Adrenalectomy Prevents the Obesity Syndrome Produced by Chronic Central Neuropeptide Y Infusion in Normal Rats

Neuropeptide Y (NPY) in the hypothalamus plays an important role in the regulation of food intake and body weight and seems to be implicated in the etiology of obesity. When intracerebroventricularly (ICV) infused for 6 days in normal rats, NPY resulted in hyperphagia, increased body weight gain, hyperinsulinemia, hypercorticosteronemia, and hypertriglyceridemia compared with vehicle-infused control rats. NPY infusion also resulted in an insulin-resistant state in muscles and in a state of insulin hyperresponsiveness in white adipose tissue, as assessed by the measurement of the in vivo glucose utilization index of these tissues during euglycemic-hyperinsulinemic clamps. All of these hormono-metabolic effects produced by chronic central NPY infusion were completely prevented when rats were adrenalectomized before NPY administration. Adrenalectomy per se had no effect on any of the parameters mentioned above. The levels of mRNA for the obese gene were increased in white adipose tissue after 6 days of ICV NPY infusion in normal rats, and white adipose tissue weight was also increased. These effects of ICV NPY infusion were markedly decreased by prior adrenalectomy, although NPY infusion was able to somewhat enhance the low white adipose tissue obese mRNA levels and tissue weight of adrenalectomized rats. In conclusion, intact adrenal glands, and probably circulating corticosterone in particular, are necessary for the establishment of most of the hormonal and metabolic effects induced by chronic ICV infusion of NPY in normal rats.