Localization of [I-125]IGF-I binding on the ovine pars tuberalis

Lynda Williams, Denise Kelly, L T Hannah, Peter John Morgan

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

In the sheep, it has been shown that the pars tuberalis of the pituitary may mediate the photoperiodic control of seasonal changes in prolactin secretion. High concentrations of melatonin receptors are present on the ovine pars tuberalis and melatonin is known to inhibit forskolin-stimulated cyclic AMP production in this tissue. Other hormonal inputs to the ovine pars tuberalis have not yet been identified. In the rat mRNA for the IGF-I receptor has been identified in the pars tuberalis using in situ hybridization. In order to define whether IGF-I may influence the function of the ovine pars tuberalis the presence of receptors for IGF-I has been investigated, Using in vitro autoradiography specific [I-125]IGF-I binding was found in high concentrations over the ovine pars tuberalis particularly associated with certain of the capillaries. Homogenate receptor assays showed saturable specific binding of [I-125]IGF-I With a mean dissociation constant (Kd) of 0.5 +/- 0.1 nM (n=4). Competition studies revealed a rank order of potency of IGF-I > IGF-II > > > insulin, in displacing [I-125]IGF-I binding, indicative of a mixed population of IGF-I and IGF-II/mannose-6-phosphate receptors and insulin-like growth factor binding proteins (IGFBPs), Cross-linking of [I-125]IGF-I to pars tuberalis membrane homogenates and analysis by SDS-PAGE under reducing conditions confirmed the presence of both IGF-I receptors and binding proteins, Autophosphorylation of a 97 kDa substrate, compatible with the beta-sub-unit of the IGF-I receptor, was increased in the presence of IGF-I, indicating the existence of functional IGF-I receptors on the ovine pars tuberalis. In contrast in the rat [I-125]IGF-I binding was restricted to the median eminence region of the brain and was not detectable over the pars tuberalis.

Original languageEnglish
Pages (from-to)931-938
Number of pages8
JournalJournal of Neuroendocrinology
Volume7
Issue number12
Publication statusPublished - Dec 1995

Keywords

  • pars tuberalis
  • IGF-I receptor
  • sheep
  • median eminence
  • rats
  • growth factor-I
  • insulin
  • pituitary
  • receptors
  • rat
  • sites
  • phosphorylation
  • brain
  • hypothalamus
  • expression

Cite this

Localization of [I-125]IGF-I binding on the ovine pars tuberalis. / Williams, Lynda; Kelly, Denise; Hannah, L T ; Morgan, Peter John.

In: Journal of Neuroendocrinology, Vol. 7, No. 12, 12.1995, p. 931-938.

Research output: Contribution to journalArticle

Williams, L, Kelly, D, Hannah, LT & Morgan, PJ 1995, 'Localization of [I-125]IGF-I binding on the ovine pars tuberalis', Journal of Neuroendocrinology, vol. 7, no. 12, pp. 931-938.
Williams, Lynda ; Kelly, Denise ; Hannah, L T ; Morgan, Peter John. / Localization of [I-125]IGF-I binding on the ovine pars tuberalis. In: Journal of Neuroendocrinology. 1995 ; Vol. 7, No. 12. pp. 931-938.
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AU - Williams, Lynda

AU - Kelly, Denise

AU - Hannah, L T

AU - Morgan, Peter John

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N2 - In the sheep, it has been shown that the pars tuberalis of the pituitary may mediate the photoperiodic control of seasonal changes in prolactin secretion. High concentrations of melatonin receptors are present on the ovine pars tuberalis and melatonin is known to inhibit forskolin-stimulated cyclic AMP production in this tissue. Other hormonal inputs to the ovine pars tuberalis have not yet been identified. In the rat mRNA for the IGF-I receptor has been identified in the pars tuberalis using in situ hybridization. In order to define whether IGF-I may influence the function of the ovine pars tuberalis the presence of receptors for IGF-I has been investigated, Using in vitro autoradiography specific [I-125]IGF-I binding was found in high concentrations over the ovine pars tuberalis particularly associated with certain of the capillaries. Homogenate receptor assays showed saturable specific binding of [I-125]IGF-I With a mean dissociation constant (Kd) of 0.5 +/- 0.1 nM (n=4). Competition studies revealed a rank order of potency of IGF-I > IGF-II > > > insulin, in displacing [I-125]IGF-I binding, indicative of a mixed population of IGF-I and IGF-II/mannose-6-phosphate receptors and insulin-like growth factor binding proteins (IGFBPs), Cross-linking of [I-125]IGF-I to pars tuberalis membrane homogenates and analysis by SDS-PAGE under reducing conditions confirmed the presence of both IGF-I receptors and binding proteins, Autophosphorylation of a 97 kDa substrate, compatible with the beta-sub-unit of the IGF-I receptor, was increased in the presence of IGF-I, indicating the existence of functional IGF-I receptors on the ovine pars tuberalis. In contrast in the rat [I-125]IGF-I binding was restricted to the median eminence region of the brain and was not detectable over the pars tuberalis.

AB - In the sheep, it has been shown that the pars tuberalis of the pituitary may mediate the photoperiodic control of seasonal changes in prolactin secretion. High concentrations of melatonin receptors are present on the ovine pars tuberalis and melatonin is known to inhibit forskolin-stimulated cyclic AMP production in this tissue. Other hormonal inputs to the ovine pars tuberalis have not yet been identified. In the rat mRNA for the IGF-I receptor has been identified in the pars tuberalis using in situ hybridization. In order to define whether IGF-I may influence the function of the ovine pars tuberalis the presence of receptors for IGF-I has been investigated, Using in vitro autoradiography specific [I-125]IGF-I binding was found in high concentrations over the ovine pars tuberalis particularly associated with certain of the capillaries. Homogenate receptor assays showed saturable specific binding of [I-125]IGF-I With a mean dissociation constant (Kd) of 0.5 +/- 0.1 nM (n=4). Competition studies revealed a rank order of potency of IGF-I > IGF-II > > > insulin, in displacing [I-125]IGF-I binding, indicative of a mixed population of IGF-I and IGF-II/mannose-6-phosphate receptors and insulin-like growth factor binding proteins (IGFBPs), Cross-linking of [I-125]IGF-I to pars tuberalis membrane homogenates and analysis by SDS-PAGE under reducing conditions confirmed the presence of both IGF-I receptors and binding proteins, Autophosphorylation of a 97 kDa substrate, compatible with the beta-sub-unit of the IGF-I receptor, was increased in the presence of IGF-I, indicating the existence of functional IGF-I receptors on the ovine pars tuberalis. In contrast in the rat [I-125]IGF-I binding was restricted to the median eminence region of the brain and was not detectable over the pars tuberalis.

KW - pars tuberalis

KW - IGF-I receptor

KW - sheep

KW - median eminence

KW - rats

KW - growth factor-I

KW - insulin

KW - pituitary

KW - receptors

KW - rat

KW - sites

KW - phosphorylation

KW - brain

KW - hypothalamus

KW - expression

M3 - Article

VL - 7

SP - 931

EP - 938

JO - Journal of Neuroendocrinology

JF - Journal of Neuroendocrinology

SN - 0953-8194

IS - 12

ER -