Local alteration in adenylate cyclase activity and stimulation response at implantation site in rabbit endometrium during early pregnancy

Adenylate cyclase activity and its hormonal stimulation were measured in endometrial tissue, and sex steroid levels were quantified in uterine tissue collected from pregnant and estrous rabbits. The tissues from pregnant animals were separated into implantation (ES) and interimplantation (IES) sites. Adenylate cyclase activity was measured in broken cell preparations by enzymatic conversion of alpha-32P-adenosine triphosphate (ATP) into 32P-cyclic adenosine 3', 5'-monophosphate using Mg2(+)-ATP as a substrate. The activity was measured with no addition (basal) and after stimulation with guanosine triphosphate (GTP), NaF, or increasing doses (1 nM to 100 microM) of isoproterenol (ISO) and prostaglandin E2 (PGE2). The presence of GTP was necessary to observe a stimulation by ISO and PGE2. During pregnancy, adenylate cyclase activity was reduced compared to activity at estrus on Day 6.5 (IES and ES) and on Day 9 (IES); however, it reached its highest level at ES (Day 9). The regulation of isoproterenol response followed a similar pattern. Dose responses to PGE2 were markedly affected by physiological status. The response was higher during pregnancy than at estrus, and response (percent of GTP), as well as sensitivity, was higher in IES than in ES on Day 6.5 and even greater on Day 9. The levels of estradiol (E2) were reduced during pregnancy, but comparable in ES and IES; however, progesterone (P) levels were reduced in ES, and the E2/P ratio was significantly higher (p less than 0.01) in ES (15 +/- 1, 17 +/- 2) than in IES (8 +/- 1, 6 +/- 0.8) on Days 6.5 and 9, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)