Estrogen receptors (ER) and progesterone receptors (PgR) were studied immunohistochemically using specific antireceptor monoclonal antibodies in uterine tissue samples from 33 women in various stages of the menstrual cycle. Immunohistochemical localization was quantified as to intensity of staining and tissue distribution in glandular epithelium, stroma, and myometrium, and the results were compared with those of standard ligand binding assays. In all samples ER and PgR localized within the nuclei of target cells. The maximal concentrations of ER and PgR occurred in the mid- to late proliferative phase of the menstrual cycle. ER content declined throughout the secretory phase. In contrast, PgR content underwent unexpectedly complex and dyssynchronous fluctuations during the secretory phase of the menstrual cycle. Specifically, the glandular epithelium had diminished PgR content, while the stroma and myometrium maintained a significant PgR content. PgR and perhaps ER are not concordant in different cell types within the uterus. Segregation of function through alteration of receptor content may be an important mechanism in steroid-dependent growth and differentiation of target tissues.

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SUMMARY1. The effect of heart rate on left ventricular output was examined in seven fetal lambs at ages of 128 to 140 gestational days. The fetuses had been surgically instrumented at least 4 days previously with an ascending aortic flow probe, left ventricular dimension transducers, and left and right atrial pacing electrodes.2. Natural variations in heart rate of the lambs taken as a group correlated positively with left ventricular output, and negatively with ventricular end-diastolic dimension and stroke volume (P < 0-0001).3. Rate did not affect output with right atrial pacing. With left atrial pacing, it correlated negatively with output (P < 0-0001). At both pacing sites, rate correlated negatively with end-diastolic dimension and stroke volume (P < 0-0001).4. The introduction of a longer interval during each pacing rate circumvented the rate-related changes in dimension and allowed the ventricle to fill to the same end-diastolic dimension. The systole at the end of the longer interval had a greater stroke volume than the preceding systoles. The faster the preceding paced rate, the greater was the stroke volume (P < 0-0001).5. This study demonstrates that experimentally induced variations in heart rate produce changes in end-diastolic volume and contractility which prominently affect stroke volume. Over a broad range of rates, however, the effect of rate on left ventricular output is either negative or absent. With naturally occurring rate changes, there are additional changes in contractility and venous return which affect stroke volume. These combine to produce a positive relation between heart rate and left ventricular output. These effects of heart rate on output are qualitatively similar to those described for the adult animal.