Infusion of beta-endorphin has no suppressive effect on the releasing hormone-stimulated pituitary-adrenal-axis of normal human subjects.
The existence of a short-loop feedback inhibition of pituitary ACTH release by administration of beta-endorphin was postulated. However, data on the effect of peripherally administered beta-endorphin in humans are highly controversial. We infused human synthetic beta-endorphin at a constant rate of 1 microgram.kg-1.min-1 or normal saline to 7 normal volunteers for 90 min. Thirty min after starting the beta-endorphin or placebo infusion, releasing hormones were injected as a bolus iv (oCRH and GHRH 1 microgram/kg, GnRH 100 micrograms, TRH 200 micrograms) and blood was drawn for measurements of beta-endorphin immunoreactivity, all other pituitary hormones, and cortisol. Infusion of beta-endorphin resulted in high beta-endorphin plasma levels with a rapid decrease after the infusion was stopped. During the control infusion, beta-endorphin plasma levels rose in response to CRH. Plasma ACTH and serum cortisol levels in response to the releasing hormone were not different in subjects infused with beta-endorphin or placebo. The PRL response to TRH was significantly higher after beta-endorphin than after placebo (area under the stimulation curve 1209 +/- 183 vs 834 +/- 104 micrograms.l-1.h). There was no difference in the response of all other hormones measured. Our data on ACTH and cortisol secretion do not support the concept of a short-loop negative feedback of beta-endorphin acting at the site of the pituitary.
Schulte
H M
HM
I. Medizinische Klinik, Christian Albrechts Universität zu Kiel, FRG.
Allolio
B
B
D000324:Adrenocorticotropic Hormone / Q000378:metabolism; D000328:Adult; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology; D005246:Feedback; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007263:Infusions, Parenteral; D008297:Male; D010902:Pituitary Gland / Q000378:metabolism; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology; D010913:Pituitary-Adrenal System / Q000187:drug effects*; D011388:Prolactin / Q000097:blood; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D001615:beta-Endorphin / Q000493:pharmacokinetics / Q000494:pharmacology*
D010906:Pituitary Hormone-Releasing Hormones; D013973:Thyrotropin-Releasing Hormone; D001615:beta-Endorphin; D000324:Adrenocorticotropic Hormone; D011388:Prolactin; D003346:Corticotropin-Releasing Hormone; D013007:Growth Hormone-Releasing Hormone; D006854:Hydrocortisone