The suppression of pulsatile luteinizing hormone secretion during lactation in the rat

S. R. Fox, M (Susan) Smith

Research output: Contribution to journalArticle

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Abstract

The inhibition of LH secretion during lactation may be the consequence of a pituitary insensitivity to GnRH stimulation and/or an inhibition of GnRH release from the hypothalamus. To assess the contribution that these mechanisms may make to the suppression of LH secretion during lactation, we described the pattern of LH secretion in lactating rats and the magnitude of LH secretion in response to a GnRH stimulus. We assessed the effect of the strength of the suckling stimulus (two and eight pups), the length of lactation (5 and 10 days), and the presence of the ovaries on the pattern of LH secretion. We also examined the pattern of LH secretion after removal of a large suckling stimulus. In the intact rat, the pattern of LH secretion during lactation was uniformly nonpulsatile, despite significant differences between animals suckling two and eight pups in pituitary responsiveness to GnRH. In intact rats suckling two pups during day 10 of lactation, significant LH secretion was stimulated by 0.4-ng pulses of GnRH every 50 min, while animals with eight pups secreted little LH in response to the same stimulus. It was concluded that a two-pup suckling stimulus was sufficient to cmpletely suppress pulsatile GnRH release without affecting pituitary function, whereas an eight-pup suckling stimulus also depressed pituitary sensitivity to GnRH. In ovariectomized (ovx) rats suckling two pups, seven of nine animals showed no postcastration rise in LH secretion or evidence of pulsatile LH secretion during day 5 of lactation. In the remaining two animals, a castrate pattern of pulsatile LH secretion was observed, with a LH interpulse interval of 31 ± 6 min. By day 10 of lactation, all animals suckling two pups had castration patterns of LH secretion, with a LH interpulse interval of 35 ± 2 min, which was significantly different from the LH interpulse interval of 26 ± 1 min observed in ovx animals without pups. Therefore, a two-pup suckling stimulus is capable of retarding the increase in LH pulse frequency characteristically seen in the rat after castration. In ovx rats suckling eight pups, the postcastration rise in LH secretion was completely inhibited in all animals examined on days 5 and 10 of lactation, and the pattern of LH secretion was uniformly nonpulsatile. A consistent pattern of pulsatile LH secretion was not reinitiated until 72 h after removal of the suckling stimulus (LH interpulse interval 31 ± 2 min). These data demonstrate that the suppression of LH secretion during lactation is the result of 1) a profound suppression of GnRH release from the hypothalamus wrought by the suckling stimulus itself and by an ovarian factor and 2) a decrease in pituitary responsiveness to GnRH stimulation in the presence of a large suckling stimulus.

Original languageEnglish (US)
Pages (from-to)2045-2051
Number of pages7
JournalEndocrinology
Volume115
Issue number6
StatePublished - 1984
Externally publishedYes

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Luteinizing Hormone
Lactation
Gonadotropin-Releasing Hormone
Suckling Animals
Castration
Hypothalamus
Ovary

ASJC Scopus subject areas

  • Endocrinology
  • Endocrinology, Diabetes and Metabolism

Cite this

The suppression of pulsatile luteinizing hormone secretion during lactation in the rat. / Fox, S. R.; Smith, M (Susan).

In: Endocrinology, Vol. 115, No. 6, 1984, p. 2045-2051.

Research output: Contribution to journalArticle

Fox, S. R. ; Smith, M (Susan). / The suppression of pulsatile luteinizing hormone secretion during lactation in the rat. In: Endocrinology. 1984 ; Vol. 115, No. 6. pp. 2045-2051.
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