Monensin, a monovalent ion-selective ionophore, facilitates the transmembrane exchange of principally sodium ions for protons. The outer surface of the ionophore-ion complex is composed largely of nonpolar hydrocarbon, which imparts a high solubility to the complexes in nonpolar solvents. In biological systems, these complexes are freely soluble in the lipid components of membranes and, presumably, diffuse or shuttle through the membranes from one aqueous membrane interface to the other. The net effect for monensin is a trans-membrane exchange of sodium ions for protons. However, the interaction of an ionophore with biological membranes, and its ionophoric expression, is highly dependent on the biochemical configuration of the membrane itself. One apparent consequence of this exchange is the neutralization of acidic intracellular compartments such as the trans Golgi apparatus cisternae and associated elements, lysosomes, and certain endosomes. This is accompanied by a disruption of trans Golgi apparatus cisternae and of lysosome and acidic endosome function. At the same time, Golgi apparatus cisternae appear to swell, presumably due to osmotic uptake of water resulting from the inward movement of ions. Monensin effects on Golgi apparatus are observed in cells from a wide range of plant and animal species. The action of monensin is most often exerted on the trans half of the stacked cisternae, often near the point of exit of secretory vesicles at the trans face of the stacked cisternae, or, especially at low monensin concentrations or short exposure times, near the middle of the stacked cisternae. The effects of monensin are quite rapid in both animal and plant cells; i.e., changes in Golgi apparatus may be observed after only 2-5 min of exposure. It is implicit in these observations that the uptake of osmotically active cations is accompanied by a concomitant efflux of H+ and that a net influx of protons would be required to sustain the ionic exchange long enough to account for the swelling of cisternae observed in electron micrographs. In the Golgi apparatus, late processing events such as terminal glycosylation and proteolytic cleavages are most susceptible to inhibition by monensin. Yet, many incompletely processed molecules may still be secreted via yet poorly understood mechanisms that appear to bypass the Golgi apparatus. In endocytosis, monensin does not prevent internalization. However, intracellular degradation of internalized ligands may be prevented.(ABSTRACT TRUNCATED AT 400 WORDS)

The progression of aflatoxicosis was evaluated in young broiler chickens (Hubbard X Hubbard). The experimental design consisted of four dietary treatments of aflatoxin (0, 1.25, 2.5, and 5.0 micrograms of aflatoxin/g of feed, ppm) and 11 replicates of 10 broilers/replicate. The broilers were maintained in electrically heated batteries with feed and water available ad libitum from hatching to 3 weeks of age. The broilers were weighed, bled, killed by cervical dislocation, and necropzied at 3, 6, 9, 12, 15, 17, and 21 days of age. Body weights were significantly decreased by 5.0 ppm aflatoxin at 6 days of age and by 2.5 ppm at 17 days of age. Aflatoxin induced a significant increase in the relative weight of the proventriculus, gizzard, spleen, and kidney. Liver atrophy was indicated in the early stages of aflatoxicosis by a decrease in the relative weight of this organ. As aflatoxicosis progressed, hepatomegaly became apparent due to lipid accumulation in the liver. Packed-cell volume and hemoglobin levels were significantly decreased by 5.0 ppm aflatoxin at 12 days and by 2.5 ppm aflatoxin at 21 days of age. Serum levels of albumin and total protein were significantly reduced at 5.0 and 2.5 ppm aflatoxin by 3 and 6 days of age, respectively. Serum levels of uric acid, triglycerides, and cholesterol were significantly decreased from control values from 12 through 21 days of age by 5.0 ppm aflatoxin and, to a lesser extent, by 2.5 ppm aflatoxin. The activity of serum lactic dehydrogenase was significantly decreased at all aflatoxin treatment levels from 12 through 21 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrastructural studies on blood leukocytes of the channel catfish, Ictalurus punctatus, show the presence of heterophils (neutrophils), small lymphocytes, monocytes, and thrombocytes. Monocytes cannot always be distinguished from large lymphocytes. Cells resembling macrophages or transitional forms between monocytes and macrophages are occasionally seen. Blood eosinophils and basophils are not found. Thrombocytes and small lymphocytes are the most abundant leukocytes, while monocytes are the least frequently encountered leukocyte. Glycogen, present in all leukocytes, is most abundant in heterophils and least abundant in monocytes. Although monocytes are similar to heterophils in size and shape, a greater amount of rough endoplasmic reticulum, free ribosomes, and fewer granules are observed in monocytes. Heterophils possess oval or elongate granules, which often contain a crystalline or striated structure; small tubules which resemble smooth endoplasmic reticulum, and cristae which traverse the long axes of the mitochondria are frequently seen. Small lymphocytes are characterized by the presence of pseudopodia, many free ribosomes, numerous large mitochondria, dictyosomes (Golgi), and long profiles of rough endoplasmic reticulum. The dictyosomes are often associated with a large zone of exclusion. Bundles of microtubules are observed near the elongated ends of thrombocytes. Deep indentations of the plasmalemma, which give the appearance of vacuoles, are also seen in thrombocytes.