Some fixed text
\begin{itemize}
\item item 1
\item item 2
\item item 3
\item item 4
% Maybe more items
\end{itemize}
Some more fixed text
\begin{itemize}
\item item 5
\item item 6
% Could have more items here
\end{itemize}
Some text at the end
\newcommand{\myenvironment}[6]{%
Some fixed text
\begin{itemize}
\item #1
\item #2
\item #3
\item #4
\end{itemize}
Some more fixed text
\begin{itemize}
\item #5
\item #6
\end{itemize}
Some text at the end
}