The physiological role of beta-endorphin in porcine ovarian follicles.
Beta-endorphin-like immunoreactivity (beta-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 beta-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 beta-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 pre-ovulatory period of the cycle. Concentrations of beta-END-LI in FF from medium follicles were relatively equal throughout the cycle (days 6-21). No significant differences in beta-END-LI levels were found between small, medium and large follicles from days 17-21. However, beta-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 (P4), testosterone (T) and 17 beta-oestradiol (E2) on beta-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 beta-END-LI output in a dose-dependent fashion. This stimulatory effect of the gonadotrophin was inhibited by the highest dose of P4 (10(-5) M). The effect of PRL and the steroids added to the cultures on beta-END-LI release was negligible. FSH- or PRL-induced P4 secretion by GCs was essentially abolished by both FK 33-824 and NAL. However, androstenedione (A4) and testosterone output by the cells was greatly potentiated by FK 33-824. In the presence of NAL, FSH or PRL, A4 release stimulated by FK 33-824 was suppressed to the basal level. Secretion of E2 was completely free from the influence of FK 33-824 or NAL; only oestrone (E1) output was modulated by them in cultures where FSH or PRL was present. In conclusion, FSH appears to be the key regulator of beta-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.
Kaminski
T
T
Department of Animal Physiology, Warmia and Masuria University in Olsztyn, Olsztyn-Kortowo, Poland.
Siawrys
G
G
Bogacka
I
I
Przala
J
J
D000818:Animals; D005405:D-Ala(2),MePhe(4),Met(0)-ol-enkephalin / Q000494:pharmacology; D004357:Drug Synergism; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D015571:Follicular Fluid / Q000737:chemistry; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D006080:Ovarian Follicle / Q000502:physiology*; D011388:Prolactin / Q000494:pharmacology; D013256:Steroids / Q000494:pharmacology; D013552:Swine / Q000502:physiology*; D001615:beta-Endorphin / Q000032:analysis / Q000378:metabolism / Q000502:physiology*
D009292:Narcotic Antagonists; D013256:Steroids; D009270:Naloxone; D001615:beta-Endorphin; D005405:D-Ala(2),MePhe(4),Met(0)-ol-enkephalin; D011388:Prolactin; D005640:Follicle Stimulating Hormone