoglobin-⁵⁹Fe absorption (22 ± 1.7%) than the increase of ferro-haemoglobin-⁵⁹Fe absorption (18 ±0.9%) so that the absorption ratio was 1.24±0.073.—This remarkable iron valence independence of haemoglobin iron absorption is in considerable contrast to the well-established valence dependence of inorganic iron absorption which favours ferrous iron absorption especially with rising iron doses. The ⁵⁹Fe³⁺/⁵⁹Fe²⁺ absorption ratio for a diagnostic 0.56 mg Fe dose increased from 0.43 in subjects with normal iron stores to 0.74 in persons with depleted iron stores, whereas this absorption ratio was augmented only from 0.21 to 0.28 for the therapeutic 50 mg Fe-dose.—The different influence of iron valence on iron absorption from inorganic and haemoglobin iron supports other evidence for the existence of two separate mechanisms for ferrous iron and haem iron absorption in humans.     

Effect of activation of protein kinase A and of protein kinase C on the kinetics of the renal basolateral PAH transporter

Summary— The aim of the present study was to examine the effect of activation of the protein kinase A (PKA) and protein kinase C (PKC) pathways on ³H-p-aminohippurate (PAH) uptake of isolated S₂ segments of proximal tubules, microdissected from rabbit kidneys without the use of enzymatic agents. Because the tubules were not perfused, and hence were collapsed, the tubular uptake of ³H-PAH reflects transport across the basolateral membrane. The phorbol ester phorbol 12-myristate 13-acetate (PMA) (10 ⁷ M), an activator of PKC, significantly increased tubular ³H-PAH uptake with steady state conditions (by 115%), whereas dibutyryl cyclic adenosine monophosphate (db-cAMP) (10^-4 M) and forskolin (10^-4 M) significantly inhibited it (by 42% and 52%, respectively). Kinetic data, which were based on 15 sec PAH uptake measurements, revealed that PMA, after a 10 min incubation period, significantly enhanced Km and Vmax of the PAH transporter (Km from 174 ± 22 to 447 ± 91 μM, Vmax from 2.76 ± 0.24 to 16.67 ± 1.85 pmol nL^-1 min^-1), whereas db-cAMP significantly decreased Vmax (from 2.76 ± 0.24 to 1.82 ± 0.19 pmol nL^-1 min^-1). The Km value was also numerically lowered by dibutyryl-cAMP (from 174 ± 22 to 139 ± 21 μM), but this change did not reach statistical significance. The data provide evidence that short time activation of the PKC pathway 1) enhances the effectiveness of PAH transport into proximal S₂ segments across the basolateral cell membrane, 2) increases the maximum transport rate of the PAH transporter and 3) decreases its affinity for PAH. Activation of the cAMP/PKA pathway induces the opposite effects.     

NG-Nitro-L-arginine methyl ester: a muscarinic receptor antagonist?

Summary— The effect of the nitric oxide synthase inhibitor N ^G-Nitro-L-arginine methyl ester (L-NAME) towards muscarinic receptors was studied in vitro and in vivo. L-NAME displaced the antimuscarinic ligand [³H]quinuclidinyl benzilate (³H]QNB) from its specific binding sites in rat cerebral cortex and cerebellum homogenates with a more than 10,000 fold lower affinity than atropine, pirenzepine and AFDX 116. Data for L-NAME binding were best fit according to a two-site model ( K _d 7.2 nM and 3,000 nM) in the rat cerebellum, whereas in rat cortex a one-site model ( K _d 1670 nM) was superior. In anesthetized rats and rabbits L-NAME (7.5–185 μmol/kg) attenuated a hypotensive response to Acetyl β-methyl-choline (Ac β-Me Ch)(6.25 nmol/kg) in a dose related fashion, but this effect was negligible as compared to that of atropine (8.8 and 17.7 nmol/kg). Furthermore, the effect of L-NAME was not specifically antimuscarinic since its attenuating effect against ATP- or histamine-induced responses was not statistically different from that of Ac β-Me Ch. A vagus stimulation induced bradycardia was entirely uninfluenced by L-NAME (37 μmol/kg). In isolated bladder experiments (rabbit) we demonstrated a complete lack of efficacy of L-NAME against Ac β-Me Ch induced contractions. In the pithed rat preparation L-NAME was ineffective against the McN-A-343 induced pressor responses. In summary, we demonstrated that the nitric oxide synthase inhibitor L-NAME shows very weak affinity at M₁- and M₂-receptors in the rat brain in vitro, but appears to have no significant antimuscarinic properties against M₁-, M₂- and M₃-receptor mediated effects in rats and rabbits in vivo.     

Serum β2-microglobulin at remission and relapse in patients with multiple myeloma

Abstract. Serum β₂-microglobulin (S-β₂m) was determined before treatment in fifty patients with multiple myeloma (MM), twenty-two of which had pure Bence Jones (BJ) myeloma. S-β₂m was related to clinical stage before, but not after, a correction of S-β₂m values for co-existent raised S-creatinine values (> 106 μmol 1^-1)- However, S-β₂m as well as corrected β₂m was a parameter of prognostic value. The median expected survival time was 14 months at S-β₂m values > 8·0 mg 1^-1 and 56 months at values<3·5 mg 1^-1. A response to treatment was associated with a decrease of S-β₂m and a stationary course with unchanged values, whereas a relapse or progressive disease was connected with an increase. In β₂m producers', i.e. patients with a clear initial high S-β₂m, serial determinations are of value for monitoring patients with MM. In particular, this is the case in BJ myelomas, as they lack a quantifiable serum M-component. With respect to β₂m no difference was found between BJ and other patients with MM.     

Transforming growth factor β1 modulates angiotensin induced calcium influx in vascular smooth muscle

Abstract. The modulatory effects of transforming growth factor β₁ (TGF β₁) on the angiotensin II (Ang II)-induced increase in cytosolic free calcium concentration ([Ca²⁺]_i) were investigated in vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). [Ca²⁺]_i in VSMC was measured using the fluorescent dye fura-2. When TGF β₁ was applied 30 s prior to Ang II, the Ang II-induced [Ca²⁺]_i increase was significantly enhanced in VSMC from SHR ( P < 0.05 compared to control), whereas after the preincubation with TGF β₁ for 30 min, the Ang II-induced [Ca²⁺]_i increase was significantly reduced in VSMC from both strains. Using the manganese-quenching technique, it was confirmed that short-term exposure to TGF β₁ enhanced the Ang II-induced trans-plasma-membrane calcium influx in SHR. The inhibition of protein kinase C by calphostin C abolished the stimulatory effect of TGF β₁ on the Ang II-induced [Ca²⁺]_i increase. It is concluded that TGF β₁ modulates the Ang II-induced calcium handling in VSMC.     

Differential response of hypertrophied rat hearts to various α1-adrenoceptor agonists

Summary— With respect to the heart, the prolonged existence of hypertension, both in man and in experimental animals is predominantly characterized by an increase in left ventricular myocardial mass. In this process, the autonomic nervous system plays an important role. Although endogenous catecholamine stimulation of the heart is mainly exerted via the β-adrenoceptors, in several mammalian species, the stimulation of cardiac α-adrenoceptors also mediates positive inotropic actions. We investigated the functional responses of isolated hypertrophied hearts taken from spontaneously hypertensive rats (SHR) and rats with an induced aortic stenosis (ASR) to various α₁-adrenoceptor agonists and compared them with those from age matched Wistar Kyoto (WKY) and "sham" operated controls. Accordingly, we studied the functional response to: methoxamine (α₁), cirazoline (α₁) and phenylephrine (α₁ > β₁). The inotropic response to the α₁-adrenoceptor agonists cirazoline and methoxamine proved to be significantly weaker in hypertrophied hearts from SHR and ASR than in non-hypertrophied hearts from WHY and "sham" operated controls ( p < 0.05). The inotropic response to phenylephrine remained intact in hypertrophied myocardial tissue. However, it was significantly reduced when the hearts were pre-treated with the intracellular Ca²⁺-antagonists ryanodine and TMB-8. These findings show that the mechanism of sarcolemmal Ca²⁺ release, activated by phenylephrine, is still intact in the hypertrophied myocardial cell. In conclusion, these data show that cardiac hypertrophy, be it of genetical or mechanical origin, leads to a reduced response of the isolated heart to α₁-adrenoceptor stimulation.     

Association of the antagonism of von Willebrand factor but not fibrinogen by platelet αIIbβ3 antagonists with prolongation of bleeding time

Summary.  Background:  The α _IIb β ₃ antagonists inhibit platelet aggregation and are used as antithrombotic agents for cardiothrombotic disease. The present study investigates the correlation of inhibition of fibrinogen and von Willebrand factor (VWF) binding by α _IIb β ₃ antagonists with the inhibition of platelet aggregation and prolongation of bleeding time (BT). Methods:  Inhibition of fibrinogen and VWF binding were assessed in a purified α _IIb β ₃-binding assay. As an in vitro cell-based assay, platelet aggregation and VWF-mediated adhesion studies were performed using human platelets. In vivo effects on BT were measured using a template device in dogs at the same time as an ex vivo aggregation study was performed. Results:   In vitro studies demonstrated that the antiaggregatory effects of α _IIb β ₃ antagonists correlate with their inhibition of fibrinogen binding, but not VWF. Interestingly, the effects of α _IIb β ₃ antagonists on BT could be differentiated from the inhibition of platelet aggregation. Furthermore, this differentiation was strongly correlated with the different inhibitory potencies between fibrinogen and VWF binding, as well as that between VWF-mediated adhesion and aggregation. Conclusions:  Our study provides novel evidence showing that the inhibitory effect of α _IIb β ₃ antagonists on VWF, but not fibrinogen binding, correlates with their ability to prolong BT.     

Quantitative studies of ver low densit lipoprotein: conversion to low densit lipoprotein in normal controls and primar hperlipidaemic states and the role of direct secretion of low densit lipoprotein in heterozgous familial hpercholesterolaemia

Abstract. Autologous ¹³¹I-labelled ver low densit lipoprotein (VLDL) and ¹²⁵I-labelled low densit lipoprotein (LDL) were injected into seven normal subjects and twent-eight geneticall classified hperlipidaemic patients to quantitate lipoprotein interconver-sion. The apoprotein B specific activit-time curves for VLDL and intermediate densit lipoprotein (IDL, densit = 1 006–1019 g/ml) intersected at or before the IDL-B maximum in thirt-one studies (five normal controls and twent-six hperlipidaemic subjects) impling that all IDL-B ma be derived from VLDL-B. The fractional conversion of VLDL-B to LDL-B (densit 1 019-1 063 g/ml) following a simultaneous spike injection of ¹³¹I-VLDL and ¹²⁵-LDL was obtained b deconvolution of the ¹²⁵I and ¹³¹I-LDL-B activit curves. 21–65% (mean = 44%) of VLDL-B was converted to LDL-B in twent-three subjects studied. The mean conversion time ranged from 10 to 24 h in ten normotriglceridaemic subjects and from 19 to 42 h (mean = 33 h) in twelve hpertriglceridaemic subjects. In one patient with broad-β disease the mean conversion time was 55 h. LDL-B production from VLDL-B and total LDL-B snthetic rate were essentiall equal in normal controls and normocholesterolaemic subjects and in the patient with broad-β disease. But in all six patients with familial hpercholesterolaemia LDL-B snthetic rate significantl exceeded LDL-B production from VLDL-B, indicating direct secretion of 20–72% of LDL-B at a rate which correlates positivel with plasma LDL concentration. Three of five patients with familial combined hperlipidaemia showed a lesser but nevertheless significant direct secretion of LDL-B.