In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Changes evoked by a single intraperitoneal injection of rilmenidine ( 600 microg / kg ) or alpha - methyldopa ( 100 mg / kg ) , selective I1 - and alpha2 - receptor agonists , respectively , in blood pressure , hemodynamic variability , and locomotor activity were assessed in radiotelemetered sham - operated and ovariectomized ( Ovx ) Sprague - Dawley female rats with or without 12 - wk estrogen replacement .
### Output Text:
Changes evoked by a single intraperitoneal injection of <span class="chemical">rilmenidine</span> ( 600 microg / kg ) or <span class="chemical">alpha - methyldopa</span> ( 100 mg / kg ) , selective I1 - and alpha2 - receptor agonists , respectively , in blood pressure , hemodynamic variability , and locomotor activity were assessed in radiotelemetered sham - operated and ovariectomized ( Ovx ) Sprague - Dawley female rats with or without 12 - wk <span class="chemical">estrogen</span> replacement . 