BIOASSAY OF LUTEINIZING HORMONE1

Abstract

The increase in content of radio-iodinated serum albumin of immature rat ovaries is employed as an index of the hyperemia produced by pituitary lutcinizing hormone. The assay method consists of the intravenous injection of an LH preparation followed by two micro-curies of radio-iodinated serum albumin two hours later. After 15 minutes, both ovaries are excised and measured for content of the tracer. The regression equation is Y = 1900 log ×+ 2300 and has an index of precision of 0.14. None of the pituitary hormones except FSH interferes with the specificity of the ovarian response to LH. FSH, when present in large amounts, decreases the slope of the LH dose-response lines to 1/4 of that given by highly purified LH and thereby invalidates LH potency estimates. After treatment of purified FSH with 6M urea for 24 hours at 40° C, the FSH potency is not affected but 75% of the contaminating LH is inactivated. Purified LH is inactivated to the extent of 98% under the same conditions.