Immunobiology of a Synthetic Luteinizing Hormone Receptor Peptide 21–41

Abstract

ABSTRACT:Immunization of adult male rabbits with a synthetic luteinizing hormone-receptor peptide (LH-RP; representing amino-acids 21-41 of the extracellular domain of the rat LH receptor) resulted in production of high-titer antibodies capable of interacting with particulate and cell-based LH receptors. The antibody produced was able to inhibit binding of 125 I-labeled human chorionic gonadotropin (hCG) to a particulate sheep luteal LH receptor preparation by 40%-50%. Maximal inhibitory activity was correlated with high antibody titer. Immunocytometry revealed that the antibody could directly bind to cells having LH receptors, such as rat granulosa and Leydig cells. The antibodies recognized a 77-kilodalton membrane protein in Western blots of mouse testicular extracts. Interaction of endogenous Leydig cell LH receptor with the LH-RP antibody resulted in both hormone agonist and antagonistic activities. The hormone-mimicking activity (increase in serum testosterone over control) was confined only to the early phase of immunization when the antibody titer was low. Blockade of LH receptor during the later part of immunization resulted in a significant reduction in serum testosterone over controls and inhibition of spermatogenesis. DNA flow cytometry showed that a specific and significant inhibition of meiosis (transformation of primary spermatocytes to round and elongated spermatids P Ͻ .01) and spermiogenesis (transformation of round spermatids to elongated spermatids P Ͻ .0001) occurred following blockade of LH function.Key words: Testicular function, spermatogenesis, receptor antibodies. J Androl 2001;22:992-998S permatogenesis in mammals is mainly regulated by 2 glycoprotein hormones; namely, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Immunization of adult male bonnet monkeys (Macaca radiata) with ovine FSH (Aravindan et al, 1993) as well as a recombinant FSH receptor protein has been shown to result in impairment of spermatogenesis . Immunization of male rabbits (Jeyakumar et al, 1995) and monkeys with ovine LH also results in blockade of testosterone production and spermatogenesis. Immunization of rabbits with a holo LH receptor (LH-R) preparation isolated from sheep corpora lutea led to the production of receptor-specific antibodies, but not to testicular dysfunction (Jeyakumar and Moudgal, 1996). This was shown to be due to the presence of antibodies expressing both hormone-mimicking and antagonistic activities throughout the period of immunization. During the early period of immunization, when only hormone-mim- icking antibodies were present, there was a sustained (lasting over several weeks) and significant (fourfold to sevenfold) increase in serum testosterone levels. The return of serum testosterone to normal levels during later periods of immunization could be correlated to the appearance of receptor antagonistic (blocking) antibodies. The occurrence of both types of antibodies in the serum could be demonstrated by in vitro tests (Jeyakumar and Moudgal, 1996). The presence of ...

Chronic Administration of Atrial Natriuretic Peptide Reduces Testosterone Production of Testes in Mice

“…The hCG, then, could have induced testosterone secretion both in vivo (Eisner et al, 2002) and in vitro (El‐Gehani et al, 2001) by binding to LH/hCG plasma membrane receptors (Ronco and Llanos, 2000). A recent study that used an antibody raised in adult male rabbits by immunization with a synthetic LH‐receptor peptide showed the interaction of endogenous Leydig cell LH receptors with this antibody and explored both hormone agonistic and antagonistic activities (Moudgal et al, 2001). Thus, the blockade of the LH receptor by hCG might affect ANP action on the production of testosterone, especially under long‐term administration.…”