FOLLICLE-STIMULATING-HORMONE STIMULATES CIRCULATING GONADOTROPIN SURGE-ATTENUATING INHIBITING FACTOR BIOACTIVITY IN COWS/

This study aimed to determine whether superovulation in cattle stimula tes gonadotropin surge-attenuating/inhibiting factor (GnSAF/IF) bioact ivity, as it does in humans. Blood samples were collected from cows (n = 7 per treatment) at -4, 8, 20, 32, 44, 56, and 68 h after injection s of saline, eCG, or FSH. Equal volumes of plasma at each treatment an d time point were pooled, and GnSAF/IF and inhibin bioactivities were measured using an established rat pituitary cell culture bioassay. Pla sma from saline- and eCG-treated cows had little effect on GnRH-induce d LH secretion (116.3 +/- 8.3%-81.6 +/- 6.0% of control), while plasma from FSH-treated cows produced a time-dependent suppression of GnRH-i nduced LH secretion, falling to 64.6 +/- 4.0% of the control value at 56 h after first FSH injection (p < 0.001). The GnSAF/IF bioactivity f rom the 56-h plasma eluted at pH 5.73 by pseudochromatofocusing-simila r to the GnSAF/IF isoelectric point value of 5.81 determined using ser um from superovulated women. Plasma from FSH-treated cows reduced basa l FSH secretion more than plasma from eCG-treated cows (to 55.5 +/- 5. 7% and 63.2 +/- 6.6% of the control value, respectively, p < 0.01) alt hough immunoreactive inhibin concentrations were similar between the t wo groups. We conclude that FSH, but not eCG, treatment causes a time- dependent production of circulating GnSAF/IF bioactivity in cattle.