Suppression of basal and stress-induced prolactin release and stimulation of luteinizing hormone secretion by alpha-melanocyte-stimulating hormone.
alpha-MSH and beta-endorphin, both synthesized from a common precursor, have opposite behavioral actions. In order to determine if these peptides have opposite effects on pituitary function, basal LH secretion and basal and stress-induced prolactin release were studied in adult male rats after intraventricular injection of alpha-MSH. Each rat also received intraventricular saline in order to serve as its own control. 18 micrograms alpha-MSH stimulated plasma LH from 16.5 +/- 2.5 (SEM) ng/ml to a peak of 27.2 +/- 4.0 and 26.0 +/- 4.9 ng/ml at 5 and 10 min, and suppressed prolactin from 3.5 +/- 0.7 ng/ml to 1.3 +/- 0.1 and 1.2 +/- 0.1 ng/ml at 15 and 30 min. Intraventricular alpha-MSH also significantly blunted the prolactin rise associated with the stress of swimming. 10 and 20 min after the onset of swimming, prolactin levels in rats pretreated with alpha-MSH were significantly diminished: 7.4 +/- 1.5 and 6.5 +/- 2.0 ng/ml vs 23.8 +/- 3.6 and 15.2 +/- 2.8 after normal saline. Similarly, des-acetyl alpha-MSH which is the predominant form of alpha-MSH in the hypothalamus, diminished the stress-induced prolactin rise from 18.4 +/- 5.3 and 11.2 +/- 3.4 ng/ml at 10 and 20 min to 10.0 +/- 2.4 and 5.5 +/- 1.6 ng/ml. We conclude that centrally administered alpha-MSH stimulates LH and suppresses basal and stress-induced prolactin release in male rats. These actions are opposite to those previously shown for beta-endorphin and suggest that alpha-MSH may antagonize the effects of beta-endorphin on pituitary function.
Newman
C B
CB
Wardlaw
S L
SL
Frantz
A G
AG
D000324:Adrenocorticotropic Hormone / Q000494:pharmacology; D000818:Animals; D007276:Injections, Intraventricular; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D008297:Male; D009074:Melanocyte-Stimulating Hormones / Q000502:physiology*; D010446:Peptide Fragments / Q000494:pharmacology; D011388:Prolactin / Q000097:blood / Q000378:metabolism*; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D013312:Stress, Physiological / Q000378:metabolism*; D013550:Swimming; D000521:alpha-MSH / Q000031:analogs & derivatives*
D010446:Peptide Fragments; D000521:alpha-MSH; D000324:Adrenocorticotropic Hormone; D011388:Prolactin; D007986:Luteinizing Hormone; D009074:Melanocyte-Stimulating Hormones