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RESEARCH |
1 Department of Veterinary Basic Sciences, Royal Veterinary College, Royal College Street, London NW1 0TU, UK, 2 School of Animal Biology, University of Western Australia, Crawley 6009, Western Australia, Australia and 3 Departamento de Biología de la Reproducción, Universidad Autónoma Metropolitana Iztapalapa, 09340 Mexico City, Mexico
Correspondence should be addressed to M Muñoz-Gutiérrez, Department of Veterinary Basic Sciences, Royal Veterinary College, University of London, Royal College Street, London NW1 0TU, UK; Email: mmunoz{at}rvc.ac.uk
The IGF system is associated with ovarian folliculogenesis. The effect of the IGFs mediated through the type I receptor (IGF-IR) and IGF-binding protein-2 (IGFBP-2), is to regulate the growth and atresia of follicles. To test if the mRNAs for IGF-IR and IGFBP-2 are differentially regulated in the follicle we used nutritional treatments that stimulate folliculogenesis and measured, by in situ hybridisation, their mRNAs expression. Groups of five anoestrous Merino ewes were fed wheat straw (control) or the control diet supplemented with lupins (500 g/day). Other ewes were fed the control diet and infused with glucose (50 mmol/h) or with glucosamine (3.5 mmol/h). Intravaginal progestagen sponges were inserted for 12 days, and nutritional treatments were started 5 days before progestagen removal. Follicular development was studied after an artificial follicular phase, simulated by progestagen for 12 days and a regime of GnRH pulses given for 36 h following progestagen withdrawal, when the animals were killed. The ovaries were collected and stored at –80 °C until sectioning at 10 µm. Every 25–28th and 29–32nd section was probed for IGF-IR and IGFBP-2 using 35S-labelled oligonucleotide probes. None of the nutritional treatments affected the number or size of follicles positive for IGF-IR, but glucose (P < 0.001) and lupin (P < 0.001) treatments reduced the follicular concentration of mRNA. The nutritional treatments all increased the number of follicles positive for IGFBP-2 (P < 0.05) and reduced their mean diameter (P < 0.05) and with the exception of lupin feeding, the concentration of mRNA (P < 0.05). The results show that all treatments affected the intrafollicular IGF system and suggest that IGF-IR and IGFBP-2 are nutritionally regulated in the follicle. However, the effects of treatments were variable and suggest the existence of multiple regulatory mechanisms that allow for normal variation in composition and balance of the ruminant diet.
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