Evidence for Alterations in Luteinizing Hormone Secreted in Rhesus Monkeys with Normal and Inadequate Luteal Phases Using Radioreceptor and Radioimmunoassay*

Abstract

A radioreceptor assay (RRA) using porcine granulose cells and [¹²⁵I]hCG was developed and validated for the measurement of LH or CG. The RRA was used in conjunction with a heterologous RIA employing antiserum against ovine LH and [¹²⁵I]ovine LH (RIA) to measure serum LH in the rhesus monkey throughout the menstrual cycle. Discrepancies were found in the measurement of serum LH using RRA and RIA. Measurements of serum LH using RIA were consistently higher than the measurements of serum LH using RRA in serum from adult intact female and male monkeys and hypophysectomized, ovariectomized, and pregnant monkeys. The highest ratio of RIA to RRA values (I:R ratio) for serum LH was observed in serum obtained under conditions of elevated LH secretion, such as at midcycle and after ovariectomy. Monkeys with inadequate luteal phases had lower LH levels using RIA and RRA than did normal monkeys. The I:R ratio for LH levels on each day of the menstrual cycle in monkeys having inadequate luteal phase progesterone levels was significantly lower than the I:R ratio in monkeys having normal luteal phase progesterone levels. It is possible that the exposure of the follicle to low LH levels leads to diminished luteal progesterone secretion. These results suggest that immunoreactive but biologically inactive LH may be present in the serum of the rhesus monkey. In addition, changes in the I:R ratio observed under various physiological conditions and in monkeys with inadequate luteal phase progesterone levels indicate that there may be qualitative changes in the nature of the LH secreted.