Ventilatory functions in pregnancy Mokkapatti, R; Prasad, E C; Venkatraman ...
Indian journal of physiology and pharmacology
35, Številka:
4
Journal Article
The apparatus used was a dry bellows spirometer and a Wright's peak flow meter. Statistical analysis using the student's t test showed a significant reduction in peak expiratory flow rate, forced ...vital capacity and first second forced expiratory volume in the third trimester compared to controls. Besides, mid-expiratory flow rates were significantly lower in the first trimester. Spirometric performance was reduced in all three trimesters when compared to controls, although values were within physiological limits. This reduction may assume importance in patients with associated diseases or those requiring surgery.
The objectives of the present study were to determine whether angiotensin II (Ang II) modifies beta-adrenoceptor-induced cAMP production in preglomerular microvascular smooth muscle cells (PMVSMCs), ...to determine whether the Ang II/beta-adrenoceptor interaction on cAMP production differs in PMVSMCs from normotensive Wistar-Kyoto (WKY) rats vs. PMVSMCs from spontaneously hypertensive rats (SHR), and to elucidate the mechanism of Ang II/beta-adrenoceptor interactions on cAMP production in PMVSMCs. In cultured PMVSMCs, isoproterenol increased cAMP levels and this effect was markedly enhanced by Ang II. The Ang II enhancement of isoproterenol-induced cAMP was significantly greater in SHR PMVSMCs compared with WKY PMVSMCs. Neither inhibition of calcineurin with FK506, inhibition of calcium-calmodulin with W-7 and calmidazolium, nor inhibition of Gi proteins with pertussis toxin attenuated Ang II enhancement of isoproterenol-induced cAMP in PMVSMCs from either SHR or WKY rats. Moreover, the effect of Ang II on isoproterenol-induced cAMP was not mimicked by alpha-2 adrenoceptor stimulation. In contrast, chelation of intracellular calcium with BAPTA-AM attenuated, increasing intracellular calcium with A23187 augmented, and inhibition of protein kinase C with either calphostin C or chelerythrine chloride abolished Ang II enhancement of isoproterenol-induced cAMP. We conclude that in cultured PMVSMCs Ang II enhances the cAMP response to beta-adrenoceptor agonists via a mechanism that involves coincident activation of adenylyl cyclase by stimulatory G proteins and protein kinase C. Thus, protein kinase C-mediated activation of adenylyl cyclase may attenuate Ang II-induced vasoconstriction in the renal microcirculation by raising the intracellular levels of cAMP, and this mechanism may be augmented in genetic hypertension.
The purpose of our study was to determine whether Gi-mediated control over adenylyl cyclase in preglomerular arteriolar smooth muscle cells (PGASMC) is enhanced in the spontaneously hypertensive rat ...(SHR). PGASMC were cultured from preglomerular microvessels isolated from adult SHR (14-15 wk of age) and age-matched WKY rats. Confluent monolayers of cells in third passage were used for the experiments. cAMP released into the media (30 min) as well as cellular levels of cAMP were measured in the presence of a phosphodiesterase inhibitor, 1-isobutyl-3-methyl-xanthine (IBMX; 100 microM) and expressed as pmol/mg protein. Total (released + cellular) cAMP was significantly lower in SHR (14.19 +/- 2.30 pmol/mg protein) as compared with WKY (28.3 +/- 3.04 pmol/mg protein). Correspondingly, the released (4.6 +/- 0.4 pmol/mg protein) as well as cellular (9.78 +/- 2.18 pmol/mg protein) cAMP levels were also significantly lower in SHR when compared with WKY (8.85 +/- 1.26 and 18.86 +/- 2.0 pmol/mg protein, respectively). The steady-state levels of none of the Gi alpha subunits, namely Gi alpha 1, Gi alpha 2 and Gi alpha 3, were higher in the SHR PGASMC. Pertussis toxin treatment (PTX; 100 ng/ml; 24 hr) caused complete ADP-ribosylation of Gi alpha subunits in both WKY and SHR PGASMC. The same treatment of PTX also produced a significant increase in total cAMP in SHR, but not in WKY, such that the total cAMP levels after PTX treatment were not significantly different between the two strains. Interestingly, PTX significantly increased the released (20.26 +/- 0.90 pmol/mg protein) but not the cellular (13.63 +/- 1.63 pmol/mg protein) cAMP in SHR. Forskolin (1 microM) induced similar increases in total cAMP and isoproterenol (1 microM) caused greater increases in total cAMP in SHR cells compared with WKY cells. These data strongly suggest that in SHR PGASMC total adenylyl cyclase activity is not altered. Furthermore, steady-state expressions of Gi alpha-1, Gi alpha-2 and Gi alpha-3 are not increased whereas Gi-mediated inhibition of adenylyl cyclase is augmented in SHR PGASMC.
The exaggerated sensitivity of spontaneously hypertensive rat (SHR) renal microvasculature to angiotensin II (ANG II) may be due to an imbalance between the effectiveness of G alpha s-utilizing ...vasodilator pathways and vasoconstrictor pathways activated by ANG II (mediated by G alpha i-1, G alpha i-2, G alpha i-3, and G alpha q). Because the alteration appears to be distal to the hormone receptors and proximal to the effector adenylyl cyclase, we hypothesized that SHR have altered amounts of signal-transducing G proteins. This was examined by quantifying the steady-state mRNA levels of specific G alpha subunits in renal microvessels of 12- to 14-wk-old SHR and control Wistar-Kyoto (WKY) rats, using a quantitative-competitive polymerase chain reaction technique coupled to reverse transcription. No significant differences were detected in the absolute levels of G alpha s (0.96 +/- 0.35 vs. 0.74 +/- 0.25 amol/50 ng RNA) or in the relative levels of G alpha i-1 (0.44 +/- 0.05 vs. 0.48 +/- 0.13). G alpha i-2 (40.9 +/- 7.8 vs. 45.2 +/- 8.9), or G alpha i-3 (0.79 +/- 0.05 vs. 0.82 +/- 0.15) normalized to the level of G alpha s for WKY vs. SHR, respectively. The ratio of G alpha q to G alpha s tended to be higher in SHR, but this difference did not achieve statistical significance (0.41 +/- 0.08 vs. 1.04 +/- 0.32, P = 0.08). In conclusion, the steady-state levels of G alpha s, G alpha i-1, G alpha i-2, G alpha i-3, and G alpha q are similar in SHR and WKY renal microvasculature, suggesting that other components of the ANG II signal transduction mechanism are responsible for the enhanced renal vascular responsiveness in SHR.
Caffeine elicits physiological responses in a variety of cell types by triggering the mobilization of Ca2+ from intracellular organelles. Here we investigate the effects of caffeine on intracellular ...Ca2+ concentration (Ca2+i) and ionic currents in anterior pituitary cells (GH3) cells. Caffeine has a biphasic effect on Ca(2+)-activated K+ current IK(Ca): it induces a transient increase superimposed upon a sustained inhibition. While the transient increase coincides with a rise in Ca2+i, the sustained inhibition of IK(Ca) is correlated with a sustained inhibition of the L-type Ca2+ current. The L-type Ca2+ current is also inhibited by other agents that mobilize intracellular Ca2+, including thyrotropin releasing hormone (TRH) and ryanodine, but in a matter distinct from caffeine. Unlike the caffeine effect, the TRH-induced inhibition "washes-out" under whole-cell patch-clamp conditions and is eliminated by intracellular Ca2+ chelators. Likewise, the ryanodine-induced inhibition desensitizes while the caffeine-induced inhibition does not. Simultaneous Ca2+i and Ca2+ current measurements show that caffeine can inhibit Ca2+ current without changing Ca2+i. Single-channel recordings show that caffeine reduces mean open time without affecting single-channel conductance of L-type channels. Hence the effects of caffeine on ion channels in GH3 cells are attributable both to mobilization of intracellular Ca2+ and to a direct effect on the gating of L-type Ca2+ channels.
This paper reports an assay for the quantification of levels of specific mRNA for the α subunits of the inhibitory G proteins Gαi–1, Gαi–2, and Gαi–3. The assay employs reverse transcription and ...competitive polymerase chain reaction (PCR) coupled to enzyme-linked oligonucleotide sorbent assay for differential detection and quantification of PCR products. The assay was conducted with conventional thermal block PCR cyclers as well as rapid air microcapillary cyclers. The detection stage consists of three steps using synthetic oligonucleotides, commercially available reagents and a conventional 96-well plate absorbance reader at settings of 450 and 630 nm. The assay is: (1) rapid, requiring about 3 h for quantification of PCR products; (2) safe, being non-radiometric; (3) relatively simple; (4) highly sensitive, being capable of detecting less than 10 initial copies of target cDNA; (5) precise, resolving two-fold differences in initial copy numbers of specific sequences as low as 10−20mol; (6) linear over a 3 log range, with two-fold differences in the quantity of cDNA producing consistent reductions in quantity of specific cDNA detected; and (7) reproducible, intra-assay and inter-assay coefficients of variation being 11·9 and 14·7%, respectively.
