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: While postjunctional beta - adrenoceptor - mediated relaxations are reduced , effects by prejunctional inhibitory muscarinic receptors may be increased .
### Output Text:
While postjunctional beta - adrenoceptor - mediated relaxations are reduced , effects by prejunctional inhibitory muscarinic receptors may be increased . 