The physiological role of ?-endorphin in porcine ovarian follicles

Abstract

-β-Endorphin-like immunoreactivity (β-END-LI) was measured by radioimmunoassay in porcine ovarian follicular fluid (FF) from small, medium and large follicles throughout the oestrous cycle. The concentration of β-END-LI in FF from small follicles collected on days 1-5 of the cycle was at least tenfold higher than in the fluid from any other follicles independently from their size and the period of the cycle. The level of β-END-LI in small follicles on days 6-10 was drastically decreased. Subsequently, on days 11-16 its concentration was enhanced and reduced again in preovulatory period of the cycle. Concentrations of β-END-LI in FF from medium follicles were relatively equal throughout the cycle (days 6-21). No significant differences in β-END-LI levels were found between small, medium and large follicles from days 17-21. However, β-END-LI concentrations in medium follicles on days 11-13 and 14-16 were statistically lower than those in small follicles. Moreover, the effects of FSH, prolactin (PRL), progesterone (P 4 ), testosterone (T) and 17 β-oestradiol (E 2 ) on β-END-LI release by granulosa cells (GCs) from large follicles and, on the other hand, the effects of the opioid agonist FK 33-824 alone or in combination with FSH, PRL or naloxone (NAL) on follicular steroidogenesis were studied. FSH drastically increased β-END-LI output in a dose-dependent fashion. This stimulatory effect of the gonadotrophin was inhibited by the highest dose of P 4 (10 -5 M). The effect of PRL and the steroids added to the cultures on β-END-LI release was negligible. FSH-or PRL-induced P 4 secretion by GCs was essentially abolished by both FK 33-824 and NAL. However, androstenedione (A 4 ) and testosterone output by the cells was greatly potentiated by FK 33-824. In the presence of NAL, FSH or PRL, A 4 release stimulated by FK 33-824 was suppressed to the basal level. Secretion of E 2 was completely free from the influence of FK 33-824 or NAL; only oestrone (E 1 ) output was modulated by them in cultures where FSH or PRL was present. In conclusion, FSH appears to be the key regulator of β-END-LI secretion by porcine granulosa cells. Moreover, steroidogenesis in pig granulosa cells is modulated by opioid peptides acting both alone and by way of interaction with FSH or PRL.opioid peptides / β-endorphin / porcine granulosa cells / steroid secretion Reprod. Nutr. Dev. 40 (2000) 63-75 63

Correlation between ovarian steroidogenesis and beta-endorphin in the Lizard Uromastyx acanthinura: Immunohistochemical approach.

“…This suggestion is supported by findings that in rat ovaries, hCG and LH significantly increase the proopiomelanocortin mRNA expression [19] and the release of endorphin [16] and that FSH stimulates the secretion of endorphins by the porcine granulosa cells [13].…”

“…In addition, the β-endorphin participates to the control of reproductive function through a direct local action within reproductive tissues. The genes encoding for precursor (proopiomelanocortin) of this opioid peptide are expressed in the porcine granulosa cells [8] and several β-endorphins derived from this precursor have been detected in ovaries and follicular fluids in mammalian species [9][10][11][12][13][14][15][16][17] and lizard [18].…”

“…The reports pertaining to the influence of endorphin on steroidogenesis in mammals granulosa cells [13], theca interna cells [9], and luteal cells [12,13,14,15,17] suggest that the opioid peptide exerts autocrine and/or paracrine effects in the ovary. The inhibitory effect of endorphin on synthesis of the estradiol and androgen was demonstrated in cells of porcine theca interna [20].…”

Molecular cloning, tissue distribution and quantitative analysis of two proopiomelanocortin mRNAs in Japanese flounder (Paralichthys olivaceus)

“…Besides the long axis, endogenous opioid peptides (EOP) are also implicated in local interactions. Both theca and granulose cells appear to be the major POMC mRNA producing cells of ovarian tissue in mammals (11,(29)(30)(31). Although its functional role is still unknown, the expression of POMC has also been detected in testis (19,32,33).…”

SUBSTANCE P AND SS-Endorphin ACT AS POSSIBLE CHEMOATTRACTANTS OF MOUSE SPERM

“…Ovarian synthesis and secretion of b -endorphin is controlled by gonadotrophins [15,22]. This opioid peptide exerts autocrine or paracrine effects in the ovary by influence on steroidogenesis in granulosa and luteal cells [6,14,15,38]. The direct effect of b -endorphin on the gametes was examined only in the case of influence of spermatozoa.…”