Hypophysectomy attenuates leptin‐induced tachycardia without affecting leptin's action on appetite and body weight.

Abstract

Leptin, a hormone produced by adipocytes, regulates energy homeostasis and cardiovascular function by activating its receptors in the central nervous system. Since leptin also modulates pituitary function we examined the role of pituitary hormones in contributing to the effects of leptin on energy homeostasis and cardiovascular function. Male 12‐week‐old hypophysectomized Sprague‐Dawley rats (Hypo, n=5) were instrumented with telemetry probes for determination of mean arterial pressure (MAP) and heart rate (HR) 24‐hrs/day and an intracerebroventricular (ICV) cannula was placed in the brain lateral ventricle for continuous infusion of leptin (15 μg/day). Compared to control rats (Ctrl, n=5), Hypo rats were lighter (215±4 vs 415±6 g), had lower MAP and HR (83±4 and 317±2 vs 105±4 mmHg and 339±4 bpm), with similar caloric intake per gram of body weight (174±19 vs 195±10 kcal/kg) and plasma glucose levels (84±4 vs 80±4 mg/dl). Chronic ICV leptin infusion for 7 days reduced caloric intake (−60%) and body weight (−10%) in both groups. Leptin treatment markedly increased HR in Ctrl rats (~25 bpm) while causing only a modest 8 bpm increase in Hypo rats. Leptin also induced a small increase in MAP in both groups (3 mmHg). These results suggest that hypophysectomy attenuates leptin's effect on HR regulation without altering leptin's ability to suppress appetite and to promote weight loss. (NHLBI‐PO1HL51971/ AHA SDG5680016)