ABSTRACT
Catecholamines secreted from the adrenal medulla are involved in the mediation of most physiologic processes. Plasma norepinephrine levels were decreased to half after both demedullation and sympathectomy, suggesting that paraganglia in the sheep provides some contribution to the resting levels of catecholamines. Increased sympathoadrenal activity is the primary autonomic response that occurs during exercise. The nonshivering thermogenesis that develops with prolonged cold exposure is stimulated in a nonlinear fashion by the infusion of norepinephrine. Lymphatic transport of norepinephrine was related quadratically to the infusion rate, indicating a similar relationship between infusion rate and influx of norepinephrine into the extravascular space. Intravenous injection of nicotine inhibited the gastric acid output elicited by stimulation of the vagus nerve and initially inhibited gastric mucosal blood flow; these effects were blocked by phentolamine or by adrenalectomy plus reserpine. Gastric acid secretion may be modulated by central mechanisms.
