\documentclass{article}
\usepackage{ptext,lipsum}
\usepackage{xepersian}
\let\oldlatin=\latin
\let\endoldlatin=\endlatin
\renewenvironment{latin}{\bgroup\oldlatin%
\baselineskip=1cm
}%
{\endoldlatin\egroup}
\begin{document}
\ptext[1]
\begin{latin}
\lipsum[1]
\end{latin}
\ptext[1]
\end{document}