Plasma cAMP Concentration Research Articles

Activity of phosphodiesterase type 5 inhibitors in patients with lower urinary tract symptoms due to benign prostatic hyperplasia

• To evaluate the impact and distribution of a single phosphodiesterase type 5 inhibitor (PDE5 I) dose (udenafil or tadalafil) in prostate tissue and plasma in patients with benign prostatic hyperplasia (BPH). • Thirty BPH patients complaining of erectile dysfunction along with moderate-to-severe lower urinary tract symptoms (LUTS) who underwent transurethral resection of the prostate (TURP) were enrolled in the present study. • The patients were randomly divided into the three groups: group 1, TURP without PDE5 Is; group 2, 200 mg of udenafil given 1 h before TURP; and group 3, 20 mg of tadalafil given 1 h before TURP. • We evaluated the concentrations of PDE5-I, cAMP and cGMP in prostate tissues and plasma, and calculated the prostate tissue-to-plasma (T/P) ratio. • The concentration of udenafil in prostate tissue and plasma was 2028.6 ± 360.8 ng/g and 463.7 ± 39.1 ng/mL, respectively, and the resulting T/P ratio was 4.4. The tadalafil concentration in prostate tissue and plasma was 385.7 ± 83.8 ng/g and 305.8 ± 41.1 ng/mL, respectively, and the T/P ratio was 1.3. • Udenafil and tadalafil significantly increased the cAMP and cGMP levels in plasma and prostate tissues. • Udenafil and tadalafil significantly increased cAMP and cGMP levels and were more highly distributed in the prostate than plasma. The T/P ratio of udenafil was higher than tadalafil. • These findings may help in the assessment of the feasibility of using PDE5 Is to concurrently treat both LUTS and erectile dysfunction.

The influence of serum theophylline concentration on the bronchodilating effect of salbutamol inhalation for bronchial asthma

To examine the effects of serum theophylline concentration on the bronchodilating effect of beta 2-stimulant inhalated by patients with bronchial asthma, 200 micrograms-Salbutamol inhalation test was performed on 30 patients with bronchial asthma (from 17 to 71 years old, averaging 49.7; 3 mild, 15 moderate, 12 severe), who had taken theophylline at various oral doses up to 6 hours before the test. Measurements of respiratory function, serum theophylline concentration, blood pressure, pulse rate and the plasma c-AMP and c-GMP concentrations before and one hour after inhalation revealed that inhalation of 200 micrograms salbutamol significantly increased FVC, FEV1.0, PEF and plasma c-AMP (p less than 0.001). No significant change was noted in plasma c-GMP, diastolic pressure or pulse rate. Systolic pressure significantly decreased (p less than 0.05). Furthermore, no significant correlation was noted between the rates of increase (%) in FVC, FEV1.0 and PEF and those in plasma c-AMP, c-GMP and c-AMP/c-GMP in one hour after inhalation. Inaddlition no significant correlation was noted between the rates of increase in FVC, FEV1.0 and PEF one hour after inhalation and serum theophylline concentrations (0-19.3 and 0-21.5 micrograms/ml before and one hour after inhalation, respectively). The above results suggest that the bronchodilating effect of salbutamol inhalated at dose of 200 micrograms is not influenced by the serum theophylline concentration both before and at one hour after inhalation of salbutamol. The bronchodilating effect of salbutamol seems to be ascribable to an increase of intracellular c-AMP level of bronchial smooth muscle.

Effect of sodium houttuyfonate on myocardial hypertrophy in mice and rats

The aim of the study was to determine the effect of sodium houttuyfonate on myocardial hypertrophy and its mechanism of action in mice and rats. A mouse model of myocardial hypertrophy was established by subcutaneous injection with isoproterenol. Mice were randomly divided into five groups: normal control; isoproterenol control; isoproterenol plus metoprolol; isoproterenol plus low- and high-dose sodium houttuyfonate. A rat model of myocardial hypertrophy was established by intraperitoneal injection with L-thyroxine. Rats were randomly divided into five groups: normal control; L-thyroxine control; L-thyroxine plus captopril; L-thyroxine plus low- and high-dose sodium houttuyfonate. At the end of the experiments, the left ventricular weight index and heart weight index were determined in mice and rats, the size of cardiomyocytes was measured in rats and the concentrations of cAMP in plasma and angiotensin II in ventricular tissue of mice were detected by radioimmunoassay. The endothelin-1 concentration was measured by radioimmunoassay and the hydroxyproline content was measured by a digestive method in ventricular tissue of rats. After 7-9 days of treatment, sodium houttuyfonate significantly reduced the left ventricular weight index and heart weight index in mice and rats with myocardial hypertrophy, decreased the size of cardiomyocytes in rats, and reduced the content of cAMP and angiotensin II in mice with myocardial hypertrophy. It also decreased the endothelin-1 concentration and the hydroxyproline content in ventricular tissue in rats. Sodium houttuyfonate can inhibit myocardial hypertrophy in mouse and rat models by restricting the activity of the sympathetic nervous system and decreasing the levels of angiotensin II and endothelin-1 in ventricular tissue.

Effect of sodium houttuyfonate on myocardial hypertrophy in mice and rats

Abstract Objectives The aim of the study was to determine the effect of sodium houttuyfonate on myocardial hypertrophy and its mechanism of action in mice and rats. Methods A mouse model of myocardial hypertrophy was established by subcutaneous injection with isoproterenol. Mice were randomly divided into five groups: normal control; isoproterenol control; isoproterenol plus metoprolol; isoproterenol plus low- and high-dose sodium houttuyfonate. A rat model of myocardial hypertrophy was established by intraperitoneal injection with l-thyroxine. Rats were randomly divided into five groups: normal control; l-thyroxine control; l-thyroxine plus captopril; l-thyroxine plus low- and high-dose sodium houttuyfonate. At the end of the experiments, the left ventricular weight index and heart weight index were determined in mice and rats, the size of cardiomyocytes was measured in rats and the concentrations of cAMP in plasma and angiotensin II in ventricular tissue of mice were detected by radioimmunoassay. The endothelin-1 concentration was measured by radioimmunoassay and the hydroxyproline content was measured by a digestive method in ventricular tissue of rats. Key findings After 7–9 days of treatment, sodium houttuyfonate significantly reduced the left ventricular weight index and heart weight index in mice and rats with myocardial hypertrophy, decreased the size of cardiomyocytes in rats, and reduced the content of cAMP and angiotensin II in mice with myocardial hypertrophy. It also decreased the endothelin-1 concentration and the hydroxyproline content in ventricular tissue in rats. Conclusions Sodium houttuyfonate can inhibit myocardial hypertrophy in mouse and rat models by restricting the activity of the sympathetic nervous system and decreasing the levels of angiotensin II and endothelin-1 in ventricular tissue.

Heart rate and plasma cyclic AMP responses to isoproterenol infusion and effect of beta-adrenergic blockade in patients with postural orthostatic tachycardia syndrome.

To clarify the pathophysiological mechanism of postural orthostatic tachycardia syndrome (POTS). the responses of heart rate and the plasma cyclic AMP (cAMP) level to isoproterenol infusion in the supine position were evaluated in 10 POTS patients and 10 age-matched controls. Also, the effect of beta-adrenergic blockade on POTS was assessed using the headup tilt test. The POTS patients consisted of two men and eight women, with a mean age of 19.7 years (range. 15-28 years). An exaggerated increase of both heart rate and the plasma cAMP concentration after isoproterenol infusion at a low dose (1 microg/min) was observed in the POTS patients, but not in control subjects. Seven POTS patients received oral beta-blocker therapy. In five of these, symptoms were abolished and there was a smaller heart rate increase during the head-up tilt test. These data suggest that POTS may be more prevalent in young women and that beta-adrenergic hypersensitivity may play a role in the mechanisms of this syndrome. However, a larger series of patients need to be studied in the future.

Antenatal and Early Postnatal Dexamethasone Treatment Decreases Cortisol Secretion in Preterm Infants

Glucocorticoids are used antenatally to accelerate the maturation of fetal respiratory and cardiovascular systems when a threat of preterm delivery exists. Postnatally, they are used to prevent and treat respiratory distress syndrome. This study investigates the effects of antenatal (ACT) and early postnatal corticosteroid treatment (PCT) on serum cortisol and plasma catecholamine and adenosine 3′,5′-cyclic monophosphate (cAMP) concentrations in preterm neonates. The infants in the ACT group had a significantly lower cortisol concentration than the infants in the non-ACT group on the first day of life. After birth, the infants were further divided into non-PCT and PCT groups. PCT suppressed cortisol levels significantly after 2 days, and the cortisol levels were still lower 2 days after discontinuation of PCT. No effect of PCT on plasma cAMP or catecholamine concentrations was observed. The results indicate that both ACT and a short PCT can significantly suppress basal cortisol levels in preterm infants.

Beta 2-adrenergic responsiveness in vivo during abdominal surgery

We have studied adrenergic function in vivo during anaesthesia and surgery. Epinephrine 50 ng kg-1 min-1 was given by i.v. infusion over 30 min to 10 healthy adult volunteers and to 10 patients undergoing abdominal operations. The cAMP response to stimulation by epinephrine, which was obtained as the area under the curve (AUC) for plasma cAMP concentration divided by the AUC for plasma concentration of epinephrine, was more pronounced during surgery (mean ratio 3.5) than in the control situation (ratio 1.4; P < 0.02). This resulted in greater hypokalaemic and hyperglycaemic responses (ratios -0.67 and 4.5) than in the control group (ratios -0.33 and 1.6, respectively; P < 0.004). Mean arterial pressure decreased in the control group while it increased in the study group, and serum cortisol concentration was higher in those who underwent surgery (P < 0.02). These results are consistent with an increased adrenergic response during abdominal surgery.

Cyclic AMP is a hepatorenal link influencing natriuresis and contributing to glucagon-induced hyperfiltration in rats.

The effects of glucagon (G) on proximal tubule reabsorption (PTR) and GFR seem to depend on a prior action of this hormone on the liver resulting in the liberation of a mediator and/or of a compound derived from amino acid metabolism. This study investigates in anesthetized rats the possible contribution of cAMP and urea, alone and in combination with a low dose of G, on phosphate excretion (known to depend mostly on PTR) and GFR. After a 60-min control period, cAMP (5 nmol/min x 100 grams of body weight [BW]) or urea (2.5 micromol/min x 100 grams BW) was infused intravenously for 200 min with or without G (1.2 ng/min x 100 grams BW, a physiological dose which, alone, does not influence PTR or GFR). cAMP increased markedly the excretion of phosphate and sodium (+303 and +221%, respectively, P < 0.01 for each) but did not alter GFR. Coinfusion of cAMP and G induced the same tubular effects but also induced a 20% rise in GFR (P < 0.05). Infusion of urea, with or without G, did not induce significant effects on PTR or GFR. After G infusion at increasing doses, the increase in fractional excretion of phosphate was correlated with a simultaneous rise in plasma cAMP concentration and reached a maximum for doubling of plasma cAMP. These results suggest that cAMP, normally released by the liver into the blood under the action of G, (a) is probably an essential hepatorenal link regulating the intensity of PTR, and (b) contributes, in conjunction with specific effects of G on the nephron, to the regulation of GFR.

Role of renal handling of extracellular nucleotides in modulation of phosphate transport

The pivotal role of nucleotides in cell function and metabolism has been acknowledged for more than three decades since the milestone work of Sutherland [1]. Intracellular nucleotides are involved in each and every event of cell life including synthesis of nuclear material, phosphorylation processes, or transduction of extracellular signals. As regards to this last point, a huge number of studies has been devoted to identifying the key role of GTP-binding proteins or G proteins, on the one hand, and of cyclic nucleotides cAMP and cGMP, on the other hand, in the early steps of cell signaling. In epithelial cells such as renal tubular cells, generation of these mediators as a hallmark of cell-hormone interaction has been investigated in detail [reviewed in 2]. More recently, experimental evidence was provided showing that extracellular nucleotides are able to affect virtually every organ and/or tissue system. These aspects have been extensively reviewed [3—7] and will not be discussed here. Instead, attention will be focused on the effect of extracellular nucleotides, primarily cAMP, on renal tubular transport of inorganic phosphate (Pi). The initial observations that systemic infusion of cAMP to parathyroidectomized rats induced phosphaturia, thus mimicking the proximal effect of parathyroid hormone (PTH), drew attention on the effects of extracellular cAMP on renal function [8, 9]. A striking feature was that other renal effects of PTH (modulation of calcium or magnesium excretion), which take place beyond the proximal tubule, or renal effects of other peptidic hormones that act through the cAMP-protein kinase A pathway in distal parts of the nephron, such as antidiuteric hormone, were not reproduced by cAMP infusion [9]. Along the same line, glucagon, infused or injected at large pharmacological doses that induced a rise of plasma cAMP concentration from hepatic origin and urine excretion of the nucleotide [8, 10], was shown to increase phosphate excretion [8]. These data raised the possibility that handling (metabolism and/or transport) of extracellular cAMP by proximal cells was involved in the effect of the cyclic nucleotide on Pi transport. In contrast with the extreme experimental conditions described above, physiological situations are characterized by a fairly constant systemic cAMP concentration, while luminal cAMP concentration varies with the parathyroid status [10—12]. These observations suggest that luminal cAMP may act as local paracrine modulator of Pi transport and raise three questions: (a) How does cAMP reach the extracellular space under normal situations; (b)

Second messenger systems in Tourette's syndrome

Abnormalities within second messenger systems have been hypothesized as the underlying pathophysiologic mechanism in a variety of neuropsychiatric disorders. In the Gilles de la Tourette syndrome (TS) prior studies have shown that the concentration of adenosine 3′,5′-monophosphate (cAMP) is reduced in cortical and putamen brain regions. In this study, postmortem cortical tissues from 4 adults (mean age 59.5 years) with the lifetime diagnosis of TS and 5 controls (mean age 63.8 years) were analyzed for functional activities within the cAMP and phosphoinositide systems. In addition, plasma cAMP was quantified in children with TS ( n = 33) and controls ( n = 17). In frontal (A4, A6) and occipital (A17) cortical tissues there were no significant differences for adenylyl cyclase activity whether assayed under basal conditions or after stimulation with GTPγS (a non-hydrolyzable GTP analog), forskolin (a selective enzyme stimulator), or (−)-isoproterenol (a β-adrenergic agonist). D2 receptor activation (quinpirole) and assessment of the inhibitory guanine nucleotide protein also showed no significant alterations in TS samples. Activity of cAMP phosphodiesterase was increased insignificantly in A4 and A17 TS brain regions. Plasma concentrations of cAMP in plasma were similar in children with TS (135.4 ± 8.3 pmol/ml) and controls (132.6 ± 7.9 pmol/ml). Postmortem membrane receptor binding for markers within the phosphoinositide (PI) system showed that TS samples had increased [ 3H]phorbol ester binding to protein kinase C sites in area A17, but normal binding in A4. In contrast, [ 3H]inositol 1,4,5-triphosphate binding to IP 3 receptors showed no significant changes. Our data suggest that alterations in the cAMP and PI second messenger generating systems are not major contributing factors in the development of TS.

Pituitary adenylate cyclase-activating polypeptide: Effects on pancreatic-adrenal hormone secretion and glucose-lipid metabolism in normal conscious dogs

The effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on plasma insulin, glucagon, catecholamine, cortisol, glucose, triglyceride (TG), free fatty acid (FFA), cholesterol, and cyclic adenosine monophosphate (cAMP) concentrations were examined in unanesthetized normal dogs. A bolus injection of 6 pmol/kg PACAP27 elicited a transient increase in plasma insulin, epinephrine, and norepinephrine concentrations, with a peak value at 2 minutes after injection. Injections of 60 and 600 pmol/kg caused greater increases in these hormone concentrations in a dose-dependent manner. The plasma cortisol concentration was not changed by a bolus injection of 6 pmol/kg PACAP27, and was gradually increased by injections of 60 and 600 pmol/kg. Significant increases were observed from 10 and 5 minutes after the injection of 60 and 600 pmol/kg, respectively. The plasma glucagon concentration was not changed by either 6, 60, or 600 pmol/kg. The plasma glucose concentration decreased with 60 pmol/kg PACAP27 and increased with 600 pmol/kg. The plasma FFA concentration was increased gradually, with a peak value at 10 minutes after the injection, in a dose-dependent manner. The plasma TG concentration was slightly increased with 600 pmol/kg with a peak value at 10 minutes, although plasma cholesterol did not change. The plasma cAMP concentration increased significantly with 600 pmol/kg PACAP27, but not with 6 or 60 pmol/kg. These effects of PACAP27 were observed with a bolus injection of PACAP38 of an equal potency. Infusion of graded doses of PACAP27 (1,3, and 10 pmol/kg/min every 20 minutes) caused a gradual increase in plasma cortisol, catecholamine, FFA, and cAMP concentrations. Plasma insulin, glucagon, TG, and cholesterol concentrations did not change during the course of this experiment. The plasma glucose concentration decreased significantly during the infusion of 1 pmol/kg/min PACAP27, and tended to increase during 3- and 10-pmol/kg/min PACAP27 infusions. These results suggest that both PACAP27 and PACAP38 can stimulate insulin, catecholamine, and cortisol secretion in vivo with considerable potency, and have various effects on glucose and lipid metabolism.

Pharmacodynamic activity of synthetic salmon calcitonin in osteoporotic patients: Comparison between rectal and intramuscular administration: Pilot study

The pharmacodynamic activity of synthetic salmon calcitonin in two different formulations (rectal and intramuscular) was compared in four osteoporotic patients in a pilot study with a crossover design. We determined the percentage variations of serum plasma total calcium and plasma cyclic adenosine monophosphate (cAMP) after each administration and the relative bioactivity in order to evaluate the biologic efficacy of the two formulations. Serum calcium levels were similar after rectal administration of 100 IU and intramuscular injection of 50 IU of synthetic salmon calcitonin, whereas plasma cAMP concentrations reached a higher peak with the suppository, although the difference was not statistically significant. Furthermore, based on the temporal variations of the two biochemical variables considered, intramuscular and rectal administration resulted in a similar pattern of activity. The acute effect produced by the two formulations also seemed similar since both the serum calcium nadir and the plasma cAMP peak were reached 60 minutes after administration of the hormone. Finally, the relative bioactivity of the suppository formulation was about 65% that of the injectable formulation.

Nocturnal Asthma: β2-Adrenoceptors on Peripheral Mononuclear Leukocytes, cAMP- and Cortisol-Plasma Concentrations

To evaluate pathophysiologic mechanisms of the predominantly nocturnal complaints in atopic bronchial asthma, the expression and function of beta 2-adrenoceptors on peripheral mononuclear leukocytes (pMNL), the cAMP--as well as the cortisol--plasma concentrations were studied in eight healthy men and ten so far untreated male asthmatic patients at 4-h intervals for 24 h. No difference was seen in the beta 2-adrenoceptor density (Bmax) on pMNL between healthy and asthmatic men (24-h means +/- SE: 908 +/- 59 sites per cell and 821 +/- 54 sites per cell, respectively). The equilibrium dissociation constant (Kd), however, was significantly higher in the asthmatic patients (24-h mean +/- SE: 8.8 +/- 1.2 pmol/L vs 3.0 +/- 0.2 pmol/L in healthy men, p less than 0.0001), which is equivalent to a lower affinity of the beta 2-adrenoceptors for the radioligand 125iodocyanopindolol. Bmax showed a statistically significant circadian variation, but Kd did not. The circadian variation in Bmax was reflected in the basal intracellular cyclic adenosine-monophosphate (cAMP) content of the cells investigated. High Kd values (equivalent to low receptor affinities) tended to be associated with small increases of the intracellular cAMP content after in vitro stimulation by 10(-7) mol/L isoprenaline (isoproterenol) (24-h mean +/- SE: 1.4 +/- 0.2 pmol/10(6) cells; r = -0.529, p = 0.05 at r = -0.549, n = 10). Plasma cAMP concentrations were found to be significantly lower in the asthmatic patients (24-h means +/- SE: 22.9 +/- 1.3 nmol/L vs 29.1 +/- 1.1 nmol/L, p less than 0.0001). Plasma cortisol concentrations were significantly higher in the asthmatic patients (24-h means +/- SE: 0.500 +/- 0.084 mumol/L vs 0.319 +/- 0.063 mumol/L). The results support the hypothesis that a lesion of the beta-adrenergic system contributes to the pathophysiology of atopic bronchial asthma. In the patients investigated in this study, such a lesion could be demonstrated in the affinity rather than in the number of beta 2-adrenoceptors expressed on peripheral cells of the immune system (pMNL). According to present-day knowledge of adrenergic effects on pMNL, such an affinity decrease of beta 2-adrenoceptors could account for overshooting immune responses. In association with other factors influencing respiratory function, it could be responsible for the predominantly nocturnal complaints in atopic bronchial asthma. Plasma cortisol concentrations did not appear to be related to the principal cause of "nocturnal asthma;" they rather reflected an endogenous defense mechanism to the disease.

The effects of perfusion of lateral ventricle with CaCl2 on the febrile response and cAMP content in plasma and cerebrospinal fluid during LP-induced fever.

Artificial cerebrospinal fluid (c.s.f.) containing 40 mmol/L excess calcium was perfused through the lateral ventricles of New Zealand white rabbits in order to reduce the Na+/Ca++ ratio in the brain and the effects on both the febrile response and adenosine cyclic monophosphate (cAMP) concentration in plasma and c.s.f. during leucocytic pyrogen (LP)-induced fever were observed. The results showed that cAMP concentration in c.s.f. increased significantly during LP-induced fever while the cAMP level in Plasma remained unchanged, and the perfusion of artificial c.s.f. containing 40 mmol/L excess calcium can significantly inhibit not only the febrile response but also the increase in c.s.f. cAMP level, while there appears no effect on plasma cAMP concentration, thus demonstrating that the increase of Na+/Ca++ ratio causing the increase of cAMP content in the brain may be an essential link in the pathogenesis of LP-induced fever.

The effect of ECT on plasma cyclic nucleotides: A simulated ECT controlled study in melancholic patients

Concentrations of cAMP and cGMP in plasma were measured in 20 drug-free melancholic patients during a simulated electroconvulsive treatment (SECT) and a bilateral ECT session. Blood samples were taken every 15 min beginning 15 min before and ending 60 min after the SECT or the ECT. Two-way ANOVA and paired t-test demonstrated a significant and greater fall in cAMP over time following SECT. ECT induced a marginal increase (P less than 0.05) at 45 min postictally. It is postulated that ECT causes an increase in cAMP levels which is masked by the decrease observed during SECT, caused presumably by the anaesthetic medication. The plasma cGMP levels were increased gradually and significantly after SECT and the same rise was observed during ECT. These effects are discussed in relation to changes in adrenergic-cholinergic activities induced by the medication and the electrical stimulus.

Decreased Numbers Of Lymphocyte β2‐Adrenoceptors In Pregnant Women Receiving β2‐Adrenergic Agonist Therapy

Intravenous infusion of buphenine hydrochloride was administered on 4 successive days to 8 pregnant women with imminent preterm labor. Serial blood samples taken before and throughout the study were assayed for lymphocyte beta 2-adrenoceptor density and cyclic adenosine-3',5'-monophosphate (cAMP). The lymphocyte beta 2-adrenoceptor density declined significantly (p less than 0.01) during the treatment. The plasma cAMP concentration was highest 4 h after commencement of infusion and decreased thereafter. Despite the decrease in lymphocyte beta 2-adrenoceptor density, the clinical response remained good and the parturients did not go into labor until several days after infusion was started.

Effects of cold exposure on cyclic AMP concentration in plasma, liver, and brown and white adipose tissues in cold-acclimated rats

Effects of acute cold exposure on plasma energy substrates and tissue 3',5'-adenosine monophosphate (cAMP) were analyzed in intact rats, to define an involvement of the nucleotide in nonshivering thermogenesis (NST) and resultant cold acclimation. After an acute cold exposure to -5 degrees C, the plasma glucose level increased gradually in warm-kept control rats (C) while it decreased significantly in cold-acclimated rats (CA). However, it was increased considerably by an extreme cold exposure to -15 degrees C in both C and CA. By contrast, plasma levels of free fatty acids (FFA) increased immediately after cold exposure and the release lasted during the period of exposure especially in C. The cold exposure also increased plasma cAMP concentration but no concomitant increase was found in the liver. In both brown (IBAT) and white (WAT) adipose tissues the nucleotide concentration showed a stepwise decrease. The observed correlation between lipolysis and plasma cAMP response after cold exposure suggests an involvement of the adenylate cyclase-cAMP system in NST via lipid metabolism, at least, in the early stages of cold acclimation.

Reevaluation of direct radioimmunoassay for plasma cAMP concentration

In order to evaluate the validity of the direct radioimmunoassay of plasma cAMP level by using Yamasa cyclic AMP assay kit, we determined the cyclic AMP concentration of normal human plasma before and after purification through anion-exchange chromatography. We found that 1) the direct assay before purification gave almost the same values as the indirect assay after purification by anion-exchange chromatography, 2) hemolysis did not affect the results of the direct assay, 3) the plasma cAMP was stable for up to 12 weeks when 5 mM EDTA was added to the blood at the time of sampling and stored below -20 degrees C and 4) the cAMP concentration did not decrease by repeated freeze-thawing of the plasma samples for up to 10 times. These results indicate that the direct radioimmunoassay of plasma cAMP concentration in normal subjects can give the same values as those obtained after purification by anion-exchange chromatography. Although further investigation is needed to clarify whether these results can be equally applied to patient's plasma with various diseases, the direct assay offers a convenient and accurate method to determine plasma cAMP concentration.

Influence of metabolic control of insulin-dependent diabetes on plasma nucleotide levels (cAMP, cGMP) during bicycle exercise.

Plasma concentrations of cyclic nucleotides (cAMP, cGMP) were measured before and during bicycle exercise in 8 well-controlled (mean pre-exercise blood glucose 5.3 mmol/l; HbA1 8.6%) and 8 moderately controlled (mean pre-exercise blood glucose 12.2 mmol/l; HbA1 10.8%) patients aged 18-32 years with insulin-dependent diabetes mellitus (IDDM) and in a group of non-diabetic control subjects matched for age and sex. Pre-exercise plasma cAMP concentrations and the rise with exercise were similar in all study groups. Significantly lower resting cGMP levels were found in well-controlled IDDM patients (3.5 +/- 0.3 pmol/ml, mean +/- SEM) compared to controls (5.6 +/- 1.1 pmol/ml; p less than 0.05) and moderately controlled IDDM patients (5.6 +/- 1.0 pmol/ml; p less than 0.05). By contrast, plasma cGMP levels increased during exercise in the diabetics but not in the controls. These findings indicate a significant difference in responses of plasma cGMP to exercise between IDDM patients and controls.

CYCLIC AMP IN NORMAL AND MALIGNANT HYPERPYREXIA SUSCEPTIBLE INDIVIDUALS FOLLOWING EXERCISE

Plasma cAMP concentrations were compared in normal and malignant hyperpyrexia susceptible individuals. Samples were taken before, at the peak, and at 60 and 120 min after a standardized physical stress test. It was found that, at the peak of the test, cAMP concentrations were significantly higher in malignant hyperpyrexia susceptible individuals. In addition, the return to control values was significantly prolonged in this group. The results support the hypothesis of abnormal cAMP metabolism in malignant hyperpyrexia susceptible individuals.