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STUDIES ON A RADIOIMMUNOASSAY FOR OVINE FOLLICLE STIMULATING HORMONE: INTERFERENCE BY OVINE ALBUMIN

Summary Urinary oestriol output in 214 series of three consecutive 24-hour periods during late pregnancy showed large day-to-day fluctuations. The clinical correlations have been based on the mean excretion value of each three-day series. From 30 weeks of pregnancy onwards there was a highly significant difference in the oestriol output between mothers who had normal-sized babies (birthweight above the 25th percentile) and those who had small-for-dates babies (birthweight below the 10th percentile). Serial oestriol determinations also showed that in pregnancies with growth-retarded fetuses the levels were persistently low, or falling, while in pregnancies with normal-sized fetuses the levels rose, often sharply. The shape of the curves was more important than the actual values in predicting the outcome with regard to the birthweight of the baby.

A heterologous radioimmunoassay system, using an antiserum to human FSH in combination with radioiodinated ovine FSH was highly specific for FSH for a number of species, and was used to measure plasma FSH levels in sheep, rat and man in a range of physiological states. Within-assay coefficient of variation (CV) was

The plasma FSH and LH responses to 17β–estradiol (E2) or to a synthetic gonadotrophin— releasing hormone (Gn—RH) were examined in anestrous ewes. FSH was measured by a heterologous double—antibody radioimmunoassay, while LH was estimated using a solid—phase method. Intravenous infusions of E2 (10 μg/hr for 4 hr) caused the plasma concentration of FSH to rise from 20–130 ng/ml NIH—FSH—S6 to peak values of 190, 350, and 400 ng/ml, respectively, in 3 animals. The release of FSH occurred over the same time interval as that previously reported for LH. In 2 animals, intracarotid infusions of Gn—RH (1.5 μg/hr for 3 hr) caused significant increases in both gonadotrophins which again rose and fell together. Plasma FSH concentrations rose from 38 and 70 ng/ml to a peak of 110 and 160 ng/ml after iy2 and 3 hr, respectively. These findings are consistent with the concept that Gn— RH is the mediator of the estrogen—induced release of LH and FSH which occurs at estrus. (Endocrinology 92: 862, 1973)