Inhibin activity in the mare and stallion

Plasma FSH, inhibin A and inhibin isoforms containing pro- and -alphaC during winter anoestrus, spring transition and the breeding season in mares

“…Previous studies have reported circulating concentrations of immunoreactive inhibin in cyclic mares (Bergfelt et al, 1991;Roser et al, 1994;Nagamine et al, 1998;Nagaoka et al, 1999). The assays used in the present study detect forms of monomeric inhibin (α inhibin) using the inhibin pro-and -αC assay, as well as dimeric inhibin A.…”

“…Circulating concentrations of inhibin A and inhibin pro-αC isoforms were higher in oestrus than in dioestrus, but only inhibin pro-αC isoforms increased on the day of ovulation. Studies using a non-selective assay showed that plasma concentrations of immunoreactive inhibin were higher in oestrus than in dioestrus and were at a maximum on the day of ovulation (Bergfelt et al, 1991;Roser et al, 1994;Nagaoka et al, 1999). The peak in circulating concentrations of pro-αC inhibin isoforms may originate from peritoneal absorption of follicular fluid at ovulation (Bergfelt et al, 1991).…”

“…Most studies in normal cyclic mares have reported circulating concentrations of immunoreactive inhibin (Bergfelt et al, 1991;Roser et al, 1994;Nagamine et al, 1998). These assays do not distinguish between the biologically active dimeric forms of inhibin and free monomeric α-subunits, which are thought not to be biologically active.…”

“…The concentrations of immunoreactive inhibin and inhibin isoforms with pro-and -αC immunoreactivity increase in late dioestrous mares and reach a peak on the day of ovulation (Bergfelt et al, 1991;Roser et al, 1994;Nagamine et al, 1998;Nagaoka et al, 1999). Immunohistochemistry studies in the equine ovary indicate that dimeric inhibin A is secreted mainly by the granulosa and theca cells of large follicles, whereas the granulosa cells of small follicles are thought to secrete inhibin α-subunit (Nagamine et al, 1998).…”

Reproductive hormone profiles in mares during the autumn transition as determined by collection of jugular blood at 6 h intervals throughout ovulatory and anovulatory cycles

“…Inhibin was measured in all samples using a radioimmunoassay (Robertson et al, 1988) that has been used to measure inhibin in horse plasma (Roser et al, 1994). The assay was based on an antiserum against bovine 31 kDa inhibin A (No.…”