When plasma glucose concentration increases, the secretion of insulin is and the secretion of glucagon is however, an increase in sympathetic activity will cause secretion of insulin and secretion of glucagon?

Increased…decreased. Decrease…increase. Glucagon and insulin hormones are used in a feedback loop during the homeostatic maintenance of glucose levels in the body. When the blood glucose levels are high, insulin is produced by the pancreas hence signaling uptake of the glucose by cells and storage of excess into glycogen by the liver. When the sugar levels drop, glucagon is produced to convert the glycogen back to glucose to maintain sugar levels. The sympathetic system also invokes during hypoglycemia. Secreted epinephrine by the nervous system increases production of glucagon by alpha-islet cells. Conversely, insulin levels are reduced.

i thinking chemical change

ok yes, but what is the question? as soon as you ask the actual question i will answer it. : )