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Five groups consisting of 72 young male Sprague-Dawley rats were submitted to dietary Zn deprivation (1 ppm versus 50 ppm for controls) for periods of 1 to 6 weeks with ad libitum or pair feeding. After 1 week of Zn deficiency, growth was almost arrested, the oesophageal epithelium became hyperplastic. After 3 weeks, the mast cell population of the bone marrow increased rapidly in ad libitum fed and also in pair-fed rats. Between 3 and 5 weeks, the thickness of the proximal epiphyseal plate of the tibia decreased by 33%. Contrary to Mg-deficient rats, Zn-deprived rats maintained their skin and thyroid mast cell populations after 5 weeks. The mast cell population of the metaphysis of the tibia increased from 1 to 5 weeks in both Zn-deficient and Zn-supplemented rats. In the Zn-deprived rats however, the mast cell population became increasingly higher than in the Zn-supplemented, from 1 to 5 weeks. In the pair-fed group, the mast cell population of the marrow was also significantly higher after 3 weeks. The special response of the bone marrow cells to Zn-depletion points to this tissue as a renewal site. Zinc may also be a maturation factor for mast cells.

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Chicks fed a rachitogenic diet for five weeks after hatching were then treated with a daily oral dose of 1,000 I.U. Vitamin D3 or a 1% addition to the feed of powdered leaves of Cestrum diurnum for periods of 1, 2, 4, 8, 16 and 30 days. Comparative studies were made on stained sections, microradiographs of undermineralized sections and alpharadiographs of demineralized sections. The present dose of Cestrum diurnum caused at first, a rapid maturation and mineralization of the epiphyseal cartilage and an intense growth and osteocytic osteolysis in the diaphysis of the tibia and femur. After 8 days however, growth decreased and the diaphysis gradually became petrotic. Under these conditions, the osteocytes degenerated and died. The areas of polysaccharide-rich, low density matrix which surrounded them, decreased gradually to become cementing lines, persistent after 30 days.

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Comparative counts of Alcian Blue-Basic Fuchsin-stained mast cells of the facial skin and bone marrow have been made in young rats of different sexes and strains, fed a diet deficient in magnesium (0.8 to 1 mg/100 g dry weight) for 4 weeks. Normal rats fed a magnesium-supplemented diet (65 mg/100 g dry weight) had about three times as many mast cells in the tibial metaphysis as in the facial skin. In both males and females fed the Mg-deficient diet, the marrow mast cells increased five to six times, while their number was concomitantly decreased in the skin. The marrow mast cells became also polymorphic, an indication of a possible preferential renewal site. Gonadectomy in the males had no effect on the above pattern. The administration of large doses of testosterone to males and estradiol to females depressed the mast cell population increase in the bone marrow and at the same time, moderated the loss of skin mast cells.

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Sterile sequentially extracted insoluble bone matrix gelatin and freeze-dried allogeneic demineralized whole bone matrix was implanted into a lumbar muscle pouch of 12 Sprague-Dawley rats fed a diet containing 0.9 ppm zinc and into 6 rats fed a diet containing 50 ppm zinc. Histological sections and microradiography demonstrated that skeletal tissue induction occurred in all instances. In the zinc-supplemented hosts, four weeks postimplantation, trabecular bone and bone marrow grew on both sides of the matrix implant which had been almost completely resorbed by matrixclast activity. However, in the zinc-deficient hosts, the central cavity of the matrix was first filled with mesenchyme and then cartilage cells which grew in the form of thin wedges into the implanted matrix. Poor vascularization appears to be an important factor in cell proliferation and abnormal differentiation in zinc deficiency.

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Bone resorption through osteocytic activity already recognized in all classes of Vertebrates, has been demonstrated in fragments of long bones from a non-identified reptile found in an Upper Cretaceous rock formation in Dinosaur National Park, Patricia, Alberta.

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Dietary magnesium deficiency has been more damaging to the mast cells in females than in males. Estradiol at a dose of 1.5 mg per week for 4 weeks and testosterone at a dose of 3 mg per week in the males have resulted in lesser mast cell depletion in the magnesium-deficient animals. Large doses of testosterone have also improved in the condition of the skin, decreased the severity of other magnesium deprivation symptoms such as nephrocalcinosis, bone hyperplasia and nervous manifestations in the males. Testosterone has had no beneficial effect on mast cells of the females but the large dose has protected the kidney against nephrocalcinosis. Estrogen administration has aggrevated the production of kidney stones in the females.

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The effects of magnesium deficiency in ovariectomized and estrogen-treated rats were examined in histological sections of bones and various soft tissues. The changes observed in the femora of intact rats deprived of magnesium for three weeks were: 1. a general increase in diaphyseal thickness, 2. the presence of localized fibrous or bony-like masses in subperiosteal and metaphyseal sites, and 3. the occurrence, although rare, of endosteal hyperplasia. In ovariectomized, magniesium-deprived animals, the incidence and location of fibrous masses were similar to that in the femora of magnesium-deficient intact rats; however, no increase in diaphyseal thickness was noted. Daily injections of 25 mug estradiol caused a reduction of the frequency of skeletal hyperplasia from 80% to 20%, as well as a reduction in femoral diaphyseal thickness. Estradiol hormone administration also brought about a marked alleviation of the dermal and neural manifestations of magnesium deficiency, but, at the same time, caused an exacerbation of renal calcinosis.

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HCl-demineralized mid-diaphyseal allogeneic segments of tibia were implanted in the lumbar muscles of rats fed either a magnesium-deficient or a magnesium-supplemented diet for one week prior to implantation and for three weeks thereafter. Histological studies, histochemical mucopolysaccharide determinations, tests for protease content of undemineralized bone tissue, and microradiography showed that in the normal hosts mostly trabecular bone grew into the heterotopic site, whereas in the deficient rats a large fibrous covering formed about the implant and in many instances cartilage was present in multiple locations under the fibrous coat. In some instances cartilage wedges, not preceded by multinucleated giant cells (matrixclasts), invaded the implant. This fibrocartilaginous response to an exogenous inductor resembled the modified growth pattern of bone recently reported in magnesium-deficient rats.

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Acetazolamide was injected into chick embryos on the 14th or 15th day of incubation. Doses ranging between 5 and 10 mg per egg produced a retardation in the growth of long bones. The affected bones contained a normal proportion of mineral as determined by ashing and presented a normal histological picture. On the basis of these findings, it is suggested that the alterations were not due to a specific direct effect of the drug on bones. The incorporation of 131-I by the thyroid glands of acetazolamide-injected embryos was analyzed radioautographically and quantitated on the same 6 mu-paraffin sections, with a thin window Geiger counter. The incorporation appeared notably reduced 3 h after the injection of acetazolamide and the reduction persisted for a least 24 h.the electron microscopical observation of thyroid follicular cells from similarly treated embryos showed that the cytological characteristics indicating an active protein synthesis were unmodified with respect to those found in control embryos. These results may indicate that acetazolamide inhibits the iodination of the throid hormone without interfering with the synthesis of the globulin. It is suggested that the growth retardation observed in the embryos treated with acetazolamide may be secondary to the action of the drug on the thyroid gland, although this action appears to be a transitory one.

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