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Insulin-Like Growth Factor-I, Insulin-Like Growth Factor-Binding Proteins, and Gonadotropins in the Hypothalamic-Pituitary Axis and Serum of Nutrient-Restricted Ewes¹

^a University of Wyoming, Department of Animal Science, Laramie, Wyoming 82071 ^b USDA, Agricultural Research Service, R.L. Hruska U.S. Meat Animal Research Center, Clay Center, Nebraska 68933 ^c University of Arizona, Department of Physiology, Tucson, Arizona 85718

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 LHß 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.

¹ Supported by a grant from the USDA NRICGP to G.E.M. (#9401472). Mention of trade names is necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable. Presented in part at the 88th meeting in 1996 of the American Society of Animal Science, Rapid City, SD.

² Correspondence. FAX: 307 766 2355; gm{at}uwyo.edu

³ Current address: 11 South Sweetgrass, Bozeman, MT 59718.

⁴ Current address: Department of Animal & Range Sciences, South Dakota State University, Brookings, SD 57007.

⁵ Current address: Rosepine Research Station, P.O. Box 26, Rosepine, LA 70659.

⁶ Current address: USDA-CSREES, 1400 Independence Ave SW, Stop 2241, Washington, DC 20250–2241.

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