Earlier studies provided evidence that the blood-follicle barrier was located at the level of the ovarian microvasculature and demonstrated that it was freely permeable to most molecules below 70-300 kDa. Surprisingly, however, it was also shown that molecules of the lal family could enter the follicular fluid only after an ovulatory surge of gonadotropin. Thus, the trans-barrier flux of these negatively charged proteins was regulated differently from neutral or positively charged proteins of similar size, suggesting that charge might also play a role in permeability of the blood-follicle barrier. A test of this hypothesis was carried out by cationizing led and demonstrating that this positively charged molecule crossed the barrier in the absence of gonadotropic stimulation.
Studies involving another serum protein, IgG, also supported this hypothesis. IgG carries a net neutral to slightly positive charge and is si mil яг in size to lal but is characterized by a strikingly different follicular distribution. No ovulatory stimulus was needed for native IgG to cross the barrier and enter the follicle. At an appropriate level of anionization, however, regulation of its trans-barrier flux was similar to that of lal. This appropriate level of anionization was achieved using CA as the charge-altering reagent. birth control pills
It is possible that the IgG, anionized at a low level, was able to enter the follicle only after hCG because of its decreased negative charge density. Alternatively, differences in protein conformation, created by the two anionizing reagents (CA or succinic anhydride), may be responsible for their trans-barrier flux properties. Thus, these data support the idea that charge can affect the trans-barrier flux of proteins within the size range of lal inhibitory glycoproteins. In contrast, however, larger proteins such as a2-M or smaller proteins such as BSA appear to interact with the barrier in a manner that is independent of charge.