Final answer:
Most second messengers create metabolic changes within the cell, such as activating enzymes and modifying ion channels, with long-term effects like stronger synaptic connections and gene activation.
Step-by-step explanation:
The immediate intracellular effect of most second messengers is to foster metabolic changes within the cell. Hormones or other extracellular signals that bind to cell surface receptors can initiate a signaling cascade, leading to the creation of second messengers like cyclic adenosine monophosphate (cAMP), inositol triphosphate (IP3), and others. These second messengers then go on to activate or inhibit various enzymes within the cell, modify ion channels to open or close them, and can even trigger gene activation resulting in protein synthesis. Within neurons, such changes can strengthen synapses and are fundamental in processes such as learning and memory. Examples of hormones that use these signaling pathways include glucagon, which impacts blood glucose levels, and angiotensin II, which is involved in blood pressure regulation through vasoconstriction.