Gastrin releasing peptide, but not pentagastrin, stimulates ACTH and cortisol secretion in conscious dogs.

Gastrin releasing peptide (GRP) is the mammalian equivalent of bombesin. Bombesin has been shown to stimulate canine ACTH and cortisol secretion in a dose-related manner. In the present study, following a 30-40 min saline infusion, a progressively-increasing, stepwise infusion of GRP (60, 600, 1200 pmol/kg per h) or pentagastrin (PG) (2, 4, 8 micrograms/kg per h) was administered. Each drug dose was infused for 40-45 min and blood samples were drawn at 20-22.5 min intervals. GRP caused significant, dose-dependent increases in plasma ACTH (145 +/- 6%, 242 +/- 49%, 270 +/- 78% of control) and cortisol (158 +/- 16%, 218 +/- 26%, 250 +/- 62% of control). The dose of GRP required for a half-maximal cortisol response was 120 pmol/kg per h, while that for ACTH was 140 pmol/kg per h. PG had no effect on either ACTH or cortisol. While PG is apparently not involved in GRP/bombesin release of ACTH or cortisol, similar mechanisms of action for GRP and bombesin are suggested by their equimolar potencies.