Trens causes rises in IGF and Prostaglandins. While IGF is a fairly well known substance in the bodybuilding world today, prostaglandins are fairly unknown in terms of formation and roles in the body.

Prostaglandins are made by two different pathways(Cyclooxygenase and Lipoxygenase), and considering prostaglandins are a group of about 20 lipid cells, they have contrary function; responsible for stimulating as well as alleviating inflammation(Inflammation stimulation is the rapid metabolism of them expelled through the bronchials), regulate blood flow to particular organs, control ion transport acrossmembranes, modulate synaptic transmission, induce sleep, mediate lipidrelease, and regulate metabolism is various tissue.

Cyclooxygenase and lipoxygenase pathways, compete with one another to form prostaglandins(as well as thromboxane or leukotriene-leukotriene being a bronchial stimulator).  In the cyclooxygenase pathway, the prostaglandins D, E and F plus thromboxane and prostacyclin are made.

Thromboxanes are made in platelets and cause constriction of vascular smooth muscle and platelet aggregation Leukotrienes are made in leukocytes and macrophages via the lipoxygenase pathway. They are potent constrictors of the bronchial airways. They are also important in inflammation and hypersensitivity reactions as they increase vascular permeability.

Because trenbolone causes the rate of production of prostaglandins to rise, the corresponding rise in Leukotrienes causes inflammation in the lungs such as wheezing and shortness of breath.

Singulair (Montelukast), a common allergy medication, is a Leukotriene Modifier. It blocks the Leukotriene receptors in your lungs, eliminating trenbolone sides such as wheezing and shortness of breath.

Put simply, taking Singulair, or certain other Leukotriene modifiers will block the tren effects on cardio.