Distribution of cyclic nucleotides in layers of the cerebellum after decapitation

The distribution of the cyclic nucleotides was examined in layers of the mouse cerebellum following decapitation. Cyclic AMP increased and cyclic GMP decreased in all three layers of the cerebellum examined. The increase in cyclic AMP in the granular layer was far greater than in either the molecular or white layers. In the cerebellum from control mice, the cyclic GMP concentration was highest in the molecular layer and lowest in the white layer. Even after decapitation, this cyclic GMP gradient in the cerebellum was maintained.     

Species-Specific Aggregation Factor In Sponges

In dissociated single cells from the sponge Geodia cydonium, DNA synthesis is initiated after incubation with a homologous, soluble aggregation factor. During the DNA -initiation phase the cyclic AMP - and cyclic GMP levels vary drastically; the cyclic AMP content drops from 2.2 pmol/10⁶ cells to 0.3 pmol/10⁶ cells while the cyclic GMP content increases from 0.6 pmol to 3.7 pmol/10⁶ cells. the activity of neither the adenylate cyclase nor of the guanylate cyclase isolated from cells which have been incubated for different periods of time with the aggregation factor, is changed. the soluble as well as the particulate enzyme activities were checked in vitro. the cyclic nucleotide receptors have been isolated from the sponge cells and characterized with respect to their molecular weight, dissociation constant for cyclic AMP or cyclic GMP and intracellular concentration. None of these parameters are altered during aggregation factor-mediated DNA initiation. From these data it is concluded that the regulation of cyclic nucleotide levels is a consequence of a changed activity of nucleotide cyclases or of phosphodiesterases, but this is presumably not caused by a changed rate of synthesis of nucleotide cyclases or of cyclic nucleotide receptors.     

The accumulation of cyclic AMP and cyclic GMP in guinea pig brain slices: Effect of calcium ions,norepinephrine and adenosine

The effect of Ca²⁺ and putative neurotransmitters on formation of cyclic AMP and cyclic GMP has been studied in incubated slices of brain tissue. Cyclic AMP levels in cerebellar slices after about 90 min of incubation ranged from 10 pmol/mg protein in rabbit, to 25 in guinea pig, to 50 in mouse and 200 in rat. Cyclic GMP levels in the same four species showed no correlation with cyclic AMP levels and were, respectively, 1.3, 20, 5 and 30 pmol/mg protein. The absence of calcium during the prolonged incubation of cerebellar slices had little effect on final levels of cyclic AMP, while markedly decreasing final levels of cyclic GMP. Reintroduction of Ca²⁺ resulted in a rapid increase in cerebellar levels of cyclic GMP which was most pronounced for guinea pig where levels increased nearly 7-fold within 5 min. Prolonged incubation of guinea pig cerebral cortical slices in calcium-free medium greatly elevated cyclic AMP levels apparently through enhanced formation of adenosine, while having little effect on final levels of cyclic GMP. Norepinephrine and adenosine elicited accumulations of cyclic AMP and cyclic GMP in both guinea pig cerebral cortical and cerebellar slices. Glutamate, γ-aminobutyrate, glycine, carbachol, and phenylephrine at concentrations of 1 mM or less had little or noe effect on cyclic nucleotide levels in guinea pig cerebellar slices. Prostaglandin E₁ and histamine slightly increased cerebellar levels of cyclic AMP. Isoproterenol increased both cyclic AMP and cyclic GMP. The accumulation of cyclic AMP and cyclic GMP elicited by norepinephrine in cerebellar slices appeared, baed on dose vs. response curves, agonist-antaganonist relationships and calcium dependency, to involve in both cases activation of a similar set of ß-adrenergic receptors. In cerebellar slices accumulations of cyclic AMP and cyclic GMP elicted by norepinephrine and by a depolarizing agent, veratridine, were strongly dependent on the presence of calcium. The stimulatory effects of adenosine on cyclic AMP and cyclic GMP formation were antagonized by theophylline. The lack of correlations between levels of cyclic AMP and cyclic GMP under the various conditions suggested independent activation of cyclic AMP- and cyclic GMP-generating systems in guinea pig cerebellar slices by interactions with Ca²⁺, norephinephrine and adenosine.     

Effects of decapitation, ether and pentobarbital on guanosine 3′,5′-phosphate and adenosine 3′,5′-phosphate levels in rat tissues

Cyclic GMP and cyclic AMP levels in eight different rat tissues were examined after animlas were immersed in liquid nitrogen. In order of decreasing concentration, cerebellu, kidney, lung and cerebral cortex contained the greatest quantities fo cyclic GMP. These tissues also contained relatively high concentrations of cyclic AMP. Compared to values in animals which were sacrificed in liquid nitrogen, levels of both nucleotides in many of the tissues examined were altered by decapitation or anesthesia with ether and pentobarbital. Decapitation increased the levels of both cyclic GMP and cyclic AMP in cerebellum, lung, heart, liver and skeletabl muscle. However, decapitation increased only cyclic AMP in cerebral cortex and kidney. Our previously reported high level of cyclic GMP in lung was attributed to ether anesthesia and surgical removal which increased the cyclic GMP content in lung, heart, testis and skeletal muscle. The effect of ether on cyclic GMP levels in lung and heart was blocked by pretreatment of animals with atropine which indicated that cholinergic agents increase cyclic GMP content in these tissues. Acetylcholine and carbachol in the presence of theophylline increased the accumulation of cyclic GMP in incubations of rat lung minces. Increases in cyclic GMP and cyclic AMP levels in cerebellum with ether anesthesia were prevented if rats were immersed in liquid nitrogen after anesthesis with ether. Anesthesia with pentobarbital decreased the levels of cyclic GMP in cerebellum and kidney and increased the nucleotide in heart, liver, testis and skeletal muscle compared to levels in tissues from animals immersed in liquid nitrogen. However, pentobarbital increased cyclic AMP levels in cerebellum and cerebral cortex and decreased the nucleotide in liver, kidney, testis and skeletal muscle. These studies provide a possible explanation for the variability in in vivo levels of cyclic GMP and cyclic AMP which have been previously reported. In addition, these studies support the hypothesis that the synthesis and degradation of cyclic AMP and cyclic GMP are regulated independently and not necessarily in a parallel or reciprocal manner. These studies also suggest that the increase accumulation of one cyclic nucleotide has no major effect on the synthesis and/or metabolism of the other; however, such interactions cannot be entirely excluded from the results of this study.     

CYCLIC NUCLEOTIDES IN MURINE BRAIN: THE TEMPORAL RELATIONSHIP OF CHANGES INDUCED IN ADENOSINE 3',5'-MONOPHOSPHATE AND GUANOSINE 3',5'-MONOPHOSPHATE FOLLOWING MAXIMAL ELECTROSHOCK OR DECAPITATION

–Adenosine 3′,5′-cyclic monophosphate (cyclic AMP) levels increase about 5-fold in the cerebral cortex and 2-fold in the cerebellum following electroconvulsive shock (ECS). The peak levels of cyclic AMP occur at 45 s after ECS in the cerebral cortex, and at 15 s in the cerebellum. In the cerebral cortex, ECS produces twice the cyclic AMP accumulation as does decapitation in a comparable time period; however, the relative effect of a number of neurotropic agents on the cyclic AMP accumulation is essentially the same, whether stimulated by decapitation or by ECS. In the cerebellum, the levels of guanosine 3′,5′-cyclic monophosphate (cyclic GMP) also increase following ECS. The cyclic GMP levels are greatest at 60 s after ECS during the postictal depression. An association between elevated cerebellar cyclic GMP and depression seems unlikely, since CNS depressants either lowered or had no effect on cyclic GMP levels. From these results, cyclic nucleotide profiles following treatments such as ECS or decapitation may be useful in elucidating the molecular events involved in seizures, brain injury and ischemia.     

Elevation of cyclic GMP levels in central nervous system by excitatory and inhibitory amino acids

—Guanosine 3′,5’cyclic monophosphate (cyclic GMP) levels in incubated slices of mouse cerebellum are increased 10-fold by glutamate and two-to three-fold by glycine or γ-aminobutyric acid (GABA). Glutamate also produces a 10-fold increase in adenosine 3′,5’cyclic monophosphate (cyclic AMP) in the same tissue. However, GABA decreases cyclic AMP levels 30-40 per cent, and glycine produces only a transient 50 per cent accumulation of this cyclic nucleotide. Theophylline slightly augments the accumulation of cyclic GMP produced by all three amino acids but markedly attenuates the accumulation of cyclic AMP produced by glutamate. In the absence of Ca²⁺, none of the three amino acids has any effect on cyclic GMP levels, and glutamate produces only a 50 per cent rise in cyclic AMP levels. The decrease of cyclic AMP levels produced by GABA is not affected by theophylline or by the absence of Ca²⁺. These data suggest an involvement of both cyclic GMP and cyclic AMP in the neurochemical actions of glutamate, GABA and glycine.     

CYCLIC NUCLEOTIDE LEVELS IN NORMAL AND BIOLOGICALLY FRACTIONATED MOUSE RETINA: EFFECTS OF LIGHT AND DARK ADAPTATION

Abstract— The content of cyclic AMP and cyclic GMP was measured in whole eyes and in normal retinas from C57BL(6)J mice, in receptorless retinas from congenic mice homozygous for the receptor dystrophy gene (rd/rd), and in retinas from mice treated postnatally with monosodium glutamate. Normal retinas contain approx 320 μg of protein: dystrophic (rd/rd) retinas contain approx 110μg of protein, lack rods but possess some surviving cone somata and terminals: glutamate-modified retinas contain approx 200 μg of protein and have both a reduced area and thickness with a marked deficiency of ganglion cells and amacrine cells. In normal mice, more than 90% of the cyclic GMP, but only 607, of the cyclic AMP of the whole eye was in the retina. In normal dark-adapted retinas isolated under dim red light cyclic AMP and cyclic GMP content was 4.1 and 20.2pmol/retina, respectively. The content of both cyclic AMP and cyclic GMP was 40% less, 2.5 and 11.5pmol/retina, respectively, in light-adapted retinas. In dark-adapted retinas isolated under infra-red light, cyclic AMP content was 40%, higher than that in retinas isolated under dim red light; cyclic GMP content was the same under these two conditions. Receptorless retinas contained approx 50% as much cyclic AMP and only 1-2% as much cyclic GMP as normal retinas. Although glutamate-modified retinas also had approx 50% as much cyclic AMP, they contained 60-85%, as much cyclic GMP as normal retinas. Light decreased by 30-50% levels of both cyclic AMP and cyclic GMP in glutamate-modified retinas, but only reduced cyclic nucleotide levels in receptorless retinas by 20%.
These data indicate that 95% or more of the cyclic GMP is in photoreceptor cells, whereas cyclic AMP is more evenly distributed throughout the retina. In addition, both cyclic AMP and cyclic GMP levels are influenced by light- and dark-adaptation.     

COMPARISON OF THE EFFECTS OF DEPOLARIZING AGENTS AND NEUROTRANSMITTERS ON REGIONAL CNS CYCLIC GMP LEVELS IN VARIOUS''ANIMALS

Abstract— The effects of 121 m m -K⁺, 10 m m -glutamate, 5 m m -GABA, 1 m m -glycine, 0.1 m m -NE, and 1–10 μ m ACh on cyclic GMP levels in tissue slices prepared from cerebral cortex and cerebellum of mouse, rabbit, guinea-pig, cat, and rat were studied. Basal levels of cyclic GMP in the cerebella of mice, guinea-pigs and cats were 4–15 and 70 pmol/mg prot in rat, whereas in the cerebral cortex of the same animals, levels were only 0.6–2 pmol/mg prot. In contrast, basal levels of the cyclic nucleotide were 1–2 pmol/mg prot in both of these regions in rabbit brain. Only 121 m m -K⁺ was capable of increasing cyclic GMP levels in all the tissues studied. Elevations ranged from 30% in rat cerebral cortex to 2800% in mouse cerebellum. Glutamate produced a 30–1000% rise of cyclic GMP levels in all tissues except rabbit cerebellum. NE elevated levels of cyclic nucleotide 2- to 3-fold in slices of cerebellum from all species studied but had no effect in cerebral cortex. GABA and glycine had no effect in any tissue except mouse cerebellum. ACh had no consistent effect on levels of cyclic GMP in any brain region investigated. These results suggest that mechanisms regulating cyclic GMP levels in mammalian CNS vary among brain regions and among animal species.     

Species-specific aggregation factor in sponges. VII. Its effect on cyclic amp and cyclic gmp metabolism in cells of Geodia cydonium.

In dissociated single cells from the sponge Geodia cydonium, DNA synthesis is initiated after incubation with a homologous, soluble aggregation factor. During the DNA-initiation phase the cyclic AMP- and cyclic GMP levels vary drastically; the cyclic AMP content drops from 2.2 pmol/10(6) cells to 0.3 pmol/10(6) cells while the cyclic GMP content increases from 0.6 pmol to 3.7 pmol/10(6) cells. The activity of neither the adenylate cyclase nor of the guanylate cyclase isolated from cells which have been incubated for different periods of time with the aggregation factor, is changed. The soluble as well as the particulate enzyme activities were checked in vitro. The cyclic nucleotide receptors have been isolated from the sponge cells and characterized with respect to their molecular weight, dissociation constant for cyclic AMP or cyclic GMP and intracellular concentration. None of these parameters are altered during aggregation factor-mediated DNA initiation. From these data it is concluded that the regulation of cyclic nucleotide levels is a consequence of a changed activity of nucleotide cyclases or of phosphodiesterases, but this is presumably not caused by a changed rate of synthesis of nucleotide cyclases or of cyclic nucleotide receptors.     

The effects of hormonal and circadian cycles, stress, and activity on levels of cyclic AMP and cyclic GMP in pituitary, hypothalamus, pineal and cerebellum of female rats

Cyclic AMP and cyclic GMP levels were measured in the anterior and posterior pituitary, hypothalamus, pineal and cerebellum of female rats sacrificed during proestrus, metestrus and diestrus. In the first experiment rats were sacrificed by microwave irradiation between 0900 and 1100, between 1600 and 1800 and between 2100 and 2300. Cyclic AMP and cyclic GMP levels did not vary in any region tested as a function of the estrous cycle except for slightly elevated cyclic GMP levels in the posterior pituitary during proestrus. However the time of day at which the animals were sacrificed affected levels of cyclic AMP in the hypothalamus and cerebellum and levels of cyclic GMP in the cerebellum. In a second experiment female rats were all sacrificed between 2130 and 2330 during proestrus and diestrus. In this experiment rats were sacrificed either immediately upon removal from the home cage or after 10 min of immobilization stress, or after 10 min of open field activity. No differences in pituitary cyclic nucleotides were seen between proestrous and diestrous animals. However, stressed animals showed large cyclic AMP increases in the pituitary, and activity increased cyclic GMP levels in the cerebellum and pineal.     

CYCLIC NUCLEOTIDE ACCUMULATION IN VITRO IN THE CEREBELLUM OF ''NERVOUS'' NEUROLOGICALLY MUTANT MICE

Abstract— Slices of cerebellum from Purkinje cell-deficient, neurologically mutant 'nervous' mice or normal littermates synthesized cyclic AMP and cyclic GMP during in vitro incubations. Resting levels of cyclic AMP were the same in the two groups, but accumulations in the presence of kainic acid, a glutamic acid analogue, or norepinephrine were significantly greater in the 'nervous' mice. Resting levels of cyclic GMP were lower in the 'nervous' mice, but the elevations produced by kainic acid were the same in both groups. Adenylate and guanylate cyclase activities in the cerebellum were not affected by the mutation. These findings indicate that cyclic nucleotide synthesis in the cerebellum does not occur solely in the Purkinje cell population.     

Effects of dose and time after administration of 4-isopropyl-2,6,7-trioxa-1-phosphabicyclo (2,2,2)octane-1-oxide (IPTBO) on cyclic nucleotide concentrations in mouse cerebellum

The concentrations of cyclic AMP and cyclic GMP in the mouse cerebellum after intracerebroventricular administration of a range of doses of IPTBO have been studied with particular interest in the temporal changes after injection. A non typical dose relationship was observed. After the lowest and non-convulsive dose used (0.06 μg/animal) cyclic AMP levels decreased and cyclic GMP levels increased within 1 min, but after higher doses cyclic AMP and cyclic GMP levels were both raised. At three different convulsive doses of IPTBO there were increased levels of cyclic AMP with time which were more apparent in convulsing animals. Raised levels of cyclic GMP however, were not so influenced by convulsions. The results suggest that (1) the immediate decrease in cyclic AMP and the immediate increase in cyclic GMP may play a part in the mechanism of action of IPTBO—possibly by triggering convulsions and (2) there is an increase in cyclic AMP in response to, or because of, the convulsions. It is concluded that time after treatment and time into convulsions are critical when studying cyclic nucleotide changes, particularly for cyclic AMP and that such factors may explain conflicting observations with respect to this nucleotide.     

Cyclic Nucleotide Response of the Hippocampal Formation to Septal Stimulation in Naive and Kindled Rats

Rats were kindled through nonmagnetic electrodes stereotaxically implanted into the medial septum. Concentrations of cyclic AMP and cyclic GMP were measured by radioimmunoassay in seven brain regions after microwave fixation during the development and expression of kindled seizures. Hippocampal concentrations were similar to untreated controls (cyclic GMP level in the left and right hippocampus, 0.66 +/- 0.04 and 0.68 +/- 0.07 pmol/mg of protein, respectively; cyclic AMP, 9.4 +/- 0.9 and 9.6 +/- 0.8 pmol/mg of protein, respectively), in kindled animals that were not stimulated, and in naive animals in response to septal stimulation, in spite of the presence in the latter group of bilateral hippocampal afterdischarges. Animals that failed to develop kindling and kindled animals that failed to have a seizure in response to stimulation also showed no change in cyclic nucleotide concentrations in any brain region. Kindled animals that developed a seizure following stimulation showed significant elevations in levels of both cyclic GMP and cyclic AMP in hippocampus and in several other brain regions. A single naive animal that had a seizure in response to its first stimulation also appeared to have elevated concentrations of both cyclic nucleotides in hippocampus. These data suggest that the elevation in levels of both cyclic GMP and cyclic AMP during kindled seizures is associated with seizure development rather than with the generation of afterdischarges or with the kindling engram.     

INFLUENCE OF DIVALENT CATIONS ON REGULATION OF CYCLIC GMP AND CYCLIC AMP LEVELS IN BRAIN TISSUE

—Depolarizing concentrations of K⁺ elevate levels of both adenosine 3′,5′monophosphate (cyclic AMP) and guanosine 3′,5′monophosphate (cyclic GMP) in incubated slices of mouse cerebellum. Calcium is an essential requirement for the K⁺ -induced accumulation of cyclic GMP. Barium and Sr²⁺, but not Mn²⁺ or Co²⁺, can substitute for Ca²⁺ in this process. Relatively high concentrations of Mg²⁺ inhibit the effect of Ca²⁺ on K⁺-induced accumulation of cyclic GMP. In contrast, depolarizing concentrations of K⁺ are capable of elevating cyclic AMP levels in brain slices suspended in media containing Mg²⁺ and no other divalent cations. High concentrations of Ca²⁺ (1 mm or greater) augment this Mg²⁺ -dependent, K⁺-induced accumulation of cyclic AMP, however. Strontium and Mn²⁺, but not Ba²⁺ or Co²⁺, can substitute for Ca²⁺ in this process, and high concentrations of Mg²⁺ are not inhibitory. The divalent cation ionophore, A-23187 (10 μm ), in the presence of extracellular Ca²⁺ elevates the level of cyclic GMP, but not cyclic AMP, in incubated mouse cerebellum slices. The results of this study indicate that intracellular Ca²⁺ concentration is a major factor regulating cyclic GMP levels in brain. In addition the present results suggest that, in brain tissue, depolarization-induced accumulation of cyclic GMP, but not cyclic AMP, is closely linked to some Ca²⁺-dependent mechanism(s) mediating release of intracellular substances.     

Adenosine 3′,5′-monophosphate and guanosine 3′,5′-monophosphate: concentrations in Morris hepatomas of different growth rates

Cyclic AMP and cyclic GMP levels were examined in Morris hepatoma explants in vivo. All eight tumor lines examined had significantly elevated cyclic AMP and cyclic GMP levels when compared to normal liver from tumor-bearing rats. No apparent correlation was observed between the rates of tumor growth and cyclic nucleotide levels; however, two tumor lines (3924A and 7288ctc) had very high levels of cyclic GMP.     

METABOLITE LEVELS IN BRAIN FOLLOWING EXPERIMENTAL SEIZURES: THE EFFECTS OF MAXIMAL ELECTROSHOCK AND PHENYTOIN IN CEREBELLAR LAYERS

Abstract— The effects of maximal electroshock (MES) and phenytoin on metabolites and cyclic nucleotides in layers of frozen-dried cerebellum have been investigated. The four layers (molecular, Purkinje-cell rich, granular and white matter) had remarkably homogeneous distributions of P-creatine, ATP, glucose, glycogen, lactate, GABA and the cyclic nucleotides. MES caused dramatic decreases in P-creatine, ATP, and glucose at 10 s after treatment, followed by a decrease in glycogen at 30 s. Lactate levels were elevated, and GABA was unchanged. Cyclic AMP concentrations were increased at 10s and cyclic GMP at 30 s. Phenytoin modified most of the MES induced changes in all the layers, although white matter was less affected by MES and/or phenytoin. Lactate concentrations were increased by MES and these effects were not altered when phenytoin was administered. The most dramatic effects of phenytoin were on the changes in cyclic nucleotides. Cyclic AMP concentrations were elevated after MES but the values returned to normal more rapidly when phenytoin was present. The drug almost obliterated the MES induced changes in cyclic GMP. The possible relationship of cyclic nucleotide concentrations and the modulation of seizure activity is discussed.     

On the role of cyclic AMP and cyclic GMP in steroid production by bovine cortical cells

The time course of corticotropin-induced steroidogenesis and changes in intracellular cyclic AMP and cyclic GMP levels were investigated in isolated bovine adrenocortical cells prepared by trypsin digestion. Corticotropin produced a pea a peak rise in cyclic AMP during the first 5 min of stimulation and enhanced steroid production after 15 min. Corticotropin also caused a decrease in cortical cyclic GMP at 5 min; this decrease in cyclic GMP reverted to a 2–3 fold increase at 15–30 min which gradually subsided by 60 min. A steroidogenic concentration of prostaglandin E₂ also produced an elevation in the levels of both nucleotides, but the rise in cyclic GMP preceded the rise incyclic AMP. These results suggest that the relative amount of cyclic AMP and cyclic GMP, rather than the absolute levels of cyclic AMP, may be a key factor in the regulation of steroidogenesis.     

Levels of cyclic nucleotides in mouse regional brain following 300 ms microwave inactivation.

Abstract— The uniformity and speed of inactivation of mouse brain adenylate cyclase, guanylate cyclase and cyclic nucleotide phosphodiesterase were measured after 6 kW microwave irradiation (MWR). Inactivation of enzymes was uniform throughout the brain during heating and 100% loss of activity was evident after 300 ms. MWR. For comparison of effects of inactivation times on levels of cyclic nucleotides measured in regional brain areas, cyclic AMP and cyclic GMP were estimated after 1.5 kW MWR requiring 4 s of heating and 6 kW MWR requiring 300 ms. Except for corpus striatum, uniformly lower levels of cyclic AMP were measured following 300 ms vs. 4s MWR . There was no change in cyclic GMP levels in regional brain areas after 4s vs. 300 ms MWR . Cyclic AMP and cyclic GMP were measured from the same regional brain tissue samples after 300 ms and ratios calculated. The finding of much lower cyclic AMP:cyclic GMP ratios than had previously been reported suggests that slow inactivation times provide for the measurement of regional brain cyclic nucleotide values which are not consistent with the in-vivo state.     

Regional sensitivity of cyclic AMP and cyclic GMP in rat brain to central cholinergic stimulation

We determined cyclic AMP and cyclic GMP levels in 18 regions of rat brain following administration of two different centrally active cholinergic agonists. Administration of oxotremorine (2 mg/Kg IP), a muscarinic agonist, 10 minutes prior to sacrifice by exposure to high power microwave irradiation resulted in significant increases in cyclic GMP in cerebellum, brainstem, hippocampus, midbrain, thalamus and septal region. Cyclic AMP levels were significantly elevated in substantia nigra, nucleus interpeduncularis, hypothalamus, brainstem, midbrain and in the pituitary where a greater than tenfold increase was observed. Levels of plasma prolactin and corticosterone did not differ in any of the groups examined, but growth hormone was significantly lower in animals exposed to oxotremorine. Physostigmine (0.5 mg/Kg) a cholinesterase inhibitor, administered IP also produced elevations in cyclic AMP and cyclic GMP in several of the brain regions examined. These results indicate that multiple regions of the brain are responsive to central cholinergic activation of not only cyclic GMP, but also cyclic AMP system.     

Effects of isoproterenol,theophylline and carbachol on cyclic nucleotide levels and relaxation of bovine tracheal smooth muscle

The effect of theophylline and isoproterenol on bovine tracheal smooth muscle tension and cyclic AMP levels was investigated. Concentrations of isoproterenol (4 × 10^?6 M) and theophylline (10 mM) that relaxed carbachol-contracted tracheal muscle by 85–95% did not significantly elevate control levels of cyclic AMP. In the absence of carbachol, several-fold increases in cyclic AMP were caused by isoproterenol although no elevations by theophylline were measurable. However, when isoproterenol and theophylline were administered together, theophylline potentiated the rise in cyclic AMP caused by isoproterenol. Phosphodiesterase studies in tracheal muscle showed the presence of a high and a low K_m enzyme which were inhibited by theophylline. Cyclic GMP levels were elevated in muscles contracted by carbachol as well as in carbachol-contracted muscles that had been relaxed by theophylline. In non-tension studies, in which the tracheal muscle was not under isometric tension, carbachol or theophylline alone increased cyclic GMP and together they synergistically elevated cyclic GMP. Atropine blocked the elevation caused by carbachol but not that caused by theophylline. In contrast to theophylline, isoproterenol did not elevate cyclic GMP, and in carbachol-contracted muscles that had been relaxed by isoproterenol, cyclic GMP levels were no different from control. Also, in non-tension studies, isoproterenol decreased basal cyclic GMP and antagonized the increase in cyclic GMP due to carbachol.The results indicate that whole-tissue levels of cyclic AMP and cyclic GMP do not correlate with the state of tracheal smooth muscle tension. Cyclic GMP levels do not clearly correlate with either contraction or relaxation. The inhibition by carbachol of increases in cyclic AMP due to isoproterenol and the inhibition by isoproterenol of increases in cyclic GMP due to carbachol provide evidence for a reciprocal cholinergic-adrenergic antagonism of cyclic AMP and cyclic GMP levels. The antagonism did not appear to be due to either cyclic nucleotide affecting the elevation of the other since the levels of both cyclic nucleotides were depressed.