Three categories of phosphatase activity toward adenosine triphosphate at pH 9.4 have been isolated histochemically: (1) phosphatase which requires -SH groups; (2) phosphatase which is inhibited by -SH groups; and (3) phosphatase which is relatively indifferent to -SH groups. This enzymatic activity was demonstrated in thin (5 µ), unfixed, frozen sections. True adenosine triphosphatase has been separated histochemically by virtue of its -SH dependence. It was demonstrated in cardiac and skeletal muscle fibers and in the mitochondria of the kidney tubules. The staining of these structures can be prevented by treatment with an -SH inhibitor, such as p-chloromercuribenzoate or salyrganic acid. Also their stainability can be restored by reversing the inhibition of the enzymes with -SH compounds, such as BAL or cysteine. There was no reaction of these particular structures when adenosine diphosphate or adenosine-5-phosphate was used, suggesting that under the conditions of this histochemical test only the terminal phosphate of adenosine triphosphate is removed. Phosphatase activity of the smooth muscle of the intestinal muscularis toward adenosine triphosphate differed from that of striated muscle in that it was less sensitive to p-chloromercuribenzoate. Sulfhydryl compounds, such as BAL or cysteine, enhanced the staining of the above mentioned sites of true adenosine triphosphatase activity. On the other hand, these -SH compounds are powerful inhibitors of alkaline phosphatase activity, especially toward adenosine-5-phosphate. When adenosine triphosphate was the substrate, BAL prevented the staining of the brush borders of the kidney tubules and intestinal epithelium, thus suggesting the participation of alkaline phosphatase in the dephosphorylation of adenosine triphosphate. Furthermore, the staining of these brush borders was unaffected by the -SH inhibitors. The strong phosphatase activity of endothelium and vascular smooth muscle toward adenosine triphosphate was seemingly indifferent to -SH groups, since the staining of these structures was not markedly influenced by -SH inhibitors or compounds. The nature of this staining has not been elucidated. Comparisons of the localization of phosphatase activity toward adenosine triphosphate, -diphosphate or -5-phosphate were made in the ventricle, tongue, kidney, and duodenum. Differences in the localization of phosphatase activity toward adenosine triphosphate and adenosine-5-phosphate were also made in liver, lung, spleen, uterus, and aorta.

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Radioautographic analysis of epithelial and stromal cell proliferation in the primate endometrial functionalis and basalis (rhesus monkey) has identified horizontal zonal patterns of mitotic activation and inhibition during natural menstrual cycles. At 1 h after a single i.v. injection of [3H]thymidine, mitotic activity in endometrial biopsies (hysterotomy) was determined on 9 days from the late proliferative to the late luteal phase (-2 days to + 14 days relative to the estrogen [E2]peak). Labeling indices (LIs) were determined within glandular segments of the 4 horizontal endometrial zones: Transient functionalis Zone I (luminal epithelium) and Zone II (uppermost gland); Germinal basalis: Zone III (middle gland) and Zone IV (basal gland). The size of the dividing epithelial populations (LI) differed zonally. During E2 dominance (-2 days to +3 days), the epithelial LIs of functionalis I (10 +/- 0.3%) and II (9.8 +/- 1.0%) were greater than those of basalis III (5.8 +/- 0.2%) and basalis IV (3.7 +/- 0.8%). During progesterone (P) dominance (+5 days to +14 days), epithelial mitosis was strongly inhibited in functionalis I (4.3 +/- 1.9%), functionalis II (0.8 +/- 0.2%), and basalis III (1.4 +/- 0.5%). Thus germinal basalis III was linked functionally with transient functionalis I and II by periovulatory uniformity in epithelial proliferation and postovulatory mitotic inhibition. A unique mitotic pattern set basalis IV apart from other zones by a steady rise in LI from 1% (-2 days) to 11% (+10 days). The LIs for stromal fibroblasts remained quite uniform in basalis IV but varied in other zones. Thus the postovulatory primate basalis was a distinct bipartite compartment in which the mitotic rate in basalis IV glandular epithelium increased steadily whereas that of basalis III was strongly inhibited. The remarkable enhancement of epithelial mitotic activity in basalis IV may reflect expansion of the stem-progenitor cell population for gestational growth or for post-menstrual regeneration.