Molecular homology between prolactin and ovarian peptides: evidence for physiologic modification of the parent molecule by the target

Nolin, J.M.

Peptides 3(5): 823-831


ISSN/ISBN: 0196-9781
PMID: 7177925
DOI: 10.1016/0196-9781(82)90022-5
Accession: 005919042

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In recent years, prolactin [PRL] has come to be recognized as an inhibitory gonadotropin, 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 PRL, but appear to be oligopeptides. This study examined whether these peptides are PRL fragments. The endpoint was immunohistochemical reactivity in ovarian follicles of cycling rats. Antisera to homologous pituitary PRL were used with and without modification by admixture either of highly purified rat pituitary PRL or of follicular fluid enriched in PRL-like bioactivities and depleted of peptides larger than 2000 MW. In growing follicles, immunohistochemical reactions, dependent upon unmodified anti-rat PRL, occurred in all 3 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 PRL as an inhibitory gonadotropin. Evidence that the reactions were dependent upon pituitary-like PRL, present in the follicle, was obtained with highly purified rat PRL which completely abolished reaction potential of the antisera in all follicles at all stages. 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 PRL and what appear to be small peptides of penultimate follicular origin and they lend support to the proposal that the mechanisms of action of PRL involve modification of the parent molecule by the target.