Variations in the occurrence of silver‐staining nucleolar organizer regions (AgNORs) in non‐proliferating and proliferating tissues

Previous studies on the subject of silver‐staining nucleolar organizer regions (AgNORs) as indicators of precise proliferative status of tissues have sometimes resulted in ambiguity. The studies, however, have most frequently addressed themselves to the prognosis of neoplasias, with the aim of using AgNORs principally to distinguish between benign and malignant tumours. This investigation was to determine a base‐line relationship of AgNOR clusters to proliferation and thus concentrated on normally proliferative tissues and conditionally renewing tissues after appropriate stimulation. Two murine transplantable tumours were also examined as examples of frank malignancy. As an example of the former, variations in AgNOR clusters were noted in the small intestine of man, mouse, and rat. The conditionally renewing systems of liver, prostate, and salivary glands were stimulated into proliferation by two‐thirds partial hepatectomy, castration followed by treatment with testosterone, and isoproterenol treatment, respectively, in rat models; the murine sarccma SaF and carclnoma CaNT provided relatively simple malignant tumours for AgNOR investigation. Proliferation was monitored by noting labelling indices after injection with bromodeoxyuridine (BrdUrd) in vivo followed by immunocytochemical visualization of S‐phase cells. In all tissues, an increase in the size of AgNOR clusters rather than their number correlated positively with elevated labelling, particularly with the emergence of silver‐staining regions of 2–3 μm visible diameter. Thus, increased AgNOR cluster size (diameter) as representative of AgNOR cluster/nucleolus volume was found to be dependent on proliferative activity in a range of normal and neoplastic tissues.