Cyclic cuanosine 3'5' phosphate, guanylate cyclase and cyclic guanosine phosphodiesterase in the eye lens

While cGMP levels of rat lenses are in the range of those of other tissues, in calf lenses their values are much lower. Guanylate cyclase activities are rather high in proliferating epithelial cells of the lens and decrease strongly with cell differentiation and aging. cGMP phosphodiesterase activities are also reduced with aging in lens epithelial cells. A slight increase seems present in differentiated cortical fibers.     

Effect of andrenalectomy on cyclic 3',5'-guanosine monophosphate metabolism of rat liver and other tissues

Adrenalectomy increased guanyl cyclase and cyclic GMP phosphodiesterase activities in liver and other rat tissues. Liver guanyl cyclase activities from adrenalectomized rats were increased above those of normal controls according to kinetic analysis, gel filtration, ion-exchange chromatography, discontinuous sucrose gradient fractionation, sulfhydryl inhibition, and secretin activation. The effects of adrenal insufficiency on hepatic guanyl cyclase and cyclic GMP phosphodiesterase were prevented by cortisone acetate administration. Immunoassay of liver and skeletal muscle cyclic GMP after adrenalectomy showed markedly decreased levels in liver, but increased levels in skeletal muscle. In liver and other tissues, basal adenyl cyclase and cyclic AMP phosphodiesterase activities were unaffected by adrenalectomy. Hepatic levels of cyclic AMP were also unchanged by adrenalectomy. Hypophysectomy raised guanyl cyclase activity in liver but had no effect on liver cyclic GMP phosphodiesterase activity. These alterations are discussed in relation to possible glucocorticoid regulation of cyclic GMP metabolism.     

Stimulation of polypeptide synthesis by cyclic 3'-5'-guanosine monophosphate

3′-5′-Cyclic GMP was found to stimulate polyphenylalanine synthesis in a cell-free system derived from rat liver. The effect of cyclic GMP is detected either in the presence or absence of GTP and appears quite specific since it is not produced by other cyclic nucleotides.     

Effect of spinal cord compression on cyclic 3',5'-guanosine monophosphate in the white matter columns of rabbit

Changes in the level of cyclic 3',5'-guanosine monophosphate (cGMP) were studied one day after a surgically induced spinal cord constriction performed at the Th7 segment level in the dorsal, lateral and ventral white matter columns and in the non-compartmentalized white matter of Th5-Th6 segments, i.e., above the site of the spinal cord constriction and in Th8-Th9 segments, located below the spinal cord constriction. The midthoracic spinal cord constriction caused a significant decrease in the level of cGMP in the ventral column of Th5-Th6 segments and a significant increase in the lateral column of Th8-Th9 segments. The level of cGMP in the dorsal column, located either rostrally or caudally to the site of the spinal cord injury, remained unchanged. In addition, no significant changes in the level of cGMP were found in the non-compartmentalized white matter of Th5-Th6 and Th8-Th9 segments in response to constriction of the Th7 segment.     

Adenosine 3',5' cyclic monophosphate in Euglena gracilis

$\text{Euglena gracilis}$ contains in high concentration the enzymes for the synthesis and degradation of cyclic AMP. The synthetic enzyme, adenyl cyclase is mainly associated with a particulate fraction which sediments at 7,000–30,000xg whereas the degradative enzyme, 3′5′ nucleotide phosphodiesterase, is soluble (does not sediment at 78,000xg). The adenyl cyclase activity is stimulated somewhat by prostaglandins and by catecholamines, agents which markedly stimulate cyclase in appropriate mammalian tissues. There is no detectable activity of guanyl cyclase, the enzyme which synthesizes cyclic GMP. $\text{Euglena}$ also contains a cyclic AMP stimulated protein kinase which is associated with a particulate fraction sedimenting at 30,000xg.     

Molybdate increases intracellular 3',5'-guanosine cyclic monophosphate and stabilizes vitamin D receptor association with tubulin-containing filaments.

With a recently developed method we detected rapid and sequential reorganization of vitamin D receptors (VDR), including their temporary association with fibers, and we showed that calcitriol induces cGMP accumulation around reorganizing VDRs. In this report we first identified the VDR-associated fibers as microtubules: they show immunoreactivity with tubulin antisera and were sensitive to tubulin-disruptive agents. Tubulin-disruptive agents also prevented calcitriol-induced alignment and intranuclear accumulation of VDR and cGMP, but did not prevent the initial cGMP accumulation in the cytoplasm. Then we studied the effect of molybdate on VDR reorganization and on cGMP accumulation. Sodium molybdate inhibits steroid receptor transformation into a DNA binding form through interaction with the steroid binding region of the receptor. The mechanism of molybdate effect on steroid receptors is not well understood and the interaction of molybdate with guanylate cyclase has not been investigated. We found in cells pretreated with molybdate that the addition of calcitriol resulted in a prolonged and accentuated association of VDR and cGMP with the microtubules. Furthermore, both immunocytology and radioimmunoassay demonstrated that molybdate is a highly potent inducer of guanylate cyclase. Neither calcitriol nor molybdate effect on guanylate cyclase were prevented by methylene blue pretreatment, suggesting that they activate particulate guanylate cyclase. Pretreatment of cells with dibutyryl-cGMP mimicked molybdate effect on VDR reorganization. The effect of molybdate on cGMP may participate in molybdate stabilization of steroid receptors. We suggest that rapid cGMP accumulation after steroid exposure plays a role in facilitation of intracellular transport of the steroid receptor through interaction with microtubules.     

A simple radioimmunoassay for 3',5', cyclic adenosine monophosphate.

A radioimmunoassay for 3′,5′ cAMP has been developed in which [³H]3′,5′ cAMP is the radioligand. Antibody-bound and free fractions are separated with dextran-coated charcoal. The sensitivity of the assay is 0.03 pmoles and antiserum specificity is 7 orders with respect to other adenine nucleotides. Samples are prepared by ethanol precipitation. Tissue levels of 3′,5′ cAMP are comparable to those reported by others.     

Effect of short-chain fatty acids on cyclic 3',5'-guanosine monophosphate-mediated colonic secretion

Short chain fatty acids (SCFA) prevent and reverse cyclic 3',5'-adenosine monophosphate (cAMP) but not Ca(2+)-mediated Cl- secretion. Mucosal [HCO3-]i has an opposite effect on these secretagogues. We examined whether SCFA and [HCO3-]i affect cyclic 3',5'-guanosine monophosphate (cGMP)-induced secretion. Stripped segments of male Sprague-Dawley rat (Rattus norvegicus) proximal and distal colon, and cultured T84 cells were studied in Using chambers, and pHi and [HCO3-]i were determined. Mucosal [cGMP] was measured in proximal colon. In T84 cells, the increase in Cl- secretion (measured as Isc) induced by mucosal 0.25 microM Escherichia coli heat-stable enterotoxin (STa) was prevented/reversed by bilateral 50 mM Na+ butyrate (71%/73%), acetate (58%/76%), propionate (68%/73%) and (poorly metabolized) isobutyrate (80%/79%). In proximal colon in HCO3- Ringer, basal Cl- secretion was not affected by [HCO3-]i or 25 mM butyrate. Mucosal 0.25 microM STa decreased net Na+ and Cl- absorption. Bilateral but not mucosal 25 mM SCFA reversed STa-induced effects on Na+ absorption and Cl- secretion. Bilateral and mucosal 25 mM SCFA but not [HCO3-]i prevented STa-induced Cl- secretion and increases in mucosal [cGMP]. STa did not produce Cl- secretion in distal colon. It was concluded that SCFA but not [HCO3-]i can prevent and reverse cGMP-induced colonic Cl- secretion.     

Chlorpropamide and tolbutamide inhibition of adenosine 3'5' cyclic monophosphate phosphodiesterase

These sulfonylurea agents inhibit the cyclic AMP phosphodiesterase, and thereby could increase the steady state level of cyclic AMP in various tissues, depending upon the tissue concentrations achieved after oral or parental administration.     

Effect of cyclic 3',5'-adenosine monophosphate on central neurons

In experiments on unanesthetized non-immobilized rabbits, unit responses in the cortex and thalamus to the cyclic 3',5'-adenosine monophosphate (cAMPh) were studied by means of microionophoresis. It was shown that cAMPh changes the pattern of background unit activity, increasing or decreasing the discharge frequency. cAMPh changes unit responses both to acetylcholine and noradrenaline. These data permit, to assume that cAMPh participates both in adrenergic and in acetylocholinergic mechanisms of excitation processing in brain neurones.     

Inhibition of growth hormone-induced lipolysis by 3',5'-guanosine monophosphate in chicken adipose tissue in vitro

The influence of cyclic 3',5'-guanosine monophosphate (cGMP) on the lipolytic and antilipolytic (inhibition of glucagon-stimulated lipolysis) responses to GH (1 microgram/ml) was examined in chicken adipose tissue in vitro. Both 8-bromo-cGMP (0.1 mM) and sodium nitroprusside (1 mM) (a guanyl cyclase stimulator) completely inhibited the lipolytic effect of GH. A cGMP-lowering agent, LY83583 (10 microM), reversed the inhibitory effect of sodium nitroprusside on GH-stimulated lipolysis. Furthermore, the suppressive effects of insulin (100 ng/ml), insulin-like growth factor I (IGF-I) (100 ng/ml), or insulin-like growth factor II (IGF-II/MSA) (100 ng/ml), but not somatostatin (1 ng/ml), on GH-stimulated lipolysis were prevented by LY83583 addition. Neither 8-bromo-cGMP, sodium nitroprusside, nor LY83583 altered GH-induced inhibition of glucagon (1 ng/ml)-stimulated lipolysis. It is proposed that cGMP may mediate inhibitory control of GH-stimulated lipolysis by insulin, IGF-I, and IGF-II in chicken adipose tissue.     

Guanosine 3':5'cyclic monophosphate and activators of guanylate cyclase inhibit secretagogue-induced corticotropin release by rat anterior pituitary cells

The secretion of corticotropin by perfused rat anterior pituitary cell columns was studied. Forty-one residue corticotropin releasing factor, vasopressin and high extracellular KC1 all stimulated the secretion of corticotropin. The hormonal response to corticotropin-releasing factor (10(-10) mol/l), vasopressin (10(-9) mol/l) as well as KC1 (48 mmol/l) was reduced by membrane permeant analogs of cGMP, such as 8-BrcGMP and dibutyryl-cGMP. The 8-BrcGMP analog (10(-5) mol/l) inhibited corticotropin release in response to corticotropin-releasing factor by 30%, that to vasopressin by 70%, and that to KCl by 50%. Atriopeptin1-28 (10(-8) and 10(-7) mol/l), a peptide known to activate membrane-bound guanylate cyclase in the anterior pituitary gland, decreased the release of corticotropin induced by vasopressin to about 30% of control. Similarly, activators of soluble guanylate cyclase, such as glyceryltrinitrate and sodium nitroprusside (10(-5) mol/l) inhibited vasopressin-stimulated corticotropin release by 60%. In conclusion, the data show that purported activators of particulate and soluble guanylate cyclase, as well as derivatives of cGMP itself are strong inhibitors of secretagogue-induced corticotropin release by corticotroph cells of the anterior pituitary gland.     

Ultracytochemical localizations of adenylate cyclase, guanylate cyclase and cyclic 3',5'-nucleotide phosphodiesterase activity on the trophoblast in the human placenta. Direct histochemical evidence

Ultracytochemical localizations of cyclic nucleotide-metabolizing enzymes, namely adenylate cyclase (AC), guanylate cyclase (GC) and cyclic 3',5'-nucleotide phosphodiesterase (PDE), have been demonstrated in the human term placenta. AC activity was found positive on the basal plasma membrane of the syncytiotrophoblast and on the pinocytotic vesicle of the fetal capillary endothelial cell. GC activity was observed to be strong on the plasma membrane of the microvilli of the syncytiotrophoblast. The cAMP PDE activity was shown positive both on the basal plasma membrane and on the microvillous membrane, while cGMP PDE activity was exclusively confined to the microvilli of the syncytiotrophoblast. These observations suggest that the syncytiotrophoblast plays an important role in the cyclic nucleotide metabolism in the human term placenta and that there might be significant functional differences between its basal plasma membrane and its microvillous membrane.