Immunoneutralization and immunocytochemical localization of inhibin alpha subunit during the mid-luteal phase in the stump-tailed macaque.

The putative endocrine role of inhibin in the control of FSH secretion during the luteal phase in the primate was investigated by immunoneutralization. Antisera against the 1-23 amino acid sequence of the N-terminus of the human inhibin alpha subunit were raised in a ewe and three macaques. Antisera (10-20 ml) were administered to macaques on day 8/9 of the luteal phase and serum samples collected during the treatment cycle and post-treatment cycle for determination of FSH, oestradiol and progesterone. In addition, localization of inhibin within the macaque ovary at this stage of the luteal phase was investigated using the ovine antiserum. Intense immunostaining was localized within the granulosa-lutein cells of the corpus luteum with absence of staining in the theca-lutein cells or other ovarian compartments. Administration of antisera was without significant effect on serum concentrations of FSH when compared with control animals, either during the first 24 h of detailed observation or for the following 10-day period of the late luteal phase and subsequent early follicular phase. These results provide further evidence that the corpus luteum is the major source of inhibin immunoreactivity during the primate menstrual cycle, but fail to support an endocrine role for inhibin in the suppression of FSH secretion.