Browsing by Subject "Vascular smooth muscle"
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Item Studies on the mechanism of the vascular action of parathyroid hormone(Texas Tech University, 1984-05) Yang, Chuen-mayThe hypotensive action of parathyroid hormone (PTH) has recently been shown to be one of the biological properties of the hormone. The purpose of this dissertation is to study the involvement of cyclic AMP (c-AMP) and calcium utilization as mechanisms in this hypotensive action of PTH. Iri. vitro vascular tension data were correlated with biochemical measurements in studying both mechanisms. In the presence of theophylline, a phosphodiesterase inhibitor (PDE-I), the 2:11 vivo hypotensive action of PTH was augmented in the dog. In the in vitro rat tail artery tension studies, the same dose of 3-isobutyl-l-methlxanthine, another PDE-I, also augmented the vasorelaxing efffect of PTH. On the other hand, in the presence of imidazole, a PDE stimulator, the vasorelaxing effect of PTH was inhibited. Measurements of c-AMP indicated that PTH increased c-AMP content in both quiescent and stimulated rat tail artery. This increase in c-AMP content and the decrease in tension of the rat tail artery preparation by PTH showed a cause-effect temporal relationship. Vasoconstrictors, such as KCl and arginine vasopressin, alone did not affect the tissue c-AMP content significantly. In the in vitro study of the involvement of calcium utilization, a parallelism was observed in the effect of PTH and D600. Both PTH and D600 were more effective in inhibiting the doseresponses to KCl than the ones to NE. They were also able to inhibit significantly the Ca^ -induced contraction in the high-K medium. The utilization of intracellular calcium by NE in a Ca^ -free medium was not significantly affected by PTH and D600. In ^^Ca^'^ fluxes studies, both PTH and D600 inhibited high-K induced ^^Ca^ uptake. PTH seemed to be a potent Ca^ entry blocker. The effect of PTH in depressing the K -induced **^Ca^ uptake was not due to an increased efflux. In conclusion, the present study suggests that both an increase in vascular c-AMP content and an inhibition of extracellular Ca^ entry are involved in the vasorelaxing effect of PTH.