Uterine Catecholamines and Prostaglandins during the Estrous Cycle of the Rat*

The uterine contents of norepinephrine, epinephrine, dopamine, and prostaglandins F and E were determined on each day of the rat estrous cycle. Catecholamines were determined by high performance liquid chromatography with electrochemical detection (HPLC-EC) as well as by a radioenzymatic technique; prostaglandins were quantitated by RIA. The norepinephrine and dopamine values obtained by the radioenzymatic assay were approximately 1.5 times as high as the values obtained by HPLC-EC (norepinephrine, 285 vs. 188 ng/g; dopamine, 11.0 vs. 7.5 ng/g). Despite this difference in levels, both analytic techniques showed a decline in uterine norepinephrine from diestrus to estrus, followed by a significant (P less than 0.01) increase in norepinephrine on the day of metestrus. A cyclic pattern was also revealed for uterine dopamine concentration. There was a decline in dopamine concentration from diestrus to proestrus (radioenzymatic, P less than 0.01), followed by a return to high levels at metestrus (HPLC-EC). Epinephrine levels were low (undetectable by radioenzymatic assay; 24 ng/g by HPLC-EC) and showed no variation during the estrous cycle. Prostaglandin F was uniformly higher than prostaglandin E (10 vs. 2.5 ng/uterus). Significant increases in the uterine contents of both prostaglandins were shown on the day of proestrus.