Inotropic and metabolic effects of dibutyryl cyclic adenosine 3', 5'-monophosphate in the perfused rat heart

The effects of DBcAMP on the expression of eNOS, iNOS and TGF-beta in rat heart tissue

Dibutryl (DB) adenosine 3',5'-cyclic monophosphate (cAMP) is an important modulator of physiological functions. To determine the protective effects of DBcAMP on heart tissue, we evaluated changes in immunoreactivity of endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS) and transforming growth factor-beta (TGF-beta) in left cervical vagotomized rats treated with DBcAMP. Male rats were divided into four groups. In Group 1, animals were subjected to a left cervical vagotomy. Group 2 received a 1 ml bolus injection of 15 ml/kg DBcAMP in addition to the left vagotomy. DBcAMP alone was given to Group 3 and Group 4 was the control group. For each animal, mean arterial pressure (MAP) and heart rate (HR) were measured. For indirect immunohistochemistry, anti-eNOS, anti-iNOS, and anti-TGF-beta primary antibodies were used. In Group 1, MAP and HR values decreased slightly. In Groups 2 and 3, DBcAMP induced a statistically significant drop in HR and MAP. In Group 1, strong eNOS, iNOS, and TGF-beta immunoreactivities were observed. Immunostaining intensities decreased in Groups 2 and 3. The results of the study reported here suggest that increased immunoreactivities of eNOS, iNOS, and TGF-beta might contribute to the effects on the heart tissue after left vagotomy and imply that DBcAMP acts on heart tissue via nitric oxide.

Increase in length of experimental skin flaps that survive with dibutyryl cyclic AMP

One of the most important research topics in plastic surgery is the extension of the length of skin flaps that survive. We have investigated the increase in the length of skin flaps that can be achieved by giving dibutyryl cyclic AMP (DB-cAMP) to rabbits with experimental skin flaps and compared the results with those in animals not given DB-cAMP. Three variables, the arrival of DB-cAMP in the critical area of circulation of the flap (n = 6), changes in the blood flow in the flap (n = 10), and increase in the length of skin flap that survived (n = 30) were investigated by high performance liquid chromatography and laser Doppler flowmetry. DB-cAMP reached the critical area of circulation in the skin flap (dye distance), increased the blood flow within this area (mean (SEM) peak value 30 minutes after operation 1.24 (0.06) ml/min/kg compared with 1.06 (0.02) in control flaps), and extended the length of the flap that survived (mean (SEM) length seven days after operation 66.1 (3.0) mm compared with 60.8 (1.8) mm in the control group). We conclude that DB-cAMP improved the blood flow in skin flaps in rabbits with a consequent increase in the length of skin flap that survived.

Influence of ischaemia and reperfusion on cardiac signal transduction. G protein content, adenylyl cyclase activity, cyclic AMP content, and forskolin and dibutyryl cyclic AMP-induced inotropy in the rat Langendorff heart

We investigated whether post-receptor alterations contribute to the diminished beta-adrenergic inotropic effects in the rat Langendorff heart following ischaemia (I) and reperfusion (R). We quantitated immunodetectable Gs and Gi protein alpha-subunit content, basal and stimulated adenylyl cyclase activity and cyclic AMP (cAMP) content in normoxic, ischaemic (30 min) and ischaemic reperfused (30 min) hearts. In addition, we measured the inotropic response of normoxic and reperfused Langendorff hearts to forskolin and dibutyryl cAMP (db-cAMP). Immunodetectable Gs and Gi alpha-subunits were unaltered by I or R. Basal adenylyl cyclase activity was decreased during I, but recovered during R. In membranes from normoxic hearts, isoprenaline, GTP, Gpp(NH)p, NaF, forskolin or Mn2+ enhanced adenylyl cyclase activity. This increase in activity was diminished in ischaemic hearts, but could be restored by R. cAMP content decreased time-dependently during I and did not recover by R, indicating ATP depletion. Forskolin and db-cAMP induced an inotropic response in normoxic hearts, which was virtually abolished after I and R. We conclude that adenylyl cyclase responsiveness is impaired during I. Since adenylyl cyclase responsiveness recovers during R, whereas inotropic responses to forskolin and db-cAMP are virtually absent in reperfused hearts, an additional mechanism downstream of cAMP formation appears to be defective during R, which prevents recovery of inotropic responses to hormonal stimulation.

Effects of dibutyryl cyclic AMP, ouabain, and xanthine derivatives on crossbridge kinetics in rat cardiac muscle

In a previous communication, we showed that beta-adrenergic stimulation of cardiac muscles was associated with an increase in the rate of cycling of crossbridges as measured by perturbation analysis in the frequency domain. In this analysis, the frequency at which dynamic stiffness is a minimum (fmin) is taken as a measure of the rate of crossbridge cycling. In this paper, we test the hypothesis that the beta-adrenergic receptor-induced increase in crossbridge cycling rate is mediated by elevation of the intracellular level of cyclic AMP. The approach taken is to compare the effects on fmin in rat papillary muscles during Ba(2+)-activated contractures of 1) an agonist of cyclic AMP that can easily penetrate the cell, namely, dibutyryl cyclic AMP, 2) agents that block cyclic AMP phosphodiesterase, namely, the xanthine derivatives isobutylmethylxanthine and caffeine, and 3) an inotropic agent that does not affect the intracellular level of cyclic AMP, namely, ouabain. Our results showed that dibutyryl cyclic AMP at a dose of 5 mM has the same actions as beta-adrenergic stimulation: it potentiated the isometric twitch force, reduced the time to peak tension and time to half relaxation, and shifted fmin by a factor of 1.8 +/- 0.1 (n = 5). Isobutylmethylxanthine at up to 1.1 mM also acted in the same manner, increasing fmin by a factor of 1.8 +/- 0.2 (n = 6), but ouabain, at a dose (0.03 mM) sufficient to potentiate twitch force by 40 +/- 2% (n = 4), was without effect on the time course of the twitch nor was fmin changed (n = 4). Our findings support the hypothesis that a beta-adrenergic receptor-mediated increase in crossbridge cycling rate is due to an increase in intracellular cyclic AMP level and illustrate the usefulness of the frequency domain analysis approach in the analysis of the mechanism of action of inotropic agents.

Hemodynamic effects of dibutyryl cyclic AMP in congestive heart failure

To evaluate the hemodynamic effects of dibutyryl cyclic AMP (DBcAMP) in congestive heart failure (CHF), right-sided cardiac catheterization was performed in 11 patients with CHF, and hemodynamic variables were investigated before and after infusion of various doses of DBcAMP at a rate of 0.025 to 0.2 mg/kg/min (mean 0.14 +/- 0.077 [standard deviation]). DBcAMP reduced total systemic vascular resistance index from 3,171 +/- 1,158 to 1,880 +/- 554 dynes s cm-5 X m2 (mean +/- standard deviation) and pulmonary arterial end-diastolic pressure from 23 +/- 13 to 20 +/- 11 mm Hg, and increased cardiac index from 2.24 +/- 0.60 to 3.41 +/- 1.02 liters/min/m2. Mean arterial blood pressure decreased from 91 +/- 14 to 84 +/- 13 mm Hg, and heart rate increased from 91 +/- 16 to 99 +/- 13 beats/min. The increase in cardiac index was accompanied by a proportional decrease in total systemic vascular resistance index in all patients except 1. In 8 patients the decrease in pulmonary arterial end-diastolic pressure was accompanied by an increase or no change in the left ventricular stroke work index. In 6 patients, DBcAMP was given in incremental doses of 0.05, 0.1, and 0.2 mg/kg/min every 20 minutes, and 5 of 6 patients tolerated the full dose and showed dose-related hemodynamic changes for the incremental doses of DBcAMP. These data suggest that DBcAMP has powerful vasodilating effects on resistance vessels in patients with CHF; hence, it can be a useful vasodilating agent for treatment of CHF.

Mechanical response of rat myocardium to dibutyryl cyclic AMP in relation to effects of alpha-and beta-adrenoceptor stimulators

Dibutyryl cyclic AMP, and alpha- and beta-adrenoceptor stimulators are all able to elicit inotropic effects. alpha- and beta-Adrenoceptor stimulation are known to change each myocardial contraction-relaxation cycle differently. In order to elucidate the myocardial function of cyclic AMP the effects of dibutyryl cyclic AMP on the contraction-relaxation cycle of isolated rat heart papillary muscle were examined and compared to the effects of alpha-and beta-adrenoceptor stimulation, respectively. Dibutyryl cyclic AMP (in the presence of propranolol) increased developed tension (Tmax) by 18%, rate of tension rise (T'max) by 46%, rate of tension fall (T'min) by 62% and onset-rate of relaxation (T"min) by 136%. These changes in the contraction-relaxation cycle were strikingly similar to those produced by isoprenaline (beta-adrenoceptor stimulation). The response to dibutyryl cyclic AMP, however, developed much more slowly than did the response to isoprenaline. The latter effect was associated with cyclic AMP elevation in a way indicating a trigger function for cyclic AMP. The alpha-adrenoceptor stimulation (by phenylephrine combined with propranolol), however, increased measures both for contraction and for relaxation by about the same degree, and the effects occurred without changes of cyclic AMP contents. Phenylephrine alone (combined alpha-and beta-adrenoceptor stimulation) elicited a substantial cyclic AMP elevation but gave mechanical effects only slightly different from the pure alpha-adrenergic response. Thus cyclic AMP effects did not seem to be fully expressed in this case. As a whole, the results indicate that the effects of both dibutyryl cyclic AMP and of isoprenaline are mediated by the cyclic AMP-system while alpha-adrenoceptor stimulation involves other mechanisms.

Cyclic AMP

Cyclic AMP mediates the effects of many hormones on their target cells. Some of the mechanisms by which this occurs are discussed in this review. The role of cyclic AMP in regulating glycogen metabolism in liver and skeletal muscle is firmly established. Data suggesting that cyclic AMP mediates hormonally stimulated salivary gland amylase secretion, cardiac muscle contractility, smooth muscle relaxation, and platelet aggregation are summarized.

The effect of dibutyryl cyclic AMP and glucagon on the myocardial cell pH1

DBcAMP or crystalline glucagon was utilized to elevate the intracellular cyclic AMP concentration in isolated rat hearts. Butyric acid, a metabolite of DBcAMP, was also investigated. Their effect on the intracellular pH (pHi) as determined by the distribution of [14C]DMO was investigated. Rat hearts, perfused with a recirculated modified Krebs-Henseleit solution maintained at 30 degrees C, were exposed to respiratory acidosis by bubbling the perfusate with 20% CO2. alpha- and beta-receptor antagonists were used to block the effects of endogenous catecholamines. Hypercapnia decreased the pHi from 7.09 to 6.82. A similar degree of hypercapnia decreased the pHi to only 6.95 in the presence of DBcAMP and to only 6.96 in the presence of glucagon. The effective buffer values (delta[HCO-3]i/deltapHi) were: control, 19; butyric acid, 16; DBcAMP, 139; glucagon, 148. These data suggest that cAMP mediates the effect of norepinephrine, which has been shown to diminish the change in pHi accompanying respiratory acidosis.

Relaxation of heart muscle by catecholamines and by dibutyryl cyclic adenosine 3',5'-monophosphate. Similarity of beta-adrenoceptors mediating contractile and relaxant effects of catecholamines in kitten pipillary muscle

1. In isometrically contracting kitten papillary muscles, dibutyryl cyclic AMP (DBcAMP) enhanced peak tension, increased rates of contraction and relaxation, decreased tension of a phasic but not of a small tonic component of KCl-contractures, and caused aftercontractions. These effects resemble closely those of catecholamines. 2. The effects of DBcAMP on kitten papillary muscle were not influenced by (-)-bupranolol, a beta-adrenoceptor antagonist. 3. DBcAMP decreased KCl-contractures in strips of frog ventricle. 4. Phasic KCl-contractures in kitten papillary muscles were decreased by (-)- and (+)-isoprenaline. For similar effects, 100-fold higher concentrations of (+)-isoprenaline than of (-)-isoprenaline were required. 5. Increases in maximum rates of contraction and relaxation, increases in peak tension of isometric contractions and reduction of phasic KCl-contractures by catecholamines were antagonized competitively to a similar extent by (-)-bupranolol. Mean apparent equilibrium constants for the beta-adrenoceptor-(-)-bupranolol complex of 0.46-0.70 nM were estimated. These constants were quite similar irrespective of whether (-)-isoprenaline, (+)-isoprenaline or (-)-noradrenaline were used as agonists. 6. Increases in contractile strength, maximum rates of contraction and of relaxation of isometric contractions and decreases in KCl-contractures by (-)-isoprenaline were surmountably blocked by (+)-bupranolol. Mean apparent equilibrium constants for the receptor-(+)-bupranolol complex were 40-50 nM. 7. The equilibrium constants of (-)- and (+)-bupranolol for the receptors mediating positive inotropic and relaxant effects of catecholamines were not significantly different from constants for bupranolol-receptor complexes in cell-free membrane particles of kitten heart ventricle. It is suggested that the same beta-adrenoceptor triggers positive inotropic, relaxant and adenylyl cyclase-activating effects of catecholamines in kitten papillary muscle. 8. The partial agonist (-)-dichloroisoprenaline (DCI) (1 muM) reduced by 79% the phasic KCl-contractures of the kitten papillary muscles. DCI stimulates adenylyl cyclase activity of ventricle membranes to less than 1/4 of maximum stimulation by (-)-isoprenaline. If cyclic AMP produced by DCI is involved in the decrease of phasic KCl-contracture, small increase in cyclic AMP should be sufficient to induce this effect.