The time sequence of response of the prolactin cells of the freshwater teleost, Poecilia reticulata, to an altered environmental salinity

The time sequence of the ultrastructural changes in the prolactin cells of the adult guppy, Poecilia reticulata, was studied in freshwater fish transferred to 1/3 seawater for 1, 4, 11 and 28 days. The morphological changes were slight and only detectable by quantitative (morphometric) procedures. The secretory granules showed a "biphasic' response to the altered environmental salinity, but the volume density of the Golgi apparatus progressively declined throughout the experiment. After an initial decrease in the volume density of the RER, that organelle regained its original prominence by 11 days in 1/3 seawater. The volume density of the nucleus was markedly higher in fish 28 days after transfer to 1/3 seawater than in any other group. Cell volume estimations showed that a shrinking of the cytoplasm rather than a swelling of the nucleus accounted for the high volume density figure. The changes in the volume density of the mitochondria closely paralleled those of the RER. Profiles of exocytosed granules were rarely found in any of the groups, but were least frequent in fish kept in 1/3 seawater for 28 days, when dense (lysosomal?) bodies were most abundant. The quantitative methods high-lighted some discrepancies in the rate and magnitude of the changes shown by some organelles and have led the authors to suggest that during adaptation of fish to dilute seawater, synthesis and release may not be coupled processes in the prolactin cell of P. reticulata.     

The magnocellular neurosecretory system of the hamster hypothalamus: an ultrastructural and morphometric study during lifetime

A quantitative study regarding the age-related changes occurring in the nucleus and the somatic organelles of neurosecretory magnocellular neurons of the hypothalamo neurohypophyseal system (HNS) was carried out in the hamster at six age-points during animal life. The magnocellular cells of both parts of the supraoptic nucleus (SON) and the paraventricular nucleus (PVN) of male Syrian hamsters between 3 and 30 months of age were examined ultrastructurally. Cells of all age groups present the same morphological ultrastructure. Standard manual morphometric techniques are used to calculate the following parameters related directly or indirectly with cellular activity: nuclear area, nucleolar area, nuclear invagination index and volumetric fractions of some intracellular structures (Golgi apparatus, mitochondria, rough endoplasmic reticulum and lipofuscin). With respect to the cell nucleus, the parameters are not modified during aging. No significant differences in the volume density of subcellular components, except lipofuscin, were detected at the age groups studies. However, there is a positive linear trend among all parameters and age except for the rough endoplasmic reticulum. Our results suggest maintenance of the synthetic activity of the magnocellular neurons in the hamster during aging but in no case an increase in their metabolic activity.     

Relationship between the Golgi apparatus, GERL, and secretory granules in acinar cells of the rat exorbital lacrimal gland

The method of secretory granuleformation in the acinar cells of the rat exorbital lacrimal gland was studied by electron microscope morphological and cytochemical techniques. Immature secretory granules at the inner face of the Golgi apparatus were frequently attached to a narrow cisternal structure similar to GERL as described in neurons by Novikoff et al. (Novikoff, P. M., A. B. Novikoff, N. Quintana, and J.-J. Hauw. 1971. J. Cell Bio. 50:859-886). In the lacrimal gland. GERL was located adjacent to the inner Golgi saccule, or separated from it by a variable distance. Portions of GERL were often closely paralleled by modified cisternae of rough endoplasmic reticulum (RER), which lacked ribosomes on the surface adjacent to GERL. Diaminobenzidine reaction product of the secretory enzyme peroxidase was localized in the cisternae of the nuclear envelope, RER, peripheral Golgi vesicles, Golgi saccules, and immature and mature secretory granules. GERL was usually free of peroxidase reaction product or contained only a small amount. Thiamine pyrophosphatase reaction product was present in two to four inner Golgi saccules; occasionally, the innermost saccule was dilated and fenestrated, and contained less reaction product than the next adjacent saccule. Acid phosphatase (AcPase) reaction product was present in GERL, immature granules, and, rarely, in the innermost saccule, but not in the rest of the Golgi saccules. Thick sections of AcPase preparations viewed at 100 kV revealed that GERL consisted of cisternal, and fenestrated or tublular portions. The immature granules were attached to GERL by multiple connections to the tublular portions. These results suggest that, in the rat exorbital lacrimal gland, the Golgi saccules participate in the transport of secretory proteins, and that GERL is involved in the formation of secretory granules.     

The Golgi apparatus is an inositol 1,4,5-trisphosphate-sensitive Ca2+ store, with functional properties distinct from those of the endoplasmic reticulum

In the past few years, intracellular organelles, such as the endoplasmic reticulum, the nucleus and the mitochondria, have emerged as key determinants in the generation and transduction of Ca2+ signals of high spatio-temporal complexity. Little is known about the Golgi apparatus, despite the fact that Ca2+ within its lumen controls essential processes, such as protein processing and sorting. We report the direct monitoring of the [Ca2+] in the Golgi lumen ([Ca2+]Golgi) of living HeLa cells, using a specifically targeted Ca2+-sensitive photoprotein. With this probe, we show that, in resting cells, [Ca2+]Golgi is approximately 0.3 mM and that Ca2+ accumulation by the Golgi has properties distinct from those of the endoplasmic reticulum (as inferred by the sensitivity to specific inhibitors). Upon stimulation with histamine, an agonist coupled to the generation of inositol 1,4,5-trisphosphate (IP3), a large, rapid decrease in [Ca2+]Golgi is observed. The Golgi apparatus can thus be regarded as a bona fide IP3-sensitive intracellular Ca2+ store, a notion with major implications for the control of organelle function, as well as for the generation of local cytosolic Ca2+ signals.     

Time course of vinblastine-induced autophagocytosis and changes in the endoplasmic reticulum in murine pancreatic acinar cells: a morphometric and biochemical study

The time course of the vinblastine(-sulfate; 10 mg/kg body weight, single injection)-induced enlargement and subsequent regression of the autolysosomal compartment was studied by electron microscopic morphometrical and cell biochemical methods in order to gain information concerning some key problems of this major route of intralysosomal degradation of the cell's endogenous macromolecules and structures. Detailed analysis of the dynamics of the total autophagic vacuole (AV) compartment and its different subcompartments (early, advanced, late, and fused AVs), as well as of changes of rough-surfaced endoplasmic reticulum (RER) showed: 1. Pancreatic acinar cells react to vinblastine biphasically, i.e. two expansion phases of the AV compartment, the first in the 0 to 90 min and the second in the 2 to 8 h post-injectional periods, were detected. 2. Fusions of AVs are not inhibited by vinblastine, at least during the second expansion phase when cytoplasmic volume fraction (CVF) of fused AVs steadily increased until the 12th h. Fusion of early, advanced and late AVs or composition of fused complex vacuoles (AVc) are somehow regulated, as the proportion of the three AV stages from the CVF of AVc, was maintained constant throughout the second expansion phase. 3. Stimulation of autophagosome formation and resulting substrate overload seems to be the primary mode of action by which vinblastine causes the enormous expansion of the autolysosomal compartment. 4. Degranulation of the rough-surfaced endoplasmic reticulum (RER) membranes occurs in a biphasic fashion, similarly to the volume and surface changes of the AV compartment, thus supporting our previous hypothesis, that labilization or change of RER may have a role in the formation of autophagosomes. 5. Vinblastine-induced autophagocytosis is a selective process, as mitochondria, Golgi elements and zymogen granules are very much underrepresented, whereas RER is more than twice overrepresented in the volume of early AVs, when compared to their volume fraction in the whole cytoplasm. 6. Immunogold electron microscopy revealed the presence of ubiquitinylated proteins in advanced and late, but not in early AVs.     

Ultrastructural studies on prolactin and growth hormone cells in Anguilla pituitaries in long term cultures

Eel hemi-pituitaries were cultured in vitro on high or low sodium media, previously shown to affect differentially prolactin and growth hormone release. After 6 days culture, there were marked differences in the ultrastructure or both prolactin and growth hormone cells from the two groups. Morphometric data on the prolactin cells from SW-adapted eels showed a greater abundance of RER and paucity of secretory granules in cells from the low sodium medium. The size of the Golgi apparatus and the number of exocytosed secretory granules did not differ markedly between experimental groups, in contrast to previous findings on short-term cultures. Differences in the profile diameters of secretory granules are recorded between the experimental groups and the pattern differs markedly from that previously recorded for short-term cultures. The growth hormone cells from low sodium media were characterised by abundant, vesiculated RER, a prominent Golgi apparatus (in SW-adapted animals) and relatively few secretory granules. The activity of these growth hormone cells is in marked contrast to previous findings relating to short-term cultures. The shape and size of the non-granulated (stellate) cells of the RPD was again affected by the osmotic pressure of the medium.     

Biological and immunological studies on a low virulence isolate of the Tulahuén strain of Trypanosoma cruzi

The binding sites and chronologic localization of elcatonin (eCT) in osteoclasts were examined by autoradiography using [125I]elcatonin (125I-eCT). In addition to the structural changes induced by calcitonin (CT) reported so far, changes were also observed in the structure of Golgi apparatus. These changes continued until 48-72 h after incubation with eCT. Developed silver grains of 125I-eCT were localized into multinucleated osteoclasts and mononuclear cells that were ultrastructurally defined as "preosteoclasts." The silver grains located on plasma membranes of those cells and were then internalized; they accumulated, especially in the Golgi apparatus, and remained for 48-72 h. A few silver grains were also detected in lysosomes and small vesicles. The decrease in the number of silver grains in the Golgi apparatus accompanied the recovery of osteoclast structures--Golgi apparatus and then ruffled borders. These findings suggest that (1) CT especially inhibits the sorting function of Golgi apparatus in osteoclasts, resulting in prolonged retention of CT in this organelle. (2) The CT in Golgi apparatus may keep its activity and cause the prolonged effect of CT on osteoclast activity.     

Qualitative and quantitative preservation of the fine structure of absorptive cells in cultured biopsies of human small-intestine

The fine structure of the absorptive cells in human small-intestinal biopsies cultured for 6, 24, and 48 h was analyzed qualitatively and quantitatively. The findings show generally good preservation of the cultured absorptive cells and a normal distribution, size, and relative volume of their cell organelles, but there was a systematic decrease in the apical cell surface and an increase in the number of apical vesicles and tubules after culturing. Since the apical vesicles and tubules are thought to have a function in the transport of cell-coat material from the Golgi apparatus to the cell surface, these findings raise the question of whether a delayed transport or extrusion of cell surface material occurs. The diminished relative volume of the mitochondria and the increased signs of autophagy in some poorly preserved absorptive cells, are assumed to be an adaption to less favourable culture conditions.     

Intracellular retention of the corticotrophin-releasing hormone (CRH) precursor within COS-7 cells

We investigated the intracellular localization of CRH in transiently transfected COS-7 cells expressing the full-length rat corticotropin-releasing hormone (CRH) precursor cDNA. CRH synthesized by transfected COS-7 cells is mainly stored intracellularly. In contrast, CHO-K1 cells expressing the same CRH precursor stored and released equal amounts of immunoreactive (IR)-CRH. Ultrastructural analysis revealed that CRH is stored in electron-dense aggregates in the RER of transiently transfected COS-7 cells and does not migrate into the Golgi apparatus. On the basis of the different intracellular localization, storage, and release of CRH in COS-7 and CHO-K1 cells, we hypothesize that the intracellular trafficking of CRH within the constitutive secretory pathway for protein secretion not only depends on its primary amino acid sequence but might also be influenced by intracellular conditions or factors.     

Effects of p-chlorophenylalanine, amiflamine and melatonin treatment on the ultrastructure of pinealocytes in Sus scrofa

The effects of p-chlorophenylalanine (pCPA), amiflamine [Fla 336(+)] as well as melatonin (MEL) treatments on the ultrastructure of pinealocytes in immature female pigs were investigated. Treatment of pCPA-tryptophan hydroxylase inhibitor resulted in the presence of numerous membrane-bound bodies type 2, with long, narrow cisterns of endoplasmic reticulum and a large Golgi apparatus. Fla 336(+) selective MAO-A inhibitor influenced the system of dense bodies, mitochondria and lysosomes (increasing their relative volume). Injections of melatonin resulted in the appearance of numerous homogeneous, round, regular shaped structures surrounded by membrane cytoplasmic structures ('granules'). The results indicate that a peculiar system of cytoplasmic dense bodies may be involved in indoleamine secretion in the pig pinealocyte.     

NSF is required for the brefeldin A-promoted disassembly of the Golgi apparatus

N-Ethylmaleimide-sensitive factor (NSF) is required for multiple pathways of vesicle-mediated protein transport. Microinjection of a monoclonal anti-NSF antibody almost completely blocked brefeldin A-promoted Golgi disassembly without affecting the rapid release of beta-COP, a subunit of the Golgi coat proteins (COPI), from the Golgi apparatus. Similar results were obtained using a dominant-negative NSF which is known to compete with endogenous NSF. The present results suggest that an NSF-mediated step is present in the brefeldin A-promoted disassembly of the Golgi apparatus.     

Arfaptin 1, an ARF-binding protein, inhibits phospholipase D and endoplasmic reticulum/Golgi protein transport

Class I ADP-ribosylation factors (ARFs) are essential for coatomer and clathrin coat assembly and vesicular transport in the Golgi apparatus. However, little is known about the in vivo regulation of ARF actions. Recently we cloned arfaptin 1, a 39 kDa protein that binds active, GTPgammaS-liganded ARF and translocates with it to Golgi membranes. Here we show that phorbol ester-stimulated phospholipase D (PLD) activity is inhibited in arfaptin 1-overexpressing NIH 3T3 cells and that arfaptin 1 inhibits ARF activation of Golgi-associated PLD. Since PLD activity is thought to play a role in regulating vesicular transport in the secretory pathway, we determined the rate of glycosylation of vesicular stomatitis virus glycoprotein as a measure of protein transport from the endoplasmic reticulum through the Golgi apparatus. Arfaptin 1 overexpression was found to decrease the rate of this reaction approximately two-fold. These data suggest that arfaptin 1 is a regulator of ARF action in the Golgi apparatus.     

Protein synthesis within dendrites: glycosylation of newly synthesized proteins in dendrites of hippocampal neurons in culture

There is increasing evidence that certain mRNAs are present in dendrites and can be translated there. The present study uses two strategies to evaluate whether dendrites also possess the machinery for protein glycosylation. First, precursor labeling techniques were used to conjunction with autoradiography to visualize glycosyltransferase activities that are characteristic of the rough endoplasmic reticulum (RER) (mannose) or the Golgi apparatus (GA) (galactose and fucose) in dendrites that had been separated from their cell bodies and in intact neurons treated with brefeldin A or low temperature. Second, immunocytochemical techniques were used to define the subcellular distribution of proteins that are considered markers of the RER (ribophorin I) and GA (p58, alpha-mannosidase II, galactosyltransferase, and TGN38/41). Autoradiographic analysis revealed that isolated dendrites incorporated sugar precursors in a tunicamycin-sensitive and protein synthesis-dependent manner. Moreover, when intact neurons were pulse-labeled with 3H-labeled sugars at low temperature or after treatment with brefeldin A, labeling was distributed over proximal and sometimes distal dendrites. Immunolabeling for RER markers was predominantly localized in cell bodies but extended for a considerable distance into dendrites of all neurons. Immunolabeling for GA markers was confined to the cell body in approximately 70% of the neurons, but in 30% of the neurons, the staining extended into proximal and middle dendrites. These results indicate that the machinery for glycosylation extends well into dendrites in many neurons.     

Morphofunctional characteristics of the Leydig cells in the testes of the humpback salmon Oncorhynchus gorbuscha during spawning migration

By means of electron microscopic study of ultrastructure of Leydig cells of male adult humpback salmons in the period of spawning migration (stages III-IV of gonad maturity) they were found to be most active before the spawning. Maximum number of mitochondria with tubulovesicular crysts and normal development of Golgi apparatus and smooth endoplasmic reticulum were marked in this period. Decrease of mitochondria number and Golgi apparatus dictyosomes so as liposome-like bodies appearance in the cytoplasm indicated reduction of Leydig cells activity in the period of spawning. After this period fatty drops were presented in the Leydig cells cytoplasm, mitochondrial matrix acquired greater electron density and dark granules appeared in it. Signs of physiological regeneration outset were seen in dying male salmons. This is regarded as an evidence of secondary monocyclicity of the Pacific Ocean salmons.     

Behavior and the law reconsidered: psychological syndromes and profiles

Three months after facial nerve transection, total numbers of motoneurons in the facial nucleus of six month (adult) Fischer 344 and Wistar rats were reduced to 83% and 75% of contralateral values, respectively (P < 0.05). This procedure in 22-26 month (ageing) Fischer 344 rats and Wistar rats resulted in a reduction of motoneuron numbers to 77% and 60% of the respective contralateral values (P < 0.05). Compared to adults, contralateral facial nuclei of aging Fischer 344 rats contained 10% fewer motoneurons (non-significant), while ageing Wistar rats had 22% fewer (P < 0.05). No significant changes were found in the proportion of surviving motoneurons expressing calcitonin gene-related peptide, galanin, receptor tyrosine kinase-C or the alpha subunit of the ciliary neurotrophic factor receptor. We conclude that ageing reduces facial motoneuron number and increases their vulnerability to axotomy in Wistar rats, but not in Fischer 344 rats. In neither strain, however, does the proportion of surviving motoneurons expressing the above neuropeptides or neurotrophic factor receptors change. This information may be relevant to those hypotheses of age-related neuronal degenerations which assume that decreased neurotrophic support renders ageing neurons more vulnerable to injury.     

Disassembly of the cholinergic postsynaptic apparatus induced by axotomy in mouse sympathetic neurons: the loss of dystrophin and beta-dystroglycan immunoreactivity precedes that of the acetylcholine receptor

In mouse sympathetic superior cervical ganglion (SCG), cortical cytoskeletal proteins such as dystrophin (Dys) and beta1sigma2 spectrin colocalize with beta-dystroglycan (beta-DG), a transmembrane dystrophin-associated protein, and the acetylcholine receptor (AChR) at the postsynaptic specialization. The function of the dystrophin-dystroglycan complex in the organization of the neuronal cholinergic postsynaptic apparatus was studied following changes in the immunoreactivity of these proteins during the disassembly and subsequent reassembly of the postsynaptic specializations induced by axotomy of the ganglionic neurons. After axotomy, a decrease in the number of intraganglionic synapses was observed (t1/2 8 h 45'), preceded by a rapid decline of postsynaptic specializations immunopositive for beta-DG, Dys, and alpha3 AChR subunit (alpha3AChR) (t1/2 3 h 45', 4 h 30' and 6 h, respectively). In contrast, the percentage of postsynaptic densities immunopositive for beta1sigma2 spectrin remained unaltered. When the axotomized neurons began to regenerate their axons, the number of intraganglionic synapses increased, as did that of postsynaptic specializations immunopositive for beta-DG, Dys, and alpha3AChR. The latter number increased more slowly than that of Dys and beta-DG. These observations suggest that in SCG neurons, the dystrophin-dystroglycan complex might play a role in the assembly-disassembly of the postsynaptic apparatus, and is probably involved in the stabilization of AChR clusters.     

Quantitative correlation of breast tissue parameters using magnetic resonance and X-ray mammography

BACKGROUND: Disassembly of cytoplasmic microtubules by nocodazole in cultured mammalian cells leads to the disruption of the continuous ribbonlike Golgi apparatus and dispersal of the Golgi elements from their normal juxtanuclear location, close to the microtubule-organizing center (MTOC), toward the cell periphery. Clearing of the drug induces reassembly of the microtubules from the MTOC and reorganization of the Golgi elements into a continuous ribbonlike juxtanuclear structure. In the yeast Saccharomyces cerevisiae, the Golgi apparatus does not form a continuous structure as in mammalian cells but instead constitutes independent units dispersed throughout the cytoplasm. It is the purpose of this article to investigate the role of microtubules in the structure and distribution of the Golgi elements in S. cerevisiae by studying the ultrastructure of cell organelles either in mutant cells deficient in beta-tubulin or in wild-type cells treated with the microtubule-depolymerizing drug nocodazole. METHODS: Two S. cerevisiae yeast strains were used in this study: a control wild-type strain, CUY226 (ade2-101, his3-delta 200, leu2-delta 1, lys2-801, ura3-52 Mat alpha), and a mutant strain, CUY66 (tub2-401, ade2-101, ura3-52, Mat alpha). Nocodazole was added to the wild-type cells cultivated at 30 degrees C, and cells were fixed 5 min, 20 min, and 60 min, respectively, after adding the drug to the culture. Both strains were fixed and examined 5 min, 20 min, and 60 min after shifting the cultures from the permissive temperature of 30 degrees C to the restrictive temperature of 14 degrees C. Cells were fixed in 2% glutaraldehyde, treated for 15 min in 1% sodium metaperiodate, postfixed in reduced osmium, and embedded in Epon. To visualize the three-dimensional configuration of cell organelles, stereopairs were prepared from sections stained with lead citrate and tilted at +/- 15 degrees from the 0 degree position of the goniometric stage of the electron microscope. RESULTS: In mutant cells shifted to restrictive temperature and wild-type cells treated with nocodazole, the main ultrastructural modification was a fragmentation of networks of membranous tubules, which probably correspond to the yeast Golgi apparatus. Secretion granules were still present in growing buds, and they were dispersed in the cytoplasm, which contained in addition numerous small vesicles in the 30-60-nm diameter range. CONCLUSIONS: In normal cells, small vesicles may originate from the endoplasmic reticulum and fuse together to give rise to Golgi networks (Rambourg et al. 1994. Anat. Rec., 240:32-41). If this hypothesis is correct, the observations reported might indicate that intact microtubules orient the flow of small vesicles and favour their fusion into Golgi networks.     

The tubular network of the Golgi apparatus

Golgi apparatus of both plant and animal cells are characterized by an extensive system of approximately 30 nm diameter peripheral tubules. The total surface area of the tubules and associated fenestrae is thought to be approximately equivalent to that of the flattened portions of cisternae. The tubules may extend for considerable distances from the stacks. The tubules are continuous with the peripheral edges of the stacked cisternae, but the way they interconnect differs across the stack. In plant cells, for example, tubules associated with the near-cis and mid cisternae often begin to anastomose close to the peripheral edges of the stacked cisternae, whereas the tubules of the trans cisternae are less likely to anastomose and are more likely to be directly continuous with the peripheral edges of the stacked cisternae. Additionally, the tubules may blend gradually into fenestrae that surround some of the stack cisternae. Because of the large surface area occupied by tubules and fenestrae, it is reasonable to suppose that these components of the Golgi apparatus play a significant role in Golgi apparatus function. Tubules clearly interconnect closely adjacent stacks of the Golgi apparatus and may represent a communication channel to synchronize stack function within the cell. A feasible hypothesis is that tubules may be a potentially static component of the Golgi apparatus in contrast to the stacked cisternal plates which may turn over continuously. The coated buds associated with tubules may represent the means whereby adjacent Golgi apparatus stacks exchange carbohydrate-processing enzymes or where resident Golgi apparatus proteins are introduced into and out of the stack during membrane flow differentiation. The limited gradation of tubules from cis to medial to trans offers additional possibilities for functional specialization of Golgi apparatus in keeping with the hypothesis that tubules are repositories of resident Golgi apparatus proteins protected from turnover during the flow differentiation of the flattened saccules of the Golgi apparatus stack.     

Effect of ethanol administration on the level of dolichol in rat liver microsomes and Golgi apparatus

Data obtained in our laboratory had suggested that acute ethanol administration (6 g/kg body weight) selectively and rapidly affects the intracellular system of protein glycosylation at the level of the Golgi apparatus. Dolichols are important membrane components, and dolichyl phosphate is a glycosyl sugar carrier for N-glycosylation of proteins in endoplasmic reticulum and is considered rate-limiting for this process. In this study, modifications in the concentration and distribution of liver microsomal dolichols after acute ethanol administration were investigated. Between 3 and 24 hr after ethanol administration, the microsomal dolichyl phosphate concentration was significantly lower than in control animals. The highest reduction was observed at 12 hr (-52%). An earlier and more marked reduction of total dolichol was observed in the Golgi apparatus, and, in particular, in the secretory fraction F1 (-70% at 6 hr). Ethanol treatment of isolated hepatocytes led to a significant reduction of the de novo synthesis of both dolichyl phosphate and free dolichol. Moreover, in vitro experiments have demonstrated that pro-oxidant agents lead to a significant decrease of both free dolichol and dolichyl phosphate. Our results suggest that acute ethanol administration induces a marked decrease of dolichols, probably by increasing the degradation and impairing the biosynthetic pathway of these molecules.     

Effects of intrapleural pressure changes on canine left ventricular function

Left ventricular diameter, pressure, and dP/dt, as well as aortic and intrapleural pressures, were recorded simultaneously from 10 acute anethetized mongrel dogs. Normal inspiration produced a significant decrease in end-diastolic diameter (46.9 +/- 1.2 to 43.1 +/- 1.0 mm) and end-systolic diameter (35.5 +/- 1.4 to 34.2 +/- 1.7 mm), reducing stroke diameter 2.5 mm. Airway occlusion (greater than or equal to 60%) produced a reduction in the decrease of end-diastolic diameter seen with normal inspiration and, to a lesser degree, in end-systolic diameter. Because only acute airway occlusion greater than or equal to 80% produced a significant increase in left ventricular afterload, the authors conclude that normal spontaneous inspiration results in a decrease in left ventricular preload due to pooling of blood in the pulmonary vasculature. The data suggest that this decrease in left ventricular preload is the predominant mechanism responsible for the inspiratory decrease in left ventricular stroke volume.