Lipoprotein lipase activity of rat cardiac muscle. The intracellular distribution of the enzyme between fractions prepared from cardiac muscle and cells isolated from the hearts of fed and starved animals.

1. Subcellular fractions, characterized by using morphological, compositional and enzymic markers, were prepared from rat heart tissue and cells isolated from the hearts of fed and 24 h-starved rats. 2. The lipoprotein lipase activity of fractions from whole tissue and isolated cells was determined in either fresh fractions or in acetone/diethyl ether powders of the fractions. 3. Lipoprotein lipase activity was present in all the fractions from tissue and cells, but was found to be of highest relative specific activity in the microsomal () fractions. 4. In fractions prepared from the isolated cells of hearts from starved rats the proportion of the total lipoprotein lipase present and its relative specific activity in the microsomal fraction were greater than in the equivalent fractions from fed animals. 5. The enhancement of lipoprotein lipase activity as a result of the acetone/diethyl ether powder preparation of fractions was most extensive in the microsomal fractions. 6. Investigation of the microsomal fraction showed that the lipoprotein lipase activity present was in two pools, one of which was within endoplasmic-reticulum vesicles. 7. The observations were consistent with the possibility that the cardiac-muscle cell could be the origin of the lipoprotein lipase activity functional in triacylglycerol uptake by the heart.     

A comparison of the sequestration of cadmium and zinc in the tissues of rainbow trout (Salmo gairdneri) following exposure to the metals singly or in combination

Rainbow trout were exposed to either cadmium (9 micrograms/l) or zinc (100 micrograms/l) in their aquarium water. They were then transferred to water containing concentrations of cadmium (54 micrograms/l) that would have otherwise proved fatal to the majority of the fish without the pretreatment. Most of the fish survived under both sets of conditions. However, two different mechanisms seem to be involved in the protection of the animals against the toxic manifestations of cadmium. In both cases, more than 99% of the total body load of cadmium was found in the liver, kidney and gills of the animals. Analysis of the metal-binding proteins in these organs was carried out. In the fish exposed to the two concentrations of cadmium, the toxic metal was found only in association with two low mol. wt specific binding proteins despite the presence of zinc- (and copper)-containing isometallothioneins in all three organs. On the other hand, cadmium was distributed between these binding-proteins and metallothioneins in the liver, kidney and gill of the trout pretreated with zinc before their exposure to cadmium.     

Colchicine inhibition of the heparin-stimulated release of clearing-factor lipase from isolated fat-cells.

When isolated fat-cells are incubated at 25 degrees C in serum-based media containing glucose, insulin and heparin, the rise that occurs in the clearing-factor lipase activity of the incubation medium is inhibited by colchicine. The rise in the fat-cell clearing-factor lipase activity that occurs during similar incubations in the absence of heparin is not affected by colchicine.     

The effect of cycloheximide on adipose-tissue clearing-factor lipase (Short Communication)

The progressive increase in clearing-factor lipase activity that occurs during the incubation of adipose tissue from starved rats in an appropriate medium at 25 degrees C is shown to occur in two stages. The first of these is not inhibited by cycloheximide, whereas the second is.     

Measurement of apolipoprotein B synthesis in perfused rat liver using stable isotopes: [15N]hippurate as a measure of the intracellular [15N]glycine precursor enrichment

Rat livers were perfused by the nonrecirculating technique with medium containing [15N]glycine and sodium benzoate. At various times, the isotopic enrichment of hepatic free glycine, hepatic glycyl-tRNA, and perfusate hippurate was measured by GLC-MS. After 60 min, these parameters had reached approximately maximal values. At 90 min, the perfusate hippurate had a 30% greater enrichment of 15N than the intracellular glycine or glycyl-tRNA. Hippurate enrichment was half that of the medium glycine. The rat livers secreted apolipoprotein B (B-100 plus B-48) at a rate of 22 micrograms/g per h. From the 15N enrichment and the secretion rate, an intrahepatic pool size of 86 micrograms/g of apoB was calculated. From the minimal intracellular transit time of 30 min, an apoB fractional synthetic rate (FSR) of 2 pools/h was indicated, whereas the FSR estimated from the 15N-enrichment was 0.26/h. A possible explanation for the discrepancy is that apoB may recycle within the hepatocyte. On the basis of the present experiments, when hippurate enrichment is used as a measure of the enrichment of intrahepatic glycine in in vivo studies with 15N-labeled glycine, a correction should be applied, under normal metabolic circumstances, of approximately 20-30%.     

A replicated climate change field experiment reveals rapid evolutionary response in an ecologically important soil invertebrate

Whether species can respond evolutionarily to current climate change is crucial for the persistence of many species. Yet, very few studies have examined genetic responses to climate change in manipulated experiments carried out in natural field conditions. We examined the evolutionary response to climate change in a common annelid worm using a controlled replicated experiment where climatic conditions were manipulated in a natural setting. Analyzing the transcribed genome of 15 local populations, we found that about 12% of the genetic polymorphisms exhibit differences in allele frequencies associated to changes in soil temperature and soil moisture. This shows an evolutionary response to realistic climate change happening over short‐time scale, and calls for incorporating evolution into models predicting future response of species to climate change. It also shows that designed climate change experiments coupled with genome sequencing offer great potential to test for the occurrence (or lack) of an evolutionary response.     

The isolation and characterisation of a putative adipocyte precursor cell type from the white adipose tissue of the chicken (Gallus domesticus)

The conditions of isolation and culture of a chicken adipose stromal-derived cell strain are described and compared with chicken lung fibroblasts in vitro. The stromal cells accumulated intracellular lipid during the post-confluency culture period, this being by contrast with lung fibroblasts. Much higher levels of intracellular lipid were accumulated by the stromal cells when whole chicken serum or chicken plasma lipoproteins were added to the culture medium. Lipoprotein lipase activity emerged in stromal cells maintained post confluency. This activity was absent from pre-confluent stromal cells and pre- and post-confluent fibroblasts. The incorporation of 14C-acetate, 3H-oleic acid and 14C-glucose into lipids by the stromal cells exhibited a pattern compatible with a concerted shift in the metabolism of the cells towards lipid storage, particularly in the form of triacylglycerols derived from exogenous fatty acids. It is proposed that, in common with the mammalian species previously studied, the white adipose tissue of the chicken (Gallus domesticus) contains a cell type with properties which allow its preliminary identification as an adipocyte precursor cell capable of adipose conversion in vitro. The confirmation of this proposition is amenable to further investigation.     

Elevated endogenous cortisol reduces autonomic neuroendocrine and symptom responses to subsequent hypoglycemia

We tested the hypothesis that increased endogenous cortisol secretion reduces autonomic neuroendocrine and neurogenic symptom responses to subsequent hypoglycemia. Twelve healthy young adults were studied on two separate occasions, once after infusions of a pharmacological dose of alpha-(1-24)-ACTH (100 microg/h) from 0930 to 1200 and 1330 to 1600, which raised plasma cortisol levels to approximately 45 microg/dl on day 1, and once after saline infusions on day 1. Hyperinsulinemic (2.0 mU x kg(-1) x min(-1)) stepped hypoglycemic clamps (90, 75, 65, 55, and 45 mg/dl glucose steps) were performed on the morning of day 2 on both occasions. These markedly elevated antecedent endogenous cortisol levels reduced the adrenomedullary (P = 0.004, final plasma epinephrine levels of 489 +/-64 vs. 816 +/-113 pg/ml), sympathetic neural (P = 0.0022, final plasma norepinephrine levels of 244 +/-15 vs. 342 +/-22 pg/ml), parasympathetic neural (P = 0.0434, final plasma pancreatic polypeptide levels of 312 +/- 37 vs. 424 +/- 56 pg/ml), and neurogenic (autonomic) symptom (P = 0.0097, final symptom score of 7.1 +/-1.5 vs. 10.6 +/- 1.6) responses to subsequent hypoglycemia. Growth hormone, but not glucagon or cortisol, responses were also reduced. The findings that increased endogenous cortisol secretion reduces autonomic neuroendocrine and neurogenic symptom responses to subsequent hypoglycemia are potentially relevant to cortisol mediation of hypoglycemia-associated autonomic failure, and thus a vicious cycle of recurrent iatrogenic hypoglycemia, in people with diabetes mellitus.     

The lipoprotein lipase (clearing-factor lipase) activity of cells isolated from rat cardiac muscle.

The total lipoprotein lipase activity recovered in suspension of cells prepared from adult rat hearts was unaffected by the nutritional state of the animals used. The enzyme activity present in the cell suspensions was almost exclusively associated with the cardiac muscle cells present as the major cell type.