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United States Department of Agriculture

Agricultural Research Service

Title: Insulin-Like Growth Factor-I, Insulin-Like Growth Factor-Binding Proteins, and Gonadotropins in the Hypothalamic-Pituitary Axis and Serum of Nutrient-Restricted Ewes

Authors
item Snyder, Jason - UNIV WYOMING, LARAMIE
item Clapper, Jeffrey - UNIV WYOMING, LARAMIE
item ROBERTS, ANDREW
item Sanson, Dave - UNIV WYOMING, LARAMIE
item Hamernik, Debora - UNIV ARIZONA, TUCSON
item Moss, Gary - UNIV WYOMING, LARAMIE

Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 5, 1999
Publication Date: N/A

Interpretive Summary: Inadequate nutritional intake results in the shut down of reproductive processes by what appears to be a disruption in normal secretion of reproductive hormones from the hypothalamus and pituitary that stimulate gonadal function. Mechanisms by which an animal perceives itself to be in a state of nutritional deficit remain to be identified. Results from this research provide evidence that nutritionally induced changes in levels of the metabolic hormone, insulin-like growth factor-1 (IGF-1) and IGF binding proteins (IGFBPs) may provide a mechanism by which nutritional stress alters reproductive function. Nutritional restriction of ewes was associated with decreased circulating levels of IGF-1 and changes in IGFBPs. Nutritional restriction of ewes also altered levels of IGFBPs in the hypothalamus and pituitary. Previous cell culture work indicates that IGF-1 may enhance the ability of the hypothalamus and pituitary to secrete hormones required for the maintenance of reproductive function. The ability of tissues to respond to IGF-1 is dependent on the levels of IGF-1 reaching the tissues, which is modulated by the levels of IGFBPs present in individual tissues. Thus diminished circulating levels of IGF-1 and altered levels of IGFBPs within the hypothalamic-pituitary axis may provide a mechanism by which animals perceive nutritional stress and shut down reproductive function in order to ensure self preservation.

Technical Abstract: Body condition scores (BCS) of ovariectomized estradiol-treated ewes were controlled to examine effects of suboptimum BCS on insulin-like growth factor (IGF)-I, IGF-binding proteins (IGFBPs), and LH in the anterior pituitary gland, hypophyseal stalk-median eminence (SME), and circulation. Serum LH increased in ewes with BCS (1 = emaciated, 9 = obese) > 3 (HIGH-BCS), but not in ewes with BCS 3 (LOW-BCS), after onset of the breeding season. Concentrations of LH and LHá subunits in anterior pituitary glands were lower in LOW-BCS than in HIGH-BCS ewes. Serum IGF-I was lower in LOW-BCS than in HIGH-BCS ewes but did not differ in SME or anterior pituitary glands. In serum, the 44-kDa IGFBP-3 and 24-kDa IGFBP-4 were lower in LOW-BCS than in HIGH-BCS ewes. In anterior pituitary glands, IGFBP-2 tended to be higher in LOW-BCS than in HIGH-BCS ewes. In the SME, IGFBP-2, -3, and -5 were lower in LOW-BCS than in HIGH-BCS ewes. Low body condition may inhibit the increased secretion of LH associated with the onset of the breeding season by altering relative amounts of IGFBPs within the hypothalamic-pituitary axis.

Last Modified: 9/10/2014
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