Identification of Insulin-Like Growth Factor I in Bovine Seminal Plasma and Its Receptor on Spermatozoa: Influence on Sperm Motility¹

^c Endocrine Physiology Laboratory, ^d Animal and Veterinary Sciences Department, Clemson University, Clemson, South Carolina 29634 ^e Department of Obstetrics and Gynecology, College of Medicine, University of Florida, Gainesville, Florida 32610 ^f Andrology Laboratory, Reproductive Endocrinology and Infertility, Greenville Memorial Hospital, Greenville, South Carolina 29605

Insulin-like growth factor I (IGF-I) has been identified in human seminal plasma. This study was conducted to determine whether IGF-I is present in bovine seminal plasma, whether sperm cells express the IGF-I receptor (IGF-IR), and whether IGF-I affects sperm motility. Semen samples were collected from bulls by electroejaculation and maintained at 37°C, and motility of sperm was assessed. After centrifugation to separate sperm cells from seminal plasma, the seminal plasma was submitted to a validated heterologous RIA for IGF-I. Significant concentrations of IGF-I (116.29 ± 40.83 ng/ml expressed as mean ± SD) were measured in bovine seminal plasma. Sperm cells were washed with buffer and subjected to either radioreceptor assay (RRA) or immunocytochemistry (IC). RRA revealed a single high affinity for the IGF-IR with a K_d of 0.83 nM as determined by the computer program LIGAND. IC, using three monoclonal antibodies, localized the IGF-IR to the acrosomal region of the sperm. Computer-assisted sperm-motion analysis was used to determine the effects of IGF-I and IGF-II on bovine sperm motility parameters. Both IGF-I and IGF-II increased sperm motility and straight-line velocity (p < 0.05) relative to the control. The presence of IGF-IR on sperm, the presence of IGF-I in semen, and the ability of IGF-I to stimulate sperm motility provide evidence that the IGF system may be involved in the fertilization process in the bovine species.

¹ This work was supported by the Animal Biotechnology Initiative (#1513), Clemson University, and a Pilot Grant from the Greenville Hospital System/Clemson University Biomedical Cooperative. Technical contribution No. 4415 of the South Carolina Agric. Experimental Station.

² Correspondence: Donald M. Henricks, AVS Department, Clemson University, Poole Ag., Building, Box 340361, Clemson, SC 29634. FAX: (864) 656–3131; dhnrcks{at}clemson.edu

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