Aging and gender affect the response of thyrotropin (TSH) to gastrin releasing peptide (GRP) in rats

We had previously shown that GRP acts directly at the pituitary gland inhib iting basal and TRH-stimulated TSH secretion in adult male rats. In this st udy we showed a gender dimorphism in this response of old animals pituitari es to GRP. In both female and male young adult animals, GRP-incubated pitui taries showed approximately 50% less basal and TRH-stimulated TSH secretion to the medium, without affecting the pituitary content of TSH. However, GR P did not have any significant effect upon TSH secretion in old male rats, but the old female showed the same degree of response to GRP as the young a dult female rat, regarding basal and TRH-stimulated TSH secretion, while th e TSH pituitary content after GRP incubation was higher than that of the yo ung female group. Our data suggest a loss of thyrotrope responsiveness to G RP in aged male rats that could contribute to the decrease in TSH pituitary stores leading to lower basal and TRH-stimulated TSH secretion. Meanwhile, the preservation of GRP responsiveness could help in the relative maintena nce of these parameters in the old female rat. (C) 2001 Elsevier Science In c. All rights reserved.