Biomedical subjects

I C Smith

Publications and source records attributed to I C Smith.

At least 109 records · Page 6Linked to original sources

PubMed1988

Adrenergic modulation of 'non-adrenergic' twitches in the rat vas deferens.

1. Field stimulation of the intramural sympathetic nerves of rat vas deferens produced a biphasic contraction. Post-tetanic twitches were potentiated (PTP) and the relationship of this to the secondary component of tetanic responses was investigated. 2. A tetanus evoked by field stimulation at 4 Hz for 50 s gave a maximum increase in twitch tension of 109 +/- 5% (n = 43). The potentiation was blocked by the alpha-adrenoreceptor antagonists phenoxybenzamine, prazosin and thymoxamine. These drugs also blocked the secondary component of the tetanic response. 3. Increasing the frequency (1-8 Hz) of tetanic field stimulation enhanced the magnitude and time course of PTP. The time course of the PTP was found to depend mainly on the number of pulses in the tetanic train. 4. Reducing transmitter release in high Mg2+ solutions shortened the duration of the PTP but prevented the decline of the secondary tetanic component. Co2+ (1 mM) or Mn2+ (1 mM) mimicked the effect of high Mg2+ ions on the secondary tetanic component. Enhanced transmitter release in zero Mg2+-Krebs had the reverse effects. 5. The presynaptic alpha 2-adrenoreceptor antagonists idazoxan and yohimbine, and the neuronal uptake blockers desipramine and metaraminol, prolonged the PTP and enhanced but shortened the secondary rise in tetanic tension. 6. Bolus injections of noradrenaline before and after the tetanus gave no evidence for post-synaptic desensitization. 7. It is concluded that both the secondary rise in tetanic tension and the post-tetanic potentiation are due to an adrenergic enhancement of the 'non-adrenergic' mechanism and not, as has been supposed, to direct activation of an adrenergic tension. Thus the action of the alpha-adrenoreceptor-mediated transmission is primarily one of modulation.

Adrenergic alpha-Antagonists↗

PubMed1988

Early induction by crotoxin of biphasic frequency changes and giant miniature endplate potentials in frog muscle.

1. Following the addition of crotoxin (250 nM) at the frog neuromuscular junction, there was an initial fall in frequency of miniature endplate potentials (m.e.p.ps), followed by a secondary rise which was characterized by the appearance of large spontaneous potentials (giants, g.m.e.p.ps) and an occasional large potential of the burst type. 2. In the presence of 2-(4-phenylpiperidino)cyclohexanol (AH5183, vesicamol), an inhibitor of vesicular acetylcholine uptake, the frequency of g.m.e.p.ps induced by crotoxin was reduced. 3. The characteristic changes in m.e.p.p. frequency and amplitude distribution were absent with crotoxin in Sr-EGTA Ringer. In the presence of high concentrations of Mn (3.6 or 5.4 mM with 0.9 mM Ca), the crotoxin-induced initial fall and the onset of the secondary rise in m.e.p.p. and g.m.e.p.p. frequencies were slower. The timing of these phases was unaffected by Ca concentrations ranging from 6.3 to 0.9 mM. 4. High concentrations of Mn ions partially inhibited the phospholipase A2 activity of crotoxin on artificial phospholipid membranes. This also supports the involvement of the Ca-dependent phospholipase A2 subunit in both phases of the physiological action of the toxin. 5. G.m.e.p.ps were associated with a moderate increase in m.e.p.p. frequency (2-3 s-1) and were of a time-course similar to that of m.e.p.ps. They persisted after washing with medium lacking Ca ions and in the presence of Ca-Mn Ringer that blocked evoked responses. 6. It is concluded that crotoxin, acting through its phospholipase A2 subunit, produces specific disturbances of synaptic exocytosis and vesicle formation in the axolemma of the motor nerve terminal which lead to biphasic changes in m.e.p.p. frequency and the onset of large spontaneous potentials.

Animals↗

PubMed1988

The functional significance of the sympathetic innervation of mucous glands in the bronchi of man.

1. Pieces of human bronchi, from lung resected for carcinoma of the bronchus, were mounted in Ussing chambers and given [35S]sulphate as radiolabelled precursor of mucous glycoproteins (mucins). The release of 35S, bound to macromolecules, into the luminal half-chamber was used as an index of mucin secretion. 2. Noradrenaline, at concentrations of 1, 10 and 100 microM, was given into both halves of the Ussing chamber. At the lowest concentration, noradrenaline failed to change mucin output, but at the two higher concentrations it stimulated output. 3. In other experiments the sympathetic nerves in the bronchial wall were labelled with 5-hydroxydopamine and examined under the electron microscope. The distances between adrenergic nerve varicosities and submucosal glands were measured; some sympathetic nerve varicosities were seen within 1 microns of gland cells. 4. A simple mathematical model for the diffusion of noradrenaline was used to predict the concentrations of the transmitter likely to result at different distances from a nerve if one or more vesicles of noradrenaline were released. 5. The model predicts that the release of a single large vesicle of noradrenaline is likely to generate an effective concentration of transmitter provided that the nerve is within 1 micron of the target cell.

Bronchi↗

PubMed1987

Pressure-induced exclusion of a local anesthetic from model and nerve membranes.

Because it is well established that the anesthetic state can be reversed by pressure, a number of molecular theories that have been proposed for the mechanism of action of both local and general anesthetics can be tested by varying the pressure. Using Fourier transform infrared spectroscopy, we report here the first direct observation of the expulsion from lipid bilayers of a local anesthetic, tetracaine, by pressure. Moreover, we establish for the first time that this phenomenon is common to both model membranes and to myelinated and unmyelinated nerve membranes, vindicating the utility of model membrane systems. A distinctive feature of this behavior in model systems is that, in saturated phosphatidylcholines at high pH, expulsion only occurs in the presence of cholesterol, whose ordering effect on the acyl chains evidently assists pressure in squeezing the anesthetic out of the bilayer. This pressure-induced phenomenon may provide insight into the molecular mechanisms underlying the antagonistic effect of pressure against anesthesia.

Animals↗

PubMed1987

Oxidant stress in malaria as probed by stable nitroxide radicals in erythrocytes infected with Plasmodium berghei. The effects of primaquine and chloroquine.

Erythrocytes from normal mice and mice infected with the malarial parasite Plasmodium berghei reduce the water-soluble spin probes 2,2,6,6-tetramethylpiperidine-4-hydroxy-N-oxyl (TEMPOL), 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and 2,2,6,6-tetramethylpiperidine-4-keto-N-oxyl (TEMPONE) at similar rates under both air and N2 atmospheres. The ESR signal of the lipid-soluble spin probe 5-doxyl-stearate is stable on incorporation into erythrocytes from normal mice. In contrast, parasitized red cells reduce this nitroxide probe, at a rate which increases with the level of parasitemia. Inhibitors of electron transport such as KCN and NaN3, increase the rate of reduction. We propose that nitroxide reduction occurs via the electron transport chain in the parasite. The antimalarial drug primaquine causes reduction of both water-soluble and lipid-soluble spin probes. This action of primaquine is independent of its ability to release H2O2 from oxyhemoglobin, and is ascribed to the ability of primaquine to accelerate flux through the hexose monophosphate shunt. The increased production of NADPH results in increased rates of reduction of the nitroxide radicals. Methylene blue, which also increases flux through the shunt, is even more effective than primaquine at reducing the nitroxides. Chloroquine has no such effect. Parasitized mice treated with chloroquine six hours prior to ESR measurements show less nitroxide reducing capacity than do untreated mice. Chloroquine is known to decrease flux through the hexose monophosphate shunt. The metabolic influences of the two antimalarial drugs are, thus, quite different.

Air↗

PubMed1987

Determination of conformational properties of glycolipid head groups by 2H NMR of oriented multibilayers.

The conformations and orientations of the glucose and glycerol moieties of a monoglucosyl lipid in hydrated bilayers have been determined in detail by deuterium nuclear magnetic resonance (2H NMR). Multibilayer membranes of 1,2-di-O-tetradecyl-3-O-(beta-D-glucopyranosyl)glycerol (DTGL), of dimyristoylphosphatidylcholine (DMPC), and of a mixture of DTGL and DMPC were oriented between glass plates. The glucolipid was selectively labeled with deuterium on the pyranose ring and at C3 of glycerol, whereas DMPC was labeled at the C4 position of the sn-2 chain. Quadrupolar splittings were measured as a function of the angle between the bilayer normal and the magnetic field direction. The results establish that the director of motional averaging, the direction about which motion and order are axially symmetric, is the bilayer normal for all the head group, the glycerol backbone, and the hydrophobic core. Segmental order parameters were determined to be 0.45, 0.65, and 0.40, respectively, for the various regions of DTGL in the membranes. The latter results indicate that there is some motion on the time scale of 10(5) s-1 about the C1'(glucose)-O-C3(glycerol) glycosidic bond but that its amplitude is very restricted. Comparison of 1H-decoupled and 1H-coupled 2H NMR spectra of the C3-labeled glycolipid gave estimates of the 2H-2H dipolar coupling between the deuterons at this position. The orientation of the glycerol C3 hydroxymethylene subunit was calculated relative to the bilayer normal, and the C2-C3 bond was found to be tilted away from the bilayer normal by 3 +/- 1 degree.(ABSTRACT TRUNCATED AT 250 WORDS)

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1987

Adrenergic and 'non-adrenergic' contributions to the two-component tetanus in the rat vas deferens.

Nerve-induced contractions of rat isolated vas deferens were examined to determine how the rapid and slow twitch phases summate to produce the two-component tetanus. The rapid phase (time to peak, 200-300 ms) had a latency of 35-50 ms and was selectively abolished by nifedipine but not verapamil. The slow phase (time to peak, 500-650 ms), as seen in the presence of nifedipine, had a latency of 100-200 ms. During a train of pulses at 0.5-2 Hz, its size declined rapidly and its latency lengthened. The rapid phase responses at these frequencies were progressively potentiated to a peak after 12-40 s, a time similar to the peak of the secondary tetanic component at 5 Hz. Doses of verapamil which abolished both this potentiation and the secondary tetanic component did not block the slow twitch phase. The results indicate that the primary tetanic component is a summation of 'non-adrenergic' (rapid phase) and direct adrenergic (slow phase) contractions. In contrast the secondary increase in tetanic tension results largely from the alpha 1-adrenoceptor induced potentiation of the rapid non-adrenergic twitch mechanism. The mechanisms for the two phases and for the potentiation each appear to involve different calcium sources.

Adrenergic alpha-Antagonists↗

PubMed1987

The dependence of glyceroglycolipid orientation and dynamics on head-group structure.

The head-group orientations and molecular dynamics of three glyceroglycolipids in aqueous dispersions, as determined by 2H-NMR, are compared. 1,2-Di-O-tetradecyl-3-O-(alpha-D-glucopyranosyl)-sn-glycerol (alpha-DTGL) and 1,2-di-O-tetradecyl-3-O-(alpha-D-mannopyranosyl)-sn-glycerol (alpha-DTML), selectively 2H-labelled on the pyranose ring, at the exocyclic hydroxymethyl group, and at C3 of glycerol, have been studied by 2H-NMR and the results compared with those reported earlier for 1,2-di-O-tetradecyl-3-O-(beta-D-glucopyranosyl)-sn-glycerol (beta-DTGL). The alpha-glucolipid exhibits a gel-to-liquid crystal phase transition and a lamellar to hexagonal mesophase transition at temperatures which are similar to those of the beta-anomer, beta-DTGL. However, alpha-DTGL exhibits head group orientations and molecular ordering in the lamellar and hexagonal phases which differ strikingly with those reported for the corresponding beta-glucolipid. Whereas the head group of beta-DTGL is extended away from the bilayer surface into the aqueous phase, that of alpha-DTGL is almost parallel to the bilayer surface. alpha-DTGL exhibits a molecular order parameter of 0.56 which is substantially greater than that of its anomer, beta-DTGL, 0.45. The latter indicates that the head group region of the alpha-glyceroglucolipid is characterized by smaller angular fluctuations than that of beta-DTGL. On entering the hexagonal mesophase the pyranose ring of the beta-glucolipid undergoes a large reorientation relative to the motional axis of the head group, whereas the alpha-anomer exhibits only a small orientational change. 1,2-Di-O-tetradecyl-3-O-(alpha-D-mannopyranosyl)-sn-glycerol (alpha-DTML) undergoes a phase transition at 47 degrees C, attributed to the unusual lamellar gel to hexagonal phase transition. The pyranose ring of alpha-DTML, in a mixture with dimyristoylphosphatidylcholine (1:9 mol ratio) to give a lamellar liquid crystalline phase, is oriented away from the bilayer surface into the aqueous environment and has an Smol of 0.75. The results for alpha-DTML, 2H-labelled at the C3 position of glycerol, suggest that this segment also has high molecular ordering. alpha-DTML in a lamellar environment has the least flexible membrane surface of the glyceroglycolipids investigated to date. 2H-NMR spin lattice relaxation times have been used to probe the head group motions of the glycolipids. The results indicate that the rate of head group motion increases in the order alpha-DTML less than alpha-DTGL less than beta-DTGL.(ABSTRACT TRUNCATED AT 400 WORDS)

Chemical Phenomena↗

PubMed1987

Effects of alpha,beta-methylene ATP on biphasic responses of rat vas deferens.

The epididymal region of isolated vas deferens of the rat was stimulated locally with field electrodes. Continuous perfusion with alpha,beta-methylene-adenosine-5'-triphosphate (mATP, 10(-5) M) desensitized the P2-purinoceptors and the effect of this on the two components of tetanic responses and the 'non-adrenergic' and adrenergic phases of single shock responses were examined. Exposure to mATP selectively prevented the contractions to adenosine-5'-triphosphate (ATP, 10(-4)-5 X 10(-4) M) but not noradrenaline (NA, 10(-5) M) and preferentially blocked the secondary but not the primary tetanic component. It also depressed markedly the non-adrenergic phase of single shocks and either reduced or abolished the adrenergic phase. Thus the secondary tension development depends in the rat vas deferens on both the activation of alpha 1-adrenoceptors and the non-adrenergic twitch mechanism. The action of mATP involves more processes than the desensitization of the P2-purinoceptors so does not positively identify purinergic transmission. Direct NA-induced contraction contributes more to the primary than to the secondary tetanic component.

Adenosine Triphosphate↗

PubMed1987

A study of the post-tetanic twitch depression at the prostatic end of the rat vas deferens.

The effects of different drugs on the post-tetanic twitch responses of the prostatic end of the isolation rat vas deferens were examined. Following repetitive field stimulation (4-5 Hz for 40-60 s), the post-tetanic twitches (0.2-0.5 Hz) were depressed relative to the steady-state pretetanic twitches. Maximum post-tetanic twitch depression (PTD) occurred 15-30 s after the tetanic stimulation. The PTD was not reversed but deepened and prolonged by the presynaptic alpha 2-adrenoceptor antagonists idazoxan (RX781094) or yohimbine (10(-7) M) alone or combined with the neuronal uptake blocker, desipramine (10(-6) M). The PTD was insensitive to the beta-adrenoceptor blocker, propranolol (10(-6) M), the P1-purinoceptor antagonist, 8-phenyltheophylline (10(-5) M) or the prostaglandin E synthesis inhibitor, indomethacin (10(-6) M). Pre- and post-tetanic contractions to superfused noradrenaline (NA), adenosine 5'-triphosphate (ATP), or beta, gamma-methylene ATP (beta, gamma-mATP) (bolus injections into superfusate, 1-8 X 10(-5) M) were not significantly (p less than 0.01) different. The PTD was absent in high magnesium (6.2-11.2 mM) solutions. These results are consistent with the PTD having an intrinsic presynaptic origin. They are discussed in relation to stimulation-induced modulation of transmitter release.

Adrenergic alpha-Antagonists↗

PubMed1986

Molecular details of melittin-induced lysis of phospholipid membranes as revealed by deuterium and phosphorus NMR.

Solid-state deuterium and phosphorus-31 nuclear magnetic resonance (2H and 31P NMR) studies of deuterium-enriched phosphatidylcholine [( 3',3'-2H2]DPPC, [sn-2-2H31]DPPC) and ditetradecylphosphatidylglycerol (DMPG-diether), as water dispersions, were undertaken to investigate the action of melittin on zwitterionic and negatively charged membrane phospholipids. When the lipid-to-protein ratio (Ri) is greater than or equal to 20, the 2H and 31P NMR spectral features indicate that the system is constituted by large bilayer structures of several thousand angstrom curvature radius, at T greater than Tc (Tc, temperature of "gel-to-liquid crystal" phase transition of pure lipid dispersions). At T approximately Tc, a detailed analysis of the lipid chain ordering shows that melittin induces a slight disordering of the "plateau" positions concomitantly with a substantial ordering of positions near the bilayer center. At T much greater than Tc, an apparent general chain disordering is observed. These findings suggest that melittin is in contact with the acyl chain segments and that its position within the bilayer may depend on the temperature. On a cooling down below Tc, for Ri greater than 20, two-phase spectra are observed, i.e., narrow single resonances superimposed on gel-type phosphorus and deuterium powder patterns. These narrow resonances are characteristic of small structures (vesicles, micelles, ... of a few hundred angstrom curvature radius) undergoing fast isotropic reorientation, which averages to zero both the quadrupolar and chemical shift anisotropy interactions. On an increase of the temperature above Tc, the NMR spectra indicate that the system returns reversibly to large bilayer structures.(ABSTRACT TRUNCATED AT 250 WORDS)

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1986

Oxygen consumption in Plasmodium berghei-infected murine red cells: a direct spectrophotometric assay in intact erythrocytes.

A spectrophotometric assay has been devised to measure oxygen consumption non-invasively in intact murine red cells parasitized by Plasmodium berghei. The method uses oxyhemoglobin in the erythrocytes both as a source of oxygen and as an indicator of oxygen consumption. Spectra of intact cells show broad peaks and sloping baselines due to light-scattering. In order to ascertain the number of varying components in the 370-450 nm range, the resolution of the spectra was enhanced using Fourier transforms of the frequency domain spectra. Calculation of oxygen consumption was carried out for two-component systems (oxyhemoglobin, deoxyhemoglobin) using absorbances at 415 and 431 nm. Samples prepared from highly parasitized mice (greater than 80% parasitemia, 5% hematocrit) showed oxygen consumption rates of (4-8) X 10(-8) microliter/cell per h. This rate was not attributable to the presence of white cells or reticulocytes. The rate of oxygen consumption in the erythrocytes is shown to be modulated by various agents: the respiratory inhibitors NaN3 and KCN (1 mM) reduced oxygen consumption 2-3-fold; salicylhydroxamic acid (2.5 mM) caused a 20% reduction in rate and 10 mM NaN3, completely blocked deoxygenation. Antimalarial drugs and metal-chelating agents were also tested. Chloroquine, EDTA and desferal (desferoxamine mesylate) did not decrease the deoxygenation rate of hemoglobin in parasitized cells. Quinacrine, quinine and primaquine reduced the rate of formation of deoxyhemoglobin but also produced substantial quantities of methemoglobin. The lipophilic chelator, 5-hydroxyquinoline, decreased the rate of deoxygenation one-third. The spectrophotometric assay provides a convenient means to monitor oxygen consumption in parasitized red cells, to test the effects of various agents thereon, and potentially to explore possible mechanisms for oxygen utilization.

Animals↗

PubMed1986

Differential effects of calcium channel blockers on the responses of the rat vas deferens to intramural nerve stimulation and exogenous drugs.

The calcium channel blockers, nifedipine and verapamil, have separate effects on the phases of nerve-induced twitches which are not reflected by their actions on the responses to exogenous NA, ATP and the stable ATP analogue, alpha, beta-mATP. This implies that different calcium channels are used according to the manner of stimulation.

Adenosine Triphosphate↗

PubMed1986

A 2H-NMR study on the interactions of the local anesthetic tetracaine with membranes containing phosphatidylserine.

The interaction of the local anesthetic tetracaine with phosphatidylserine-containing model membranes has been studied by 2H-NMR. Charged tetracaine exhibited an unusually large partition coefficient into multilamellar dispersions of phosphatidylserine. The 2H-NMR spectra consisted of a Pake doublet and a narrow line, with the former corresponding to tetracaine in the bilayer and the latter to tetracaine free in solution. A strong pH dependence of the quadrupole splittings indicated different membrane locations for charged and uncharged tetracaine. In equimolar mixtures of phosphatidylserine and phosphatidylcholine the partition coefficients and 2H-NMR spectra were much more like those observed in neat phosphatidylcholine than in neat phosphatidylserine. Dilution studies at pH 5.5 indicated that in phosphatidylserine/phosphatidylcholine mixtures tetracaine experiences a three-site exchange similar to that found earlier for tetracaine in phosphatidylcholine. Tetracaine is in fast exchange between sites weakly bound to membrane and free in solution, and in slow exchange with a strongly bound site in the membrane.

Deuterium↗

PubMed1986

Classification of human tumours by high-resolution magnetic resonance spectroscopy.

Malignant tumours yield a high-resolution proton magnetic resonance (MR) spectrum. Fifty-one tumour biopsy specimens from patients with cancer of the ovary or colon were examined by magnetic resonance spectroscopy (MRS) to determine whether it was possible to identify tumour subtypes with metastatic potential. Relaxation parameters (T2) for visible lipid methylene protons were within the range of those measured for three animal metastasis models. Primary carcinomas with metastases gave T2 values greater than 350 ms, whereas carcinomas not associated with known metastases at the time of tumour excision gave a range of values from 150 to 1500 ms. All but two carcinomas gave a long T2 (greater than 350 ms) indicating metastatic potential. The MRS method designated five of six histologically borderline epithelial ovarian tumours as malignant with metastatic potential. MRS may be sensitive enough to detect malignant cells in a tumour which is of intermediate or borderline malignancy by light microscopy. Malignancy without a potential for metastasis is uncommon.

Colonic Neoplasms↗

PubMed1986

Assignment of methylene proton resonances in NMR spectra of embryonic and transformed cells to plasma membrane triglyceride.

Some biological characteristics of cancer cells and solid tumors are identifiable by the high resolution NMR relaxation behavior of their nonaqueous components. Chemical analysis and two-dimensional scalar correlated (COSY) NMR spectroscopy show these resonances arise from neutral lipid in the plasma membrane. Triglyceride is shown to be the main plasma membrane component giving rise to the NMR spectrum, while soluble nonmembrane components account for 90% of the remaining resonances in the spectrum of intact cells. The presence of triglyceride has been detected by chemical analysis in highly purified plasma membranes from two different cell lines. The COSY spectra of cancer cells are comparable with that obtained for the triglyceride-rich very low density human lipoprotein.

Adenocarcinoma↗

PubMed1986

Effects of antimalarial drugs on oxygen consumption by erythrocytes infected with Plasmodium berghei: an ESR study.

Oxygen consumption in mouse erythrocytes infected with Plasmodium berghei has been followed by electron spin resonance (ESR) spectroscopy of nitroxide radical spin probes. The parasitized red cell suspension is mixed with the spin probe CTPO (3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy) in a closed chamber. Oxygen consumption is monitored by the increasing resolution of the superhyperfine splittings of the spin label. The antimalarial drugs quinacrine, primaquine, and quinine are shown to decrease the rate of oxygen consumption of the parasitized erythrocyte suspensions. The spin-label method offers advantages over conventional polarographic and spectrophotometric assays for highly parasitized cell populations where cells are fragile and contain oxidized hemoglobin as well as hemoglobin-derived pigments.

Animals↗

PubMed1986

A detailed analysis of the motions of cholesterol in biological membranes by 2H-NMR relaxation.

Spin-lattice relaxation, T1z, measurements of [2,2,3,4,4,6-2H6]cholesterol in model membranes of DMPC were performed as a function of temperature, Larmor frequency and position of labelling in the fused ring system. The results are interpreted according to a hierarchy of motions, such that motion i of correlation time tau i reduces the residual ordering set, characterizing motions i-1, i-2, etc..., by the amount Si = d(2)00(beta i), where beta i is the angle between the axes of motional averaging of motions i and i-1, respectively and d(2)00 is the Wigner rotation matrix element. The appearance of minima in the temperature dependence of T1z for cholesterol, at 46.1 MHz and 30.7 MHz, and the scaling of these T1z (min) according to the orientation of each individual C-2H bond with respect to the axis of motional averaging of cholesterol, allows assignment of the sterol axial rotation to the second fastest motion, characterized by a correlation time of 3.2 X 10(-9) s at 25 degrees C and an activation energy of 32 +/- 5 kJ X mole-1. The fastest motion of cholesterol in DMPC could be a very rapid libration, 'wobbling', which does not contribute significantly to the T1z relaxation of cholesterol at physiological temperatures and Larmor frequencies smaller than 50 MHz, but does reduce the ordering of the cholesterol molecule in DMPC from S0 = 1 to S1 = 0.8, at 25 degrees C.

Cholesterol↗