Nicotine primarily acts as a stimulant in the body. Among the options provided, the correct response is:
increases heart rate
Nicotine stimulates the release of adrenaline, which can lead to an increase in heart rate and blood pressure. It does not typically have a sedative effect, so it does not make one feel sleepy, and it is more likely to increase rather than slow the breathing rate. Additionally, nicotine does not lower blood pressure but can initially raise it.