Custom Post Type Publish Action Hook. Original code: http://www.wphub.com/custom-post-type-publish-action-hook/

WP Hook - CPT publish

// function to be executed when a custom post type is published
function run_when_post_published()
{
    // your function code here
}
 
// replace {custom_post_type_name} with the name of your post type
add_action('new_to_publish_{custom_post_type_name}', 'run_when_post_published');  	
add_action('draft_to_publish_{custom_post_type_name}', 'run_when_post_published');		
add_action('pending_to_publish_{custom_post_type_name}', 'run_when_post_published');