Final answer:
Conditions and drugs that decrease LES tone include hypoxia, acidosis, hyperkalemia, and certain synthetic drugs. These factors can cause the LES to relax and open more easily.
Step-by-step explanation:
The conditions and drugs that decrease LES (lower esophageal sphincter) tone include hypoxia (decreased oxygen concentrations), acidosis (falling pH), hyperkalemia (increasing concentrations of potassium ions), and certain synthetic drugs such as beta blockers and calcium channel blockers. These conditions and drugs can lead to the relaxation of the LES, causing it to open more easily. For example, increased carbon dioxide concentrations, lactic acid buildup, and histamines can stimulate the release of NO (nitric oxide), which is a powerful vasodilator and can also decrease LES tone.