Lack of Modulation of Pituitary Hormone Stress Response by Neural Pathways Involving Opiate Receptors*

Abstract

To evaluate the role of the opiate—like peptidergic pathways in modulating thepituitaryhormone response to stress, we measured the GH, PRL, and cortisol responses to hypoglycemia and exercise in normal subjects with and without pretreatment with naloxone, given in the centrally active dose of 0.4 mg iv. Basal serum levels of GH, PRL, and cortisol were not changed significantly by prior naloxone administration. The maximum incremental response of GH to exercise was significantly blunted (13.1 ± 1.6 vs. 6.0 ± 1.4; P < 0.001) by priornaloxone administration.Pretreatment with naloxone did not affect the responses of GH, PRL, or cortisol to hypoglycemia orthe PRL response to L-dopa. On the basis of these studies we conclude that the.opiate—like peptidergic pathwaysare not important in the regulation of basal levels of GH, PRL, and cortisol and haveonly a modestmodulating influence on the stressinduced release of the hormones, which may be obscured in the face of severe stress.