ABSTRACT
The aim of this study was to determine whether losartan, an angiotensin II (Ang II) type 1 (AT(1)) receptor could influence the CA release from the isolated perfused model of the rat adrenal medulla. Losartan (5~50 microM) perfused into an adrenal vein for 90 min produced dose- and time-dependent inhibition of the CA secretory responses evoked by ACh (5.32 mM), high K(+) (56 mM, a direct membrane depolarizer), DMPP (100 microM) and McN-A-343 (100 microM). Losartan failed to affect basal CA output. Furthermore, in adrenal glands loaded with losartan (15 microM) for 90 min, the CA secretory responses evoked by Bay-K-8644 (10 microM, an activator of L-type Ca(2+) channels), cyclopiazonic acid (10 microM, an inhibitor of cytoplasmic Ca(2+)-ATPase), veratridine (100 microM, an activator of Na(+) channels), and Ang II (100 nM) were markedly inhibited. However, at high concentrations (150~300 microM), losartan rather enhanced the CA secretion evoked by ACh. Collectively, these experimental results suggest that losartan at low concentrations inhibits the CA secretion evoked by cholinergic stimulation (both nicotininc and muscarinic receptors) as well as by membrane depolarization from the rat adrenal medulla, but at high concentration it rather inhibits ACh-evoked CA secretion. It seems that losartan has a dual action, acting as both agonist and antagonist to nicotinic receptors of the rat adrenal medulla, which might be dependent on the concentration. It is also thought that this inhibitory effect of losartan may be mediated by blocking the influx of both Na(+) and Ca(2+) into the rat adrenomedullary chromaffin cells as well as by inhibiting the Ca(2+) release from the cytoplasmic calcium store, which is thought to be relevant to the AT(1) receptor blockade, in addition to its enhancement of the CA release.
ABSTRACT
Split hand/split foot malformation (SHFM; ectrodactyly) is genetically heterogeneous, with mutations identified at five loci (SHFM1 at 7q21.3, SHFM2 at Xq26, SHFM3 at 10q24, SHFM4 at 3q27 and SHFM5 at 2q31). In this study, we attempted to identify and localize the causative allele of a Korean case of SHFM. Pedigree analysis showed that the Korean SHFM was autosomally dominant and its penetrance was high, indicating that it was not caused by SHFM2. Clinical features were variable, but limited to the four limbs unlike SHFM1, SHFM4 and SHFM5. G-banding and FISH failed to identify any chromosomal abnormalities. We also performed mutation screening by SSCP and DNA sequencing, as well as loss of heterozygosity (LOH) analysis, to exclude the possibility that SHFM4 or SHFM5 were involved; these revealed no mutations in gene p63 and no LOH on 2q31, respectively. It therefore appears that the Korean SHFM may be caused by mutation of SHFM3. In fact, linkage analysis using informative microsatellite markers indicated that SHFM3 was linked to D10S577 with a maximum LOD score of 1.15 at recombination fraction zero. Finally, we identified two novel alleles (191 and 211 bp) of D10S577 that have not been found in Western populations.
