EXPRESSION AND LOCALIZATION OF RELAXIN IN THE OVARY OF THE MARE

Immunoreactive, chromatographic and molecular techniques were used to study the expression of relaxin in mare ovaries at different stages of the oestrous cycle. Relaxin in follicular fluid ranged from 1.6 to 2. 5, from 1.4 to 5.2, from 1.2 to 6.7 and from 1.0 to 3.5 ng ml(-1) in s mall (less than or equal to 2 cm), medium (> 2 less than or equal to 3 cm), medium-large (> 3 less than or equal to 4 cm) and large (> 4 cm) follicles, respectively, and total content of fluid relaxin per folli cle increased (P< 0.05) with follicular size. When subjected to revers e phase HPLC analysis, follicular fluid yielded absorbance profiles co rresponding closely to those of purified relaxin, and immunoreactive p eaks in follicular fluid fractions measured by radioimmunoassay matche d peaks of the relaxin standard. While relaxin was localized immunocyt ochemically to granulosa and theca cells of preovulatory follicles, no rthern blot and reverse transcriptase-PCR followed by Southern blot an alysis failed to detect a relaxin transcript in these tissues. A singl e relaxin transcript (428 bp) corresponding to mRNA encoding relaxin w as identified in early, mid-and late stage corpora lutea but not in co rpora haemorrhagica or albicantia. Northern blot analysis revealed a w eakly expressed 1 kb transcript in total cellular RNA from mature corp ora lutea. In situ hybridization studies localized the mRNA to the lar ge luteal cells of mature corpora lutea and relaxin protein was detect ed by immunocytochemistry in the same tissue. This is the first report demonstrating relaxin in the equine ovary and its expression by lutea l cells, thereby suggesting a role for relaxin in follicular or corpus luteum function in cyclic mares.