Which two hormones activate hormone-sensitive lipase to promote lipolysis?

Hormone-sensitive lipase plays a crucial role in the process of lipolysis, which is the breakdown of stored fats into free fatty acids and glycerol. The two hormones that stimulate this enzyme and promote lipolysis are catecholamines, particularly epinephrine, and growth hormone.

Epinephrine, released from the adrenal medulla in response to stress or low glucose levels, activates hormone-sensitive lipase through a signaling pathway involving beta-adrenergic receptors. This activation leads to an increase in intracellular cyclic AMP (cAMP), which in turn stimulates the lipase activity.

Growth hormone also promotes lipolysis, although its mechanism is more complex and can involve increased insulin resistance, leading to greater fatty acid mobilization as well. This effect is particularly evident during fasting or when the body's energy demand increases.

In contrast, other hormones mentioned in the choices either inhibit lipolysis or do not activate hormone-sensitive lipase directly. For example, insulin typically promotes fat storage by inhibiting lipolysis, whereas cortisol, though it has some lipolytic activity, does not act as directly as the hormones specified in the correct choice. Thus, epinephrine and growth hormone collectively serve to effectively stimulate lipolysis through their actions on hormone