Complex sentence: Activation of the GLP-1 receptor will also cause a decrease in glucagon, which is produced by the pancreas when the blood glucose level is low, causing the liver to convert stored glycogen into glucose and release it into the blood stream (3).
Split into simpler sentences: Activation of the GLP-1 receptor will also cause a decrease in glucagon, which is produced by the pancreas when the blood glucose level is low. This will cause the liver to convert stored glycogen into glucose and release it into the blood stream (3).