A comparison of liver tumor diagnoses from seven PCB studies in rats

Through a policy assumption, all polychlorinated biphenyls (PCBs) are considered probable human carcinogens by most regulatory agencies based on experimental studies in rodents where an increased incidence of liver tumors has been observed. Recognizing that new consensus criteria for the diagnoses of liver tumors in rats had been promulgated, a reevaluation of liver tumor diagnoses from seven PCB studies in rats was undertaken. These seven studies, in which rats were fed PCB mixtures containing 42, 54, or 60% chlorine, were considered to be the best studies from which to evaluate the cancer potential of PCB mixtures. The reevaluation results, where consistent diagnoses now exist across all studies, clearly indicate major differences in carcinogenic potential based on degree of chlorination. Studies of mixtures with 60% chlorination consistently resulted in a high incidence of liver tumors, whereas studies in which rats were fed mixtures with 54 or 42% chlorination showed no statistically significant increases in liver tumors. These data indicate that continuation of a science policy of assuming that all PCBs are probable human carcinogens with a potency equivalent to the mixture that contains 60% chlorine has no scientific foundation and should be reconsidered.

Continuous coronary flow velocity monitoring during coronary interventions: velocity trend patterns associated with adverse events

Continuous measurement of blood flow velocity during interventional procedures has the potential to provide an early warning of coronary flow instability, which can lead to abrupt closure or other adverse events before angiography. The magnitude and fluctuations of the average velocity over time (trend) was studied by using a 0.018-inch Doppler-tipped angioplasty guide wire in 32 patients after coronary angiography (n = 20), atherectomy (n = 2), urgent stent (n = 6), urgent vein graft thrombolysis (n = 4), or acute myocardial infarction (n = 2). The patients (mean age 60 +/- 11 years) had postprocedural in-laboratory flow monitoring for a mean of 19 +/- 11 (range 8 to 36) minutes. The coronary artery monitored was the left anterior descending in 13, circumflex in 6, right coronary artery in 9, and saphenous vein graft in 4. Seven patients had flow-related events during continuous flow velocity monitoring before serial angiographic study. These events included coronary vasospasm (abrupt flow acceleration), vasovagal flow cessation, cyclical flow variations resulting from accumulation of intraluminal thrombus, and rapid decline of flow velocity. The last two patterns were associated with abrupt vessel closure during angioplasty. Continuous flow velocity monitoring is easily incorporated into routine interventional procedures and provides an early indication of unstable flow and the potential for abrupt vessel closure and other adverse events.

Nuclear magnetic resonance studies of anticonvulsant enaminones

1H nuclear magnetic resonance (NMR) spectra of enaminones were determined and compared to the anticonvulsant activity of the compounds. Although the precise employment of the NMR data to predict anticonvulsant activity of the enaminones could not be established, general inferences were made. The NMR data confirmed that the enaminones existed predominantly in the amino tautomer, and no evidence was found for the imino tautomer. The ketamine form of the enaminones was supported by the observed spin-spin splittings of the NH with the alpha-protons on certain enaminones. The NH of secondary enaminones was very important in conferring anticonvulsant activity to the enaminones. The peak for the NH proton which could be seen between delta (ppm) 4.50 and 9.70 was present in all of the active enaminones. The tertiary enaminones, which were devoid of the NH proton, were uniformly inactive. It appeared that a combination of steric and electronic effects, lipophilicity, and hydrogen bonding were necessary for the anticonvulsant activity of the enaminones. The cyclic enaminones existed in the trans-S-trans fixed conformation, and the NMR data supported our hypothesis that enantioselectivity is retained in synthesizing enaminones from cyclic, diasteriomeric 1,3-diketones. In addition, the AB system and many unique features were observed in some enaminones. The para, meta, and ortho substituted patterns were observed for monosubstituted phenyl protons, and the NMR patterns for di- and trisubstituted phenyl groups were elucidated.

Ancrod infusion for anticoagulation during and after PTCA in a patient with heparin-induced thrombocytopenia

Ancrod is a rapid-acting defibrinogenating agent derived from the venom of the Malayan pit viper which has been used successfully as an alternative to heparin sulfate for anticoagulation during peripheral vascular procedures and coronary artery bypass surgery. We describe the first use of ancrod for anticoagulation before and during percutaneous transluminal coronary angioplasty (PTCA) in a patient with heparin-associated thrombocytopenia.

Coronary flow velocity during coronary angioplasty in regions of myocardial infarction

In patients undergoing angioplasty for angina after myocardial infarction, patterns of post-stenotic coronary blood flow velocity depend not only on satisfactory dilation of the flow-limiting lesion, but also on the vasoregulatory capacity of infarcted myocardium. The case examples demonstrate both normal and persistently abnormal flow velocity patterns following successful coronary angioplasty for post-infarction ischemia. Recognition of collateral flow patterns, easily available using the Doppler angioplasty guidewire, may provide valuable information predicting the viability of post-infarcted myocardium and the resolution of abnormal distal coronary flow patterns.

Synthesis and evaluation of amino analogues of valproic acid

Valproic acid, an antiepileptic drug, is extensively metabolized in humans. Two putative metabolites, 2-n-propyl-3-aminopentanoic acid (3-aminovalproic acid, 3-amino-VPA; 2a) and 2-n-propyl-4-aminopentanoic acid (4-amino-valproic acid, 4-amino-VPA; 4a), which may result from the transamination of the respective keto acids 1a and 3a may explain the unusual extended seizure protection elicited by valproic acid. The title compounds were synthesized as their diasteriomeric ethyl esters 2b and 4b and submitted for anticonvulsant evaluation by the Antiepileptic Drug Development Program of the National Institute of Neurological and Communicative Disorders and Stroke. The results verified our hypothesis, as 4b was active in the subcutaneous pentylenetetrazol (scMet) evaluation at 30 mg/kg. Both compounds were highly toxic at 300 mg/kg.

Synthesis, reactions, and preliminary evaluations of enaminone esters

The objective of this work was to design enaminone esters that would possess potential medicinal properties. The reaction between beta-hydroxyketo esters and primary or secondary amines yielded secondary or tertiary enaminone esters, respectively. The UV spectra of the enaminone esters were determined in acidic, alkaline, and neutral media; the spectra have a hypsochromic shift in acidic media in comparison with neutral media. The enaminone esters provided nucleophilic and electrophilic sites for a variety of reactions. Thus, the enaminone esters were converted into enaminone amides and O-alkylation products exclusively. Although the enaminone esters were generally resistant to reduction by metal hydrides, one unhindered enaminone ester was reduced to an alcohol with sodium borohydride. Another enaminone ester reacted with guanidine to give the corresponding quinazolinone. Due to the variety of nucleophilic and electrophilic sites in the enaminone system, enaminone esters possess a great potential as reaction intermediates and medicinal compounds. Preliminary evaluations of the enaminone esters revealed a histaminergic effect, uterine relaxant properties, and anticonvulsant activity.

Cyclization reactions leading to beta-hydroxyketo esters

The purpose of the research was to synthesize beta-diketo esters and to evaluate them for anticonvulsant activity. The reaction of methyl vinyl ketone with dimethyl malonate in the presence of potassium carbonate gave an uncyclized product that underwent a Claisen condensation to yield methyl 2-hydroxy-4-oxocyclohex-2-en-1-oate (5a). Similarly, other cyclized beta-hydroxyketo esters were prepared, and their spectrometric data confirmed that the enol tautomers were preferred to the beta-diketo tautomers. The synthetic work clarified the reaction pathway for the Michael addition of malonate esters to enones. Of the intermediates and products tested for anticonvulsant activity, dimethyl 2,2-bis-(3-oxobutyl)malonate (9a) was found to possess anticonvulsant property. However, it is emphasized that the beta-hydroxyketo esters could be useful intermediates in the synthesis of enaminone anticonvulsants.

A kinematic technique for describing wrist joint motion: analysis of configuration space plots

This paper describes an experimental method for determining the minimum number of degrees of freedom of a human joint. Application of this technique to the wrist suggests that the normal, intact wrist joint uses only two degrees of freedom to move in a plane that is not aligned with the anatomic planes. The technique may be useful in identifying emerging joint pathologies and in simplifying kinematic models of joint function.

Synthesis and CLOGP correlation of imidooxy anticonvulsants

Continuing structure-activity studies on the anticonvulsant activity of analogs of N-(benzyloxy)-2-azaspiro[4.4]nonane-1,3-dione (2a), which displayed anti-electroshock seizure (MES) activity and a protective index (TD50/ED50) of > 4.5 are reported. An in-depth analysis of this moiety was studied employing the Topliss structure activity and the Craig plot analytical approaches as well as a semiempirical method. CLOG P analysis was also applied to this series after experimentally determining the NOR fragment. All compounds were minimized and these physicochemical parameters correlated to anticonvulsant activity. Several interesting substituted benzyloxy compounds emerged from this study: the 2',4'-dichloro (2b), 4'-(trifluoromethyl) (2c), 2'-bromo (2d), 3'-chloro (2o), 2'-chloro (2r), 2'-fluoro (2p), and 3'-fluoro (2w) analogs, all of which had comparable, or better activity than the parent unsubstituted analog (2a). X-ray crystal analysis of the active 2a versus inactive N-benzyl-2-azaspiro[4.4]nonane-1,3-dione (10) is discussed.

Synthesis and anticonvulsant activity of enaminones. 2. Further structure-activity correlations

This report continues the in-depth evaluation of methyl 4-[(p-chlorophenyl)amino]-6-methyl-2-oxocyclohex-3-en-1-oate , 1 (ADD 196022), and methyl 4-(benzylamino)-6-methyl-2-oxocyclohex-3-en-1-oate, 2, two potent anticonvulsant enaminones. These compounds were evaluated employing the amygdala kindling model. Neither 1 nor 2 was active against amygdala kindled seizures, further supporting the corneal kindled model as a definitive tool for antielectroshock seizure evaluation as previously reported. Additional intraperitoneal (ip) data on 1 revealed toxicity at 24 h at 100 mg/kg. Several active analogs have been prepared with the view to minimizing toxicity. In a special ip rat screen developed by the Antiepileptic Drug Development (ADD) Program, these newer analogs were evaluated for protection against maximal electroshock seizures (MES) at 10 mg/kg and neurotoxicity at 100 mg/kg. From this screen, several compounds were shown to be safer alternatives, the most notable was methyl 4-[(p-bromophenyl)amino]-6-methyl-2-oxocyclohex-3-en-1-oate, 13. Compound 13 had an ip ED50 of 4 mg/kg in the rat and a TD50 of 269 mg/kg, providing a protective index (TD50/ED50) of > 67. By variation in the ring size, additional aromatic substitutions and the synthesis of acyclic analogs, these newer compounds provide a more definitive insight into the structure-activity correlation. CLOGP evaluation and molecular modeling studies are also provided to further elaborate the molecular characteristics of potential anticonvulsant enaminones.

Re-aiming the canon

Although it is unlikely that the national goals for educational reform--such as that, by the year 2000, U.S. students will be first in the world in science and mathematics achievement--can be achieved, a vigorous effort must be made to reach those goals as rapidly as possible. Reform will come not from a massive expansion of what we now do but from a basic shift in the manner in which we educate students in grades K-16 in the sciences and mathematics. Important elements in that basic shift must include an increase in teaching of science, mathematics, and technology (SMT), to about 20%-25% of the curriculum; SMT must include rich hands-on experiences, with an emphasis on concepts and understanding, rather than on facts and memorization, and on how science as a way of knowing differs from other ways of knowing; SMT must consider human problems; and SMT must deal with the basic problem facing humanity--how we must adjust our behavior so as not to exceed, on a worldwide basis, the carrying capacity of the environment.

Influence of model and marker on digesta kinetic estimates for sheep

Several models and markers are available for digesta kinetic studies. In this study, kinetic estimates derived from chromium-mordanted hay or pellets were compared to estimates derived from rare earth markers (Yb, Dy, or Er) applied individually to samples. Twelve yearling rams (52 kg) were given ad libitum access to either hay or a commercial pelleted diet in a crossover experiment. Digesta kinetic estimates were obtained both by nonlinear analysis with two age-independent rates (G1G1) or with gamma time dependency in the fast compartment (G2G1 to G4G1) and by linear regression of natural log transformed fecal marker concentrations (LN method of estimate). Model did not influence total tract (P > .21) or ruminal mean retention times (P > .87). Partitioning of total retention time was similar (P > .21) for the LN, G3G1, and G4G1 models, but the G1G1 and G2G1 models did not adequately fit these data. Nonlinear models overestimated, and LN underestimated, fecal DM output by 9% (SEM = 4.7) for the hay diet. All the nonlinear models provided fecal DM output estimates that were within 5% of actual fecal DM output, but the LN model underestimated it by 18% (SEM = 3.3) for the pelleted diet. Ruminal outflow rate was slower (P < .01) and both ruminal and total mean retention time estimates were longer (P < .01) for Cr than for the rare earths. Despite the marker chosen, relative diet effects were similar. The three rare earth markers gave identical results for digesta kinetic estimates, indicating that they are useful for simultaneous study of more than one ingredient or particle, but direct comparison of rare earth and Cr-mordant passage rates is not advisable.

Structural remodeling of cardiac myocytes in patients with ischemic cardiomyopathy

BACKGROUND

Chronic ischemic heart disease may lead to ventricular dilation and congestive heart failure (ischemic cardiomyopathy [ICM]). The changes in cardiac myocyte shape associated with this dilation, however, are not known.

METHODS AND RESULTS

Left ventricular myocyte dimensions were assessed in cells isolated from explanted human hearts obtained from patients with ICM (n = 6) who were undergoing heart transplantation. Cells were also examined from three nonfailing donor hearts with normal coronary arteries (NCA). Compared with cells from patients with NCA, myocyte length was 40% longer in hearts from patients with ICM (197 +/- 8 versus 141 +/- 9 microns, p less than 0.01), cell width was not significantly different, and cell length/width ratio was 49% greater (11.2 +/- 0.9 versus 7.5 +/- 0.6, p less than 0.01). Sarcomere length was the same in myocytes from both groups. The extent of myocyte lengthening is comparable to the increase in end-diastolic diameter commonly reported in patients with ICM.

CONCLUSIONS

These data suggest that increased myocyte length (an intracellular event), instead of myocyte slippage (an extracellular event), is largely responsible for the chamber dilation in ICM. Furthermore, maladaptive remodeling of myocyte shape (e.g., increased myocyte length/width ratio) may contribute to the elevated wall stress (e.g., increased chamber radius/wall thickness) in ICM.

Synthesis and anticonvulsant activity of enaminones

A new series of novel enaminones has been synthesized from cyclic beta-dicarbonyl precursors which were condensed with morpholine, pyrrolidine, phenethylamine, hydrazines, substituted benzyl amines, and substituted anilines. These compounds were subsequently evaluated for anticonvulsant activity in a variety of anticonvulsant models by the National Institute of Neurological and Communicative Disorders and Stroke and in our laboratory. Several of these compounds exhibited potent anticonvulsant activity with a remarkable lack of neurotoxicity. The most active analog, methyl 4-[(p-chlorophenyl)amino]-6-methyl-2-oxo-cyclohex-3-en-1-oate++ + (27), was protective in the maximal electroshock (MES) seizure test in the rat with an oral ED50 of 5.8 mg/kg with no toxicity noted at doses up to 380 mg/kg, thus providing a protective index (TD50/ED50) of greater than 65.5. A similar protective index for 27 was noted upon intraperitoneal (ip) administration in mice. The anticonvulsant effect of 27 occurred within 15 min of administration and the compound remained active beyond 4 h. Compound 27 was also active in the rat corneal kindled model. The application of Free-Wilson analysis to structure-activity correlation in this series is discussed.

Nuclear DNA content and nucleation patterns in rat cardiac myocytes from different models of cardiac hypertrophy

Nuclear DNA content and number of nuclei were examined in cardiac myocytes isolated from controls and rats with volume and pressure overload hypertrophy to determine if haemodynamic overload alters these nuclear parameters. The experimental groups were comprised of normotensive (WKY) and Spontaneously Hypertensive rats (SHR). Additionally, Sprague-Dawley rats with aortic constriction (AC), pulmonary stenosis (PS), myocardial infarction (MI), and 5 month arteriovenous fistulas (F) were studied along with appropriate shams for each of these groups. Nuclear DNA content was measured from DAPI-stained nuclei using an image analysis microdensitometry system. Myocyte volume was measured with a Coulter Channelyzer system. Approximately 83% of the left ventricular myocytes from the SHR and WKY groups contained a diploid DNA content with the remainder being tetraploid. The remaining experimental and sham groups, all female Sprague-Dawley rats (SD), were approximately 93% diploid. The nucleation patterns differed slightly between rat strains with the SHR/WKY expressing approximately 85% binucleation, 14% mononucleation and 5% tri- or tetranucleation. All SD groups, control and hypertrophied, showed approximately 89% binucleation, and 10% mononucleation with the remainder being tri- or tetranucleated. In summary: (1) cardiac myocytes from SHR/WKY strains are predominantly diploid but to a lesser degree than myocytes from SD; (2) nuclear number follows the same pattern with SHR/WKY showing a smaller percentage of binucleated myocytes than SD myocytes; (3) neither the duration, severity, or type of overload caused a significant change in the extent of polyploidy in overloaded hearts from SD rats; and (4) the extent of polyploidy in cardiac myocytes from both the right and left ventricles of SHR and WKY animals does not differ statistically.

Regional increase in isolated myocyte volume in chronic myocardial infarction in cats

Healing of myocardial infarction is associated with hypertrophy of a region surrounding the scar. In order to characterize the pattern of regional hypertrophy after healing of small myocardial infarctions, we used a Coulter Channelyzer to measure directly regional cell volume and light microscopy to measure cell length of isolated myocytes. Acute left ventricular myocardial infarctions were surgically created in adult cat hearts. After healing for 10.4 +/- 5.0 months, cells were dissociated by collagenase perfusion. Myocardial cells were isolated from three regions of the infarcted ventricle and the same three anatomical regions of unoperated control hearts: (1) remote from the infarct, (2) non-scarred tissues adjacent to the infarct, and (3) from the infarct. The volume of cells from control hearts was correlated significantly with individual body weight resulting in large inter-animal variations, but small intra-animal variations. Inter-animal comparisons were made by normalizing adjacent and infarct regions to percent change from its remote region. Myocyte volumes from hearts with healed infarcts were increased by 31% in the infarct region and by 20% in the adjacent region, relative to the corresponding regions from control hearts (P less than 0.05). Cell lengths were not different from control in any region. Calculated cross-sectional areas followed the same pattern as was observed for cell volumes. We conclude that there is a region of hypertrophy surrounding a small, transmural healed myocardial infarction that is characterized by increased myocyte cross sectional area with no change in cell length. This pattern is typical of the concentric hypertrophy observed with pressure overload rather than eccentric hypertrophy observed with volume overload.

Adrenergic modulation of preoperative anxiety: a comparison of temazepam, clonidine, and timolol

To assess the influence of adrenergic modulation on preoperative anxiety, we used a randomized, double-blind, placebo-controlled trial to compare temazepam, clonidine, and timolol as preanesthetic medications in patients undergoing minor orthopedic surgery. All the active treatments resulted in less preoperative anxiety than the placebo (control) did. Induction of anesthesia was smoother in all the treated patients compared with the control group. Recovery was slowest in the temazepam and clonidine groups, but there were no significant differences between the groups after 90 min. Cardiovascular changes were most marked in the timolol group. Pain scores were lower in the temazepam and clonidine series in the early postoperative period. Neither clonidine nor timolol offers any major advantage over temazepam for premedication in these patients.

Interspecies scaling of clearance and volume of distribution data for five therapeutic proteins

The clearance and volume of distribution of five human proteins (recombinant CD4, CD4 immunoglobulin G, growth hormone, tissue-plasminogen activator, and relaxin) in humans and laboratory animals were analyzed as a function of body weight using allometric scaling techniques. These proteins cover a 16-fold range of molecular weight (6 to 98 kD), are produced by recombinant or synthetic methods, and may be cleared by different mechanisms. The analyses revealed that the clearance and volume data for each protein were satisfactorily described by an allometric equation (Y = a Wb). The allometric exponent (b) for clearance (ml/min) ranged from 0.65 to 0.84, the allometric exponent for the initial volume of distribution (ml) ranged from 0.83 to 1.05, and the allometric exponent for the volume of distribution at steady state (ml) ranged from 0.84 to 1.02. Exponent values from 0.6 to 0.8 for clearance and 0.8 to 1.0 for volumes are frequently cited for small molecules and are expected based on empirical interspecies relationships. When the preclinical data were analyzed separately, the preclinical allometric relationships were usually predictive of the human results. These findings indicate that the clearance and volume of distribution of select biomacromolecules follow well-defined, size-related physiologic relationships, and preclinical pharmacokinetic studies provide reasonable estimates of human disposition. Employing this methodology during the early phases of drug development may provide a more rational basis for dose selection in the clinical environment.

Respiratory and enteric cryptosporidiosis in humans

A 24-year-old homosexual man with acquired immunodeficiency syndrome presented with intractable diarrhea and fever. Examination of a rectal biopsy specimen and stool revealed Cryptosporidium. Approximately 4 months after admission he developed respiratory failure and died. Postmortem examination revealed cryptosporidiosis involving the entire gastrointestinal tract as well as the tracheobronchial tree. To our knowledge, this is one of the rare presented cases of tracheobronchial cryptosporidiosis documented histologically.

Results of prenatal alcohol exposure on the dimensions and binucleation of cardiac myocytes in neonatal and weanling rats

Sprague-Dawley rats were exposed to ethyl alcohol in utero. The effect of chronic prenatal exposure was examined by giving mature females alcohol in isocaloric liquid diets which served as the sole source of liquid and caloric intake before mating and throughout gestation. Controls consisted of females maintained on laboratory chow or an isocaloric liquid diet minus alcohol before and during gestation. The offspring were sacrificed at 21 days of age (weanlings) and the hearts dissociated enzymatically to give purified cardiac myocytes. The effects of daily acute prenatal alcohol exposure were studied by gastric intubation of alcohol to chow-fed females for the duration of pregnancy. The doses used approximated 4 and 5 shots of 80 proof liquor per day by a person weighing 150 lb. These offspring were sacrificed at 2, 6, and 21 days postnatal and cardiac myocytes prepared as above. Heart weights were determined and cardiac myocytes were analyzed for cell length, volume, cross-sectional area, and percent binucleation. Additionally, nuclear DNA content was measured in all of the 21 day offspring. Statistical analysis of the data showed no significant differences between hearts exposed to prenatal alcohol and nonexposed controls with either regimen with the exception of percent binucleation which was significantly but only slightly higher in the 6-day-old hearts. These findings are discussed in relation to anatomical heart defects found in patients with full fetal alcohol syndrome.

Wheat straw or alfalfa hay in diets with 30% neutral detergent fiber for lactating Holstein cows

Twenty-four Holstein cows near peak lactation were fed diets formulated to contain 30% NDF with forage NDF from chopped wheat straw or chopped alfalfa hay in proportions of 0:3, 1:2, 2:1, and 3:0 in an 8-wk trial to evaluate effects of fiber source on lactational performance. Concentrate was based on highly degradable carbohydrate in steam-flaked sorghum grain. Forage to concentrate ratio decreased from 49:51 to 28:72 when straw was substituted for alfalfa hay. Milk yield (38.4 kg/d) and DMI (23.1 kg/d) were not influenced by forage source. Milk fat percentage decreased and milk protein percentage increased linearly with increasing straw. Yields of 3.5% FCM and fat showed linear and quadratic responses, because they appeared to be reduced only on the 0:3 diet, and protein yield showed a quadratic response and was highest for the 1:2 diet. Digestibility of NDF averaged 43.5, 45.4, 40.7, and 31.2%, and acetate to propionate ratio was 3.0, 2.4, 2.2, and 1.9 with increasing dietary straw. Passage rates were not influenced by diet and averaged 9.3, 7.6, 6.1, and 4.7%/h for fluid, grain, alfalfa hay, and wheat straw, respectively. It is suggested that the ratio of forage NDF to ruminally degradable starch be maintained greater than or equal to 1:1 when diets based on low quality forage are fed to cows in early lactation.

Nuclear size and DNA content in rat cardiac myocytes during growth, maturation and aging

Changes in nuclear volume and DNA content were examined in cardiac myocytes isolated from 21-day-old (weanling, W), 3-month-old (adult, A), and 2-year-old (old, O) rats to document normal parameters for nuclear growth and DNA content. Nuclear volume was calculated from direct measurements of isolated myocyte nuclear profiles and DNA content was measured from DAPI-stained nuclei using an image analysis microdensitometry system. Myocyte volume was measured with a Coulter Channelyzer system. Nuclear volume increased 79% from W to A as a result of an increase in nuclear length. Nuclear width was unchanged. Nuclear volume was not changed from A to O. Approximately 98% of the left ventricular myocytes from all three rat groups contained a diploid DNA content with the remainder of nuclei being tetraploid. The degree of polyploidy increased slightly, but significantly, in right ventricular myocytes from O. Due to the substantially greater increase in myocyte volume relative to nuclear volume, nuclear volume percentage decreased from 3.65 +/- 0.28 to 1.64 +/- 0.13 from W to A but was unchanged from A to O. To summarize: (1) nuclear volume of rat cardiac myocytes increases significantly during normal physiological growth (W to A) but the rate of nuclear growth is less than that of cell volume; (2) the increase in nuclear size from W to A is not due to an increase in DNA content; (3) cardiac myocytes from Sprague-Dawley rats are predominantly diploid; and (4) there is little change in DNA content of cardiac myocytes from rats of this strain during growth, maturation and aging.