Anterior pituitary (AP) is formed by five different cell types, each one producing a different AP hormone whose secretion is regulated by a specific hypothalamic releasing hormone (HRH). On the other hand, a significant number of AP cells express multiple HRH receptors (multiresponsive cells). Plastic changes in expression of HRH receptors in individual AP cells are involved in critical endocrine events. Here we have characterized the changes in functional responses to CRH, LHRH, TRH and GHRH in individual AP cells throughout the whole lifespan of the rat. For this end, calcium responses to the HRHs were followed by single-cell imaging in freshly dispersed AP cells prepared from rats of different ages (0 to 540 postnatal days). Three different cell pools were identified: (i)monoresponsive cells, holding a single class of HRH receptor; (ii)multiresponsive cells; and (iii) non-responsive cells. The relative abundance of each pool changed with age. Non-responsive cells were abundant at birth, multiresponsive cells were abundant at puberty and monoresponsive cells dominated at senescence. The relative abundance of each HRH receptor changed largely with age, but not with gender. In addition, the contribution of monoresponsive and multiresponsive cells to responses to each HRH changed very much with age. Thus, the anterior pituitary shows large changes in cell populations typed by functional responses to HRHs during maturation, puberty and senescence.