Fill dropdownlist

 Dear readers,
I have the next question,
When i search on a page and found what i want, a gridview shows the artikels, what i want is when the gridview shows the found artikels, three dropdownlisten become visible where ik can filter the gridview on article name  article type article width.   (colum-names of the gridview)

 Now it comes How can i fill the dropdowlist with the colum-names of the found articles
.
 Here the code to search:
  
Protected Sub btnzoek_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnzoek.Click
Dim search As String
'maak connectie met de database
Dim con ...