The presence of IGFs and their associated binding proteins (IGFBPs) in human follicular fluid is well documented. Furthermore, most of the constituents of the IGF system in follicular fluid have been found to vary, either in total amount or by proteolytic cleavage, depending on the health status of the follicle. In this study we have examined the acid-labile subunit (ALS) and found that levels in follicular fluid (mean 146 nmol/l) were almost 50% of those in the circulation. This amount of ALS was considerably greater than that found in other extracirculatory fluids (20.9 for synovial fluid and 31.4 nmol/l for skin blister fluid). As in the circulation, ALS levels were in molar excess and did not vary between atretic and dominant follicles. Although the source of ALS is probably from blood (conditioned medium from ovarian cell cultures had no measurable ALS) it would appear that this glycoprotein is not merely diffusing from the circulation as the capillary endothelium becomes more permeable in dominant follicles and this is not reflected in the level of ALS. Analysis of the distribution of IGF-I, IGF-II and IGFBP-3 in fluid from healthy and atretic follicles revealed that the majority of these growth factors (> 80% of total IGF-II) were in the 150KDa complex, indicating that the ALS present was functional, in that it formed the ternary complex with a molecule of IGFBP-3 and IGF. No free IGF-II was found in any of the follicular fluids analysed nor was there any increase in the amount of unsaturated IGFBP-3 in atretic follicles. In summary, we have shown that the majority of IGF measured in follicular fluid, whether from healthy or atretic follicles, is bound in the ternary complex.

This article has been cited by other articles:

				J. W Kim, R. P Rhoads, N. Segoale, N. B Kristensen, D. E Bauman, and Y. R Boisclair Isolation of the cDNA encoding the acid labile subunit (ALS) of the 150 kDa IGF-binding protein complex in cattle and ALS regulation during the transition from pregnancy to lactation. J. Endocrinol., June 1, 2006; 189(3): 583 - 593. [Abstract] [Full Text] [PDF]

				I. Ueki, G. T. Ooi, M. L. Tremblay, K. R. Hurst, L. A. Bach, and Y. R. Boisclair Inactivation of the acid labile subunit gene in mice results in mild retardation of postnatal growth despite profound disruptions in the circulating insulin-like growth factor system PNAS, June 6, 2000; 97(12): 6868 - 6873. [Abstract] [Full Text] [PDF]