How to display limit text (code)?

Hi
i’m trying to use this function in my theme to display 5 related posts in single.php
and it’s work good! but i need to add something to make it display limit text from the first of each post.

function my_related_posts() {
if (is_single()) {
	global $post;
	$current_post = $post->ID;
	$categories = get_the_category();
foreach ($categories as $category) :
	?>
<div class="content-loop">
<h4>Related Posts</h4>
<ul>
<?php
$posts = get_posts('numberposts=5&category='. $category->term_id . '&exclude=' . $current_post);
foreach($posts as $post) :
?>
<li class="hentry">
<a href="<?php the_permalink(); ?>" rel="bookmark"><?php the_post_thumbnail('entry-thumb', array('class' => 'entry-thumb','alt' => get_the_title(),'title' => get_the_title())); ?></a>
<h2 ><a href="<?php the_permalink() ?>" rel="bookmark" title="<?php the_title_attribute(); ?>"><?php the_title(); ?></a></h2>

<div class="entry-excerpt">
    <?php /* here i want function get limit text from first of content*/ ?>
    <a href="<?php the_permalink(); ?>" class="read-more">read more...</a>
</div>

</li>
<?php endforeach; ?><?php endforeach; ?>
</ul>
</div>
<?php
		}
	wp_reset_query();
}
add_action('thesis_hook_after_post','my_related_posts');

please help
thanks