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Effects of ovariectomy and FecB^B genotype on the median charge and circulating half-life of pituitary FSH isoforms of ewes

This study investigated the effects of short-term (20 days) ovariectomy, the effects of FSH assay (radioimmunoassay, receptor assay or in vitro bioassay) and of FecB^B genotype on the characteristics of pituitary FSH from Booroola ewes. Pituitary extracts were obtained from ovariectomized homozygous carriers (BB) and non-carriers (++, n = 8 per genotype) and ovary-intact controls (n = 4 per genotype). The extracts (n = 4 per genotype per treatment) were subjected to agarose suspension electrophoresis and the eluates were assayed by the three FSH methods. There were significant effects of ovariectomy (P < 0.01) and assay system (P < 0.05) but not of genotype on the median charge of FSH isoforms. The mean ± SEM migration rates for FSH in intact and ovariectomized ewes were 0.469 ± 0.006 and 0.439 ± 0.006 albumin mobility units, respectively (P < 0.01), indicating a shift to more basic isoforms after short-term ovariectomy. When the pituitary extracts were subjected to anion-exchange HPLC, there was a significant (P < 0.01) shift to more basic isoforms in the ovariectomized ewes as shown using agarose electrophoresis, and no gene effects were noted. When the pituitary extracts (n = 4–8 per group) were injected into mature female mice, there were no significant effects of ovariectomy or genotype on the circulating half-lifes of the pituitary FSH isoforms. These results indicate that after short-term ovariectomy, the increase in plasma FSH concentrations is accompanied by a shift in the median charge of pituitary FSH isoforms without any observable change in their metabolic clearance rates. Moreover, the FecB^B gene has little effect on the median charge or half-life of pituitary FSH.