The Effect of Relaxin on Cyclic Adenosine 3′, 5′-Monophosphate Concentrations in Human Endometrial Glandular Epithelial Cells1

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Abstract
The effects of relaxin (RLX), forskolin (Fk), and 4-(3-butoxy-4-methoxybenzyl)-2-imidazolidinone (Ro, a phophodeisterase inhibitor) on the accumulation of cyclic adenosine 3',5'-monophosphate (cAMP) in human endometrial glandular epithelial cells were studied. Epithelial glands were isolated from the endometrium by digesting the viable tissue fragments with collagenase. The epithelial glands were incubated with Ro, RLX, and Fk separately or in combination. The amount of cAMP was determined at the end of incubation. A moderate increase in cAMP content was observed in epithelial glands incubated with Ro alone. Accumulation of cAMP after incubation with RLX was observed only in the presence of Ro. Increase of cAMP content in response to RLX and Ro was time- and dose-dependent. The accumulation of cAMP was apparent in 5 min, reached the maximum after 15 min, and remained elevated for 17 h incubation. One nanogram per millileter RLX was effective to increase the cAMP content, with a maximal response at 100 ng/ml. The effect of Ro and the combined effect of Ro and RLX on cAMP accumulation were studied in epithelial glands of 20 endometrial specimens obtained during different stages of the menstrual cycle. When epithelial glands were incubated with Ro alone, the cAMP concentration in glands from proliferative endometria was 120 +/- 67 pmol/mg protein (n = 6, means +/- SD), significantly higher than that of secretory endometria, 42 +/- 37 (n = 14, p = 0.007). RLX and Ro caused an additional increase of cAMP accumulation, 2- to greater than 10-fold increase over the sample incubated with Ro alone. There was no significant difference between proliferative and secretory phases (500 +/- 410, n = 6, and 470 +/- 300, n = 14, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)