SUMMARYWe have quantified the ultrastructure of myocardial cells in tissue samples obtained from six adult normal Yucatan swine, tissue samples were obtained from 20 different sites in the left ventricle, right ventricle, and interventricular septum. The samples were processed for electron microscopy and quantitative morphometric analysis. The percent relative volumes of myoflbrils, mitochondria, transverse tubular system, sarcoplasmic reticulum, and clear intracellular space were determined using stereologic&l morphometric methods. Overall, the data were distributed homogenously among the 20 individual sites. However, when certain eubcellular components were examined regionally, some differences appeared. The mitochondrial:myofibril volume ratios were significantly increased in the left ventricle and interventricular septum compared to the right ventricle. They also were greater in the endocardial region compared to the epicardium, which is consistent with higher metabolic activity of these zones. Similarly, the sarcoplasmic reticulum :myofibril ratio was greater in the endocardial region vs. the epicardial region and the basal layer compared to the mid-layer, suggesting the greater need for provision of calcium ions in these particular cones. Since the swine is a convenient large animal fur physiological studies, these results indicate that swine can also be used for quantitative morphometric measurements of myocardial changes in normal and pathologic hearts, and for the study of regional changes in various layers and regions of heart walls. Circ Res 49: 434-441, 1981 MANY experimental models of cardiac hypertrophy have been used to describe the different functional, structural, and biochemical alterations that occur during the development of hypertrophy and failure in the heart. We nave used swine as a model of cardiac hypertrophy (White et al., 1979) since its response to exercise stress is similar to that in humans. Also, the swine has a coronary artery distribution similar to that of the normal human (Lumb and Hardy, 1963), a limited coronary collateral circulation (Blumgart et al., 1950), and a similar ratio of heart weight to body weight to that of man (Schaper, 1971). Therefore it is an appropriate model for comparison to man (Blumgart et al., 1950; Lumb andSingletary, 1961;1962;Lumb and Hardy, 1963;Kong et al., 1969). However quantitative ultrastructural studies of the normal and hypertrophic heart have been conducted mainly in smaller species, e.g., rats (Page et al., 1971;Anversa et al., 1976Anversa et al., , 1978Legato, 1976; Wendt-Gallitelli and Jacob, 1977;McCallister et al., 1979;Tomanek et al., 1979), rabbits (Anversa et al., 1971;Goldstein et al., 1974), hamsters (Colgan et al., 1978), cats (Sheridan et al., 1977), and ferrets (Breisch et aL, 1980). Although ultrastructural studies have been conducted on the hearts of dogs (Vitali-Mazza and Anversa, 1972;Winkler et al., 1977;McCallister et al., 1978;Legato, 1979), it was not known whether the percentages of cell volume of ultrastructural ...

Ferritin-concanavalin A (Fer-Con A) was used to label the apical plasma membrane of the lactating cell to determine whether membrane internalization takes place. Rat glands were infused in vivo via the teat with 0.2 mg of Fer-Con A in 0.2 ml tris buffer (pH 7.0) containing 0.1% trypan blue, the latter acting as a marker of the infusate. Tissues were obtained from separate animals 5, 10 and 60 min postinfusion. Fer-Con A was seen in alveolar lumina bound to the outer surfaces of apical plasma membrane, microvilli and milk fat globules. It was observed within lactating cells on the inner membrane surfaces of endocytotic vesicles, Golgi cisternae, and secretory vesicles containing casein micelles, and in multivesicular bodies and lysosomes. Internalization of the ferritin-lectin conjugate into casein-containing secretory vesicles was detectable in the 5-min postinfusion tissue. Lysosomes were the only structures in control tissue that contained particles bearing some resemblance to Fer-Con A. The data provide evidence that apical plasma membrane is internalized and distributed to a number of intracellular compartments.

The mammary gland is an appropriate substrate for genetic engineering because of its capacity to synthesize and secrete molecules of biological importance. An approach to mass production of such molecules involves transfer of genes into the lactating cell by infusion via the teat and duct system. We describe an infusion technique with the rat, a useful animal in which to develop such technology. By dye maker, trypan blue, and the ultrastructural marker, ferritin-concanavalin A, infusions by this route can permeate the entire gland and deliver molecules to apical membranes of lactating cells.

The plant lectin, concanavalin A (Con A) suppresses milk secretion when infused into the mammary gland or when incubated with lactating tissue in vitro. Toward defining its mode of action, we infused Con A into rat and goat mammary glands via the teats and observed effects on lactating cells. Lectin dosages were 2 and 25 mg per gland for rats and goat, respectively. Tissue samples were taken 1 and 3 h post infusion for rats and at 24 h for the goat. Control and Con A-treated tissues were observed by light microscopy and by both thin section and freeze fracture electron microscopy. In comparison to controls, Con A-treated tissues of both species exhibited alveoli with enlarged cells and relatively empty lumina; cells were distended with secretory vesicles and fat droplets. Apical plasma membranes of lectin-affected cells of the rat displayed a marked reduction in the number of microvilli, and exhibited an atypical branching and folded structure. Morphometry was employed to quantitate changes in cell and secretory product parameters in both rat and goat tissue. Microtubule numbers and distribution did not appear to be altered by Con A but considerable changes were noted in the arrangement of microfilaments associated with the secretory surface of lectin-treated epithelial cells. Various related ultrastructural changes and the role of Con A in perturbing the microfilament system are discussed.

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