Effects of insulin-like growth factor-1 on luteinizing hormone secretion in sheep

Clare Lesley Adam, P.A. Findlay, A H Moore

Research output: Contribution to journalArticle

28 Citations (Scopus)

Abstract

Circulating insulin-like growth factor-1 (IGF-1) may be involved in nutritional modulation of reproductive status. Acute effects of IGF-1 on luteinizing hormone (LH) secretion were studied in two experiments, each using eight castrate male sheep surgically prepared with an elevated carotid artery, four with (E +) and four without (E -) subcutaneous oestradiol implants. Blood samples were taken every 12 min for 8 h at weekly intervals, with IGF-1 given at 4 h. In Experiment 1, sheep were fed to maintain live weight (maintenance) and IGF-1 doses tested were 25, 50, 100 and 150 mu g kg(-1) given via the carotid (i.c.). Plasma LH concentrations were 6.2 +/- 0.35 (E -) and 4.2 +/- 0.49 (E +) ng ml(-1) pre-IGF-1, were increased after 25 mu g kg(-1) IGF-1 (E -, 15%; E +, 11%) but were either unaltered (E -) or decreased (E +, -16%) after 150 mu g kg(-1); thus, mean LH response was negatively related to IGF-1 dose (E -, b = -0.007, P < 0.01; E +, b = -0.011, P < 0.05). LH pulse frequencies (p.f.) were 4.6 +/- 0.42 (E -) and 3.9 +/- 0.35 (E +) pulses per 4 h pre-IGF-1, were unaltered after 25 mu g kg(-1) IGF-1, but were decreased after 150 mu g kg(-1) (E -, -33%; E +, -51%); thus, p.f. was also negatively related to IGF-1 dose (E -, b = -0.016, P < 0.01; E +, b = -0.019, P > 0.05). LH pulse amplitude and baseline were not significantly altered by IGF-1. Plasma glucose concentrations decreased after 100 and 150 mu g kg(-1) IGF-1 from 3.40 to 2.50 and 2.34 mmol l(-1), respectively (SED 0.314, P < 0.001), but were not significantly altered after lower doses. Thus, hypoglycaemia caused LH inhibition after higher doses of IGF-1, which counteracted CE -) or overcame (E +) the stimulatory effects on LH seen after lower doses. In Experiment 2, sheep were fed 50% maintenance; saline vehicle i.c., then IGF-1 doses 25 and 50 mu g kg(-1) given i.c. or i.v, were tested. In E - and E + sheep, respectively, mean LH pre-IGF-1 was 8.7 +/- 0.97 and 1.9 +/- 0.16 ng ml(-1), p.f. was 3.8 +/- 0.44 and 0.8 +/- 0.44 pulses per 4 h, and amplitude was 3.6 +/- 0.49 and 0.4 +/- 0.08 ng ml(-1). Saline vehicle had no effect on LH. IGF-1 at both doses and by both administration routes in E-sheep increased mean LH (22-29%, P < 0.001), and in E + sheep increased mean LH(12-36%, P < 0.001), p.f. (94-219%, P < 0.001) and amplitude (125-803%, P < 0.01). Thus, low doses of peripherally-administered IGF-1 stimulated LH output in sheep, consistent with its putative physiological role as a nutritional modulator of reproduction. (C) 1997 Elsevier Science B.V.

Original languageEnglish
Pages (from-to)45-56
Number of pages12
JournalAnimal Reproduction Science
Volume50
Issue number1-2
DOIs
Publication statusPublished - 27 Feb 1998

Keywords

  • sheep endocrinology
  • LH
  • insulin-like growth factor-1
  • IGF-I BINDING
  • PITUITARY-GLAND
  • FEMALE PUBERTY
  • ESTROGEN
  • PLASMA
  • LOCALIZATION
  • MECHANISM
  • RECEPTORS
  • ESTRADIOL
  • RELEASE
  • insulin-like growth factor-1
  • IGF-I binding
  • pituitary-gland
  • female puberty
  • estrogen
  • plasma
  • localization
  • mechanism
  • receptors
  • estradiol
  • release

Cite this

Effects of insulin-like growth factor-1 on luteinizing hormone secretion in sheep. / Adam, Clare Lesley; Findlay, P.A. ; Moore, A H .

In: Animal Reproduction Science, Vol. 50, No. 1-2, 27.02.1998, p. 45-56.

Research output: Contribution to journalArticle

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abstract = "Circulating insulin-like growth factor-1 (IGF-1) may be involved in nutritional modulation of reproductive status. Acute effects of IGF-1 on luteinizing hormone (LH) secretion were studied in two experiments, each using eight castrate male sheep surgically prepared with an elevated carotid artery, four with (E +) and four without (E -) subcutaneous oestradiol implants. Blood samples were taken every 12 min for 8 h at weekly intervals, with IGF-1 given at 4 h. In Experiment 1, sheep were fed to maintain live weight (maintenance) and IGF-1 doses tested were 25, 50, 100 and 150 mu g kg(-1) given via the carotid (i.c.). Plasma LH concentrations were 6.2 +/- 0.35 (E -) and 4.2 +/- 0.49 (E +) ng ml(-1) pre-IGF-1, were increased after 25 mu g kg(-1) IGF-1 (E -, 15{\%}; E +, 11{\%}) but were either unaltered (E -) or decreased (E +, -16{\%}) after 150 mu g kg(-1); thus, mean LH response was negatively related to IGF-1 dose (E -, b = -0.007, P < 0.01; E +, b = -0.011, P < 0.05). LH pulse frequencies (p.f.) were 4.6 +/- 0.42 (E -) and 3.9 +/- 0.35 (E +) pulses per 4 h pre-IGF-1, were unaltered after 25 mu g kg(-1) IGF-1, but were decreased after 150 mu g kg(-1) (E -, -33{\%}; E +, -51{\%}); thus, p.f. was also negatively related to IGF-1 dose (E -, b = -0.016, P < 0.01; E +, b = -0.019, P > 0.05). LH pulse amplitude and baseline were not significantly altered by IGF-1. Plasma glucose concentrations decreased after 100 and 150 mu g kg(-1) IGF-1 from 3.40 to 2.50 and 2.34 mmol l(-1), respectively (SED 0.314, P < 0.001), but were not significantly altered after lower doses. Thus, hypoglycaemia caused LH inhibition after higher doses of IGF-1, which counteracted CE -) or overcame (E +) the stimulatory effects on LH seen after lower doses. In Experiment 2, sheep were fed 50{\%} maintenance; saline vehicle i.c., then IGF-1 doses 25 and 50 mu g kg(-1) given i.c. or i.v, were tested. In E - and E + sheep, respectively, mean LH pre-IGF-1 was 8.7 +/- 0.97 and 1.9 +/- 0.16 ng ml(-1), p.f. was 3.8 +/- 0.44 and 0.8 +/- 0.44 pulses per 4 h, and amplitude was 3.6 +/- 0.49 and 0.4 +/- 0.08 ng ml(-1). Saline vehicle had no effect on LH. IGF-1 at both doses and by both administration routes in E-sheep increased mean LH (22-29{\%}, P < 0.001), and in E + sheep increased mean LH(12-36{\%}, P < 0.001), p.f. (94-219{\%}, P < 0.001) and amplitude (125-803{\%}, P < 0.01). Thus, low doses of peripherally-administered IGF-1 stimulated LH output in sheep, consistent with its putative physiological role as a nutritional modulator of reproduction. (C) 1997 Elsevier Science B.V.",
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T1 - Effects of insulin-like growth factor-1 on luteinizing hormone secretion in sheep

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AU - Findlay, P.A.

AU - Moore, A H

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N2 - Circulating insulin-like growth factor-1 (IGF-1) may be involved in nutritional modulation of reproductive status. Acute effects of IGF-1 on luteinizing hormone (LH) secretion were studied in two experiments, each using eight castrate male sheep surgically prepared with an elevated carotid artery, four with (E +) and four without (E -) subcutaneous oestradiol implants. Blood samples were taken every 12 min for 8 h at weekly intervals, with IGF-1 given at 4 h. In Experiment 1, sheep were fed to maintain live weight (maintenance) and IGF-1 doses tested were 25, 50, 100 and 150 mu g kg(-1) given via the carotid (i.c.). Plasma LH concentrations were 6.2 +/- 0.35 (E -) and 4.2 +/- 0.49 (E +) ng ml(-1) pre-IGF-1, were increased after 25 mu g kg(-1) IGF-1 (E -, 15%; E +, 11%) but were either unaltered (E -) or decreased (E +, -16%) after 150 mu g kg(-1); thus, mean LH response was negatively related to IGF-1 dose (E -, b = -0.007, P < 0.01; E +, b = -0.011, P < 0.05). LH pulse frequencies (p.f.) were 4.6 +/- 0.42 (E -) and 3.9 +/- 0.35 (E +) pulses per 4 h pre-IGF-1, were unaltered after 25 mu g kg(-1) IGF-1, but were decreased after 150 mu g kg(-1) (E -, -33%; E +, -51%); thus, p.f. was also negatively related to IGF-1 dose (E -, b = -0.016, P < 0.01; E +, b = -0.019, P > 0.05). LH pulse amplitude and baseline were not significantly altered by IGF-1. Plasma glucose concentrations decreased after 100 and 150 mu g kg(-1) IGF-1 from 3.40 to 2.50 and 2.34 mmol l(-1), respectively (SED 0.314, P < 0.001), but were not significantly altered after lower doses. Thus, hypoglycaemia caused LH inhibition after higher doses of IGF-1, which counteracted CE -) or overcame (E +) the stimulatory effects on LH seen after lower doses. In Experiment 2, sheep were fed 50% maintenance; saline vehicle i.c., then IGF-1 doses 25 and 50 mu g kg(-1) given i.c. or i.v, were tested. In E - and E + sheep, respectively, mean LH pre-IGF-1 was 8.7 +/- 0.97 and 1.9 +/- 0.16 ng ml(-1), p.f. was 3.8 +/- 0.44 and 0.8 +/- 0.44 pulses per 4 h, and amplitude was 3.6 +/- 0.49 and 0.4 +/- 0.08 ng ml(-1). Saline vehicle had no effect on LH. IGF-1 at both doses and by both administration routes in E-sheep increased mean LH (22-29%, P < 0.001), and in E + sheep increased mean LH(12-36%, P < 0.001), p.f. (94-219%, P < 0.001) and amplitude (125-803%, P < 0.01). Thus, low doses of peripherally-administered IGF-1 stimulated LH output in sheep, consistent with its putative physiological role as a nutritional modulator of reproduction. (C) 1997 Elsevier Science B.V.

AB - Circulating insulin-like growth factor-1 (IGF-1) may be involved in nutritional modulation of reproductive status. Acute effects of IGF-1 on luteinizing hormone (LH) secretion were studied in two experiments, each using eight castrate male sheep surgically prepared with an elevated carotid artery, four with (E +) and four without (E -) subcutaneous oestradiol implants. Blood samples were taken every 12 min for 8 h at weekly intervals, with IGF-1 given at 4 h. In Experiment 1, sheep were fed to maintain live weight (maintenance) and IGF-1 doses tested were 25, 50, 100 and 150 mu g kg(-1) given via the carotid (i.c.). Plasma LH concentrations were 6.2 +/- 0.35 (E -) and 4.2 +/- 0.49 (E +) ng ml(-1) pre-IGF-1, were increased after 25 mu g kg(-1) IGF-1 (E -, 15%; E +, 11%) but were either unaltered (E -) or decreased (E +, -16%) after 150 mu g kg(-1); thus, mean LH response was negatively related to IGF-1 dose (E -, b = -0.007, P < 0.01; E +, b = -0.011, P < 0.05). LH pulse frequencies (p.f.) were 4.6 +/- 0.42 (E -) and 3.9 +/- 0.35 (E +) pulses per 4 h pre-IGF-1, were unaltered after 25 mu g kg(-1) IGF-1, but were decreased after 150 mu g kg(-1) (E -, -33%; E +, -51%); thus, p.f. was also negatively related to IGF-1 dose (E -, b = -0.016, P < 0.01; E +, b = -0.019, P > 0.05). LH pulse amplitude and baseline were not significantly altered by IGF-1. Plasma glucose concentrations decreased after 100 and 150 mu g kg(-1) IGF-1 from 3.40 to 2.50 and 2.34 mmol l(-1), respectively (SED 0.314, P < 0.001), but were not significantly altered after lower doses. Thus, hypoglycaemia caused LH inhibition after higher doses of IGF-1, which counteracted CE -) or overcame (E +) the stimulatory effects on LH seen after lower doses. In Experiment 2, sheep were fed 50% maintenance; saline vehicle i.c., then IGF-1 doses 25 and 50 mu g kg(-1) given i.c. or i.v, were tested. In E - and E + sheep, respectively, mean LH pre-IGF-1 was 8.7 +/- 0.97 and 1.9 +/- 0.16 ng ml(-1), p.f. was 3.8 +/- 0.44 and 0.8 +/- 0.44 pulses per 4 h, and amplitude was 3.6 +/- 0.49 and 0.4 +/- 0.08 ng ml(-1). Saline vehicle had no effect on LH. IGF-1 at both doses and by both administration routes in E-sheep increased mean LH (22-29%, P < 0.001), and in E + sheep increased mean LH(12-36%, P < 0.001), p.f. (94-219%, P < 0.001) and amplitude (125-803%, P < 0.01). Thus, low doses of peripherally-administered IGF-1 stimulated LH output in sheep, consistent with its putative physiological role as a nutritional modulator of reproduction. (C) 1997 Elsevier Science B.V.

KW - sheep endocrinology

KW - LH

KW - insulin-like growth factor-1

KW - IGF-I BINDING

KW - PITUITARY-GLAND

KW - FEMALE PUBERTY

KW - ESTROGEN

KW - PLASMA

KW - LOCALIZATION

KW - MECHANISM

KW - RECEPTORS

KW - ESTRADIOL

KW - RELEASE

KW - insulin-like growth factor-1

KW - IGF-I binding

KW - pituitary-gland

KW - female puberty

KW - estrogen

KW - plasma

KW - localization

KW - mechanism

KW - receptors

KW - estradiol

KW - release

U2 - 10.1016/S0378-4320(97)00089-4

DO - 10.1016/S0378-4320(97)00089-4

M3 - Article

VL - 50

SP - 45

EP - 56

JO - Animal Reproduction Science

JF - Animal Reproduction Science

SN - 0378-4320

IS - 1-2

ER -