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PubMed1976

Hormonal studies of uridine utilization in an insect cell line CP-1268 derived from the codling moth Laspeyresia pomonella.

Ecdysterone decreased cellular growth and the incorporation of uridine into RNA following 4 days of hormone exposure. This hormone did not affect uridine incorporation following short-term exposure up to 25 hours. Juvenile hormone and farnesol both significantly decreased uridine uptake and incorporation into RNA; however, uridine uptake was inhibited to a greater extent than uridine incorporation. Cyclic AMP increased the incorporation of uridine into RNA but had no demonstrable effect on the uptake process. This stimulation was not the result of cAMP degradation products. Cyclic AMP and ecdysterone together produced a significant increase in uridine incorporation into RNA. These studies demonstrate the potential utilization of insect cell lines for studying the mode of action of insect developmental hormones.

Cell Line↗
PubMed1976

The different modes of action of thyrotropin and prostaglandin E1 on cyclic adenosine 3',5'-monophosphate synthesis in human thyroid, as studied by sequential stimulations.

PGE1 was equally effective in increasing 3H-cyclic AMP in normal and in toxic thyroids, whereas TSH was less effective but over a longer time in the toxic thyroids. Stimulation by a large second dose of TSH could not be elicited after prior stimulation by large doses of TSH. Similar results were obtained with regard to the effect of PGE1. However, stimulation by a large dose of PGE1 was still effective after the slices became refractory to TSH. Similarly, stimulation by a large dose of TSH was still effective after the slices became refractory to PGE1. It is suggested that the site and/or mode of action of TSH is quite different from that of PGE1.

Cyclic AMP↗
PubMed1976

Hyperreactive arterial endothelial cells: a clue for the treatment of atherosclerosis.

Arterial endothelial cells, which are capable of phagocytizing carbon particles of the same size as beta- and pre-beta-lipoprotein, were found only in endothelial cells of arterial segments susceptible to atheromatous changes in susceptible animal species, and the distribution closely corresponded to the susceptibility. The distribution of such endothelial cells is dense in large arteries, in the openings to their branches, especially in downstream portions, of rabbits, hens, and cocks; however, the distribution is relatively scanty in arteries of rhesus monkeys and is very scanty in dogs. Carbon particles were also rare in the suckling rabbit and tended to increase with age. They were not found in Wistar rats but were found in spontaneously hypertensive rats, which showed a characteristically diffuse distribution, even in relatively small arteries. The carbon particles, phagocytized, were released to the subendothelial space but were difficult to pass through the internal elastic lamina and tended to stagnate there for more than one month. The authors therefore call these cells hyperreactive endothelial cells. Various vasoactive substances, such as angiotensin II, histamine, and serotonin, significantly enhanced the phagocytic activities of arotic endothelial cells in rabbits; epinephrine and norepinephrine also slightly enhanced these activities. Various smooth muscle relaxants, such as ATP, pyridinol carbamate (ATP synthesis-enhancing substance), cycli-AMP, dibutyryl cycli-AMP, phthalazinol (cyclic-AMP phosphodiesterase inhibitor), iproveratril (calcium entry-inhibiting substance), colchicine, and vinblastine, with their different modes of action, commonly inhibited phagocytic activities, a finding that suggests a significant role for contractile protein in the permeability problem of atherogenesis. The atheromatous lesions of cholesterol-fed rabbits exhibited a striking increase in hyperreactive endothelial cells, accompanied by a marked rise in the activity of low-Km cyclic-AMP phosphodiesterase activity in atheromatous lesions and adjacent muscular layers, especially in rabbits with rapidly progressing atheroma.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1979

The role of cyclic AMP in aldosterone production by isolated zona glomerulosa cells.

The role of cyclic AMP in the regulation of aldosterone production by adrenocorticotropic hormone (ACTH), angiotensin II (A II), potassium, and serotonin was examined in collagenase-dispersed adrenal glomerulosa cells. The ability of 8-bromo cyclic AMP and choleragen to stimulate maximum aldosterone production indicated that cyclic AMP could act as second messenger for certain of the aldosterone-stimulating factors. The actions of ACTH and choleragen on aldosterone and cyclic AMP production were correlated in dog and rat cells, and a similar relation was seen during stimulation of rat cells by serotonin. In contrast, A II and potassium did not cause changes in cyclic AMP formation while stimulating aldosterone production. Intracellular and receptor-bound cyclic AMP were increased 3-fold by 10(-7) M ACTH but not by A II. Addition of a phosphodiesterase inhibitor increased the magnitude of the cyclic AMP response to ACTH but did not change the lack of stimulation by A II or potassium. In dog cells, the effects of A II and potassium on aldosterone production were partially additive to those of ACTH, choleragen, and 8-bromo cyclic AMP. In contrast, no additivity was observed between A II and potassium, or between combinations of the cyclic AMP-dependent stimuli. These results indicate that the actions of ACTH on aldosterone secretion are mediated by cyclic AMP formation, whereas A II and potassium stimulate aldosterone production through an independent mechanism. The lack of additivity between steroid responses to A II and potassium suggests that these factors could share a common mode of action on steroidogenesis in zona glomerulosa cells.

Adrenal Cortex↗
PubMed1975

Actions of bile salts and of papaverine and intracellular cyclic AMP in isolated rat uterus.

Both antioxytocin and antiphosphodiesterase activities of desoxycholate were potentiated by lowering the pH of the medium. The results suggest the possibility that it is the bile salt in the non-ionized form which exerts the antioxytocin and antiphosphodiesterase action. The concentration of tissue cyclic AMP was measured at different times during relaxation of the uterus. The results show a significant increase in tissue cyclic AMP concentration at a time when the muscle was just beginning to relax in response to papaverine, but not in response to chenodesoxycholate. The intracellular level of cyclic AMP during relaxation of the uterus produced by papaverine or chenodesoxycholate was, however, significantly increased when relaxation was about 90% complete. The difference between the mode of action of papaverine and that of the bile salts is discussed.

Animals↗
PubMed1975

Limited hydrolysis of tRNA by phosphodiesterase.

Digestion of tRNA by electrophoretically pure phosphodiesterase is limited to a short sequence of nucleotides at the 3'-terminus. On the average, four percent of all nucleotides can be released from tRNA. The optimum Mg2 concentration is 10mM and the optimum pH 9.2. The mode of action is a random attack by the enzyme on the substrate. The terminal AMP is completely removed at 15 degrees C after short incubation; about 400 mol of AMP were removed per min by 1 mol of enzyme. The following CMP residues are released much more slowly; at 15 degrees C incompletely, and at 37 degrees C more or less completely in 1 h. In about 50% of the tRNA molecules, the fourth nucleotide could be removed in very long incubations or with very high enzyme concentrations.

Adenosine Monophosphate↗
PubMed1978

Inhibition of noradrenaline-stimulated lipolysis and cyclic AMP accumulation in isolated rat adipocytes by purified phospholipase C and theta-toxin from Clostridium perfringens.

Purified phospholipae C (phosphatidylcholine cholinephosphohydrolase, EC 3.1.4.3) and theta-toxin from Clostridium perfringens both inhibited noradrenaline-stimulated lipolysis and cyclic AMP accumulation in isolated rat adipocytes in a dose-dependent manner. The action of phospholipase C was gradual in onset, while the effect of theta-toxin was almost immediate. Phospholipase C, but not theta-toxin, hydrolyzed membrane phospholipids and inhibited adenylate cyclase (EC 4.6.1.1) in a crude membrane fraction from fat cells. The inhibitory effects of phospholipase C were associated with morphological alterations detectable by electron microscopy, whereas effects of theta-toxin were observed at a time when no clearcut morphological alterations could be observed. It is concluded that the two purified principles from C. perfringens, which are both present in commercial preparations of phospholipase C, antagonize noradrenaline-stimulated cyclic AMP accumulation and lipolysis. Although their exact mechanisms of action have not been elucidated, phospholipase C and theta-toxin have different modes of attack.

Adenylyl Cyclases↗
PubMed1979

Inhibition of fundic strips from guinea-pig stomach: the effect of theophylline on the membrane potential, muscle contraction and ion fluxes.

The effect of theophylline on the smooth muscle cells of the fundic part of the stomach of the guinea pig was investigated. Theophylline hyperpolarized the membrane, inhibited spike discharges and slow waves and produced relaxation of the muscle cells. Furthermore, the theophylline-induced relaxation was not affected in low sodium solution or during inhibition of the sodium pump. Partial inhibition of the theophylline relaxation was seen in muscle depolarized by a high potassium solution and also when ATP was the relaxant. The potassium efflux was enhanced by ATP, but was not markedly changed by theophylline. A change in calcium efflux in the presence of theophylline could not be measured in quiescent preparations. The calcium influx was not changed by theophylline in Krebs, by low Ca, or by high K solution. Furthermore, the tissue content of cyclic AMP was increased by 59.6% in the presence of theophylline (2 x 10(-3) M). The conclusion is reached that the most likely mode of action of theophylline is a suppression of spontaneous activity and an extensive calcium binding to internal sites.

Animals↗
PubMed1975

Nicotine-induced stimulation of steroidogenesis in adrenocortical cells of the cat.

1. The effect of nicotine on steroid production and release from trypsin-dispersed cat adrenocortical cells was investigated. 2. Nicotine, like adrenocorticotrophin (ACTH), elicited a dose-dependent increase in steroidogenesis, which depended upon the presence of calcium in the medium. 3. Augmented steroid production evoked by submaximal concentrations of ACTH monobutyryl cyclic adenosine 3',5'-monophosphate (AMP), or prostaglandin E2 was further enhanced by steroidogenic concentrations of nicotine. 4. These results are discussed in relation to the possible mode of action of nicotine on cortical cells and to the potential consequences of smoking during stress.

Adrenal Cortex↗
PubMed1978

Mode of action of the hemin-controlled inhibitor of protein synthesis.

Despite the finding that the hemin-controlled translational inhibitor in reticulocyte lysates is a cyclic AMP-independent protein kinase that phosphorylates the small subunit of the initiation factor eIF-2, the mechanism of inhibition of translation remained unexplained. Whereas treatment of hemin-containing lysates with inhibitor in the presence of ATP inhibited translation, the same treatment of highly purified eIF-2 did not affect its ability to form a ternary complex with initiator Met-tRNA and GTP or a 40S initiation complex. We have isolated from ribosomal salt washes a protein (eIF-2 stimulating protein) that enhances the capacity of unphosphorylated eIF-2 to form ternary or 40S initiation complexes but has no effect on the phosphorylated factor. At low concentrations, eIF-2 is virtually inactive without this stimulating protein. Therefore, the translational inhibitor acts by converting eIF-2 to a form that is not stimulated by the stimulating protein.

Heme↗
PubMed1976

The mode of action of adenosine 3':5'-cyclic phosphate in the regulation of insulin secretion.

Changes in the pancreatic beta-cell concentrations of adenosine 3':5'-cyclic phosphate (cyclic AMP) may lead to changes in rates of insulin release, although little is known of the exact mechanism by which this nucleotide may influence the secretory process. Previous studies indicated that in the beta-cell, as in other mammalian cell types, the effects of cyclic AMP may be exerted by the activation of a cyclic AMP-dependent protein kinase, and we have attempted to identify possible substrates for this enzyme in beta-cells. Cyclic AMP stimulated the phosphorylation of specific non-nuclear protein substrates; this effect was observed both in intact cells preincubated with sodium [32P]phosphate to label intracellular ATP and in broken cell preparations incubated with [gamma-32P]ATP. The substrates for protein kinase in islets are unknown but as in other tissues might include microtubular protein and specific proteins of the granule and plasma membranes. In separate experiments cyclic AMP stimulated the efflux of calcium from an organelle-bound (probably mitochondrial) pool, and this may result in rapid changes of intracellular calcium distribution in the beta-cell; these might in turn play an important role in the regulation of secretion. These results suggest that cyclic AMP may directly affect cytosolic calcium concentrations in the beta-cell, as well as promoting the phosphorylation and activity of other components which may be necessary for the maintenance of adequate secretory responses.

Animals↗
PubMed1975

Classification and biological distribution of histamine receptor sub-types.

The distribution and classification of histamine receptors in mammalian and avian tissues have been summarized in Tables 1-4. It is evident that histamine receptors are present on a number of morphologically distinct cell types and the proportion of cells bearing H1- and H2-receptors varies not only with the species but also with the cell source. The pharmacological receptors mediating mepyramine-sensitive histamine responses have been defined as H1-receptors. Receptors mediating mepyramine-resistant, but burimamide or metiamide-sensitive histamine responses have been classified as H2-receptors. Histamine responses mediated via H2-receptors seem to involve the adenylcyclase system resulting in elevation of intracellular cyclic-AMP level, which is susceptible to burimamide blockade but insensitive to beta-adrenergic blocking agents. This mode of action of histamine involving H2-receptors and the adenyl cyclase system has been shown to stimulate the mammalian heart; promote gastric acid secretion; inhibit antigen-induced histamine release from leucocytes and inhibit lymphocyte-mediated cytotoxicity. It can further be concluded that both H1- and H2-receptors are widely distributed throughout the animal body in the gastro-intestinal, reproductive, respiratory and cardiovascular systems, nervous system and on mast cells and blood leucocytes. In these tissues, histamine receptors play an important role in physiological, immunological and immunopathological processes. Interaction of histamine with both H1- and H2-receptors in varying proportions modulates the overall manifestation of cardiovascular and respiratory syndromes during certain immunopathological conditions (e.g. inflammation, allergy and anaphylaxis). Histamine receptors also appear to play and important role in the development of immuno-competence and immunity.

Adrenal Medulla↗
PubMed1977

Further studies on the mechanisms controlling prostaglandin biosynthesis in the cat adrenal cortex: the role of calcium and cyclic AMP.

In light of previous studies which have implicated prostaglandin (PG) formation as a link in ACTH-induced steroid production by isolated cat adrenocortical cells, experiments were carried out to provide additional information regarding the role of PGs in adrenal steroidogenesis and their interactions with calcium and cyclic AMP. Perfusion of cat adrenal glands with Locke's solution plus beta(1-24)-ACTH resulted in an immediate increase in PGF2alpha release, which rapidly declined to basal levels after the stimulus was withdrawn. In contrast, maximal rates of steroid release were manifest some 30 min after removal of ACTH. ACTH and its onitrophenyl sulfenyl derivative (NPS-ACTH) increased PG (PGF2alpha and PGE2) and steroid release by trypsin-dispersed cat cortical cells, but NPS-ACTH, unlike ACTH, did not augment cortical cyclic AMP levels. In this same preparation, indomethacin completely blocked ACTH and NPS-ACTH facilitated PGF2alpha and PGE2 release but failed to suppress steroid release markedly. Calcium-deprivation blocked PG and steroid release evoked by these two polypeptides, and depressed PG release elicited by monobutyryl cyclic AMP (bcAMP) without affecting steroid release. These experiments offer additional evidence to support the concept that PGs play a role in the mode of action of ACTH; however, they do not appear to be obligatory intermediates in the steroidogenic process. The importance of calcium in regulating PG formation is discussed with special regard for the idea that this cation has a direct action on the enzyme systems which control PG synthesis.

Adrenal Cortex↗
PubMed1975

Adrenal cells in tissue culture the effects of choleragen and ACTH on steroid and cyclic-AMP metabolism.

Primary cultures of mouse adrenocortical tumors provide a sensitive system for investigating the effects of the enterotoxin of the V. cholerae (choleragen) on cyclic-AMP metabolism in the intact cell. Like ACTH, the toxin stimulates the synthesis and release of steroids from these cells but its mode of action differs from that of ACTH. The steroidogenic response to ACTH is immediate and of limited duration. The initial rate of steroidogenesis is the highest. In contrast, the steroidogenic response to choleragen is preceded by a 30-240 minute lag period which is inversely related to the concentration of the toxin. Whereas prolongation of the response to a single dose of ACTH requires hormone concentrations above those producing maximal initial steroidogenic activity, persistent steroidogenesis is induced at all levels of the toxin. Steroidogenic responses are detectable with 10 pg/ml of choleragen or less. The respective effects of ACTH and choleragen on cyclic-AMP synthesis and release into the medium parallel those on steroidogenesis. Intracellular cyclic-AMP levels in ACTH-treated cells reach a peak within 20-30 minutes and decline to normal levels within 2-4 hours. In choleragen-treated cells, after the lage period, the levels of intracellular cyclic-AMP remain above control levels indefinitely. The effects of ACTH and choleragen on cyclic-AMP biosynthesis are additive at all levels of the two compounds. The effects of choleragen are blocked by prior treatment of the toxin with a five-fold molar excess of ganglioside GM1, a presumed constituent of the toxin-binding site.

Adrenal Cortex↗
PubMed1975

Renal adenylate cyclase-effects of diuretics.

The in vitro effect of various diuretics on rat kidney adenylate cyclase was investigated in crude homogenates of the cortex, the outer and inner medulla. 10-3 M furosemide inhibited adenylate cyclase by 40% in the cortex, by 16% in the outer medulla and by 43% in the inner medulla. 10-3 M ethacrynic acid inhibited adenylate cyclase activity by 65% in the cortex, 59% in the outer medulla and by 57% in the inner medulla. Amiloride produced no significant inhibition of the adenylate cyclase reaction. In the cortex, furosemide partially inhibited adenylate cyclase under basal, fluoride-stimulated and parathyroid hormone-stimulated conditions. Ethacrynic acid produced a strong inhibition of adenylate cyclase activation by F- and parathyroid hormone. In the inner medulla 10-2 M F- and 1 mU antidiuretic hormone reversed the furosemide effect on adenylate cyclase. Ethacrynic acid produced a strong inhibition of adenylate cyclase in the presence of F- and antidiuretic hormone. It is suggested that inhibition of renal adenylate cyclase might be a possible mode of action of certain diuretics.

Adenylyl Cyclases↗