Lack of synchrony between feeding activity and pulsatile growth hormone secretion in rats

Plasma growth hormone (GH) was determined in blood sampled at 15 minute intervals in undisturbed chronically cannulated adult male rats while continuously monitoring feeding activity. Ten animals were studied; five were optic nerve sectioned from 24 days of age and five were intact. The sampling time was from 15:00 hours to 21:00 hours, which included 5 hours of light and the first hour of dark. Both GH secretion and feeding activity exhibited a pulsatile pattern. There was no consistent coordination of bursts of feeding activity and GH secretion. We conclude that feeding activity and GH secretion may be controlled by central timing mechanisms; however, it appears that these mechanisms are separate and are not synchronized.