Angiogenesis is a pivotal event in endochondral ossification. Vessels grow into the hypertrophic cartilage and erode it to produce a scaffold on which osteoblasts settle to produce woven bone. A new culture system was used to determine whether growth-plate chondrocytes produce an angiogenic molecule. Chondrocytes from primary growth plates of bovine fetuses were separated into maturationally distinct subpopulations. When cultured these cells produce an extensive extracellular matrix and the prehypertrophic cells mature to express the hypertrophic phenotype defined by the synthesis of type X collagen and matrix calcification. The culture medium collected from the hypertrophic cells contains a chemoattractant, nonmitogenic molecule for bovine endothelial cells which can induce angiogenesis in vivo in the rabbit cornea model. This molecule has a Mr of approximately 120 x 10(3). The production of this molecule by hypertrophic cells is enhanced by both 1,25-(OH)2 vitamin D3 and 24,25-(OH)2 vitamin D3 at 10(-8)-10(-12) M, but only in pre- and early hypertrophic cells. In contrast, these metabolites have either no effect or an inhibitory effect on the more mature hypertrophic cells. These results describe for the first time the production of an angiogenic molecule by hypertrophic chondrocytes. They demonstrate an important role for vitamin-D3 metabolites in regulating hypertrophy and angiogenesis during normal skeletal growth and differentiation. Thus, a defective regulation of these processes, due to the lack of vitamin-D metabolites, may explain the observed enlargement of the hypertrophic zone and impairment of skeletal growth in rickets which is induced clinically and experimentally by a deficiency of vitamin D.

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A survey of 188 psychiatric social workers indicated an overall positive level of job satisfaction. Overall job satisfaction was found to be primarily determined by position satisfaction. The major correlate of position satisfaction was the professional respect received from other disciplines and not the specific tasks performed. These findings were interpreted as reflecting the obfuscating effect of hospital team interactions on job satisfaction. In these settings, the social workers were often so dependent on the quality of these team interactions to derive the variety, autonomy, and value in their work that it was difficult for them to keep subjectively clear the actual level of satisfaction with the work itself. Social work supervisors need to focus on developing a stronger sense of practice excellence and forging a subjective separation between task-derived achievement and interpersonal enjoyment. Results also showed the importance of educational and professional development opportunities in maintaining overall job satisfaction.