Qualitative and quantitative differences in hLH species in the first and second LH release induced by continuous stimulation with synthetic LHRH in normal menstrual cycle as assessed by isoelectrofocusing.

It is known that continuous stimulation with LHRH induces a biphasic release of LH. The two pools theory is generally accepted in interpreting this phenomenon. The present study was conducted in order to elicit qualitative differences in LH included in the two pools. Five hundred micrograms synthetic LHRH was infused for 2h in 10 women in various phases of the menstrual cycle and 5 h blood sampling was performed during and after the infusion. Biphasic release of LH was demonstrated in all the cases investigated. The responsiveness to LHRH was most predominant in the midcycle, followed by the luteal phase. Pools of plasma samples at 30-105 min and 150-225 min of the LHRH infusion (plasma pools I and II; corresponding to the initial and the second LH release, respectively) were subjected to isoelectrofocusing (IEF) fractionation, pH range of 3.5-10. LH in plasma was classified in terms of isoelectric point (pI); i.e. A(pI = 9.13), B(8.60), C(8.16), D(7.67), E(7.24), and F(LH species migrating in the acidic pH area). Percentage of high alkaline LH species was significantly elevated in plasma pool I of the midcycle. No phasic difference was observed in the IEF profiles in plasma pool II. Consistent and significant increase and decrease in the percentage of acidic and high alkaline LH species, respectively, were observed throughout the menstrual cycle when the IEF profiles of plasma pool II were compared with those of pool I. The ratio of biological to immunological LH activities (B/I ratio) was markedly depressed in acidic LH species. The highest B/I ratios were obtained in the LH species migrating in the mid-alkaline region. The acidic LH species might represent the young generation of LH molecules prior to acquisition of biological potency. LH species migrating in the mid-alkaline region might be mature and bio-potent forms of the hormone. High alkaline LH species might represent LH molecules over-processed and having lost a degree of biological potency during a prolonged period of storage.