The embryo influences adenylate cyclase activity and hormonal response in rabbit myometrium during early pregnancy

The effect of pseudopregnancy (PSPG; days: 0 (estrus), 1, 6.5, 9 and 15) and pregnancy (PG; days: 6.5, 9 and 15) on adenylate cyclase (AC) activity was verified in rabbit myometrium. During PSPG, there was a time related decline in basal activity from 71 +/- 16.2 (D 0) to 13.1 +/- 1.6 (PSPG-D9) pmoles cAMP formed/mg prot-min. Stimulation of the enzyme by GTP, Isoproterenol (ISO), Prostaglandin E2 (PGE2) or Sodium Fluoride (NaF) followed a similar pattern. AC activity was compared in myometrial tissues of pregnant animals (PG) separated into embryonic (ES) and interembryonic (IES) sites. On days 6.5 and 9, AC activity measured in tissues from PG rabbits (ES and IES) was always higher than that found in tissues from PSPG animals on corresponding days. On day 6.5, AC activity was slightly higher (p less than 0.01) in ES than in IES. This was confirmed on day 9 where basal as well as GTP, ISO and PGE2 stimulated activities were higher in ES than in IES (p less than 0.001). Dose response to ISO, expressed as % of GTP, were similar on D0, 1, 6.5 and 15 of PSPG. However, on day 9, there was a striking diminution in response reflected by a lower stimulation at suboptimal dose (0.1 microM; p less than 0.05) from 115 +/- 2 on day 0 to 104 +/- 4 on day 9. These results suggest that protein content which is increased during pseudopregnancy could be responsible for the decline of AC activity. However, results obtained on day 9 and 15 suggest that other factors are involved. Dose responses to ISO during PG showed an alteration in response on days 6.5 and 9 at ES. It was reflected by a higher stimulation at suboptimal (0.1 microM) and optimal doses (100 microM). These results suggest that myometrial AC activity could be regulated by the presence of the embryo.