Changes of gonadotrophin surge inhibiting/attenuating factor activity in pig follicular fluid in relation to follicle size.
The activity of GnSI/AF was measured in pig follicular fluid (pFF) from 58 individual follicles of various sizes, by bioassay using rat pituitary cells, to investigate the relationship between gonadotrophin surge inhibiting/attenuating factor (GnSI/AF) activity and follicular development. In addition, the correlation between GnSI/AF and inhibin activities and the content of sex steroids (oestradiol, progesterone and testosterone) of follicles was examined. The activity of GnSI/AF in pFF varied significantly (0.155-1.69 U microliter-1) with size of the follicle. The activities (mean +/- SEM) were intermediate and constant in follicles with diameters from 3 to 5 mm (0.583 +/- 0.080 U microliter-1, n = 24), were higher and reached the highest value in follicles with diameters between 6 and 8 mm (0.863 +/- 0.068 U microliter-1, n = 21), and were lower, reaching the lowest value in follicles with diameters of 9 and 10 mm (0.401 +/- 0.089 U microliter-1, n = 13). In contrast, inhibin activity was almost constant during the development of follicles, although individual values varied from 0.9 to 2.5 U microliters-1. For follicles with diameters of 4-8 mm, inhibin activity was 1.754 +/- 0.042 U microliters-1 (n = 39); activity was higher in the smallest follicles with diameters of 3 mm (2.063 +/- 0.015 U microliters-1, n = 6) and was lower in follicles with diameter of 9 mm, reaching the lowest value in follicles with diameter of 10 mm (1.176 +/- 0.068 U microliters-1, n = 7); inhibin activity was not significantly correlated with GnSI/AF activity.(ABSTRACT TRUNCATED AT 250 WORDS)