EVIDENCE THAT NEUROPEPTIDE Y (NPY) COULD REPRESENT A NEUROENDOCRINE INHIBITOR OF SEXUAL MATURATION IN UNFAVORABLE METABOLIC CONDITIONS IN THE RAT

NPY is known to be involved in the central regulation of appetite, metabolic processes, and reproductive functions. We have demonstrated that central administration of NPY results in an inhibition of the gonadotropic axis in the rat. In the female rat, sexual maturation can be delayed by severe diet restriction and in this situation, NPY is increased in the paraventricular nucleus (PVN). In order to evluate a potential role of NPY for this delay, we attempted to prolong this period of sexual immaturity by infusing NPY centrally after restauration of normal feeding condition. Sexual maturation was prevented by maintaining food allowance at 5.5 g/day. At 50 days of life (d), a cannula was placed in the lateral ventricle and at 60 d, the animals were implanted with Alzet pumps delivering 18 μg NPY daily to the cannula, or vehicle. One day later, food restriction was discontinued. The switch to ad libitum feeding produced a rapid acceleration of growth rate and, in the animals receiving vehicle, the expected full sexual maturation after 2 to 5 days. Animals receiving NPY exhibited an even more important increase in weight gain, but only one out of 9 rats studied had experienced vaginal opening after 6 days, at the end of pump capacity. In another series, sexual immaturity could be prolonged for 13 days. Thus, since NPY is increased in the PVN of food-restricted rats and that administration of NPY could prolong the situation of sexual immaturity observed during food restriction, it is tempting to speculate that NPY is instrumental for inhibiting GnRH release and sexual maturation in unfavorable metabolic conditions.