Activation of Dopamine Receptors Does Not Affect Phosphoinositide Turnover in NCB-20 Cells

Dopamine inhibits and serotonin stimulates adenylate cyclase activity in a neuroblastoma X Chinese hamster brain explant cell line (NCB-20). The inhibition of cyclic AMP accumulation by dopamine was blocked by pretreatment of the cells with pertussis toxin. Carbachol and bradykinin stimulated the accumulation of water-soluble inositol phosphates whereas thyrotropin-releasing hormone, vasopressin, neurotensin, and phenylephrine were without effect. Dopamine and serotonin had no significant effect on carbachol-induced phosphoinositide hydrolysis or the levels of the parent lipids within the membrane. Forskolin induced a much larger stimulation of cyclic AMP than did serotonin, and caused an increase in the levels of phosphatidylinositol-4-phosphate and phosphatidyl inositol-4,5-bisphosphate in the cell membrane.     

Growth hormone-releasing factor releases ACTH from an AtT-20 mouse pituitary tumor cell line but not from normal pituitary cells

Corticotropin-releasing factor (CRF) and both human pancreatic growth hormone-releasing factor (hp-GRF) and rat hypothalamic GRF (rh-GRF) stimulated ACTH release from neoplastic AtT-20 mouse pituitary tumor cells in a dose-dependent fashion, with CRF inducing a 10-fold increase and GRF a maximal increment of approximately one-half that of CRF. Neither rh-GRF nor hp-GRF induced ACTH release in normal anterior pituitary cells. Pretreatment with either dexamethasone or somatostatin prior to the addition of rh-GRF inhibited the increase in ACTH release. Both ovine CRF and rh-GRF stimulated adenosine 3,5-monophosphate production in AtT-20 cells. The weak but clearly discernible effect of GRF on ACTH release from AtT-20 cells may be due to an abnormality in the AtT-20 cell receptor.     

The effect of muscarinic and beta-adrenergic blockade on cysteamine-induced gastrin secretion by the isolated perfused rat stomach

Cysteamine-induced duodenal ulceration in rats is accompanied by increased circulating gastrin. Although cysteamine appears to exert a direct action on the gastrin cell some groups have provided evidence for an involvement of the autonomic nervous system. The current experiments were performed to determine whether beta-adrenergic or cholinergic (muscarinic) pathways are involved in the acute effect of cysteamine on gastrin secretion in the isolated perfused rat stomach. Cysteamine (1 mM) increased gastrin (IRG) secretion to a maximum ranging between 100% and 192% above basal. A cysteamine concentration of 5mM resulted in peak levels ranging between 150% and 1050% above basal. Addition of atropine or propranalol did not influence the responses obtained. The present results, therefore, do not support a role for either cholinergic or beta-adrenergic pathways in cysteamine-induced gastrin release at the level of the stomach and suggest that in vivo such autonomic effects are mediated extrinsically.     

Relationships between the effects of insect herbivory and sheep grazing on seasonal changes in an early successional plant community

Summary The effects of spring grazing by sheep and of natural levels of insect herbivory were studied in 1985 on a limestone field abandoned from arable land for four years. A split-plot design was adopted in which paddocks, arranged in Latin squares, were either left ungrazed or heavily grazed by sheep for ten days in April. Within each paddock plots were either sprayed regularly with Malathion-60 or untreated.Natural levels of insect herbivory, compared to the reduced levels in insecticide-treated plots, had effects of similar magnitude to those from the short burst of spring grazing. Many attributes of the grazed/insecticide-treated sward were either increased or decreased by a factor of two within a season. Both types of herbivore caused changes in the direction of plant succession as well as in its rate. Effects on early successional species were large and similar when caused by either type of herbivore. Effects on later successional species were often smaller, but also showed differences in the action of the two herbivore types, as did effects on sward height, species richness and total cover. The effects of sheep and insect herbivory were not always additive or in the same direction.The results suggest that manipulations of both mammal and insect herbivores may be powerful tools for directing changes in plant community composition.     

Measurement of plasma adenosine concentration: methodological and physiological considerations

This study tested the hypothesis that measurements of plasma adenosine concentration made on samples of blood obtained in dipyridamole and EHNA (i.e., "stopping solution") may be falsely elevated as a result of ongoing in vitro production and accumulation of adenosine during sample processing. Studies were performed with samples of anticoagulated blood obtained from anesthesized domestic swine. Adenosine concentration of ultra filtrated plasma was determined by high-pressure liquid chromatography (HPLC). The following parameters were evaluated: (i) rate of clearance of [3H]adenosine added to plasma, (ii) endogenous adenosine concentration of matched blood samples obtained in "stopping solution" alone, "stopping solution" plus EDTA, and perchloric acid (PCA), (iii) plasma and erythrocyte endogenous adenosine concentration in nonhemolyzed samples, and (iv) plasma adenosine concentration of samples hemolyzed in the presence of "stopping solution" alone or "stopping solution" plus EDTA. We observed that (i) greater than or equal to 95% of [3H]adenosine added to plasma is removed from it by formed elements of the blood in less than 20 s, (ii) plasma adenosine concentration of samples obtained in "stopping solution" alone is generally 10-fold greater than that of matched samples obtained in "stopping solution" plus EDTA, (iii) deliberate mechanical hemolysis of blood samples obtained in "stopping solution" alone resulted in substantial augmentation of plasma adenosine levels in comparison with matched nonhemolyzed specimens--addition of EDTA to "stopping solution" prevented this, and (iv) adenosine content of blood samples obtained in PCA agreed closely with the sum of plasma and erythrocyte adenosine content of samples obtained in "stopping solution" plus EDTA. The data obtained demonstrate that (i) plasma adenosine concentrations are falsely elevated in samples of blood obtained in "stopping solution" alone, and (ii) addition of EDTA to "stopping solution" blocks in vitro production and accumulation of adenosine. Finally, rapid removal of adenosine from plasma by formed elements of blood may make it difficult to employ measurements of plasma adenosine concentration to assess physiological processes even in the absence of in vitro production of the nucleoside.     

Fatty acids of rice coleoptiles in air and anoxia

The metabolism of lipids, like that of other components, was adversely and strongly affected when rice (Oryza sativa L.) coleoptiles were grown anaerobically. In aerobic coleoptiles, the amounts of total fatty acid, phospholipid, and total lipid per coleoptile increased by 2.5- to 3-fold between days three and seven, whereas under anoxia, the increases were all less than 60%. The total amount of lipid at day seven in anoxia was less than 30% of that in air. In air, the total fatty acid content at day three was 25 nanomoles per coleoptile and this increased to over 71 nanomoles per coleoptile at day seven. All acids except 18:0 showed substantial increases. In anoxia, the corresponding values for total fatty acids were 24 nanomoles and 27 nanomoles. The small increases were confined to the saturated fatty acids; no significant increase occurred in unsaturated fatty acids. A minor fatty acid constituent (16:1) increased from 0.09 to 1.99 nanomoles per coleoptile between days three and seven in air. This component was never observed in any fatty acid preparation from anaerobic coleoptiles. The major phospholipids under all conditions were phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidic acid. A small amount of unidentified phosphoester, not present on thin layer chromatography plates from aerobic coleoptiles, was seen in extracts of anaerobic coleoptiles. The fatty acyl substituents of each of the phospholipids were analyzed at days three and seven in coleoptiles grown aerobically and in anoxia. Each phospholipid had its own distinctive fatty acid composition which remained fairly constant under all treatments; 16:0 and 18:2 were the most abundant fatty acids in every phospholipid class. In air, the percentages of total fatty acids that were in the phospholipids were 86% on day three and 87% on day seven. In anoxia, the values at the corresponding ages were 47 and 57%. Since no net synthesis of unsaturated fatty acids occurred in anaerobic conditions, the small increase in total unsaturated acids in the phospholipids between days three and seven must have occurred at the expense of fatty acids preexisting in the neutral lipid. No unusual pathways of biosynthesis or unusual precursors are required to explain the presence of unsaturated fatty acids in the rice coleoptile. The present study and results of experiments where coleoptiles were fed [¹⁴C]acetate (BB Vartapetian et al. 1978 Plant Sci Lett 13:321-328) clearly show that unsaturated fatty acid synthesis in rice coleoptiles requires O₂, as it does in other plants.     

Molecular species specificity of phospholipid breakdown in microsomal membranes of senescing carnation flowers

During senescence of cut carnation flowers, there is extensive breakdown of microsomal phospholipid. This is attributable, at least in part, to lipolytic activity associated directly with the microsomal membranes. Evidence indicating that one or more of the lipid-degrading enzymes in these membranes preferentially degrade phospholipid molecular species containing two diunsaturated acyl chains or at least one polyunsaturated acyl chain has been obtained by using radiolabeled phosphatidylcholine substrates. 16:0^*/16:0^*, 16:0/18:2^*, and 18:1^*/18:1^* phosphatidylcholine were degraded only minimally over a 3 hour period by microsomes isolated from senescing flowers. By contrast, [U-¹⁴C]phosphatidylcholine, which comprises various molecular species including those containing polyunsaturated acyl chains, and 18:0/20:4^* phosphatidylcholine were extensively degraded. Under identical conditions, but in the absence of added radiolabeled substrate, endogenous 18:2/18:2, 18:1/18:3, and 18:2/18:3 phosphatidylcholine were selectively depleted from the membranes. During natural senescence of the flowers, there was a sharp decline in microsomal 16:0/18:1 and 18:1/18:2 phosphatidylcholine, whereas molecular species containing two diunsaturated acyl chains or at least one polyunsaturated acyl chain remained unchanged or decreased only slightly. The data have been interpreted as indicating that provision of particular molecular species susceptible to lipase attack is a prerequisite to phospholipid catabolism in senescing membranes.     

Mammographic changes following reduction mammaplasty

Mammographic findings after reduction mammaplasty may be similar to those seen with carcinoma. A knowledge of the expected mammographic alterations would be helpful in differentiating postoperative changes from those seen with carcinoma of the breast. Accordingly, the clinical records and mammograms of patients who underwent reduction mammaplasty at the Dartmouth-Hitchcock Medical Center between March of 1977 and July of 1985 were analyzed. Forty-two patients had at least one mammographic examination following reduction mammaplasty. Periareolar soft-tissue changes and inferior pole alterations were present in almost all examinations of patients during the first 6 months after operation, but they decreased during the next few years. Asymmetrical densities were present in approximately half the patients throughout the follow-up period but decreased in degree. Parenchymal calcifications occurred later; few x-rays showed these calcifications during the first year, but 50 percent were apparent after 2 years. Evidence of fat necrosis occurred in approximately 10 percent. Four patients had biopsies for suspicious densities. Chronic inflammation and inclusion cyst were reported. We believe that changes after reduction mammaplasty are predictable and can usually be differentiated from those associated with cancer.     

Further evidence from sectioned material in support of the existence of a linear terminal complex in cellulose synthesis

Summary Transmembrane linear terminal complexes considered to be involved in the synthesis of cellulose microfibrils have been described in the plasma membrane ofBoergesenia forbesii. Evidence for the existence of these structures has been obtained almost exlusively using the freeze etching technique. In the present study an attempt has been made to complete these studies using conventional fixation, staining, and sectioning procedures. In developing cells ofBoergesenia forbesii, strongly stained structures traversing the plasma membrane and averaging 598.9 nm ± 171.3 nm in length, 28.7 nm ± 4.2 nm in width, and 35.2 nm ± 6.6 nm in depth have been demonstrated. These structures are considered to be linear terminal complexes. At their distal (cell wall) surface, they appear to be closely associated with cellulose microfibrils. At the proximal (cytoplasmic) surface, they are associated with microtubules and polysomes. A model of the possible interrelation of the terminal complexes and microtubules leading to the generation of cell wall microfibrils is proposed.     

Radiosensitization in multifraction schedules. I. Evidence for an extremely low oxygen enhancement ratio

Stable monolayers of contact-inhibited C3H 10T1/2 cells were used in multifraction radiation experiments to measure the oxygen enhancement ratio (OER) at low doses/fraction under conditions where cell cycle effects (repopulation, redistribution) were minimal. Consistent with there being a dose-dependent reduction in the OER at low doses, an extremely low OER of 1.34 was measured after 20 fractions of 1.7 Gy every 12 h. The sparing effects of fractionating radiation doses were not apparent for cells irradiated under hypoxic conditions (i.e., multifraction survivals were lower than acute single-dose values) until doses exceeding 15 Gy were reached. This result suggested a deficiency in the recovery from sublethal and/or potentially lethal damage might exist after hypoxic irradiations, thereby reducing the OER. The capacity to repair potentially lethal damage was found to be nearly the same after hypoxic as compared to aerobic irradiations. However, there was an apparent absence of sublethal damage repair by 10T1/2 cells between two hypoxic irradiations which could be a major contributing factor to the extremely low OER value measured in this multifraction schedule.