[Effects of total saponins of Panax notoginseng on increasing PGI2 in carotid artery and decreasing TXA2 in blood platelets]

Total saponins of Panax notoginseng (PNS) were given orally 100 mg/(kg.d) to rabbit for 8 wk. Aortic atherosclerotic plaque formation was restrained as compared to the control group. Radioimmunoassay was used to investigate the effects of PNS on the contents of prostacyclin in carotid artery and thromboxane A2 in blood platelets of rat. Oral administration of PNS 25,50,100 mg/(kg.d) for 10 d, the caused an increase of prostacyclin in carotid artery and a decrease of thromboxane A2 in blood platelets as compared to the control group. These results show that the anti-atherosclerotic action of PNS may be a result of the correction of the unbalance between prostacyclin and thromboxane A2.

Sex determination of Chinese femur by discriminant function

The objective of this study was to provide a method of sex determination for Chinese femur, especially for fragmentary remains. Statistical analysis of 17 measurements based on 141 northeastern Chinese femora shows that all measurements have significant sex differences. Sex determination by the midpoint method of a single measurement can obtain an average accuracy of 76.8%. The results indicate that of all dimensions the maximum head diameter is the best discriminator of sex. It alone can determine the sex of a femur with 85.1% accuracy. The results also show that maximum head diameter, transverse head diameter, epicondylar breadth, upper breadth, and medial condylar length have higher sexual dimorphisms than the dimensions of length. According to the result to stepwise discriminant analysis and the need for sexing fragmentary remains, 22 discriminant functions composed of various combinations of variables were calculated which can determine the sex of the femur correctly 82.3 to 87.2%. The methods of sex determination provided by this paper can be used to sex poorly preserved femora.

A dihydropyridine-sensitive calcium channel in rodent osteoblastic cells

Rat osteogenic sarcoma cells (UMR 106-01) and normal rat trabecular bone osteoblasts (ROB) were studied using the whole cell version of the patch clamp technique to determine the existence of calcium (Ca2+) channels. Pipette and bath solutions were designed to separate Ca2+ channel currents from other voltage-dependent currents, and Ba2+ was used as the charge carrier. In both UMR 106-01 and ROB cells, a Ba2+ current was measured, which expressed the characteristics of an L-channel, such as activation range, dihydropyridine sensitivity, and little or no inactivation. In some cases, this channel was detectable only with BAY-K-8644 in the bath solution. The dihydropyridine agonist increased the current intensity and shifted the peak inward current to more negative potentials. This study, confirming previous observations, demonstrates the existence of a Ca2+ channel in both transformed and normal osteoblastic cells.

A murine early thymocyte developmental sequence is marked by transient expression of the interleukin 2 receptor

Precursors of all T-lineage cells are found in the population of thymocytes that lacks the CD4 and CD8 surface markers. These "double-negative" thymocytes are heterogeneous and can be divided into discrete subpopulations based on their expression of other surface markers. We have determined the relative maturity of these subpopulations based on the extent of rearrangement and expression of their T-cell receptor genes, their cell cycle status, and their thymus reconstitution capacity. Within the subpopulation of double negatives expressing high levels of the heat-stable antigen, the additional markers phagocytic glycoprotein 1 (Pgp-1) and interleukin 2 receptor (IL-2R) can be used to define the sequence IL-2R- Pgp-1+----IL-2R+ Pgp-1-----IL-2R- Pgp-1-, which occurs before the expression of CD4 and CD8. Transient expression of the IL-2R marks an important developmental point in the sequence just prior to a burst of cell proliferation and a loss of thymus reconstitution ability. The earliest cells in this sequence are already partially rearranged for genes in the C beta 1 region. IL-2R expression marks a second wave of T-cell antigen receptor of beta-chain gene rearrangement and the initiation of T-cell antigen receptor alpha- and beta-chain gene expression.

Transcriptional activation by the pseudorabies virus immediate early protein requires the TATA box element in the adenovirus 2 E1B promoter

The adenovirus E1A protein and immediately early (IE) protein of pseudorabies virus stimulate transcription from many promoters. It has been postulated that these proteins function via cellular intermediates. We analyzed the transcription of adenovirus E1B promoter mutants in response to the stimulatory effect of IE protein in comparison with E1A. Far upstream deletions and precise Sp1 and TATA box substitution mutations were examined. Only mutations affecting the TATA box element interfered with transactivation by IE protein. This result is similar to observations for E1A transactivation (L. Wu et al. Nature (London) 326, 512-515, 1987), suggesting that both E1A and IE proteins mediate transactivation of the E1B promoter through a common cellular intermediate which interacts with the TATA box.

Inference of a molecular defect of apolipoprotein B in hypobetalipoproteinemia by linkage analysis in a large kindred

Heterozygous hypobetalipoproteinemia is characterized by reduced plasma concentrations of LDL cholesterol, total triglycerides, and apo B to less than 50% of normal values. The molecular basis of this disorder remains unknown. The phenotype cosegregates with a DNA haplotype of the apo B gene in an Idaho pedigree, with a maximum decimal logarithm of the ratio (LOD) score of 7.56 at a recombination rate of zero. Individuals carrying this haplotype had total cholesterol levels of 96 mg/dl, LDL cholesterol levels of 37 mg/dl, triglycerides levels of 51 mg/dl, and apo B levels of 38 mg/dl. This study strongly suggests that apo B mutations underlie hypobetalipoproteinemia, and demonstrates the power of the candidate gene approach in linkage analysis for unraveling genetic determinants in metabolic disorders of undefined etiology.

Developmental status and reconstitution potential of subpopulations of murine thymocytes

In this chapter we have summarized our view of the subsets of murine CD4- CD8- thymocytes which can be identified with a range of monoclonal antibodies. We have shown the division rate and turnover time of the main subsets and have listed what we know of the TcR gene rearrangement, and expression at the RNA and protein levels. We have been unable to completely segregate gamma delta-TcR-expressing cells from alpha beta-TcR-expressing cells by any of the markers we have used, although the proportions of the two receptor forms vary widely in the different subsets. Experiments involving intrathymic transfer of the CD4- CD8- subsets are described, which indicate that all the TcR- subsets of the CD4- CD8- thymocytes display some precursor activity and which suggest a progression of at least five stages through the TcR- subpopulations of CD4- CD8- cells. The earliest precursor is a Thy 1 low, HSA low, Pgp-1 high cell which has unrearranged C beta and is non-dividing and which closely resembles the bone marrow prothymocyte. The later precursors are Thy 1 high, HSA high, Pgp-1 low, have rearranged C beta and are rapidly dividing. We tentatively conclude that none of the TcR+ CD4- CD8- cells are precursors of the major thymocyte subsets or of typical peripheral T cells, and we have found no evidence so far of separate precursors for the different mature subsets of thymocytes or peripheral T cells.

Preparation of both DNA and RNA for hybridization analysis from limiting quantities of lymphoid cells

This report describes a method for preparing both DNA and RNA simultaneously from as few as 5 X 10(5) lymphoid cells. The method is suitable for cultured cells or any tissue from which a cell suspension can be prepared and for the small samples of purified cells obtained by fluorescence activated cell sorting. Cells are lysed with Nonidet P-40 and the nuclear and cytoplasmic fractions separated by centrifugation. Nuclei are embedded in low-gelling-temperature agarose and the proteinase K and restriction enzyme digestions performed whilst the DNA is immobilized in this form. Total RNA is prepared from the cytoplasmic fraction. This method is simple but reliable and is therefore particularly useful for preparing and analyzing the DNA and RNA from multiple samples when material is limited.

Constraints on spacing between transcription factor binding sites in a simple adenovirus promoter

The adenovirus 2 E1B transcription unit has an extremely simple promoter consisting of a TATA box and a closely situated GC box. The interaction between the TATA box and the GC box was analyzed using insertion mutations which expand the distance between the two elements. We observed that the E1B promoter has an unusually rigid architecture. When the GC box, which is a binding site for transcription factor Sp1, was separated further from the TATA box than in the wild-type promoter, in vivo transcription quickly diminished to a level comparable to the elimination of the Sp1 site. Yet all the insertion mutants bound Sp1 factor in vitro with an affinity approximately equal to that of the wild-type promoter. From these results, we argue that Sp1 binding alone is not sufficient to stimulate transcription. The increased distance might disrupt direct contacts between Sp1 and transcription factors bound at the TATA box, contacts required for transcription stimulation by Sp1. The insertion mutations do not interfere with the transcription activation process mediated by the adenovirus large E1A protein or the pseudorabies virus immediate early protein.

Contribution of the urea appearance rate to diuretic-induced azotemia in the rat

Studies were performed to evaluate the contribution of the urea appearance rate to the elevated plasma urea concentration found during diuretic-induced sodium depletion. Negative sodium balance of -1162 + 29 microEq/100 g body wt was induced over a four day period by the administration of furosemide, 20 to 30 mg/kg/d i.p., to rats ingesting a sodium free diet. When compared with sodium replete controls, sodium depletion significantly increased the plasma urea concentration (65.0 +/- 3.1 vs. 26.4 +/- 1.1 mg/dl) through both an increase in the urea appearance rate (160 +/- 5.2 vs. 125 +/- 3.5 mg/day/100 g body wt), and a decrease in the urea clearance rate (1.99 +/- 0.14 vs. 3.16 +/- 0.12 ml/min/kg). The urea appearance rate increased on the first day of diuretic administration, remained elevated three days after stopping diuretics, rapidly returned to control levels after sodium repletion, and was significantly correlated with the magnitude of sodium deficit. Similar results were obtained when diuretic-induced sodium depletion was produced in adrenalectomized animals. After four days of sodium depletion the plasma concentration was increased for some amino acids but not for the plasma total amino acid, nitrogen concentration. The results indicate that sodium depletion increases the urea appearance rate through a mechanism that is independent of adrenal function. Thirty to sixty percent of the elevation in plasma urea concentration that occurs in the rat during diuretic-induced sodium depletion can be accounted for by an enhanced urea appearance rate.

Preliminary evidence for genetic determination of intraerythrocytic sodium concentration in Utah pedigrees

Intraerythrocytic sodium concentration has been reported to be increased in hypertensive individuals and some of their normotensive relatives. We investigated the "familiality" of this trait in 572 nonhypertensive subjects from 34 Utah kindreds. Most of these kindreds were selected because of a high incidence of hypertension, heart attack, or stroke. Intraerythrocytic sodium concentration was correlated with the sex of the subject and suprailiac skinfold thickness. Intraerythrocytic sodium concentration was adjusted by linear regression for these 2 factors. The residual values were positively correlated in parent-offspring pairs and among sibs, both those presumed to be living together and those presumed to be living apart. The spouse-spouse correlation was not significant. Pedigree analysis suggested a mixed major-gene/polygenic model of inheritance, but these data did not allow us to distinguish between dominant and recessive inheritance for the major gene component. Total heritability due to both major-gene and polygenic components was estimated to be 90-95%; the proportion of the total variance due to polygenes was estimated to be 60-75%. These results suggest that further study of the relationship between the inheritance of intraerythrocytic sodium and the pathophysiology of hypertension is warranted.

A TATA box implicated in E1A transcriptional activation of a simple adenovirus 2 promoter

Adenovirus E1A proteins stimulate transcription by RNA polymerases II and III from many promoters. The detailed mechanism of transcriptional activation (transactivation) by E1A proteins remains unclear, but genetic and biochemical results suggest that E1A products might act to stimulate the activity of cellular transcription factors. In this study, a detailed mutational analysis of the adenovirus E1B promoter was undertaken to define the DNA sequences required for proper basal transcription and E1A transactivation. Two key findings emerged: first the E1B promoter is an unusually simple RNA polymerase II promoter requiring only two sequence elements for proper regulation, the TATA box and a binding site for transcription factor Sp1; and second only mutations in the TATA box interfere with E1A-transactivation, suggesting that E1A mediates its effect on this promoter through the TATA-box transcription factor.

Major locus inheritance of apolipoprotein B in Utah pedigrees

A major locus that determines levels of apolipoprotein B (apoB) was revealed by likelihood analysis on 331 members of 36 pedigrees. The major locus explained 43.2% of the observed variance, with the remainder attributed to random environmental factors. Estimated mean apoB levels (mg/dl) were 110.5 +/- 2.5, 141.9 +/- 4.4, and 208.1 +/- 11.5 for low homozygotes, heterozygotes, and high homozygotes, respectively. The corresponding genotypic frequencies were 0.718, 0.259, and 0.023. The apoB locus explained 13% and 14% of the variance in total and low-density-lipoprotein cholesterol levels, respectively. Persons with elevated apoB had normal to high levels of total serum cholesterol and triglyceride and low to normal levels of high-density lipoprotein and apolipoprotein A-I. Sixteen members of three of the pedigrees were heterozygous for familial hypercholesterolemia (FH). Their apoB levels were estimated as 35.72 +/- 7.16 mg/dl above the apoB genotypic means, assuming that the two loci act independently. Therefore, two major loci, the FH locus and the apoB locus, affect two levels, apoB and LDL cholesterol.

A DNA probe for the LDL receptor gene is tightly linked to hypercholesterolemia in a pedigree with early coronary disease

A large, multigenerational family with dominantly inherited hypercholesterolemia was analyzed for genetic linkage between blood levels of low-density lipoprotein (LDL) cholesterol and the locus for the LDL receptor. A genetic marker was identified by restriction fragment length polymorphism (RFLP) in a cloned segment of the LDL receptor gene. We found no exceptions to segregation of the high-LDL cholesterol phenotype with a unique allele at the LDL receptor locus in this pedigree; tight linkage was indicated by a maximum lod score of 7.52 at theta = 0. Knowledge of the LDL receptor genotype will enable investigators to study variability of phenotypic expression in response to environmental influences or to different genetic determinants.

Methylenedioxymethamphetamine: a potentially neurotoxic amphetamine analogue

The amphetamine analogue, methylenedioxymethamphetamine (MDMA) has received considerable attention recently as a novel and increasingly popular psychoactive agent. When administered acutely to rats in high doses, MDMA caused a selective and dramatic decrease in brain concentrations of serotonin and its metabolite, 5-hydroxyindoleacetic acid. The depletion of serotonin and its metabolite persisted for up to at least one week after a single injection of MDMA at approximately four to five times the acute dose reported for humans. These results are discussed in terms of the possible neurotoxic effects of MDMA.

Relationship between the structure of chromosomal protein HMG1 and its accumulation in the cell nucleus

When microinjected into the cytoplasm of cultured mammalian cells, non-histone chromosomal protein HMG1 migrates into the nucleus and binds to the chromatin. To define the features of the HMG1 molecule which are essential for this activity, fragments of HMG1 and chemically modified HMG1 molecules were injected into HeLa cells and the capacity of each of these probes to accumulate in the nucleus was measured by an autoradiographic technique. Fragments representing the C-terminal and central portions of HMG1 did not concentrate in the nucleus; a fragment which consisted of the N-terminal two-thirds of the molecule and which lacked the 41 consecutive aspartate and glutamate residues located near the C-terminal end of the molecule accumulated to about the same extent as intact HMG1. When the amino groups of HMG1 were chemically modified, there was a progressive loss in the ability of the protein to accumulate in the nucleus; derivatization of one-fourth of the total amino groups reduced the concentration of microinjected protein in the nucleus relative to that in the cytoplasm to one-half of the original value. In contrast, modification of one-fourth of the total carboxyl groups did not significantly affect the capacity of HMG1 to accumulate in the nucleus, although further modification resulted in decreased nuclear accumulation. Iodination of tyrosine residues was without effect and modification of the cysteine residues had only a modest effect on the ability of HMG1 to concentrate in the nucleus.

Binswanger's disease: progressive subcortical encephalopathy or multi-infarct dementia?

Since Binswanger's description of subcortical arteriosclerotic encephalopathy in 1894, numerous cases have been reported. Several authors doubt the validity of this malady, although the majority consider it to be a disease entity. We report seven cases with this type of pallor of myelin, only two of which are accompanied by a history of dementia. Among the seven cases, two had arteriosclerosis of penetrating arteries and arterioles in cerebral white matter. Electron microscopy showed splitting of myelin sheaths, probably the result of edema. In reviewing the blood supply of the cerebral white matter, we conclude that no pathological alterations of medullary branches of the cerebral arteries, the same vessels supplying the white matter, can give rise to such diffuse pallor of white matter and spare the arcuate fibres. This pallor can only be due to cerebral edema, most likely of hypoxic-ischemic, hypotensive, or acidotic origin. We also contend that arteriosclerosis can only cause dementia through multiple infarcts or lacunae, if it indeed leads to dementia.

Systemic venous and pulmonary arterial flow patterns after Fontan's procedure for tricuspid atresia or single ventricle

Despite increasing use of Fontan or modified Fontan repairs, the comparative hemodynamic efficacy of different types of connections are unresolved. Accordingly, we undertook a prospective study designed to determine postoperative flow patterns after Fontan's operation. Seven subjects had tricuspid atresia and eight had single ventricle. Ages ranged from 5 to 38 years (mean 16.4). Ten subjects had nonvalved right atrial-to-pulmonary arterial connection, and four had nonvalved right atrial-to-right ventricular communication. A valved conduit established continuity between the right atrium and right ventricle in one subject. Doppler flow profiles were recorded in the pulmonary artery and in the superior and inferior venae cavae of each. A reference electrocardiogram was used for timing purposes. In 14 patients, forward flow in the pulmonary artery was biphasic. Flow began at the end of the T wave (early ventricular diastole), peaked at or before the P wave (atrial systole), and returned to baseline by the peak of the R wave. Forward flow recommenced at the peak of the R wave (ventricular systole) and returned to baseline at the end of the T wave. Flow in the superior vena cava varied, and could not be recorded in three subjects. Between the end of the P wave and peak of the R wave (atrial systole) flow was reversed in eight, absent in three, and forward in one patient. Forward flow occurred between the peak of the R wave and the end of the T wave and was either continuous or biphasic. Fourteen patients had adequate studies of inferior vena cava flow; reversed flow during atrial systole occurred in 10 subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Properties of electroretinographic intensity-response functions in retinitis pigmentosa

Dark-adapted electroretinogram (ERG) b-wave amplitudes and implicit times were recorded as a function of stimulus luminance for 15 retinitis pigmentosa (RP) patients and 15 normal subjects. B-wave amplitude as a function of log stimulus luminance was fit by non-linear regression with the Naka-Rushton equation, which has 3 independent parameters: The maximum response (Rmax), slope (n) and half-saturation constant (K). B-wave implicit-time as a function of log stimulus luminance was fit by linear regression. Compared to normal, the RP Rmax values were markedly reduced, suggesting response compression; the RP K values were elevated by an average of 0.76 log unit, suggesting relatively small losses in retinal sensitivity. There was no correspondence between Rmax and visual field area for the RP patients (coefficient of correlation = -0.02). All but 2 of the 15 RP patients had normal or shallower-than-normal implicit-time intensity-response functions, indicating that over most of the dynamic range of the ERG, the implicit-times were either normal or faster-than-normal. These results are discussed in terms of possible RP disease mechanisms.

Pharmacological properties of two amino esters of diphenylpropanoic acid

N, N-Diethylaminoethyl ester and 3-quinuclidinyl ester of 2, 2-diphenylpropanoic acid (compound 1 and 2, respectively) were prepared and pharmacologically evaluated in vitro and in the intact animal. Both compounds attenuated the effects of increasing doses of ACh in the isolated rat ileum (pA2 = 8.40 and 8.55, respectively). These effects were comparable to that of atropine (pA2 = 8.73). The duration of methacholine-induced salivation in male Swiss-Webster mice was significantly decreased by compound 2 but not by compound 1. Cardiorespiratory studies in adult male Sprague-Dawley rats revealed that both compounds shifted the dose-response curves to methacholine in terms of arterial blood pressure, heart rate and respiration upwards; indicative of cholinergic blockade. The observed pharmacological differences between the two compounds may be attributed to apparent in vivo hydrolysis of compound 1 by esterases.

Molecular cloning and expression of the mouse ornithine decarboxylase gene

We used mRNA from a mutant S49 mouse lymphoma cell line that produces ornithine decarboxylase (OrnDCase) as its major protein product to synthesize and clone cDNA. Plasmids containing OrnDCase cDNA were identified by hybrid selection of OrnDCase mRNA and in vitro translation. The two of these with the largest inserts together span 2.05 kilobases of cDNA. Southern blot analysis of DNA from wild-type or mutant S49 cells, cleaved with EcoRI or with BamHI, revealed multiple bands homologous to OrnD-Case cDNA, only one of which was amplified in the mutant cells. RNA transfer blot analysis showed that the major OrnD-Case mRNA in the mouse lymphoma cells is 2.0 kilobases long. A similar size mRNA was found in mouse kidney and was more abundant in the kidneys of mice treated with testosterone, an inducer of OrnDCase activity in that tissue.

Location of amino acid alterations in mutants of aspartate transcarbamoylase: Structural aspects of interallelic complementation

Recent genetic studies of the pyrB locus of Escherichia coli resulted in the characterization of 29 mutant strains harboring defects in the structural gene that encodes the catalytic chains of aspartate transcarbamoylase (carbamoylphosphate: L-aspartate carbamoyltransferase, EC 2.1.3.2). Three alleles, pyrB554, pyrB730, and pyrB748, have been cloned, and their nucleotide sequences have been determined along with that of the wild-type pyrBI operon in order to locate the sites of the alterations in the catalytic chains. Missense mutation pyrB554 leads to replacement of serine-52 by phenylalanine, and the inactive mutant enzyme has properties similar to those of wild-type aspartate transcarbamoylase. The amber mutation pyrB730 results in unstable truncated polypeptide chains 27 amino acids shorter than wild-type chains. Deletion mutation pyrB748 causes the removal of 181 amino acids. Combining these results with knowledge of the crystallographic structure of the wild-type enzyme provides a basis for tentative structural mechanisms for the observed complementation behavior of the mutant proteins.

Experimental study in rabbits of the antishock effect of anisodamine (654-2), and its mechanism of action

The antishock effect of anisodamine (654-2) was observed in different kinds of experimental shock in groups of rabbits--due to late hemorrhage, superior mesenteric artery occlusion, and septic shock from peritonitis. The drug 654-2 significantly alleviated the progress of shock and increased the survival rate of the animals. The therapeutic effect of 654-2 was much better than that of other vasoactive drugs commonly used, such as norepinephrine, phenoxybenzamine, dopamine, and aramine. The antishock mechanism of 654-2 is probably partly due to its protective action on intestinal shock in preventing its effects becoming irreversible. The antishock action of 654-2 both by basic research workers and clinicians merits further study.

Comparative studies on microinjected high-mobility-group chromosomal proteins, HMG1 and HMG2

The nonhistone chromosomal proteins, HMG1 and HMG2, were iodinated and introduced into HeLa cells, bovine fibroblasts, or mouse 3T3 cells by erythrocyte-mediated microinjection. Autoradiographic analysis of injected cells fixed with glutaraldehyde consistently showed both molecules concentrated within nuclei. Fixation with methanol, on the other hand, resulted in some leakage of the microinjected proteins from the nuclei so that more autoradiographic grains appeared over the cytoplasm or outside the cells. Both injected and endogenous HMG1 and HMG2 partitioned unexpectedly upon fractionation of bovine fibroblasts, HeLa, or 3T3 cells, appearing in the cytoplasmic fractions. However, in calf thymus, HMG1 and HMG2 molecules appeared in the 0.35 M NaCl extract of isolated nuclei, as expected. These observations show that the binding of HMG1 and HMG2 to chromatin differs among cell types or that other tissue-specific components can influence their binding. Coinjection of [125I]HMG1 and [131I]HMG2 into HeLa cells revealed that the two molecules display virtually equivalent distributions upon cell fractionation, identical stability, identical intracellular distributions, and equal rates of equilibration between nuclei. In addition, HMG1 and HMG2 did not differ in their partitioning upon fractionation nor in their stability in growing vs. nongrowing 3T3 cells. Thus, we have not detected any significant differences in the intracellular behavior of HMG1 and HMG2 after microinjection into human, bovine, or murine cells.

The C-wave of the rabbit electroretinogram during dark-adaptation and the steady-state

C-waves of the rabbit ERF under urethane anesthesia were elicited by a Grass photostimulator during dark adaptation and under steady-state conditions. After strong pre-adaptation with light, the amplitude and time-to-peak of the c-wave increased in parallel with the a- and b-waves, reaching a maximum of 90-130 min. In the dark-adapted steady-state, repetitive stimuli at intervals ranging from 15 sec to 5 min elicited a stable c-wave response except for a small dip in amplitude that occurred 2-6 min after initiating the shortest interval (15 sec) flashes. Although the changes in light and dark used in these experiments should have elicited shifts in the standing potential, no fluctuations of the c-wave amplitude were evident with a time course corresponding to a light response of the standing potential.

A prospective study of mitral valvular prolapse in young men

A cardiac history, a physical examination, an electrocardiogram, phonocardiograms in the supine and standing positions, and an M-mode echocardiogram were obtained in 100 randomly selected, presumably healthy, male medical students (mean age, 26 years). Four percent met standard echocardiographic criteria for mitral valvular prolapse. No midsystolic clicks or late systolic murmurs were appreciated in this group, and none complained of chest pain or palpitations. To elucidate further the clinical implication of the echocardiographic pattern of mitral valvular prolapse, 24-hour ambulatory ECGs, multistage exercise tests, and scintiscans of myocardial perfusion at rest and after exercise (using radioactive 13nitrogen-labelled ammonium) were obtained, with normal results. The absence of life-threatening arrhythmias and exercise-induced abnormalities in these four asymptomatic subjects without abnormal physical findings suggests that the echocardiographic pattern of mitral valvular prolapse in such individuals may represent a variant of normal which does not require extensive evaluation.