Isometheptene

Isometheptene's vasoconstricting properties arise through activation of the sympathetic nervous system via epinephrine and norepinephrine (or their molecular analogues as is the case with this drug). These compounds elicites smooth muscle activation leading to vasoconstriction. These compounds interact with cell surface adrenergic receptors. Such stimuli result in a signal transduction cascade that leads to increased intracellular calcium from the sarcoplasmic reticulum through IP3 mediated calcium release, as well as enhanced calcium entry across the sarcolemma through calcium channels. The rise in intracellular calcium complexes with calmodulin, which in turn activates myosin light chain kinase. This enzyme is responsible for phosphorylating the light chain of myosin to stimulate cross bridge cycling.

Once elevated, the intracellular calcium concentration is returned to its basal level through a variety of protein pumps and calcium exchangers located on the plasma membrane and sarcoplasmic reticulum. This reduction in calcium removes the stimulus necessary for contraction allowing for a return to baseline. The drug can also cause vesicular displacement of noradrenaline from the neuron into the synapse with a similar effect as tyramine.