Increase In Guanosine Research Articles

The control of liver regeneration after partial hepatectomy in the rat.

1. Normal rat liver slices were incubated for 24 h in culture medium to which had been added freeze-dried plasma, prepared from the blood of rats which had undergone partial hepatectomy (60-70% of liver removed) 10 min, 4 or 24 h previously. No changes in the dry weight of the slices were observed. 2. Similarly, there were no changes in the dry weight or protein content of incubated liver slices when freeze-dried plasma prepared from the blood of rats unilaterally nephrectomized 10 min, 4 or 24 h previously was added to the culture medium. 3. Slices from the remaining liver stump, taken 4 h after partial hepatectomy (60-70% of liver removed) and incubated for 4 h in culture medium, did not release a factor capable of increasing the dry weight of normal liver slices incubated in the same medium. 4. After partial hepatectomy (60-70% of liver removed), there was no increase of guanosine 3':5'-cyclic monophosphate in the remaining part of the liver. 5. No measurable amount of esterase activity was found in normal liver or in the remaining liver stump after partial hepatectomy (60-70% of liver removed). 6. It is suggested that the stimulatory mechanism for liver regeneration is of a different nature from that involved in compensatory renal hypertrophy.

Rapid increase in guanosine 3′,5′-cyclic-monophosphate in interferon-treated mouse leukemia L1210 cells: Relationship to the development of the antiviral state and inhibition of cell multiplication

Treatment of mouse leukemia L1210 cells with electrophoretically pure mouse interferon caused a rapid (1 to 5 min) and transitory (duration 5 to 10 min) increase in the intracellular concentration of guanosine 3′,5′-cyclic monophosphate (cyclic GMP). No significant increase in the intracellular concentration of adenosine 3′,5′-cyclic monophosphate (cyclic AMP) was observed until 2 to 3 hr after the addition of interferon. Electrophoretically pure mouse interferon caused a dose-dependent increase in the intracellular concentration of cyclic GMP at concentrations ranging from 1.0 to 10 4 unite/ml. The interferon-induced increase in cyclic GMP was abrogated by specific antibody to mouse interferon. Furthermore, interferon had no effect on the intracellular concentration of cyclic GMP in a line of L1210 cells resistant to the action of interferon. The interferon-induced increase in cyclic GMP was calcium dependent and was inhibited by indomethacin and aspirin at concentrations of 10 −7 to 10 −6 M. Depletion of intracellular calcium prior to the addition of interferon abrogated the interferon-induced increase in cyclic GMP without preventing either the development of the antiviral state or the inhibition of cell multiplication in interferon-treated L1210 cells. These results suggest that cyclic GMP may not mediate these two biologic effects of interferon but may rather reflect rapid changes in interferon-treated cells.

Stringent control of RNA synthesis in the absence of guanosine 5‘-diphosphate-3‘-diphosphate.

Severe curtailment of RNA synthesis and widespread readjustment of cellular activities, together with an increase of guanosine 5'-diphosphate-3'-diphosphate (ppGpp) have been demonstrated in Escherichia coli cells starved for amino acid or energy. The rates of growth and RNA synthesis are reduced by shifting the growth temperature from 40 degrees C to 20 degrees C. The intracellular pool of ppGpp diminishes under such conditions. Furthermore, the accumulation of ppGpp normally attainable by either amino acid- or energy-limitation can be totally blocked by a downshift of temperature imposed prior to the starvation. However, the synthesis of stable RNA is still stringently restricted under these conditions. Two other nucleotides were also effected. The intracellular level of phantom spot (Gallant, J., Shell, L., and Bittner, R. (1976) Cell 7, 75-84) decreased upon temperature fall. Guanosine 5'-diphosphate-3'-monophosphate, whose concentrations have been linked to stringent response and stable RNA synthesis, did not change by the simple temperature downshift, but increased following amino acid limitation even when a downshift of temperature was imposed before the starvation. These results suggest that ppGpp is not always needed for inhibition of stable RNA synthesis during stringent response, and that a compound such as guanosine 5'-diphosphate-3-monophosphate may be involved in the stringent regulation of stable RNA synthesis, at least under the temperature downshift conditions.

Release of prostaglandins from the isolated frog ventricle and associated changes in endogenous cyclic nucleotide levels.

1. A study has been made of the decline in contractility and some associated metabolic changes which occur in the isolated frog ventricle during the development of hypodynamic depression. 2. The release of two identified prostaglandins (PG), E1 and E2, together with several as yet unknown prostaglandin-related substances (PRS), accompanies the development of hypodynamic depression. There is a close correlation between the extent to which the isometric twitch is depressed and the quantity of prostaglandin released into the superfusate. 3. Fractionation of extracts of 'used' superfusates, using preparative-scale thin-layer chromatography, revealed the presence of six major components, four of which (PGE1 and PGE2 and two unidentified components) were found to be cardioactive and potentiated contraction when tested subsequently on hypodynamic preparations. 4. Two agents which influence prostaglandin biosynthesis, arachidonic acid and indomethacin, are found to affect both the rate at which the hypodynamic state develops and the extent to which the 'steady-state' twitch tension is depressed, in a dose-dependent manner. Indomethacin, a PG-synthetase inhibitor, accelerates the decay and depresses the final 'steady-state' tension attained, whereas arachidonic acid, the principal precursor for prostaglandin biosynthesis, has the converse effects. 5. Measurements of endogenous 3'5'-cyclic nucleotide levels reveal a time-dependent decrease in intracellular adenosine 3'5'-cyclic monophosphate (3'5'-cyclic AMP) and a concomitant increase in guanosine 3'5' cyclic monophosphate (3'5'-cyclic GMP). The decline in isometric twitch tension is paralleled almost exactly by an equivalent reduction in the ratio 3'5'-cyclic AMP: 3'5'-cyclic GMP. 6. Superfusion of isolated ventricles with Ringer solution containing exogenous, lipid-soluble derivatives of 3'5'-cyclic AMP and 3'5'-cyclic GMP affects both the rate of decline of the isometric twitch and the steady-state tension ultimately reached: thus, 8-bromo-3'5'-cyclic GMP accelerates the decline in contractility and depresses the steady-state level, whereas dibutyryl 3'5'-cyclic AMP delays the development of hypodynamic depression, and elevates the final twitch tension. The effects of both 3'5' cyclic nucleotide derivatives are dose-dependent. 7. The possible involvement of prostaglandins and 3'5'-cyclic nucleotides as causal agents in the mechanism of hypodynamic depression is discussed. The biochemical basis for the implied antangonistic effects of 3'5'-cyclic AMP and 3'5'-cyclic GMP in regulating ventricular contractility is considered in the following paper (Flitney & Singh, 1980).

Increased responsiveness of the hepatic guanylate cyclase-guanosine 3′,5′-monophosphate system to nitrosoguanidine following partial hepatectomy

When tested at concentrations producing submaximal responses, the N-nitroso carcinogen, N-methyl- N′-nitro- N-nitrosoguanidine (methylnitro-nitrosoguanidine) elicited a 2-fold greater increase in guanosine 3′,5′-monophosphate (cyclic GMP) accumulation in slices and a 5-fold greater stimulation of guanylate cyclase activity in whole homogenates of rat liver examined 24 h after 75% hepatectomy compared to the corresponding methylnitro-nitrosoguanidine responses in sham-operated and unoperated controls. Enhanced methylnitro-nitrosoguanidine sensitivity of guanylate cyclase in whole homogenates of regenerating liver was attributable to altered responsiveness of the enzyme activity of the 100 000 × g soluble fraction, which contained 98% of the methylnitro-nitrosoguanidine responsive activity. Basal cyclic GMP accumulation and guanylate cyclase activities of these systems, and their responses to concentrations of methylnitro-nitrosoguanidine eliciting maximal stimulation were unchanged after partial hepatectomy or sham operation, compared to unoperated controls. The findings of (a) increased heme concentrations in the supernatant and the high molecular weight Sephadex G-25 fraction of sham operated, compared to regenerating liver, (b) suppression of methylnitro-nitrosoguanidine responsive activity after addition of exogenous hemoglobin to supernatants from regenerating liver, and (c) enhancement of the responsiveness of soluble guanylate cyclase from sham operated liver to submaximal methylnitro-nitrosoguanidine after reduction of endogenous heme content by in situ perfusion, all suggested that the difference in methylnitro-nitrosoguanidine action observed in control vs. regenerating liver are related to a lower heme-protein content of the latter. These results emphasize the importance of endogenous heme as a factor modulating the response of the hepatic guanylate cyclase system to methylnitro-nitrosoguanidine.

Stimulation of Guanosine 3',5'-Monophosphate-Phosphodiesterase Activity by Adrenocorticotropic Hormone-Activated Increase of Guanosine 3',5'-Monophosphate in Isolated Adrenocortical Carcinoma Cells*

The decline of the ACTH-stimulated cGMP to the basal level in isolated adrenocortical carcinoma cells was inhibited by cyclic phosphodiesterase inhibitors. Time-course experiments showed that the ACTH-induced level of cGMP preceded the activation of phosphodiesterase. Cells incubated with increasing concentrations of exogenous cGMP responded with a corresponding increase in the cGMP-phosphodiesterase activity. cAMP was 100-fold less effective than cGMP in the activation of cGMP-phosphodiesterase, indicating the nucleotide specificity of enzyme activation. The activation of cGMP-phosphodiesterase by ACTH-induced cGMP or exogenous cGMP was rapid. In contrast to these observations, there was no activation of cAMP-phosphodiesterase by exogenous cAMP or cGMP. These results indicate that one mechanism by which isolated adrenocortical carcinoma cells regulate the ACTH-induced increase in cGMP is the cyclic nucleotide control of the activity of its phosphodiesterase, thereby regulating cGMP degradation.

Guanosine 3',5'-monophosphate in sympathetic ganglia: increase assoicated with synaptic transmission.

Brief stimulation of cholinergic preganglionic nerve fibers resulted in an increase in guanosine 3',5'-monophosphate (cyclic GMP) in the bullfrog sympathetic ganglion. When the release of synaptic transmitter was prevented by a high-magnesium, low-calcium Ringer solution, stimulation of preganglionic nerve fibers did not increase cyclic GMP in the ganglion. The increase in cyclic GMP caused by preganglionic stimulation was also blocked by the muscarinic antagonist, atropine. The data indicate that the increase in cyclic GMP is associated with synaptic transmission and support the possibility that cyclic GMP may mediate the postsynaptic action of acetylcholine at muscarinic cholinergic synapses.