Resumen de Efecto de la dieta y de la melatonina exógena sobre la respuesta hipofisaria a la gnrh durante el anestro y la estación reproductiva en ovejas rasa aragonesa
José Alfonso Abecia Martínez, F. Forcada, M.I. Vázquez, Inmaculada Palacín
In order to determine the effect of level of feed intake and exogenous melatonin on pituitary responsiveness to GnRH, both during anestrus (A) and breeding season (BS), 19 OVX+E2 ewes were used. Animals were divided in 4 groups, treated (+Mel) or not (-Mel) with melatonin and fed to provide 1.5 (Control, C) or 0.5 (low, B) times maintenance requirements. Both in April and November, a GnRH challenge was performed, consisting on collecting blood samples every 10 min for 3 h. After the first hour, GnRH was injected and LH analyzed. The highest LH simple (DLH) and the area under the curve of the first h (AUC1) and the total period (AUCT) were calculated. There was a significant effect of diet (C: 0.93±0.21; B: 1.46±0.29; p<0.05) and (BS: 1.44±0.20; A: 0.96±0.19 ng/ml; p<0.05) on basal LH concentrations before GnRH challenge with no effect of melatonin. GnRH increased dramatically LH both in A and BS. DLH was not affected by melatonin, diet or season, although AUC1 and AUCT were significantly affected by season (p<0.05). The highest basal LH levels showed by undernourished ewes could be due to an increment of LH pulse amplitude described in the literature.
