45CaCl2was injected into gerbils in single or multiple doses, and the resulting radioactivity in serum, otoconial CaCO3, bone samples, and selected labyrinthine epithelium was determined by liquid scintillation spectr...
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45CaCl2was injected into gerbils in single or multiple doses, and the resulting radioactivity in serum, otoconial CaCO3, bone samples, and selected labyrinthine epithelium was determined by liquid scintillation spectrometry. Incorporation into both utricularand saccu-lar otoconia occurred at the rate of 0.06–0.07 nmole Ca++per day, corresponding to a fractional rate of uptake of 0.1%. The retention of radioactivity had a half-life of approximately 11 days. The rate of incorporation of calcium for the middle ear ossicles was 5–7 times that for otoconia and was similar to that for otic capsule and skeletal bone. The level of45Ca++was higher in the pigmented regions of the utricular membranous wall than in the non-pigmented areas of the utricular and ampullary wall and in the stria vascularis.
Isolated superfused field stimulated biopsy specimens of human peripheral arteries and veins, preincubated with 3H-( - )-NOradrenaline (NA) to label the neural stores of NA, were used to study the potency of dopamine ...
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Isolated superfused field stimulated biopsy specimens of human peripheral arteries and veins, preincubated with 3H-( - )-NOradrenaline (NA) to label the neural stores of NA, were used to study the potency of dopamine (DA) and of NA as triggers of alpha-adrenoceptor mediated negative feedback control of sympathetic neurotransmitter secretion, evoked by stimulation with trains of 300 shocks at 1 Hz. In this preparation DA was found to be only slightly less potent than NA in depressing both the secretion of 3h-na, and the contractile response, evoked by nerve stimulation. DA depressed the contraction evoked by exogenous NA as well, but to a very much smaller extent. On the other hand, DA was a very weak agonist on the alpha receptors of the smooth muscle; nearly 1000 times higher concentrations of DA were required to mimick contractions evoked by exogenous NA. The results show that the neural alpha-receptor function involved in control of NA secretion differs considerably from the alpha-receptors of e.g. smooth muscle, with respect to sensitivity to DA. It seems possible that the observed depressing effect of DA on NA secretion may be of pharmacological and clinical interest; it may at least in part explain the vasodilating effect of DA infusions in man.
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