Properties of Equine Luteinizing Hormone Alpha Subunit Alone and in Combination with Various Beta Subunits1

Abstract

Previous studies have shown that equine luteinizing hormone (eLH) inhibits production of cyclic adenosine monophosphate (cAMP) induced by follicle-stimulating hormone (FSH) in preparations of seminiferous tubules from immature rats. It was also shown that the inhibitory effect was a function of the equine LH (eLH) alpha subunit. To explore this phenomenon further, the intrinsic FSH-like activities of eLH alpha alone and in combination with ovine (o) LH beta, ovine FSH beta, and equine FSH beta were evaluated in several assay systems. In a radioreceptor assay employing 125I-o-FSH and testis membranes from day-old calves, eLH was twice as active as oFSH, eLH alpha was 6% as active as oFSH, and other subunits showed a lack of activity (less than 1.5%). Whereas oLH was only 0.1% as active as oFSH, the hybrid eLH alpha-oLH beta was 3.0% as active. The binding activity of eLH alpha-FSH beta hybrids tended to be higher than the oFSH alpha-FSH beta hybrids. In the cAMP production assay, eLH alpha-FSH beta hybrids exhibited dampened dose-response curves when compared to the oFSH alpha-FSH beta hybrids. In a plasminogen activator assay (PAA) employing granulosa cells from intact 21-24-day-old female rats primed with diethylstilbestrol, eLH had activity comparable to that of oFSH, while eLH alpha was inactive. When eLH alpha was recombined with oFSH beta, eFSH beta, or oLH beta, the PAA stimulatory activity was not altered compared to that of the hybrids oLH alpha-oFSH beta, oFSH alpha-eFSH beta, and the recombinant oLH alpha-oLH beta, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)