Molecular homology between prolactin and ovarian peptides: evidence for physiologic modification of the parent molecule by the target.
In recent years, prolactin has come to be recognized as an inhibitory gonadotrophin, with the ovarian follicular compartment as its target. In parallel with this, is evidence that granulosa cells give rise to substances secreted into follicular fluid that mimic the inhibitory actions of prolactin, but appear to be oligopeptides. The question that was examined here was whether these peptides are prolactin fragments. The endpoint was immunohistochemical reactivity in ovarian follicles of cycling rats. Antisera to homologous pituitary prolactin were used with and without modification by admixture either of highly purified rat pituitary prolactin or of follicular fluid enriched in prolactin-like bioactivities and depleted of peptides larger than 2000 MW. In growing follicles, immunohistochemical reactions, dependent upon unmodified anti-rat prolactins, occurred in all three follicular compartments but the microdistribution patterns and intensity of the reactions varied within follicles at different stages of development. These differences were compatible with the biological role of prolactin as an inhibitory gonadotrophin. Evidence that the reactions were dependent upon pituitary-like prolactin, present in the follicle, was obtained with highly purified rat prolactin which completely abolished reaction potential of the antisera in all follicles, at all stages. In contrast, the results with antisera to which oligopeptide follicular fluid had been added were end-point dependent; both partial and complete loss of antiserum potency, dependent upon cycle stage and sub-compartmentation of individual follicles were observed. These findings demonstrate molecular homology between pituitary prolactin and what appear to be small peptides of penultimate follicular origin and they lend support to the proposal that the mechanisms of action of prolactin involve modification of the parent molecule by the target.
D000818:Animals; D005260:Female; D008970:Molecular Weight; D006080:Ovarian Follicle / Q000502:physiology / Q000648:ultrastructure; D010053:Ovary / Q000502:physiology*; D010455:Peptides / Q000302:isolation & purification*; D011388:Prolactin / Q000032:analysis*; D051381:Rats
D010455:Peptides; D011388:Prolactin