There are substantial changes in maternal skeletal dynamics during pregnancy, lactation, and after lactation. The purpose of this study was to correlate changes in cortical and cancellous bone mass, structure, and dynamics with mechanical properties during and after the first reproductive cycle in rats. Rats were mated and groups were taken at parturition, end of lactation and 8 wk after weaning, and were compared with age-matched, nulliparous controls. Measurements were taken on femoral cortical bone and lumbar vertebral body cancellous bone. At the end of pregnancy, there was an increase in cortical periosteal bone formation and an increase in cortical volume, but a suppression of turnover in cancellous bone with no change in cancellous or cortical mechanical properties. Lactation was associated with a decrease in cortical and cancellous bone strength with a decrease in bone volume, but an increase in turnover on cancellous and endocortical surfaces. After lactation, there was a partial or full restoration of mechanical properties. This study demonstrates substantial changes in bone mechanics that correlate with changes in bone structure and dynamics during the first reproductive cycle in rats. The greatest changes were observed during the lactation period with partial or full recovery in the postlactational period.

There is a decrease in cancellous bone mass and strength during lactation but these are partially or completely reconstituted in the postlactational period. The purpose of this study was to determine changes in cancellous bone structure and formation after lactation in established breeder rats. For this, rats were taken at the end of the second pregnancy (Preg-2) and second lactation (Lac-2) and 2, 4, and 6 weeks after weaning. Nulliparous (NP) groups were included for comparisons. Bone structure was measured using morphometric methods and bone dynamics by histomorphometry. Tibial metaphyseal cancellous bone was lost during the first reproductive cycle, as expected, and again depleted during the Lac-2. Bone formation indices were elevated at the end of Lac-2, compared with those at the end of the second pregnancy or in the nulliparous animals. Within 2 weeks after the second weaning, the amount of double-labeled surface (dLS) increased ϳ800%, the mineralizing surface (MS) increased >400% with similar increases in bone formation rates (BFRs), compared with already elevated bone formation measured at the end of Lac-2. From 2 to 4 weeks after lactation, there were commensurate increases in cancellous bone mass and structural indices with essentially complete restoration of cancellous bone volume and structure compared with that measured at the end of Preg-2. The results show rapid and substantial increases in bone formation with reconstitution of cancellous bone mass and structure after lactation in rats. The skeletal changes that occur during the postlactational period may serve to prepare and protect the maternal skeleton for subsequent reproductive cycles. (J Bone Miner Res 2002;17:1954 -1960

Macrophages are common in rat testicular interstitial tissues. Interstitial-tissue macrophages were characterized using ultrastructural, cytochemical, immunologic, and autoradiographic methods. Testicular interstitial-tissue macrophages have a single indented nucleus, paranuclear Golgi complex, rough endoplasmic reticulum, coated vesicles, and numerous heterogeneous lysosomal vacuoles. Long filopodia and lamellopodia extend from the macrophage cell body into the lymphatic space. Macrophages are usually found adjacent to Leydig cells, and numerous Leydig cell processes are inserted into coated membrane invaginations on the macrophage surface. Secondary lysosoma1 vacuoles in the macrophage are cytochemically reactive for acid phosphatase (trimetaphosphatase) and aryl sulfatase. Testicular interstitial macrophages are endocytically active, avidly incorporating exogenously administered trypan blue dye and monomeric plutonium-citrate. Macrophages were isolated from the testes by allowing them to adhere to glass. The isolated macrophages were found to have receptors for the Fc portion of immunoglobulin G on their surface. The association of macrophages with Leydig cells and their endocytic and immunologic activity suggests that these cells may play an important role(s) in testicular functions. In addition, the ability of these cells to incorporate exogenous materials indicates that they could have a role in gonadal toxicity reactions.

No abstract

Bone-lining cells cover the majority of trabecular bone surfaces in adult long-lived mammals. The morphology, ultrastructure, and population density of bone-lining cells was investigated in several fatty marrow trabecular bone sites in adult beagles of different ages. Although there is a low population density of bone-lining cells on bone surfaces, their total numbers greatly exceed the numbers of osteoblasts and osteoclasts found on these bone surfaces. In one of the bone sites studied, there are significantly fewer bone-lining cells in very old beagles (12-16 years old) when compared to young adult beagles (1.5-3 years old), otherwise there are no differences in the cell population that could be attributed to aging. Bone-lining cells are flattened against bone surfaces and have flat or sometimes ovoid-shaped nuclei which are often located adjacent to areas in the fatty marrow where capillaries are found. When viewed in the electron microscope, bone-lining cells contain few organelles, and the attenuated cytoplasm of these cells is well extended over bone surfaces. The bone-lining cell cytoplasm does not appear to form a continuous layer over the bone surface, as numerous gaps and spaces are seen. Bone-lining cell processes are frequently joined by junctions morphologically similar to gap junctions. Between the lamina limitans of the bone matrix and the bone-lining cell, as well as between the bone-lining cell and the adjacent fat cells, there are layers of connective tissue containing collagenous fibers and other amorphous material. These findings are discussed in relation to the possible role of bone-lining cells in the regulation of mineral homeostasis.