Inhibitory effects of central neuropeptide Y on the somatotropic and gonadotropic axes in male rats are independent of adrenal hormones

Neuropeptide Y (NPY) in the hypothalamus exerts multiple physiological func tions including stimulation of adipogenic pathways such as feeding and insu lin secretion as well as inhibition of the somatotropic and gonadotropic ax es. Since hypothalamic NPY-ergic activity is increased by negative energy b alance, NPY enables coordinated regulation of growth and reproduction in pa rallel with energy availability. Chronic pathological increases in central NPY-ergic activity contribute to obesity. Many of the adipogenic effects of NPY are specifically dependent on adrenal glucocorticoids. However, in the current study we show that central NPY does not require adrenal hormones t o inhibit the somatotropic and gonadotropic axes in rats. Male adrenalectom ized and sham-operated normal rats were intracerebroventricularly (ICV) inf used with NPY (15 mug/day) or saline for 5-7 days, and plasma leptin, insul in-like growth factor (IGF-1) and testosterone were assayed, and epididymal white adipose tissue (WATe) was weighed. In normal intact rats, WATe weigh t and leptinemia were significantly increased by NPY and these effects were prevented by adrenalectomy. In normal rats, NPY markedly reduced plasma IG F-I levels (470 +/- 40 versus 1260 +/- 90 ng/ml) and testosterone (0.53 +/- 0.28 versus 5.4 +/- 0.80 nmol/l in saline-infused controls, p < 0.0001). A drenalectomy decreased plasma IGF-I concentrations to 290 <plus/minus> 30 ( p < 0.0001 versus normal rats), which were significantly reduced further by NPY. However, adrenalectomy had no significant effect on basal nor on NPY- induced plasma testosterone concentrations. In conclusion unlike the stimul atory effects of NPY on fat mass and leptinemia, NPY-induced inhibition of the somatotropic and gonadotropic axes in male rats do not require adrenal hormones. <(c)> 2001 Elsevier Science Inc. All rights reserved.