AJP - Endocrinology and Metabolism, Vol 245, Issue 5 502-E507, Copyright © 1983 by American Physiological Society
Interaction of atropine with naloxone to alter anterior pituitary hormone secretion
X. Y. Huang and S. M. McCann
The effects of third ventricular injection of naloxone and atropine, alone
and together, on plasma concentrations of luteinizing hormone (LH),
follicle-stimulating hormone (FSH), prolactin (PRL), growth hormone (GH),
and thyroid-stimulating hormone (TSH) were studied in conscious,
ovariectomized (OVX) rats. Samples were removed from unrestrained rats that
had been previously implanted with an atrial cannula, and plasma hormone
levels were determined by radioimmunoassay. Intraventricular injection of
naloxone (30 micrograms) induced increases in plasma LH and GH
concentrations, decreased plasma PRL levels, but did not alter plasma TSH.
When atropine (100 micrograms) was injected intraventricularly, there was a
decrease in plasma LH and an increase in PRL levels but no alterations in
the levels of the other hormones. The action of naloxone on PRL and GH
release was eliminated by simultaneous administration of atropine, but
there was only a slight reduction in its effect on LH. The results indicate
that central cholinergic neurons may play an important role, via muscarinic
type receptors, in mediation of the effects of naloxone and presumably
opiates on PRL and GH release, whereas the effects on LH appear to proceed
independently of cholinergic neurons.
