Inhibin: 1985 update on action and purification.

Inhibin is a gonadal hormone, which exerts a specific negative feedback action on the pituitary secretion of follitropin (FSH) in male and female animals. The existence of inhibin was postulated over 60 years ago. Yet, until recently, little progress has been made in its isolation and characterisation. This lack of progress may be attributed to several factors: first, the use of a variety of assay systems of ill-defined specificity, secondly, the use of a variety of sources for unpurified inhibin, and thirdly, the inability of investigators to purify inhibin using classical purification procedures. During the last few years, and in particular during the last year, several publications on the isolation and characterisation of inhibin have appeared. This review attempts to place the various reports on the nature of inhibin into perspective. It is concluded that there are at least 2 classes of proteins with inhibin-like activity: a relatively large molecular weight material with apparent molecular mass between 40 and 70 kDa found in gonadal extracts and fluids, and a smaller material, with molecular mass between 5 and 20 kDa, found in seminal plasma. However, the observations that various purified seminal plasma inhibin preparations are either inactive in in vitro assays used to characterize gonadal inhibin or have been shown to be prostatic in origin suggest that they are unlikely to be involved in the gonadal regulation of FSH secretion. It has yet to be established if the purified gonadal inhibin preparations are the biological active forms involved in controlling FSH secretion in vivo.