Cell Cross-sectional Area Research Articles

Morphometric and biochemical characteristics of ventricular hypertrophy in male rainbow trout (Oncorhynchus mykiss).

We examined the morphometric and biochemical effects of ventricular hypertrophy in male rainbow trout (Oncorhynchus mykiss) during sexual maturation. Our investigation focused on characterizing the growth of ventricular layers, on cardiomyocyte dimensions (length, cross-sectional area and cell volume) and on the activities of enzymes involved in intermediary metabolism. Relative ventricle mass (100 x ventricle mass/body mass) increased by as much as 2.4-fold during sexual maturation [as defined by an increasing gonadosomatic index (100 x gonad mass/body mass)], and this resulted in an increased proportion of epicardium relative to endocardium. Ventricular enlargement was associated with increased length (+31 %) and transverse cross-sectional area (+83 %) of cardiomyocytes, which resulted in an expansion of up to 2.2-fold in mean myocyte volume (from 1233 to 2751 micron3). These results indicate that sexual maturation induces ventricular enlargement through myocyte hypertrophy. Cell length and cross-sectional area were similar in both myocardial layers, and myocytes were elliptical rather than circular in transverse cross section. Ventricular hypertrophy did not alter transverse cell shape, perhaps reflecting the maintenance of short diffusion distances for small molecules as cells hypertrophy. Myocyte hypertrophy could not account entirely for the sevenfold range of ventricle masses from different-sized fish, indicating that myocyte hyperplasia contributes substantially to ventricular growth as trout grow. Measurements of the maximal activities of metabolic enzymes demonstrated that ventricular hypertrophy was associated with (1) higher epicardial but not endocardial activities of citrate synthase (by 23 %) and beta-hydroxyacyl-CoA dehydrogenase (by 20 %); (2) lower activities of hexokinase (by 50 %) in both layers, and (3) no change in lactate dehydrogenase or pyruvate kinase activities, which were also similar between layers. These results suggest that the energetic needs of the hypertrophied trout ventricle may be met through increased reliance on fatty acid oxidation, particularly by the endocardium, but decreased reliance on glucose as a metabolic fuel in both layers.

Morphometric changes in the chick nucleus magnocellularis following acoustic overstimulation

The present investigation considered the effects of cochlear damage caused by exposure to intense sound on the nucleus magnocellularis of the chick. Neonatal chicks exposed to intense sound were separated into four groups with post-exposure recovery durations of 0, 15, 27, and 43 days. Four age-matched, non-exposed control groups were also formed. At each recovery interval, the control and exposed birds were sacrificed and their brains prepared for paraffin embedding. The brain stem region containing the nucleus magnocellularis (NM) was serially sectioned in the coronal plane. All sections containing NM cells were identified and then coded in terms of their percentile distance from the most caudolateral section. Sections along the nucleus at the 15th, 30th, 50th, 65th, 80th, and 95th percentile positions were selected for evaluation, and the cross-sectional areas of individual NM cells in these sections were then measured. Cell areas were corrected for the bias introduced by eccentricity of the nucleus. The number of NM cells per 1,000 microm2 was also calculated at the 50th and 65th percentile positions. These procedures were repeated for the age-matched, non-exposed control animals. The cross-sectional cell area in exposed animals, immediately after the exposure, was reduced significantly at all positions, but returned to near normal by 43 days of recovery. However, the coronal area of NM in the sections at the 50th and 65th percentile position, as well as NM cell density, were unaffected by the exposure at all recovery intervals. The observation of structural recovery in NM cells at 43 days post-exposure was remarkable because it occurred at least 4 weeks after complete functional restoration of single-cell activity in the NM. The shrinkage in NM cell size throughout the nucleus may be due to a general reduction in spontaneous activity in the cochlear nerve fibers caused by the acoustic injury to the chick basilar papilla.

Spouted bed electrowinning of zinc: Part I. Laboratory-scale electrowinning experiments

Two types of laboratory cells have been constructed to electrowin zinc from sulfate electrolytes: one cell was cylindrical while the other had a rectangular (flat) geometry. Cells were operated on industrial or synthetic electrolytes to electrodeposit zinc onto a spouted bed of zinc particles in the range of 0.75 to 1.45 mm. Current efficiencies and cell voltages have been measured during the course of batch experiments, enabling the calculation of the energy consumption per kilogram of zinc deposited. Electrolyte samples have been analyzed. Current densities (current per unit of cell cross-sectional area) were in the range of 1380 to 6200 A/m2. Most catholytes were initially neutral and contained on the order of 150 g/L of zinc. Final acid contents were in the range of 39 to 114 g/L of sulfuric acid. The performance of the cells (particularly with respect to current efficiency) was superior to prior work on fluidized bed electrowinning from similar electrolytes. The flat cell was superior to the cylindrical cell and showed energy consumptions of less than 3 kWh/kg zinc at current densities up to 3500 A/m2 when used to take the zinc content from 150 to 100 g/L zinc. Current efficiencies in this application ranged from 91 to 92 pct.

Action potentials, ion channel currents and transverse tubule density in adult rabbit ventricular myocytes maintained for 6 days in cell culture.

Adult rabbit ventricular myocytes were cultured in a basic medium (Medium 199) for up to 6 days to assess preservation of morphology and ion channel currents. In culture, cells remained rod shaped and striated but their ends became progressively rounded. Cell cross-sectional area declined slightly (by 14%) over the first 24 h, in contrast, whole-cell capacitance (which reflects external surface membrane plus membrane infoldings) decreased by 42% over the same time. Using whole-cell patch-clamp, we observed that the typical "N" shape steady-state current-voltage (I-V) relation became flattened after 24 h in culture. L-type Ca channel density was assessed as barium flux (IBa,L) via the channel. IBa,L (normalised to cell capacitance) declined by 50% after 24 h and recovered partially by days 4 and 6. The density of inward rectifier K current declined by 54% after 24 h and showed no recovery subsequently. In contrast, there was no significant decline in the density of transient outward K current after 24 h, but it declined subsequently by 65% after 6 days. We speculate that the time course of change in each ion channel density may reflect a change in pattern of ion channel expression, or differential membrane loss since the density of transverse tubules decreased by 57% after 6 days in culture. These results suggest that even by 24 h in culture, ion channel density in myocytes has changed substantially from the acutely isolated state.

Endothelial cell “swelling” in ischaemia and reperfusion

The endothelial cells of cardiac capillaries have been reported to swell as a result of ischaemia and reperfusion although there has not previously been any attempt to quantify this observation. Whole capillary and luminal cross-sectional areas, abluminal and luminal membrane lengths were measured from electron micrographs of isolated rat hearts subjected to 30 or 60 min of global ischaemia both with and without subsequent reperfusion for 15 min. All the experimental protocols resulted in capillaries which appeared swollen by electron microscopy. Measurements, however, showed that, after 30 and 60 min ischaemia, this appearance was brought about by a decrease in both whole capillary and luminal area causing an increase in the distance between abluminal and luminal membranes without any change in the endothelial cell cross-sectional area. Reperfusion after 30 min caused an increase in capillary dimensions to larger than control levels. Only after 60 min ischaemia with reperfusion were the cells really swollen with an increase in cross-sectional area. We conclude that (1) we may be observing capillary constriction and (2) the word "swelling" in this context should be used with caution.

Ontogenesis of somatic and germ cells in sheep fetal testis

Testicular development of sheep fetuses was studied between day 42 of gestation and birth. Testis mass and the total number of testicular cells increased curvilinearly with fetal age and a positive linear relationship was established between the logarithmic values of age and testis mass, sex cord total length, total number of Sertoli cells, germ cells and Leydig cells per testis. The mean number of gonocytes per unit length of sex cord, the Sertoli cell nuclear cross-sectional area and the Leydig cell cross-sectional area decreased linearly with age between day 42 of gestation and birth. Hypophysectomy and hemicastration were performed to study the regulation of testicular cell divisions during fetal life and to determine whether they were under pituitary control and whether a feedback mechanism was present. Hypophysectomy at day 100 or 110 of gestation nonsignificantly decreased (0.05 < P < 0.01) the testis mass, total length of sex cords and total number of Sertoli cells and significantly decreased (P < 0.05) the cross-sectional area of Leydig cells and nuclei of Sertoli cells. Sex cord diameter and total number of gonocytes were unaltered. Hemicastration at day 110 of gestation significantly increased (P < 0.05) the total number of Leydig cells per testis without changing any other testicular parameter. In male sheep fetuses, the proliferation of testicular somatic and germ cells occurs throughout testicular fetal growth at a higher rate before day 100 of gestation than later, but without any differentiation. Mitotic divisions of Sertoli cells are more numerous before birth than afterwards. Before birth, the proliferation of gonocytes is not under pituitary control.

Morphological gradients in sensory hair cells of the amphibian papilla of the frog, Rana pipiens pipiens

The sensory hair cells of the amphibian papilla (AP) of the northern leopard frog were examined in a light-microscopic analysis. Hair cell length and cross-sectional area were found to vary systematically along the rostro-caudal axis of the endorgan. The AP was readily divided into three morphological regions. Rostrally-located hair cells are tall, cylindrically-shaped cells with large crosssectional areas and long stereocilia; caudally-located hair cells are short, goblet-shaped cells with small cross-sectional areas and short stereocilia. In the middle region, hair cells exhibit features intermediate to those of hair cells located at the AP extremes. The detailed pattern of changes in hair cell morphology along the endorgan correlates well with its observed tonotopy and may have implications for the intrinsic tuning of the AP.

The Endothelial Vesicular System in Cardiac Capillaries Subjected to Hypoxia

The precise role of the numerous plasmalemmal vesicles in capillary endothelia is unclear. They undoubtedly play a part in macromolecular transport across the endothelium but, as serial section studies have shown the vast majority of vesicles to be attached to either the luminal or abluminal membrane, it is possible that transport is not their primary role. The suggestion that vesicles form a membrane reserve was explored in capillaries of isolated perfused rat hearts subjected to hypoxia, which has been reported to cause endothelial cell swelling. Luminal, "cytoplasmic," and abluminal vesicles were counted and their diameters measured in well-oxygenated and hypoxic hearts and a number of other endothelial cell parameters were measured. Total capillary and luminal cross-sectional area and luminal and abluminal membrane length decreased in hypoxia. There was no change in endothelial cell cross-sectional area despite an appearance of swelling. The numbers of abluminal and "cytoplasmic" vesicles did not change as a result of hypoxia. Luminal vesicles were, however, reduced in number but increased in size and density. The results are consistent both with the theory that the vesicles are a membrane reserve and that they may be present in order to expose membrane enzymes and receptors on the cell surface or internalise them in response to a variety of external stimuli.

The relation between latissimus dorsi skeletal muscle structure and contractile function after cardiomyoplasty

Past reports suggest that structural changes within the latissimus dorsi muscle occur with chronic electrical stimulation during cardiomyoplasty. However, the specific changes in the structure of the latissimus dorsi muscle and the relation to muscle contractile function with cardiomyoplasty are unknown. Accordingly, this study examined regional changes in latissimus dorsi muscle structure and function after cardiomyoplasty. The left latissimus dorsi muscle was mobilized and wrapped around the heart in pigs with the use of standardized techniques and the latissimus dorsi muscle chronically paced at ambient heart rates (90 beats/min; 20 Hz, 5 V amplitude, n = 6). After 6 weeks, the paced latissimus dorsi muscle and the contralateral control muscle were removed and divided into proximal (0 to 3 cm), middle (3 to 6 cm), and distal (6 to 12 cm) regions. By computer-assisted morphometry, muscle cell myofibril volume, cross-sectional area, and collagen percent area were determined. In the paced latissimus dorsi muscle, myofibril volumes increased by more than 50% in the proximal and middle regions compared with those in the contralateral control muscle. However, myofibril volumes were significantly lower in the distal region of the paced latissimus dorsi muscle compared with those in control muscles (33% ± 5% versus 20% ± 3%, p < 0.05). In the paced latissimus dorsi muscle, cross-sectional area was significantly reduced from that of control muscles in all regions. A further reduction in cross-sectional area was noted in the distal region of the paced latissimus dorsi muscle compared with that in both the contralateral control muscle and the proximal and middle regions of the paced latissimus dorsi muscle. Collagen content significantly increased in the paced latissimus dorsi muscle compared with that in control muscle with a more fibrotic pattern observed in the distal region. Latissimus dorsi muscle strips (less than 2 mm2 cross-sectional area) were harvested, and peak and velocity of tension development were examined after field electrical stimulation at 0.2 to 1.2 Hz. At 0.2 Hz, the velocity of tension development was unchanged in the paced latissimus dorsi muscle compared with that in control muscle. However, peak tension development degraded by only 28% in the paced latissimus dorsi muscles but fell by 51% in control muscles with increased stimulation frequencies. In summary, the contractile function of the chronically stimulated latissimus dorsi muscle was associated with fatigue resistance and increased contractile protein content. However, more distal regions of the paced latissimus dorsi muscle demonstrated atrophy and fibrosis. These region-specific changes within the chronically stimulated latissimus dorsi muscle may significantly influence the long-term performance of this skeletal muscle after cardiomyoplasty. (J THORAC CARDIOVASC SURG 1994;107:868-78)

Myofibrillar adaptations during cardiac hypertrophy.

The main purpose of this study was to determine the transmural adaptive changes that occur in cell size, myofibrils, and myosin isoforms from the endocardium (ENDO) to the epicardium (EPI) of the left ventricle (LV) of the rat heart during compensatory hypertrophy. Hypertrophy was induced by supra-renal aortic constriction for periods of 2, 7, 15 and 30 days. Percent left ventricular hypertrophy averaged 63 +/- 9.7% at 30 days following constriction. A significant (p < 0.05) transmural gradient in the V3 myosin isoform (9 +/- 0.7% ENDO vs. 5 +/- 1.8% EPI) was initially observed at 7 days and was still evident by 30 days (25 +/- 3.6% ENDO vs 15 +/- 2.0% EPI). Cell cross-sectional area was also greater (p < 0.05) in the ENDO than in the EPI at 7, 15 and 30 days. MF diameter was determined only at 30 days and was found to be similar to control values in both the hypertrophied ENDO (sham 1.24 +/- 0.05 vs hyp 1.18 +/- 0.09 microns) and EPI (sham 1.17 +/- 0.08 vs hyp 1.06 +/- 0.08 microns). The combined effects of cardiac myocyte hypertrophy with no change in MF diameter resulted in a calculated increase of approximately 70% in the number of myofibrils per myocyte both in the ENDO and EPI. It was concluded that the adaptive strategy of the left ventricular free wall to pressure overload was to initially increase myocyte cross-sectional area and then switch myosin expression from V1 to V3, both of which proceeds transmurally from the sub-endocardium towards the sub-epicardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Attenuation of acute lung injury and oxygen radical production by the 21-aminosteroid, U-78518F.

Oxygen radicals play an important role in the mechanism of acute lung injury. The 21-aminosteroid lazaroid, U-78518F, is a potent antioxidant. We examined the effect of intravenous U-78518F on acute lung injury in septic guinea pigs over 8 h. The experimental groups (n = 6) were 1) saline control, 2) Escherichia coli (2 x 10(9)/kg i.v.), 3) pretreatment (U-78518F 5 mg/kg bolus + 1 mg.kg-1 x h-1, 15 min before E. coli injection), and 4) posttreatment (U-78518F 30 min after E. coli injection). We measured wet-to-dry weight ratio (W/D) as an index of pulmonary edema and concentration ratios of 125I-labeled albumin in lung tissue and bronchoalveolar lavage fluid compared with plasma (L/P and BAL/P, respectively) as indexes of lung protein fluxes. In septic guinea pigs, pretreatment with U-78518F attenuated W/D, L/P, and BAL/P and posttreatment attenuated W/D and BAL/P (P < 0.05 for each). Furthermore, we studied the effect of U-78518F on human neutrophil oxygen radical production (ORP) by using flow cytometry to assess intracellular ORP and lucigenin-dependent chemiluminescence to assess extracellular ORP. Neutrophils (5 x 10(5) were stimulated with 0.5 micrograms/ml of phorbol myristate acetate. With flow cytometry, we measured intracellular ORP, cross-sectional cell area, and degranulation in neutrophils. U-78518F (minimum concn 1.0 microM) decreased intracellular ORP (n = 4; P < 0.05) when the dihydrorhodamine 123 assay was used. U-78518F (minimum concn 1.0 microM) inhibited phorbol myristate acetate-induced neutrophil chemiluminescence (n = 4; P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Testosterone propionate administration prevents the loss of neurons within the central part of the medial preoptic nucleus.

In the rat, the central part of the medial preoptic nucleus (MPNc) of the male is larger in volume and has a greater number of neurons than that of the female. The nucleus of the female, however, can be "sex reversed" by exposing the rat to gonadal steroids perinatally. The purpose of the present study was to examine the development of the MPNc to determine when the sex difference first appears and whether this difference occurs due to the relative accumulation of neurons into the compact part of the MPNc of the male and sex-reversed female rat or to the loss of MPNc neurons in the control female. Pregnant, female Sprague-Dawley rats were given an injection of [3H]methyl thymidine on embryonic day 18 (E18). Rats were exposed to testosterone propionate (TP) or vehicle from E20 to postnatal day 10 (PN10) or until the time of sacrifice. Pups from three groups [males (oil), females (oil), and sex-reversed females (TP)] were sacrificed on PN2, PN4, PN7, PN10, or PN30. The volume of the compact part of the MPNc increased in males and sex-reversed females after PN4 but the volume in the nucleus of females remained relatively constant. The number of neurons and [3H]thymidine-labeled cells remained elevated from PN2-PN30 in males or sex-reversed females but decreased dramatically in oil-treated females between PN4 and PN7, reaching a minimal number by PN10. Cell cross-sectional area increased with age while cell density decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial cell hypertrophy after myocardial infarction with reperfusion in dogs.

The potential role of myocardial cell hypertrophy in the ischemic zone in the mechanism of late recovery of regional contractile function after myocardial infarction followed by reperfusion has not been examined. Eight chronically instrumented, conscious dogs were subjected to 90-120 minutes of circumflex coronary artery occlusion followed by reperfusion. The thickness and function of the anterior (AT) and posterior (PT) walls was measured by ultrasonic gauges at control, during occlusion, and after reperfusion. After 3 weeks, cross-sectional areas of surviving cells were determined from subepicardial (epi), midwall (mid), and subendocardial (endo) regions in six dogs and compared with those from six animals without infarction, including three sham-operated control dogs. PT systolic wall thickening showed dyskinesia during occlusion but recovered after reperfusion to 48% of control at 1 week and 67% at 3 weeks. End-diastolic thickness of the PT wall increased markedly after reperfusion, but AT and PT walls were only slightly thicker (p = NS) than in control dogs at 3 weeks. Cross-sectional areas of reperfused dogs in the infarct region averaged 279 (PTepi), 291 (PTmid), and 317 microns 2 (PTendo) and were significantly larger than in control animals (237 [PTepi], 241 [PTmid], and 233 microns 2 [PTendo]). PT cell areas were significantly larger than AT cells, ENDO cell areas were larger than EPI cells (both p < 0.05), and ENDO cells of the AT wall were larger than those of noninfarcted dogs (p < 0.05). In dogs with myocardial infarction followed by reperfusion, the cross-sectional areas of cells in the infarcted PT wall were larger than those in the noninfarcted AT wall, and within both the infarcted and noninfarcted zones, cell areas were larger in the endocardial than the epicardial region. In all regions of the infarcted wall and in the ENDO region of the noninfarcted wall, cell areas were generally larger than those of control dogs without infarction, and the control dogs showed no transmural differences in cell areas. The mechanisms responsible for this significant remodeling of the reperfused infarcted zone, which involves myocardial cellular hypertrophy, are unknown, but it is possible that hypertrophy of surviving regions of the infarcted wall played a role in the late recovery of regional function that accompanied this hypertrophic response.

Exercise-induced cellular alterations in the diaphragm.

Limited data exist concerning the effects of exercise training on cellular oxidative capacity in the diaphragm of senescent animals. In this study we examined the changes in cellular oxidative capacity, muscle cell cross-sectional area (CSA), and capillarity within the costal diaphragm of senescent animals after a 10-wk endurance-training program. Twelve 24-mo-old female Fischer 344 rats were divided into either a sedentary control group (n = 6) or exercise training group (n = 6). The trained animals exercised on a motor-driven treadmill (60 min/day, 5 days/wk) at a work rate equal to approximately 55-65% VO2max. Capillaries were identified histologically and fiber types determined using adenosinetriphosphatase (ATPase) histochemistry. Succinate dehydrogenase (SDH) activity and CSA in individual fibers were measured using a computerized image analysis system. Exercise training did not increase (P > 0.05) the capillary-to-fiber ratio for any fiber type. However, training significantly decreased CSA (P < 0.05) and increased capillary density (capillary number/CSA) (P < 0.05) in type I, type IIa, and type IIb fibers. Furthermore, exercise training resulted in small but significant increase in SDH activity (P < 0.05) in type I and IIa fibers, whereas training did not alter SDH activity (P > 0.05) in type IIb fibers. These data demonstrate that endurance training in senescent animals results in small relative improvements in both oxidative capacity and capillary density in costal diaphragmatic type I and IIa muscle fibers. The increase in both capillary density and fiber SDH activity was largely due to a reduction in fiber CSA.

Normalization of contractile parameters in canine airway smooth muscle: morphological and biochemical.

Asthma research has recently highlighted the importance of correctly normalizing force development for purposes of comparing stiffness properties of smooth muscle between different airways, between airways at different stages of maturity, and between airways from different animal species. This problem does not exist in striated muscle where the entire tissue consists almost entirely of muscle and where cross bridges cycle at the same rate throughout a contraction when load correlation is made. In the bronchus, cross-sectional area of true muscle may constitute only 20-30% of the total tissue cross section, and load-independent cycling rate varies fourfold during the course of a contraction because of the occurrence of normally cycling and latch bridges. These features are responsible for the difficulty in force normalization in smooth muscle. Our studies indicate that normalization with respect to true muscle cell cross-sectional area (derived by quantitative morphometry of appropriate tissue transverse sections) is the most valid. This is only so, however, when it has been proved that the actomyosin content per unit weight of the different muscle tissues is the same.

Isometric contraction by fibroblasts and endothelial cells in tissue culture: a quantitative study.

We have used an isometric force transducer to study contraction of two types of nonmuscle cells in tissue culture. This method permits the quantitative measurement of contractile force generated by cells of defined type under the influence of external agents while allowing detailed morphological observation. Chick embryo fibroblasts (CEF), which form a contractile network inside a collagen matrix, and human umbilical vein endothelial cells (HUVE), which are located in a monolayer on the surface of the collagen matrix, were studied. CEF and HUVE in 10% FCS produce a substantial tension of 4.5 +/- 0.2 x 10(4) dynes/cm2 and 6.1 x 10(4) dynes/cm2, respectively. Both cell types contract when stimulated with thrombin, generating a force per cell cross-sectional area of approximately 10(5) dynes/cm2, a value approximately an order of magnitude less than smooth muscle. The integrity of the actin cytoskeleton is essential for force generation, as disruption of actin microfilaments with cytochalasin D results in a rapid disappearance of force. Intact microtubules appear to reduce isometric force exerted by CEF, as microtubule-disrupting drugs result in increased tension. Contraction by HUVE precedes a dramatic rearrangement of actin microfilaments from a circumferential ring to stress fibers.

Development and Modulation of Experimental Right Ventricular Hypertrophy in Rats

Two models of right ventricular (RV) hypertrophy in rats have been created and characterized: chronic myocardial infarction and pulmonary artery stenosis. A Millar ultraminiature catheter pressure transducer designed specifically for right heart catheterization was used for the measurement of RV function in closed-chest, anesthetized rats. Four weeks after coronary artery ligation, left ventricular (LV) function was depressed as evidenced by the reduction of LV systolic pressure (LVSP), the maximal rate of rise in LV pressure (LV dp/dtmax), cardiac output, and by the elevation of LV end-diastolic pressure (LVEDP). There was an increase in RVSP and an elevation in RV dp/dtmax as well as an increase in the RV weight/body weight ratio. Myocytes isolated from the RV 4 weeks after coronary artery ligation had a greater volume and cross-sectional area. In addition, 14 days after pulmonary artery stenosis, there also was an elevation in RVSP and in RV dp/dtmax. In this model, the effect of angiotensin-converting enzyme (ACE) inhibition with ramipril (1 mg/kg daily) was examined. The increase in RVSP from 35 +/- 2 to 61 +/- 4 mm Hg after pulmonary artery stenosis was not influenced by ramipril (63 +/- 4 mm Hg), neither was the elevation of RV weight. However, the increase in cell volume and cross-sectional area of myocytes isolated from the RV was less pronounced in the ramipril-treated group (+27% compared with +58% in untreated animals). Thus, ACE inhibition with ramipril altered the hypertrophic response at the cellular level.

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.

The morphology of the developing canine conducting system: Bundle branch and Purkinje cell architecture from birth to week 12 of life

This is a qualitative and quantitative study of dog bundle branch and Purkinje cell development from day 0 to week 12 of life; we correlate the morphologic data with changes observed in the functional properties of developing dog Purkinje tissue. The bundle branch itself has a roughly cylindrical shape and is surrounded by a collagen sheath covered with endocardium. Within the bundle, Purkinje cells are packed closely together in fascicles distributed evenly around a central artery. Cross-sectional area doubles in the right bundle and increases 5-fold in the left bundle system between day 0 and week 12 of life. About one third of the bundle by volume is Purkinje tissue; the rest is extracellular space containing an increasing amount of collagen as the animal ages. Purkinje cell cross-sectional area is constant during the first week of life, but its length doubles and the cell changes from a relatively round to a more cylindrical shape. Between day 7 and week 12, cell diameter doubles; Purkinje cell surface area increases 5-fold and its volume almost 10-fold. As a consequence, the surface to volume ratio halves and approaches the value reported for adult dogs by week 12 of life. The percent of the intercalated disc occupied by nexal junctions virtually doubles by week 12, the same period over which Purkinje fiber conduction velocity increases. The disc itself becomes less dominant as the cell enlarges; the total percent of sarcolemma involved in its formation decreases by a fourth and has achieved the adult value by week 12 of life. As this happens, the percent of cell membrane facing on clefts increases almost 6-fold, so that the total percent of sarcolemma facing on small spaces (approximately 340Å wide) is constant over the age period studied. The paucity of clefts in newborn tissue compared with the value reported for the adult dog may help explain the relative lack of responsiveness to extracellular potassium concentration of the resting membrane potential described for fetal Purkinje tissue. Within the Purkinje cell itself, the percent by volume occupied by mitochondria remains relatively constant over the age span studied, while sarcomeric mass increases 3-fold over the same period of time; these data are consonant with the relative resistance of this tissue to hypoxia.

Allometric Scaling of Light Absorption and Scattering by Phytoplankton Cells

Examination of the allometric scaling of light absorption (acell) and scattering (bcell) by 28 phytoplankton species showed that light absorption is scaled to the cross-sectional area of the cells (log acell(square micrometres per cell) = −1.06 + 2.32 log d (micrometres)) whereas light scattering is scaled to their volume (log bcell(square micrometres per cell) = −1.09 + 3.45 log d (micrometres)). The scaling of light absorption to the cross-sectional area of algal cells is explained by a decrease in intracellular chlorophyll a concentration as cell size increases, thereby avoiding inefficient light capture by photosynthetic pigments. The scaling of light scattering to cell volume conforms to the general theory for large particles (Mie theory). Light absorption by phytoplankton cells, unlike light scattering, deviates from that of nonliving particles because of the covariation between pigment content and cell size that help prevent self-shading.