Call an Event Handler

Question

hi experts,
i have a problem calling an event handler from another control

scenario:
1-i have two drop down lists the main dropdown list :
when the selected index changed event is called, another drop down list appears with a certain value according to the selected value of the main....

2-the second drop down list selected index changed event executes some functions on a check boxes list


the problem :
when the value of the second dropdown list is assigned i need to call the selected index changed event of the second drop down list to execute the functions on the check boxes list

any ideas ????