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Insulin-Like Growth Factor-I Serum Levels Show a Midembryogenesis Peak in Chicken That Is Absent in Growth-Retarded Embryos Cultured ex Ovo^*

HENRI L. ROBCIS, TRINIDAD CALDES and FLORA DE PABLO

Diabetes Branch, National Institutes of Diabetes and Digestive and Kidney Diseases (H.L.R., T.C., F.D.P.), and the Veterinary Resources Program, National Center for Research Resources (H.L.R.), National Institutes of Health Bethesda, Maryland 20892

Address all correspondence and requests for reprints to: F. De Pablo, Building 10, Room 8S-243, National Institutes of Health, Bethesda, Maryland 20892.

Abstract

Insulin-like growth factor-I (IGF-I) is the primary mediator of GH action after birth, but its role as a regulator of prenatal growth is unclear. In a previous study we showed that IGF-I mRNA was expressed in chicken embryos beginning at the blastoderm stage (day 0, newly laid egg). Here we present the ontogeny of serum IGF-I in normal and growth-retarded chicken embryos. Serum samples were pooled from multiple embryos starting on day 4 of development in ovo until hatching (day 21). Extracts of day 2 and 3 whole embryos were also studied. IGF-binding proteins were removed by filtration on Sep-Pak C-18 cartridges. IGF-I was quantitated by a heterologous RIA validated for chicken species. Embryonic IGF-I showed a HPLC profile similar to that of adult chicken serum IGF-I. Serum IGF-I was measurable on day 6 of development (-0.04 ng/ml), reached a peak on day 15 (18 ng/ml), and decreased to a low concentration (0.2 ng/ml) the day before hatching. Embryos cultured ex ovo showed progressive growth retardation after day 10 of development, and by day 20 their weight was 50% of normal. The serum IGF-I concentration of ex ovo cultured embryos was normal on day 10, but remained low until day 21, without the midembryogenesis rise observed in normal embryos. These results support the concept that IGF-I may have a role in general embryonic growth in addition to any paracrine/autocrine action in individual tissues. (Endocrinology 128: 1895–1901, 1991)

Footnotes

^* Presented in part at the 72nd Annual Meeting of The Endocrine Society, Atlanta, GA, June 1990 (Abstract 1139).

On leave from the Hospital de Especialidades Quirurgicas, Universidad Complutense, Madrid, Spain.

Received September 21, 1990.

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