The positive inotropic effects of catecholamines have been postulated to result from an increase in the intracellular level of cyclic AMP (adenosine 3',5'-monophosphate) produced by activation of adenyl cyclase. Although lack of an inotropic effect by exogenously administered cyclic AMP has cast doubt on this hypothesis, cardiac cells are not readily permeable to cyclic AMP. The N-2'-O-dibutyry...

The discovery of adenosine 3',5'-monophosphate (cyclic AMP) has provided a focal point for studies on the mode of action of hormones. Cyclic AMP seems to function as an ' intracellular second messenger' mediating the action of many different hormones (Sutherland, 0ye & Butcher, 1965; Sutherland & Robison, 1966; Robison, Butcher & Sutherland, 1968). The primary hormonal message arriving at a cel...

Effects of norepinephrine, J3-adrenergic blocking agents, theophylline ethylenediamine (TEDA) and digoxin on myocardial cyclic AMP concentration and those of various vasodilators both on myocardial cyclic AMP in vivo and phosphodiesterase (PDE) activity in vitro were investigated by radioimmunoassay of cyclic AMP. The mean concentration of myocardial cyclic AMP was 0.318 p mole/mg in the left v...

The protein-bound cyclic AMP and the activity of cytosolic protein kinases in the presence and absence of cyclic AMP were determined in rat liver up to 2h after injection of glucagon. On the basis of the different salt-sensitivities of the activated cyclic AMP-dependent proteinkinases I and II, an activation of protein kinase II restricted to the high cyclic AMP concentrations present in the fi...

A unilateral 30-min application of anodal direct current to the promotor cortex of rabbits was repeated 10 times, and cyclic AMP accumulation in response to histamine was investigated in slices of different cortical areas. Polarization with 1.0 microA decreased the cyclic AMP accumulation in the cortical area contralateral to the polarization, by which regional dominance in cyclic AMP accumulat...

Evidence is presented that modulation of the maximum velocity of a particulate low K-m cyclic adenosine 3':5'-monophosphate (cyclic AMP) phosphodiesterase by thyroid hormones is one mechanism for the regulation of the responsiveness of rat epididymal adipocytes to lipolytic agents such as epinephrine and glucagon. Fat cells of propylthiouracil-induced hypothyroid rats are unresponsive to lipoly...

Cyclic-di-AMP is a relative newcomer to the large family of nucleotide-based signaling molecules, which notably includes cyclic-AMP, cyclic-di-GMP, and ppGpp(p) (1). Cyclic-diAMP was first implicated as a possible signaling molecule when it was unexpectedly found bound to the active site of the Bacillus subtilis DisA protein, the prototype for a diverse family of diadenyl cyclases (DAC) (2). Sh...

Intracellular cyclic adenosine monophosate (AMP) levels regulate the generation of thromboxane by platelets by inhibiting the hydrolysis of arachidonic acid from membrane phospholipids. However, there is conflicting evidence regarding the role of cyclic AMP in the control of the subsequent oxygenation of arachidonic acid by cyclooxygenase. We studoed the regulation of cyclooxygenase activity by...

A cyclic AMP (adenosine 3’, 5’-monophosphate)-dependent protein kinase has been found in membranes derived from human erythrocytes which accounts for greater than 70% of the total cyclic AMP-dependent protein kinase activity of these cells. Components of the erythrocyte membranes were phosphorylated by membrane-bound protein kinase, but stimulation of the rate of phosphorylation by cyclic AMP w...

Kinetic parameters and the renal clearances of plasma adenosine 3',5'-monophosphate (cyclic AMP) and guanosine 3',5'-monophosphate (cyclic GMP) were evaluated in normal subjects using tritium-labeled cyclic nucleotides. Each tracer was administered both by single, rapid intravenous injection and by constant intravenous infusion, and the specific activities of the cyclic nucleotides in plasma an...