Neuroendocrine control of immunoreactive growth hormone and bioactive prolactin secretion in neonatal rats

Ontogeny and interactions between the serotonergic, cholinergic and alpha2-adrenergic systems

Bálint Kacsóh, B. Tóth, Clark E. Grosvenor

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Abstract

The effects of the α-agonist clonidine (CLO), the serotonin (5-HT) precursor 5-hydroxy-L- tryptophan (5-HTP), the 5-HT2/histamine (H1) antagonist cyproheptadine (CYPRO), the muscarinic cholinergic antagonist atropine (ATR), and an affinity-purified polyclonal antirat growth hormone-releasing hormone (rGHRH) immunoglobulin on serum concentrations of growth hormone (GH) and prolactin (PRL) were tested in 2- and 10-day-old litter- mate rat pups. Serum levels of GH and PRL were detected in RIA and Nb2 lymphoma bioassay, respectively. The effects of two different drugs either alone or in combination with each other were evaluated by two-factor analysis of variance. The data indicated that secretion of GH and PRL was regulated by α2-adrenergic, serotonergic and cholinergic mechanisms; the pathways regulating the two hormones, however, were distinct. 5-HTP stimulated GH secretion as early as day 2 postpartum via cholinergic mechanisms not involving GHRH; this pathway was also present in 10-day-old pups. An additional serotonergic pathway was functional in 10-day-old pups which mediated CLO-induced release of GH, and did not include cholinergic transmission. The α2-adrenergic regulation of GH secretion appeared to involve three distinct mechanisms:(1) a sexually uniform GH-stimulating α2-ad- renergic pathway was demonstrated with CLO in 2-day-old pups only after pretreatment with ATR;(2) a sexually dimorphic CLO-induced secretion of GH was observed that was mediated by mechanisms sensitive to CYPRO but not to ATR, and occurred by day 10; and (3) 5-HTP-induced GH secretion was counteracted by CLO in 10-day-old pups of both sexes indicating that a sexually uniform GH-inhibiting α2-adrenergic pathway was present. The concentration of PRL was not affected by 5-HTP up to day 10, and was decreased by ATR in 10-day-old (but not in 2-day-old) pups. Secretion of GH and PRL appeared to be stimulated by different sets of cholinergic neurons because (1) ATR inhibited GH secretion on day 2 but inhibition of PRL secretion appeared later, and (2) CLO-induced PRL secretion was diminished by ATR, whereas CLO-induced release of GH was not affected in 10-day-old pups. CYPRO increased serum levels of PRL in 10-day-old pups;thus. PRL-in- hibiting network was functional at this age. Whether the inhibition of this pathway was due to the serotonin, histamine (H1) or dopamine antagonist action of CYPRO requires further investigation.

Original languageEnglish
Pages (from-to)195-203
Number of pages9
JournalNeuroendocrinology
Volume57
Issue number2
DOIs
Publication statusPublished - 1993

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Prolactin
Adrenergic Agents
Cholinergic Agents
Growth Hormone
Clonidine
Atropine
Cyproheptadine
5-Hydroxytryptophan
Tryptophan
Histamine H1 Antagonists
Serotonin
Serum
Serotonin Receptor Agonists
Growth Hormone-Releasing Hormone
Cholinergic Neurons
Muscarinic Antagonists
Dopamine Antagonists
Biological Assay
Postpartum Period
Statistical Factor Analysis

Keywords

  • 5-HTP
  • Atropine
  • Clonidine
  • Cyproheptadine
  • Growth hormone-releasing hormone
  • Nb2 lymphoma assay

ASJC Scopus subject areas

  • Endocrinology
  • Endocrinology, Diabetes and Metabolism
  • Cellular and Molecular Neuroscience
  • Endocrine and Autonomic Systems
  • Neuroscience(all)

Cite this

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title = "Neuroendocrine control of immunoreactive growth hormone and bioactive prolactin secretion in neonatal rats: Ontogeny and interactions between the serotonergic, cholinergic and alpha2-adrenergic systems",
abstract = "The effects of the α-agonist clonidine (CLO), the serotonin (5-HT) precursor 5-hydroxy-L- tryptophan (5-HTP), the 5-HT2/histamine (H1) antagonist cyproheptadine (CYPRO), the muscarinic cholinergic antagonist atropine (ATR), and an affinity-purified polyclonal antirat growth hormone-releasing hormone (rGHRH) immunoglobulin on serum concentrations of growth hormone (GH) and prolactin (PRL) were tested in 2- and 10-day-old litter- mate rat pups. Serum levels of GH and PRL were detected in RIA and Nb2 lymphoma bioassay, respectively. The effects of two different drugs either alone or in combination with each other were evaluated by two-factor analysis of variance. The data indicated that secretion of GH and PRL was regulated by α2-adrenergic, serotonergic and cholinergic mechanisms; the pathways regulating the two hormones, however, were distinct. 5-HTP stimulated GH secretion as early as day 2 postpartum via cholinergic mechanisms not involving GHRH; this pathway was also present in 10-day-old pups. An additional serotonergic pathway was functional in 10-day-old pups which mediated CLO-induced release of GH, and did not include cholinergic transmission. The α2-adrenergic regulation of GH secretion appeared to involve three distinct mechanisms:(1) a sexually uniform GH-stimulating α2-ad- renergic pathway was demonstrated with CLO in 2-day-old pups only after pretreatment with ATR;(2) a sexually dimorphic CLO-induced secretion of GH was observed that was mediated by mechanisms sensitive to CYPRO but not to ATR, and occurred by day 10; and (3) 5-HTP-induced GH secretion was counteracted by CLO in 10-day-old pups of both sexes indicating that a sexually uniform GH-inhibiting α2-adrenergic pathway was present. The concentration of PRL was not affected by 5-HTP up to day 10, and was decreased by ATR in 10-day-old (but not in 2-day-old) pups. Secretion of GH and PRL appeared to be stimulated by different sets of cholinergic neurons because (1) ATR inhibited GH secretion on day 2 but inhibition of PRL secretion appeared later, and (2) CLO-induced PRL secretion was diminished by ATR, whereas CLO-induced release of GH was not affected in 10-day-old pups. CYPRO increased serum levels of PRL in 10-day-old pups;thus. PRL-in- hibiting network was functional at this age. Whether the inhibition of this pathway was due to the serotonin, histamine (H1) or dopamine antagonist action of CYPRO requires further investigation.",
keywords = "5-HTP, Atropine, Clonidine, Cyproheptadine, Growth hormone-releasing hormone, Nb2 lymphoma assay",
author = "B{\'a}lint Kacs{\'o}h and B. T{\'o}th and Grosvenor, {Clark E.}",
year = "1993",
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journal = "Neuroendocrinology",
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T1 - Neuroendocrine control of immunoreactive growth hormone and bioactive prolactin secretion in neonatal rats

T2 - Ontogeny and interactions between the serotonergic, cholinergic and alpha2-adrenergic systems

AU - Kacsóh, Bálint

AU - Tóth, B.

AU - Grosvenor, Clark E.

PY - 1993

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N2 - The effects of the α-agonist clonidine (CLO), the serotonin (5-HT) precursor 5-hydroxy-L- tryptophan (5-HTP), the 5-HT2/histamine (H1) antagonist cyproheptadine (CYPRO), the muscarinic cholinergic antagonist atropine (ATR), and an affinity-purified polyclonal antirat growth hormone-releasing hormone (rGHRH) immunoglobulin on serum concentrations of growth hormone (GH) and prolactin (PRL) were tested in 2- and 10-day-old litter- mate rat pups. Serum levels of GH and PRL were detected in RIA and Nb2 lymphoma bioassay, respectively. The effects of two different drugs either alone or in combination with each other were evaluated by two-factor analysis of variance. The data indicated that secretion of GH and PRL was regulated by α2-adrenergic, serotonergic and cholinergic mechanisms; the pathways regulating the two hormones, however, were distinct. 5-HTP stimulated GH secretion as early as day 2 postpartum via cholinergic mechanisms not involving GHRH; this pathway was also present in 10-day-old pups. An additional serotonergic pathway was functional in 10-day-old pups which mediated CLO-induced release of GH, and did not include cholinergic transmission. The α2-adrenergic regulation of GH secretion appeared to involve three distinct mechanisms:(1) a sexually uniform GH-stimulating α2-ad- renergic pathway was demonstrated with CLO in 2-day-old pups only after pretreatment with ATR;(2) a sexually dimorphic CLO-induced secretion of GH was observed that was mediated by mechanisms sensitive to CYPRO but not to ATR, and occurred by day 10; and (3) 5-HTP-induced GH secretion was counteracted by CLO in 10-day-old pups of both sexes indicating that a sexually uniform GH-inhibiting α2-adrenergic pathway was present. The concentration of PRL was not affected by 5-HTP up to day 10, and was decreased by ATR in 10-day-old (but not in 2-day-old) pups. Secretion of GH and PRL appeared to be stimulated by different sets of cholinergic neurons because (1) ATR inhibited GH secretion on day 2 but inhibition of PRL secretion appeared later, and (2) CLO-induced PRL secretion was diminished by ATR, whereas CLO-induced release of GH was not affected in 10-day-old pups. CYPRO increased serum levels of PRL in 10-day-old pups;thus. PRL-in- hibiting network was functional at this age. Whether the inhibition of this pathway was due to the serotonin, histamine (H1) or dopamine antagonist action of CYPRO requires further investigation.

AB - The effects of the α-agonist clonidine (CLO), the serotonin (5-HT) precursor 5-hydroxy-L- tryptophan (5-HTP), the 5-HT2/histamine (H1) antagonist cyproheptadine (CYPRO), the muscarinic cholinergic antagonist atropine (ATR), and an affinity-purified polyclonal antirat growth hormone-releasing hormone (rGHRH) immunoglobulin on serum concentrations of growth hormone (GH) and prolactin (PRL) were tested in 2- and 10-day-old litter- mate rat pups. Serum levels of GH and PRL were detected in RIA and Nb2 lymphoma bioassay, respectively. The effects of two different drugs either alone or in combination with each other were evaluated by two-factor analysis of variance. The data indicated that secretion of GH and PRL was regulated by α2-adrenergic, serotonergic and cholinergic mechanisms; the pathways regulating the two hormones, however, were distinct. 5-HTP stimulated GH secretion as early as day 2 postpartum via cholinergic mechanisms not involving GHRH; this pathway was also present in 10-day-old pups. An additional serotonergic pathway was functional in 10-day-old pups which mediated CLO-induced release of GH, and did not include cholinergic transmission. The α2-adrenergic regulation of GH secretion appeared to involve three distinct mechanisms:(1) a sexually uniform GH-stimulating α2-ad- renergic pathway was demonstrated with CLO in 2-day-old pups only after pretreatment with ATR;(2) a sexually dimorphic CLO-induced secretion of GH was observed that was mediated by mechanisms sensitive to CYPRO but not to ATR, and occurred by day 10; and (3) 5-HTP-induced GH secretion was counteracted by CLO in 10-day-old pups of both sexes indicating that a sexually uniform GH-inhibiting α2-adrenergic pathway was present. The concentration of PRL was not affected by 5-HTP up to day 10, and was decreased by ATR in 10-day-old (but not in 2-day-old) pups. Secretion of GH and PRL appeared to be stimulated by different sets of cholinergic neurons because (1) ATR inhibited GH secretion on day 2 but inhibition of PRL secretion appeared later, and (2) CLO-induced PRL secretion was diminished by ATR, whereas CLO-induced release of GH was not affected in 10-day-old pups. CYPRO increased serum levels of PRL in 10-day-old pups;thus. PRL-in- hibiting network was functional at this age. Whether the inhibition of this pathway was due to the serotonin, histamine (H1) or dopamine antagonist action of CYPRO requires further investigation.

KW - 5-HTP

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