Response of serum inhibin B and pro‐αC levels to gonadotrophic stimulation in normal men before and after steroidal contraceptive treatment

Human Reproduction Vol.18, No.4 pp. 734±743, 2003 DOI: 10.1093/humrep/deg140 Response of serum inhibin B and pro-aC levels to gonadotrophic stimulation in normal men before and after steroidal contraceptive treatment Kati L.Matthiesson1,2, David M.Robertson1,2, Henry G.Burger1,2 and Robert I.McLachlan1,2,3 1 Prince Henry's Institute of Medical Research, Monash Medical Centre and 2Department of Obstetrics and Gynaecology, Monash University, Clayton, Victoria 3168, Australia 3 To whom correspondence should be addressed at: Prince Henry's Institute of Medical Research, PO Box 5152, Clayton, Victoria 3168, Australia. E-mail: BACKGROUND: Testicular regulation of inhibin B may be in¯uenced by the germ cell complement. METHODS: We examined the effects of gonadotrophin stimulation on serum inhibin B and pro-aC in 25 normal men at (i) control (stimulation test 1), (ii) after spermatogenic suppression induced by testosterone plus progestin treatment (stimulation test 2), and (iii) during spermatogenic recovery induced by FSH and/or hCG treatment (stimulation test 3). For each test, subjects received a single injection of 1200 IU FSH or 5000 IU hCG or both. RESULTS: Inhibin B and pro-aC fell with spermatogenic suppression (75 and 51% of pre-treatment baseline respectively, P < 0.05). Inhibin B response to FSH (130±144%) was similar in controls and after germ cell suppression. Pro-aC response after germ cell suppression compared with control was signi®cantly increased (P < 0.05) with both FSH (210±229% versus 140±185%) and hCG (254±261% versus 145%). All treatments partially restored spermatogenesis with no clear relationship apparent between inhibin B and sperm count. CONCLUSIONS: We conclude that: (i) serum inhibin B and pro-aC are only partially gonadotrophin dependent, (ii) spermatogenic suppression does not modify inhibin B response to FSH but enhances pro-aC response to both FSH and hCG, and (iii) inhibin B is a poor marker of spermatogenesis in this model of gonadotrophic manipulation in normal men. Key words: FSH/inhibin/LH/Sertoli cell/testosterone Introduction Inhibin exists as two biologically active forms, inhibin A and B, which share a common a-subunit linked to either a bA- or bB-subunit by a disulphide bond (Vale et al., 1988). Inhibin B is the primary form found in the adult male (Anawalt et al., 1996). It is now recognized that there is a reciprocal relationship between serum FSH and inhibin B (Anawalt et al., 1996; Illingworth et al., 1996; Anderson, 2001; Hayes et al., 2001; Meachem et al., 2001). In addition to the dimeric inhibin forms, the partially processed form of the free asubunit (pro-aC) is found in the circulation. The testis is the primary circulatory source of both inhibin B and pro-aC as orchidectomy results in very low or non-detectable levels (Anawalt et al., 1996). In-situ hybridization and immunocytochemical studies have revealed different patterns of a- and bB-subunit expression in the tissue depending on the developmental age and species studied (Bergh and Cajander, 1990; Forti et al., 1992; Vannelli et al., 1992; Majdic et al., 1997; Andersson et al., 1998). Using immunocytochemical methods, the a-subunit is localized to human spermatocytes, 734 Sertoli and Leydig cells, while the bB-subunit is localized to Sertoli and Leydig cells and more controversially to spermatocytes and early spermatids (Bergh and Cajander, 1990; Forti et al., 1992; Vannelli et al., 1992; Majdic et al., 1997; Andersson et al., 1998). The secretion of inhibin is controlled by many factors including gonadotrophins and intrinsic factors involving Sertoli, Leydig and germ cells. In normal men, a single large dose (3000 IU) of recombinant human FSH (rhFSH) led to a doubling of serum inhibin B levels, reaching a peak within 72 h (Anawalt et al., 1996) with more recent studies showing that a dose of 225 IU was ineffective (Kinniburgh and Anderson, 2001). A dose±response study showed that administration of rhFSH (1000, 2000 and 3000 IU) led to signi®cant increases in inhibin B, with the later two doses showing a signi®cantly greater area under the curve than placebo or 1000 IU rhFSH (Kamischke et al., 2001). Both FSH and hCG have been shown to signi®cantly increase pro-aC levels (Kamischke et al., 2001; Kinniburgh and Anderson, 2001). It is also recognized that the relationship between serum FSH and inhibin B is modulated by other factors. Several ã European Society of Human Reproduction and Embryology Gonadotrophin stimulation of inhibin Figure 1. Study protocol; 25 men enrolled in control phase, 15 men re-randomized for remainder of study protocol. Six week minimum interval between control and suppression phases. *Only FSH-alonetreated men received a second testosterone (T) implant at the onset of the recovery phase. Recovery was achieved over a 12 week period with either FSH 300 IU twice weekly or hCG 5000 IU weekly or a combination of FSH plus hCG. DMPA = depot medroxyprogesterone acetate. studies have shown that inhibin B levels fall markedly following severe testicular insults (chemotherapy, irradiation) correlating with the disappearance of germ cells (Wallace et al., 1997; Foppiani et al., 1999; Petersen et al., 1999). Similar ®ndings have been observed in rats following methoxyacetic acid treatment (Allenby et al., 1991). On the other hand, gonadotrophic suppression following exogenous sex steroid administration led to little or only a partial suppression of serum inhibin levels (Anderson et al., 1997; Zhengwei et al., 1998; Buchter et al., 1999; Martin et al., 2000; McLachlan et al., 2002) with no relationship with either the duration of treatment or the extent of suppression of sperm count (Anderson et al., 1997). The basis for this differential effect may be that the extent of inhibin B suppression is related to the degree of damage to the spermatogenic process with toxic agents leading to a more profound loss of germ cells, compared with that achieved with gonadotrophin suppression. To examine the potential in¯uence of germ cells on inhibin release from the testis (of both Sertoli and Leydig cell origin) we examined the acute effects of FSH and/or LH (using hCG as an LH substitute) administration on serum inhibin B and pro-aC levels in normal men, and compared this response with that seen following spermatogenic suppression induced by a regimen developed for the purpose of hormonal contraception (Handelsman et al., 1996). In addition we wished to examine the relationships between spermatogenic recovery, induced by FSH and/or hCG treatment, and serum inhibin B. Methods and materials Subjects Twenty-®ve healthy men were recruited through media advertisement to participate in this study conducted at Prince Henry's Institute of Medical Research in accordance with the guidelines of the Southern Healthcare Network Human Research Ethics Committee. Of these 25 men, 15 were enrolled to participate in both the suppression and recovery phases. All men underwen (...truncated)