Positive inotropic action of insulin on piglet heart

This study was designed to investigate changes in cardiac performance during hypoglycemia produced by the administration of insulin in the newborn piglet. With heart rate, aortic pressure, and aortic flow held constant, the treated group demonstrated a pronounced positive inotropic response manifested by an increase of dP/dt max to 138% of control values. Central nervous system function and beta adrenergic activity were excluded from the preparation by ligation of the brachiocephalic vessels and administration of practolol. For reasons discussed, it is unlikely that the findings can be ascribed to glucagon contamination. Therefore, the increase in contractility presumably resulted from a direct effect of insulin upon the myocardium. Clinical and laboratory data suggest that the resistance of the neonate to hypoxia is modified by glycogen stores. Insulin is known to increase glycogen synthesis, and this effect might be expected to augment myocardial resistance to hypoxia. Under the conditions of these experiments, however, pretreatment with insulin had no demonstrable influence on the rate of deterioration of cardiac function during hypoxia. The mechanism of cardiac stimulation by insulin is unknown but may involve calcium fluxes.

Autogenous immunity to endogenous RNA tumor virus: reactivity of natural immune sera to antigenic determinants of several biologically distinct murine leukemia viruses

Sera from normal (C57BL/6XC3H/Anf)F1(B6C3F1) mice reacted with several biologically distinct murine leukemia virus(es) (MuLV) by radioimmune precipitation assays with the use of purified tritiated leucine-labeled virus. The reactivities of this natural antibody to viral envelope antigens of two laboratory strains (Rauscher and Moloney) and two endogenous mouse C-type viruses (AKR and BALB:virus-2) were further analyzed and compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Similar patterns of antibody reactivities to AKR MuLV and the two member viruses of the Friend-Moloney-Rauscher group were found. Three major antigenic determinants of the virus envelope, gp71, gp43, and p15, were recognized by and precipitated natural antibody. In all viruses examined, normal B6C3F1 sera precipitated comparable amounts of gp71 and gp43. However, compared with the other viruses, the amount of p15 (relative to the glycoproteins) precipitating from BALB:virus-2 was significantly lower. This appears to be due to a lesser amount of p15 on the xenotropic virus. While heterologous antisera to purified gp71 and p15 of MuLV reacted to a certain degree with rhabdomyosarcoma virus 114 and rat leukemia virus, natural mouse antibody did not. These results suggest that MuLV have common antigenic determinants recognized by natural antibody, and that the reactivities of natural antibody in an autogenous immune response are restrictive in contrast to immune antibody produced in a heterologous host.

Nuclear magnetic resonance studies in normal and edematous brain tissue

The nmr relaxation rate results show unequivocally that there are at least two fractions of tissue water in both normal and edematous white matter which do not exchange on an nmr time scale (i.e. at times of the order of milli-seconds to fraction of a second). In conjunction with the electron microscopic determination of the extracellular volumes of normal and edematous white matter, the relaxation results can be interpreted in terms of the following model. The two slowly-exchanging water components giving rise to the non-exponential relaxation correspond to cellular and extracellular water; edema changes the relaxation rate of the extracellular component much more than that of the cellular component (the extracellular component becoming more "liquid-like" in its relaxation). Such behavior is consistent with the properties of the extracellular water being due to rapid exchange between motionally restricted water adsorbed at the surface of myelin sheaths, and relatively unrestricted, bulk water. Edema presumably increases the relative amount of the "bulk" water between the axons.

Production of ferritin by rat hepatoma cells in vitro. Demonstration of protein subunits and ferritin by immunofluorescence

Using precipitating antibodies to ACI rat liver ferritin and to sodium-dodecyl-sulfate-dissociated protein subunits of ACI rat liver ferritin, we have demonstrated the presence of ferritin-positive sites and subunit-positive sites in situ in several rat hepatoma cell lines by immunofluorescence. Hepatoma cells from three transplantable rat hepatomas (Reuber H-139, Reuber H-35, and Morris 5123) were explanted and propagated. Rabbit antibodies specific for either protein subunits of ferritin or ferritin were prepared by affinity chromatography or by dissociation of antibody-antigen complexes with 0.1 M acetic acid followed by differential ultracentrifugation. Explants of Reuber H-139, Reuber H-35, and Morris 5123 hepatoma cells, grown either in ordinary McCoy's 5a medium or in such medium enriched with iron (0.002% Fe), gave positive immunofluorescence for subunits as well as ferritin. Exposure of a clonal strain of Morris 5123 hepatoma cells to iron-enriched culture medium for varying lengths of time of up to 24 hours resulted in progressive increase in the quantity of ferritin-specific immunofluorescent cytoplasmic material, which was at first present diffusely, and later in clumps. By contrast, during the initial 24-hour period, subunit-specific immunofluorescence remained at relatively low intensity, with diffuse distribution through the cytoplasma. Our findings indicate a) the presence, in the cytoplasm, of the three kinds of hepatoma cells, of unassembled or only partly assembled subunits of fragments of subunits as well as of ferritin, and b) rapid assembly of the protein subunits into apoferritin and ferritin after administration of iron, so that the concentration of subunits in the cytoplasm was not significantly increased.

Laryngeal chemosensitivity: a possible mechanism for sudden infant death

In 32 anaesthetized piglets 1 to 42 days of age the distal trachea was cannulated and pressure changes were recorded. The proximal trachea was cannulated for introduction of test fluids into the laryngeal area. Arterial pressure, heart rate, and central venous pressure were continuously recorded. Arterial blood samples were obtained at intervals and analyzed for PO2, PCO2, pH, and hematocrit. Normal saline produced no, or brief, transitory alterations of the respiratory pattern and arterial pressure. In contrast, instillation of distilled water produced apnea in 29 of 30 piglets. In 20 the apnea was sustained. Eleven died within approximately 50 minutes of asphyxia. An additional nine were expected to die with continuing apnea (PO2, 10 to 15 mm Hg; PCO2 greater than 100 mm Hg; pH smaller than 6.8) but the sequence was interrupted by replacement of water with saline. Twenty-three of 29 piglets showed an apneic response to cow's milk similar to that seen with distilled water. Seven died of asphyxia and an additional three showed sustained respiratory inhibition until milk was replaced with saline. The responses were completely abolished by superior laryngeal nerve (SLN) sectioning. Electrical stimulation of the SLN produced sustained apnea in seven of eight piglets tested. Studies in two 3-day-old lambs showed similar discrimination but only transitory apnea with water or cow's milk. Both died during SLN stimulation. Two ewes showed insignificant responses. These findings suggest a lethal reflex mechanism with implications for the SIDS problem.

A comparison of ventricular weights and geometry in newborn, young, and adult mammals

The weight of individual anatomic segments of the heart and calculated left ventricular chamber volumes have been studied in the hearts of 214 normal mammals of seven species (sheep, swine, dogs, cats, rabbits, guinea pigs, and rats). Comparisons have been made between newborn, young, and adult age groups. In addition, the heart weight-to-body weight ratio, percentage of right ventricular free wall weight in relation to left ventricular free wall weight (RVF/LVF), the relationship between calculated ventricular volume and weight and the left ventricular major minor axis ratios were examined in each age range. Heart weight (HW) in relation to body weight (BW) was greater in the newborn than adult in all species except the dog. HW/BW was twice as great in the adult dog as other species. In newborns RVF/LVF ranged from 55 percent in rats to 100 percent in puppies. Less species variation was present in adult hearts. Species with a more spherical adult LV configuration demonstrated a greater chamber mass-to-volume ratio. This may be attributable to greater wall tension.

Autogenous immunity to endogenous RNA tumor virus: differential reactivities of immunoglobulins M and G to virus envelope antigens

The autogenous humoral immune response of mice to their endogenous leukemia virus has been examined in terms of the reactivities of individual classes of antibody present in normal B6C3F(1) serum. Whole serum and the immunoglobulin (Ig) M and IgG fractions of serum from animals of different age groups were compared by radioimmune precipitation assays and viral infectivity neutralization assays. Both IgM and IgG fractions were able to precipitate virus, although not as effectively as whole serum. Virus-specific antibody levels, as well as total antibody concentrations in whole serum, appeared to increase with age. Sodium dodecyl sulfate gel electrophoresis analysis was performed with immune precipitates obtained when whole serum or 19 or 7S fractions from animals of different age groups were reacted with disrupted virus. The 19S antibody fraction reacted with three antigenic determinants on the viral envelope. These antigens have apparent molecular weights of 17,000, 43,000, and 68,000. The last two appear to be glycoproteins and may correspond to the M(2) and M(1) antigens. In contrast, the 7S component reacted only with the 17,000-molecular-weight protein. Neutralization assays against BALB:virus-2, a xenotropic endogenous mouse type C virus, revealed that 19S and whole serum but not the 7S fraction possessed neutralizing activity. These findings indicate that there are differential reactivities of IgM and IgG antibodies in normal serum of B6C3F(1) mice, with respect to both recognition of viral envelope antigens and neutralization of endogenous MuLV. These results are consistent with the hypothesis that the autogenous humoral immune response is a systemic host function that may be important in the regulation of endogenous type C virus expression in vivo.

Detection of protein subunits of ferritin in situ in cells by immunofluorescence

Antisera raised in rabbits against protein subunits of rat liver ferritin contain antibodies (IgG) that precipitate subunits and other antibodies (IgG) that precipitate undissociated ferritin and apoferritin. Removal of the latter antibodies from IgG fractions of immune sera by repeated addition of ferritin leaves antibodies that specifically precipitate subunits. Using these subunit-specific antibodies, we have demonstrated the presence of subunit-positive sites in cells by immunofluorescence. Subunit-positive sites were best demonstrated in rats that had been loaded with iron. These sites were diffusely spread through the cytoplasm of hepatocytes and Kupffer cells in rat livers and of macrophages and fibroblasts in rat livers and hearts. With antibodies to ferritin, the presence of ferritin was demonstrated in the same kinds of cells. Although, by immunofluorescence, the intracellular localization of ferritin-positive and subunit-positive sites was similar, ferritin-positive immunofluorescence was most intense in Prussian blue-positive cytoplasmic granules in which high concentrations of ferritin were presumed to be present on the basis of electron microscopic studies. Our findings can be interpreted to indicate either the presence of unassociated subunits or of fragments of subunits in the cytoplasm of the several kinds of cells studied. It is also possible that partly assembled molecules of ferritin or apoferritin in these cells reacted with subunit-specific antibodies. Subunit-specific antibodies may be useful for localizing sites of assembly of ferritin molecules at the level of cell fine structure and for elucidation of the biosynthesis of ferritin.