Physiology and Biochemistry of Ovarian Inhibin 1

There are three recent reports of amino acid sequence studies on inhibin preparations. The preparation obtained in Bombay and partially sequenced by collaborators in Stockholm dealt with a preparation from human seminal plasma. This preparation had a molecular weight of approximately 14,000 (1). On the other hand, Seidah and colleagues in Montreal (2) reported a mixture of four peptides that they sequenced simultaneously to determine 31 of a possible 35 residues in a "complete" peptide. Three of the peptides sequenced as though they were derived from the larger complete peptide. The molecular weight of this peptide was estimated to be 4-5000. In a subsequent paper from this laboratory and two collaborators from the University of California in San Francisco (3), the principal peptide in the mixture was isolated and sequenced (31 residues) and a synthetic peptide with this sequence was shown to have inhibin activity equal to or slightly greater than the native peptide. We will comment further on these studies later in this review. The landmark value of these studies lies in the fact that after many years investigators of inhibin are beginning to talk of exact biochemical structures that can be checked and verified in other laboratories. Most importantly, well-defined compounds can be used to compare results from laboratory to laboratory. Prior to now there was always wide discrepancy between reports (often these were little more than undocumented claims) from various laboratories. This led many to doubt the reality of an inhibin that suppressed the follicle stimulating hormone (FSH) secretion of the pituitary without affecting the luteinizing hormone (LH). Much still remains to establish the true physiological significance of inhibin and the exact nature of the native inhibin secreted by the Sertoli cells or granulosa cells of the gonads.