Extravascular lung water in the exercising horse.

Seven Standardbred horses were exercised on a treadmill at speeds (approximately 12 m/s) producing maximal heart rate, hypoxemia, and a mean pulmonary arterial pressure of approximately 75 mmHg. Extravascular lung water was measured by using transients in temperature and electrical impedance of the blood caused by a bolus injection of cold saline solution. Lung water was approximately 3 ml/kg body wt when standing but did not increase significantly with exertion. We conclude that any increase in fluid extravasation from the pulmonary hypertension accumulates in the lung at a level that is less than that detectable by this method. At maximal exertion, the volume of blood measured between the jugular vein and the carotid artery increased by approximately 8 ml/kg, and the actively circulating component of the systemic blood volume increased by approximately 17 ml/kg with respect to corresponding values obtained when walking before exertion. These volume increases, reflecting recruitment and dilatation of capillaries, increase the area for respiratory gas exchange and offset the reduced transit times that would otherwise be imposed by the approximately eightfold increase in cardiac output at maximal exertion.     

Persistence of acquired immunity to Trichostrongylus colubriformis in sheep after termination of infection

Lambs were infected with 6000 Trichostrongylus colubriformis L3 per week for 18, 12 or 6 weeks, beginning at ages 14, 20 and 26 weeks, respectively. At the end of the primary infection subgroups had geometric mean adult worm burdens of 5000, 15,000 and 18,000, respectively. In the remaining sheep the worm population was removed with anthelmintic, and sheep had no further larval intake until challenged with T. colubriformis 1,6, 12, 18 or 24 weeks later. In the groups given 18 or 12 weeks primary infection, establishment of challenge doses was low (less than 25% of establishment in helminth naive controls) in most animals at all challenge times. However, for the groups given 6 weeks primary infection, establishment was low only at the first two challenge times. Thereafter it had similar mean to control groups, but much greater variance. Other subgroups were challenged with T. colubriformis, Ostertagia circumcincta and Haemonchus contortus 1 week after worm removal. In these animals T. colubriformis establishment was not different to animals challenged at the same time with T. colubriformis alone, however immunity to T. colubriformis afforded little protection against the other species. The results of this experiment were incorporated into a simulation model of the population dynamics of T. colubriformis.     

Assessment of fetal number, and fetal and placental viability throughout pregnancy in cattle

Production of identical twin calves by embryo demisection requires a reliable system for continual monitoring of pregnancy. Both halves of bisected embryos were replaced nonsurgically into one uterine horn on Day 7 in 80 recipients. Monthly blood sampling began on Day 22 of pregnancy and transrectal echography took place between 50 and 80 days. Fifty-four recipients had elevated plasma progesterone concentrations on Day 22 (67% pregnancy rate). Of 21 pregnancies diagnosed as twins by echography, 15 live sets were born, 3 singles accompanied by a stillbirth, and 3 complete abortions. Twenty-five singleton pregnancies resulted in 23 live calves, 1 still-birth and 1 abortion. It was not possible to monitor echographically the remaining 8 pregnancies. At all stages of pregnancy studied, mean concentrations of bovine pregnancy-specific protein B (bPSPB) and estrone sulphate were higher (P<0.01) in twin (n = 17) than in single (n = 26) pregnancies, but the high individual variation obviated any predictive value for fetal number. Although bPSPB and estrone sulphate concentrations were positively correlated at most stages of normal pregnancies after Day 100, divergence was observed in the unsuccessful pregnancies between the concentrations of all 3 hormones, suggesting synthesis/release is under independent control. Measurement of bPSPB may be useful for prediction of fetal well-being, whereas estrone sulphate may reflect placental viability.     

Pathogens and the structure of plant communities

There is increasing interest in the direct and indirect effects of pathogens and parasites on the structure of plant communities. The direct influence of pathogens is seen in cases where pathogens reduce the populations of adult and seedling plants or prevent the recruitment of seeds. Indirect effects occur when epidemic outbreaks or endemic parasites of herbivores lead to reductions in grazing pressure, which temporarily allow plants to escape from the detrimental effects of their herbivores. In both cases, the presence of pathogens can lead to changes in the relative abundance of the species in a plant community, which are discernible for many years after the initial disease outbreak has passed.     

Population biology of Trichostrongylus tenuis, a parasite of economic importance for red grouse management

The caecal nematode, Trichostrongylus tenuis, is associated with dramatic decreases in the density of red grouse (Lagopus lagopus scoticus) resulting in a significant loss of sporting income to many upland estates in the UK. In this article Peter Hudson and Andrew Dobson describe the dynamics of the grouse-T. tenuis system, show that the parasites can cause population crashes and present preliminary findings from the development of new control methods.     

In vitro adherence of erythrocytes infected with Babesia bigemina and Babesia rodhaini to thrombospondin

The adherence of erythrocytes infected with Babesia bigemina and Babesia rodhaini to thrombospondin (TSP) in vitro is demonstrated. Blood with a range of parasitaemias was used and counts of cells which bound to TSP on plastic were significantly different from the controls with both Babesia species. These studies indicated that TSP receptors are present on the surface of red blood cells infected with the two Babesia species, although these parasites do not alter the membranes of infected erythrocytes obviously and do not cause cerebral symptoms in their hosts. Erythrocytes infected with either B. bigemina or B. rodhaini do not adhere to other erythrocytes in vivo, probably because these parasites induce mild infections in their hosts, but they can adhere to TSP in vitro.     

The Gibbs-Donnan near-equilibrium system of heart

The gradients of the major inorganic ions across the plasma membrane of heart were examined to determine the factors controlling the extent and direction of the changes induced during injury, certain diseases, and electrolyte disturbances. The ionic environment was altered by changing only the concentration of inorganic phosphate, [sigma Pi]o, from 0 to 1.2 to 5 mM in the Krebs-Henseleit buffer perfusing working rat hearts. Raising [sigma Pi]o from 1.2 to 5 mM resulted in a decrease in total Mg2+ content and calculated free cytosolic [Mg2+] from 0.44 to 0.04 mM, conversion of 4 mmol of MgATP2- to ATP4- and a decrease in measured intracellular [Cl-]i from 41 to 16 mM. At all levels of [sigma Pi]o, both the [Na+]i and [K+]i were invariant at about 3 mM and 130 mM, respectively, as was the energy of hydrolysis of the terminal phosphate bond of sigma ATP, delta GATP Hydr, of -13.2 kcal/mol. The relationship maintained between the ions on both sides of the plasma membrane by the 3Na+/2K(+)transporting ATPase (EC 3.6.1.37) and an open K+ channel was: (formula; see text) The energy of the gradients of the other inorganic ions across the plasma membrane, delta G[ion]o/i, exhibited three distinct quanta of energy derived from the prime quantum of delta GATP Hydr of -13.2 kcal/mol. The second quantum was about one-third of delta GATP Hydr or +/- 4.4 kcal/mol and comprised the delta G[Na+]o/i, delta G[Mg2+]o/i, and delta G[HPO42-]o/i. These results indicated near-equilibrium was achieved by the reactants of the 3Na+/2K(+)-ATPase, the K+ channel, the Na(+)-Pi co-transporter, and a postulated net Mg2+/H2PO4- exchanger. The third quantum was one-third of delta G[Na+]o/i or about +/- 1.5 kcal/mol and comprised delta G[H+]o/i, delta G[HCO3-]o/i, and delta G[Cl-]o/i. The delta G[K+]o/i was 0, indicating near-equilibrium between the chemical energy of [K+]o/i and the E across the plasma membrane of -83 mV. It is concluded that the gradients of the major inorganic ions across the plasma membrane and the potential across that membrane constitute a Gibbs-Donnan equilibrium system catalyzed by transport enzymes sharing common substrates. The chemical and electrical energies of those gradients are equal in magnitude and opposite in sign to the chemical energy of ATP hydrolysis.     

1-Butyryl-glycerol: a novel angiogenesis factor secreted by differentiating adipocytes.

Differentiation of adipocytes is accompanied by secretion of molecules stimulating angiogenesis in vivo and endothelial cell growth and motility in vitro. We demonstrate that the angiogenic and motility-stimulating activities secreted by adipocytes are separable from the endothelial cell mitogenic activity by fractionation of adipocyte-conditioned medium. The major differentiation-dependent angiogenic molecule was purified and identified by GCMS as 1-butyryl-glycerol (monobutyrin). Monobutyrin levels increase at least 200-fold during adipocyte differentiation and represent a major fraction of the total angiogenic activity. Synthetic monobutyrin shows the same spectrum of biological activities as the adipocyte-derived factor: stimulation of angiogenesis in vivo and microvascular endothelial cell motility in vitro, with no effect on endothelial cell proliferation. Angiogenesis is stimulated at doses as low as 20 pg when tested in the chick chorioallantoic membrane assay. These results strongly suggest that monobutyrin is a key regulatory molecule in an angiogenic process linked to normal cellular and tissue development.     

Structure and polymorphism of human telomere-associated DNA

We have analyzed the DNA sequences associated with four different human telomeres. Two are members of distinct repeated sequence families which are located mainly but not exclusively at telomeres. Two are unique in the genome, one deriving from the long arm telomere of chromosome 7 and the other from the pseudoautosomal telomere. One telomere-associated repeated sequence has a polymorphic distribution among the chromosome ends, being present at a different combination of ends in different individuals. These data thus identify a new source of human genetic variation and indicate that the canonical features of the organization of telomere-associated DNA are widely conserved in evolution.