Alpha and Beta cells with Alpha producing Glucagon and Betha Producing Insulin...

Insulin is a carrier that brings sugar into the cell while Glucagon "makes" liver release/convert fat into simple sugar. In case of low blood sugar (most cases) there is pleanty of insulin to carry sugar intot he cell but there is not enough sugar. So shooting insulin would be wrong (unless you have pleanty of sugar in your blood but no insulin - diabetes). Glucagon delivers sugar so does simple IV with dextorse or glass of OJ.

ANd to answer your question directly: glycogen stores glucose which would be released by administration (artificial: injection or natural: pancreas) of glucagon.