In the current project I am working on (using Symfony framework), I came across a situation where I had to call one action within another action and capture the content of 2nd action. This content is included within the result from 1st action. After doing some research found that it it possible to do so by calling getPresentationFor method of the controller object.
Within the action's execute method,
$content = $this->getController()->getPresentationFor($module, 'my2ndAction');
$this->content = $content;