EFFECT OF LONG-TERM ADMINISTRATION OF HEXARELIN ON THE SOMATOTROPIC AXIS IN AGED RATS

The growth hormone-releasing peptide Hexarelin (Hexa; 80 mu g/kg(-1), s.c.) was administered for 30 and 60 days to old rats. The GH-releasin g effect of Hexa was maintained during chronic treatment. At the end o f the treatment, old rats were administered once with Hexa which elici ted a greater GH response in rats chronically treated with the peptide than in those receiving a placebo. Pituitary GHmRNA concentrations we re significantly lower in the older rats than in the younger animals, irrespective of Hexa treatment, while the GH protein content was simil ar in all the groups studied. The same was true for hypothalamic GHRH, whose synthesis was reduced in all the older animals but not in the y oung, in the presence of maintained concentrations of the peptide. Som atostatin mRNA concentrations were significantly higher in the hypotha lami of older rats and administration of Hexa for 30 or 60 days brough t the concentrations of somatostatin mRNA of aged rats to 'young' leve ls. Treatments with Hexa failed to alter the circulating levels of IGF -1. The data reported in this article indicate that long-term treatmen t with Hexa normalized some biological indices of somatotrophic functi on in aged rats. (C) 1997 The Italian Pharmacological Society.