[30,31] In the coronary arteries, this vasodilatory effect improves perfusion and oxygen delivery to the heart, improving inotropy
The cardiac ARs in the myocardium contribute to the control of inotropy
, rate of relaxation with the changing levels of intracellular [Ca.sup.2+], and heart rate.
Diverse responses to NO, such as positive or negative inotropy
, biphasic effect, or no response, have been observed.
Therapeutic benefit results from decreased chronotropy and inotropy
. This subsequently causes diastolic prolongation.
As was demonstrated by the work of Ladenson and Ridgway the treatment with 50 [micro]g L-triiodothyronine or 100 [micro]g L-thyroxine intravenous was able to result in reversal of blunted ventilator responsiveness, increase in cardiac inotropy
, renal excretion of water load, and basal metabolic rate within hours to days after the start of treatment [25, 26].
See Hoe et al., "Bitter taste receptor agonists elicit G-protein-dependent negative inotropy
in the murine heart," FASEB Journal, vol.
The recommended first-line agent is phenylephrine,  with the notable exceptions being the patient who responds to spinal anaesthesia with bradycardia and hypotension, or has undiagnosed cardiac disease and unexpectedly requires positive inotropy
. Recent literature has moved the debate from the choice between ephedrine and phenylephrine to the manner in which phenylephrine should be given.
Also, the high levels of NOS2 in failing myocytes appear to be, at least in part, a cause of the blunted myocardial inotropy
after [beta]-adrenergic stimulation [80, 81].
Circulating A also causes increased heart rate, cardiac output, inotropy
, vasodilatation in muscle and liver (24).
When the concentration of cGMP-inhibited phosphodiesterase is low, it increases the intracellular level of cyclic adenosine monophosphate (cAMp), which can be considered a positive inotropy
Howlett, Increases in diastolic [Ca2+] can contribute to positive inotropy
in guinea pig ventricular myocytes in the absence of changes in amplitudes of Ca2+ transients.
Tota, "Nitrite exerts potent negative inotropy
in the isolated heart via eNOS-independent nitric oxide generation and cGMP-PKG pathway activation," Biochimica et Biophysica Acta.