Research reportAdolescents and adults differ in the immediate and long-term impact of nicotine administration and withdrawal on cardiac norepinephrine

- Nicotine increases heart norepinephrine in adult rats, and spikes upon withdrawal.
- This response is absent in adolescents given nicotine.
- Adolescents instead show later-emerging, persistent changes in heart norepinephrine.
- Adolescent nicotine may produce less aversive autonomic responses to withdrawal.
- Persistent effects are consistent with elevated risk of hypertension and CHD.

Cardiovascular responses to smoking cessation may differ in adolescents compared to adults. We administered nicotine by osmotic minipump infusion for 17 days to adolescent and adult rats (30 and 90 days of age, respectively) and examined cardiac norepinephrine levels during treatment, after withdrawal, and for months after cessation. In adults, nicotine evoked a significant elevation of cardiac norepinephrine and a distinct spike upon withdrawal, after which the levels returned to normal; the effect was specific to males. In contrast, adolescents did not show significant changes during nicotine treatment or in the immediate post-withdrawal period. However, beginning in young adulthood, males exposed to adolescent nicotine showed sustained elevations of cardiac norepinephrine, followed by later-emerging deficits that persisted through six months of age. We then conducted adolescent exposure using twice-daily injections, a regimen that augments stress associated with inter-dose withdrawal episodes. With the injection route, adolescents showed an enhanced cardiac norepinephrine response, reinforcing the relationship between withdrawal stress and a surge in cardiac norepinephrine levels. The relative resistance of adolescents to the acute nicotine withdrawal response is likely to make episodic nicotine exposure less stressful or aversive than in adults. Equally important, the long-term changes after adolescent nicotine exposure resemble those known to be associated with risk of hypertension in young adulthood (elevated norepinephrine) or subsequent congestive heart disease (norepinephrine deficits). Our findings reinforce the unique responses and consequences of nicotine exposure in adolescence, the period in which most smokers commence tobacco use.