The Effects of PGE<SUB>2</SUB>, 2-DG and L-arginine on Hypothalamic GHRH and SRIF Releases in Conscious Rats, with Respect to GH Secretion

Abstract

The effects of prostaglandin E2 (PGE2), 2-deoxy-D-glucose (2-DG) and L-arginine on hypothalamic GHRH and SRIF release with respect to GH secretion were studied in conscious male rats. Intracerebroventricular (icv) injection of 5 micrograms PGE2 and intravenous (iv) infusion of 1 g/kgBW L-arginine caused an increase in plasma GH levels, but icv (36 micrograms) or iv (400 mg/kgBW) injection of 2-DG suppressed spontaneous GH surge in conscious rats. The concentration of hypothalamic GHRH was decreased in all three groups of the animals, but the concentration of hypothalamic SRIF was decreased only in 2-DG-treated animals. In the perifusion system using rat hypothalamus, PGE2 (0.28 microM, 2.8 microM), 2-DG (22 mM) and L-arginine (3 mM) stimulated GHRH release from rat hypothalamus. 2-DG also stimulated SRIF release more predominantly than GHRH release. Passive immunization with anti-GHRH serum inhibited the GH secretion induced by icv injection of 5 micrograms PGE2 and by iv infusion of 1 g/kgBW L-arginine in conscious rats. In contrast, GH secretion induced by iv injection of 50 micrograms/kgBW PGE2 was not affected by the pretreatment with the antiserum. These results suggest that the central effect of PGE2 and peripheral effect of L-arginine to stimulate GH secretion are mediated by hypothalamic GHRH release, and that the inhibitory effect of 2-DG on GH secretion is predominantly mediated by hypothalamic SRIF release rather than GHRH release in rats.