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Effects of Aging and Dietary Restriction on mRNA Levels of Receptors for Growth Hormone–Releasing Hormone and Somatostatin in the Rat Pituitary

^a Department of Pathology, Nagasaki University School of Medicine, Nagasaki City, Japan
^b Department of Physiology, University of Texas Health Science Center at San Antonio

Isao Shimokawa, Department of Pathology, Nagasaki University School of Medicine, 1-12-4 Sakamoto, Nagasaki City 852-8523, Japan E-mail: shimo{at}net.nagasaki-u.ac.jp.

Decision Editor: Jay Roberts, PhD

Aging impairs and dietary restriction may modulate pituitary response to growth hormone (GH)–releasing hormone (GHRH) and somatostatin (SRIH) for GH secretion. Using the semiquantitative reverse-transcription polymerase chain reaction method, we analyzed the mRNA levels of the GHRH receptor (grfr) and SRIH receptor subtype 2 (sstr2) and subtype 5 (sstr5) in anterior pituitaries of male rats fed ad libitum or 30% dietary restricted. Aging reduced the mRNA levels of these receptors in a slightly different manner. The levels of grfr progressively decreased between 6 and 24 months, whereas those of sstr2 and sstr5 declined after 16 months. Dietary restriction did not diminish the aging-dependent changes, although it slightly augmented the levels of grfr, but not sstr2 and sstr5. The present results suggest that the aging-dependent impairment in pituitary response for GH secretion could result mostly from a decline in grfr rather than relative increase of sstrs. Although DR could slightly enhance the pituitary sensitivity to GHRH, the antiaging action may be minor at the level of gene expression.