Effects of neuromedin U on the pulsatile LH secretion in ovariectomized rats in association with feeding conditions

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Abstract

We examined the effects of intracerebroventricular injection of neuromedin U (NMU), at a dose that is reported to induce satiety in rats, on the pulsatile luteinizing hormone (LH) secretion in adult ovariectomized (OVX) rats under a normal feeding or a 48-h fasted condition. In OVX rats under the normal feeding condition, injection of NMU (1 nmol/3 μl) significantly decreased the mean LH concentration without affecting the frequency or amplitude of LH pulses, but under the 48-h fasted condition, it significantly decreased the mean LH concentration and the frequency of LH pulses without affecting the amplitude. The interpulse interval was significantly lengthened by NMU injection under the normal and the 48-h fasted condition, but the effect under the 48-h fasted condition was greater than under the normal feeding condition. We also confirmed that the 48-h fasted condition per se did not affect the pulsatile LH secretion in OVX rats. We suggest that NMU and fasting synergistically inhibit the pulsatile LH secretion, even though NMU has been said to act as a satiety factor.

Section snippets

Materials and methods

Animals. Female rats of Wistar strain (Charles River, Yokohama, Japan) were obtained at 7 weeks of age and maintained under controlled lighting conditions (lights on 05:00–19:00 h) with food and water available ad libitum. They were ovariectomized (OVX) and, for the intracerebroventricular (icv) injection, stereotaxically implanted with a guide cannula into the third ventricle according to the atlas of Albe-Fessard et al. [24] (stereotaxic coordinates: A=6.0, V=2.0, and L=0.0) under sodium

Experiment 1

Fig. 1 shows representative individual LH profiles and the mean LH concentration before and after icv injection of aCSF or NMU in OVX rats under the normal feeding condition. The pulsatile fluctuation of serum LH was evident during the blood sampling in aCSF-injected OVX rats, suggesting that icv injection of aCSF had no significant effect on the pulsatile LH secretion. NMU injection, on the other hand, seemed to inhibit the pulsatile LH secretion, since the serum LH concentration at the

Discussion

The present study shows for the first time that the central administration of NMU inhibits the pulsatile LH secretion and this effect is significantly enhanced under the 48-h fasted condition, which by itself does not markedly affect the pulsatile LH secretion. Since satiety factors such as leptin and glucagon-like peptide-1 stimulate the LH secretion [21], [23], while orexinergic factors such as ghrelin, orexin, and melanin-concentrating hormone inhibit it [15], [16], [28], the inhibitory

Acknowledgements

We are grateful to Dr. K. Wakabayashi of Gunma University School of Medicine and the NIDDK for providing radioimmunoassay materials.

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