Newborn rat calvariae, cultured for 24 h in the presence of cortisol (10(-6) M) have a cAMP response to parathyroid hormone (PTH) about twice as high as calvariae cultured in a control medium. This effect of cortisol is dose related; a maximal effect is evident at 10(-6) M, while none is detectable at 10(-9) M or less. With 10(-6) M estradiol, progesterone, or cholesterol, no effect on cAMP responsiveness is observed. This indicates that the effect observed with cortisol is specific. The effect of cortisol is more pronounced when isobutyl-methylxanthine (10(-4) M) is present during the subsequent incubation with PTH. Preincubation of the tissue with cortisol for 30 min before the addition of PTH has no effect. Similarly, when cortisol is added in conjunction with PTH, no effect is found. In no case did cortisol (10(-6) M) alter the time course of the PTH-induced cAMP effect when compared to the response of fresh calvariae. The results indicate that corticosteroids have an important function in maintaining cAMP responsiveness of bone to PTH in vitro.
The biological activities of bovine parathyroid hormone (BPTH) and fragments comprising portions of its amino-terminal sequence have been compared in three different assay systems using embryonic rat bone in vitro. Whereas the 3-34 fragment was without significant activity the 1-34 fragment caused all the actions characteristic of BPTH 1-84, extending to bone previous evidence that the amino-terminal residues are sufficient for expression of the biological effects of intact parathyroid hormone. However, the relative potencies of the fragment and the intact hormone were different in the various systems. BPTH 1-34 showed relatively low osteolytic activity and induced anabolic effects in both osteoblasts and cartilage cells of cultivated embryonic mouse radii which were not evoked by the intact hormone. Further work is required to determine the mechanisms responsible for these interesting alterations in relative potency of fragment and native hormone.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.