Modifications in alpha-MSH concentrations in different hypothalamic areas during the estrous cycle in the rat.

The present experiments were undertaken to examine the pattern of alpha-MSH during the estrous cycle in different hypothalamic areas and assess if during the whole estrous cycle the MSH which arises from proopiomelanocortin (POMC) has the same concentrations pattern as MSH from the dorso-lateral hypothalamus. MSH concentration of the mediobasal hypothalamus (MBH), preoptic area (POA) and dorso-lateral hypothalamus (DLH) was measured using a specific radioimmunoassay. The rats were sacrificed every four hours by perfusion. It is possible to observe a circadian rhythm in all the areas studied except in MBH during estrus. The MSH concentration in MBH was high during the light period, inversely, in POA the concentration remained low. In general, when MSH is high in MBH, it is low in POA and vice versa. The pattern of MSH in DLH is very similar to that observed for the peptide in POA.