Median charge of gonadotrophin isoforms in the pituitary gland and in the circulation of sheep fetuses from mid- to late gestation.

The heterogeneity of LH and FSH in the sheep fetus was studied by determining the median charge of pituitary and circulating isoforms. Pituitary extracts from male and female fetuses at days 75, 95, 120 and 135 of gestation were subjected to agarose suspension electrophoresis. For all fetuses except the day 75 age group, the median mobility of the gonadotrophin isoforms in matching serum samples from the individual fetuses were also determined. LH and FSH in extracts, peripheral samples and column eluates were measured using sensitive and specific sandwich fluoroimmunoassays for ovine gonadotrophins. The median charge of pituitary LH became more basic (P < 0.001) with gestational age, whereas for pituitary FSH more acidic forms (P < 0.001) were present in the older groups. The female fetuses had more basic pituitary isoforms of LH than the males (P < 0.01) between days 95 and 135, and for FSH at day 75 (P < 0.05). In the matching serum samples, the median charge of the LH (P < 0.001) and FSH (P < 0.05) isoforms were more acidic than those in the pituitary gland. No significant effects of age or sex were detected in the median charge of the gonadotrophin isoforms in serum, but in a number of instances the median charge could not be determined due to low serum concentrations which affected the group sizes. These data show that in the sheep fetus LH and FSH are differentially regulated in qualitative as well as quantitative terms, and that the charge of fetal gonadotrophin isoforms changes according to the age and sex of the fetus.