Nitric oxide synthase acutely regulates progesterone production by in vitro cultured rabbit corpora lutea

Abstract

We examined the presence and the regulation of nitric oxide (NO) synthase (NOS) using in vitro cultured corpora lutea (CL) obtained from rabbits at days 4 and 9 of pseudopregnancy. The role of NO and NOS on steroidogenesis was also investigated using the same CL preparations after short-term incubations (30 min and 2 h) with the NO donor, sodium nitroprusside (NP), the NOS inhibitor, N -nitro--arginine methyl ester (-NAME) and prostaglandin (PG) F-2 . The basal NOS activity was greater in CL at day 4 than at day 9, and was also differently modulated by PGF-2 , depending on the age of the CL. The addition of PGF-2 to day 4 CL had no effect, but PGF-2 on day 9 caused a threefold increase in NOS activity. NP caused a two-to fivefold decrease in release of progesterone from CL of both ages, and this inhibitory effect on steroidogenesis was reversed by -NAME. All treatments failed to modify basal androgens and 17 -oestradiol was not detectable in either control or treated CL. These results suggest that NO is effectively involved in the regulation process of steroidogenesis, independently of 17 -oestradiol. PGF-2 had no effect on day 4, but induced luteolysis on day 9, by reducing progesterone (Pc0·01) to about 18% of control. The luteolytic action of PGF-2 was completely reversed by co-incubation with -NAME, thus supporting the hypothesis that luteolysis is mediated by NO. The addition of NP or -NAME did not modify the in vitro release of PGF-2 . We hypothesised that PGF-2 upregulates NOS activity and, consequently, the production of NO, which acutely inhibits progesterone release from day 9 CL of pseudopregnant rabbits.

Nitric oxide synthase activity and progesterone release by isolated corpora lutea of rabbits in the early and mid-luteal phases of pseudopregnancy are modulated differently by prostaglandin E-2 and prostaglandin F-2alpha via adenylate cyclase and phospholipase C

“…Regarding the functional study of NOS, the present data confirm our previous results (Gobbetti et al 1999), as CL collected in the early luteal phase of pseudopregnancy, at day 4, had greater basal activity than did CL collected in the mid-luteal phase, at day 9. Preliminary evidence that rabbit luteal tissue expresses endothelial NOS, which affects progesterone release in vitro, together with the present finding that its levels of activity are differently modulated by PGs, strongly supports a functional role for NOS in the regulation of steroidogenic capacity in the CL of this species in response to both luteolytic and luteotrophic factors.…”

“…injection of 0·8 µg gonadotrophinreleasing hormone (GnRH) analogue (Receptal; RousselHoechst, Frankfurt, Germany). Previous experiments in our laboratory showed that this hormonal protocol was effective in inducing ovulation in does (Gobbetti et al 1999). The day of GnRH injection was designated day 0.…”

“…Subsequent work demonstrated that the NO/NOS system is involved in the regulation of steroidogenesis in rabbit CL and that NO plays a relevant role in the events characterising prostaglandin F-2 (PGF-2 )-induced luteolysis (Gobbetti et al 1999).…”

“…With this in view, total NOS activity and progesterone output were monitored after short-term coincubation of in vitro cultured CL obtained on days 4 and 9 of pseudopregnancy with a number of inhibitors of the phospholipase C (PLC)/protein kinase C (PKC), and cAMP/protein kinase A (PKA) systems, together with either PGE-2 or PGF-2 . The study focused on these two sets of CL for their well-established differences in vivo (Marcinkiewicz et al 1992 and in vitro responsiveness to PGF-2 (Gobbetti et al 1999).…”

Estudio de los factores materno-embrionario que determinan la fertilidad y prolificidad en una línea de conejo seleccionada por velocidad de crecimiento

“…En conejas pseudogestantes, la actividad enzimática NOS se ha relacionado con los niveles luteales y plasmáticos de progesterona, de foma que una disminución de estos niveles va acompañado de un aumento en la actividad de esta enzima entre los días 15 y 18, momento en el que los cuerpos lúteos pasan de la última fase luteal al estado de cuerpo lúteo en regresión funcional (Boiti et al, 2004). Gobbetti et al (1999) demostraron que el óxido nitroso (NO) inhibe la producción de progesterona por parte de los cuerpos lúteos y, a su vez, la prostaglandina F-2α (PGF2α) regula la actividad de la enzima óxido nitroso sintasa (NOS). Durante el desarrollo luteal, eNOS e iNOS (NOS endotelial e inducible, respectivamente) regulan la actividad de NO (Boiti et al, 2003).…”