Effects of aging and dietary restriction on mRNA levels of receptors for growth hormone-releasing hormone and somatostatin in the rat pituitary

Aging impairs and dietary restriction may modulate pituitary response to gr owth hormone (CH)-releasing hormone (GHRH) and somatostatin (SRIH) for GH s ecretion. Using the semiquantitative reverse-transcription polymerase chain reaction method, we analyzed the mRNA levels of the GHRH receptor (grfr) a nd SRIH receptor subtype 2 (sstr2) and subtype 5 (sstr5) in anterior pituit aries of male rats fed ad libitum or 30% dietary restricted. Aging reduced the mRNA levels of these receptors in a slightly different manner. The leve ls of grfr progressively decreased between 6 and 24 months, whereas those o f sstr2 and sstr5 declined after 16 months. Dietary restriction did not dim inish the aging-dependent changes, although it slightly augmented the level s of grfr, but not sstr2 and sstr5. The present results suggest that the ag ing-dependent impairment in pituitary response for GH secretion could resul t mostly from a decline in grfr rather than relative increase of sstrs, Alt hough DR could slightly enhance the pituitary sensitivity to GARH, the anti aging action may be minor at the level of gene expression.