High dilutions of homeopathic remedies induce relaxation of rat aorta precontracted with Noradrenalin

BACKGROUND Homeopathic potencies have been reported to produce alteration of contraction in isolated rat ileum in an organ bath. Potentized homeopathic drugs like Lycopus V and Aurum met are used for the treatment of hypertension. AIM The purpose of this study is to see whether Lycopus V 30 CH and Aurum met 30 CH could produce relaxation of isolated rat aorta in the organ bath. METHODS The aorta of rats were dissected out, placed in Krebs-Henseleit solution, cleared of connective tissue and endothelium and cut into 2-2.5 mm long rings. The rings were fixed in organ baths with the upper end connected by a string to an isometric transducer which was finally attached through a data acquisitation equipment to a computer. Aurum met 30 CH Lycopus V 30 CH, and their medium 90% ethanol were added separately to the bathing fluid containing the aorta rings which were precontracted with noradrenalin (NA). RESULTS Both the drugs produced significant relaxation of the aorta (p

Cardiac myocytes control release of endothelin-1 in coronary vasculature

α-Adrenergic vasoconstriction in the coronary circulation is mediated through α-adrenoceptors on cardiac myocytes and subsequent release of endothelin, a very potent, long-lasting vasoconstrictor. Recent studies found that adult cardiac myocytes do not express the preproendothelin gene. Thus we hypothesized that α-adrenoceptor stimulation on the cardiac myocytes results in the production of an endothelin-releasing factor, which stimulates the coronary vasculature to produce endothelin. We tested this hypothesis by using an in vitro model in which isolated adult rat cardiac myocytes can be stimulated with an α-adrenoceptor agonist (phenylephrine). Their bathing fluid is then transferred to isolated coronary arterioles, and vasoactive responses are measured. To identify the source of endothelin, the endothelin-converting enzyme inhibitor phosphoramidon was added to either the myocytes or the isolated arterioles. Phenylephrine enhanced the vasoconstrictor properties of the myocyte bathing fluid. Administration of phosphoramidon (in either the presence or the absence of phenylephrine) to the myocytes had no effect on the vasoactive properties of the bathing fluid. In contrast, administration of phosphoramidon to the isolated arteriole before administration of the bathing fluid converted vasoconstriction to vasodilation, similar to the effect of the endothelin A receptor antagonist JKC-301, indicating that the endothelin is indeed produced by the coronary vasculature. Administration of the angiotensin type 1 receptor antagonist losartan to the vessel bath enhanced vasodilation to the bathing fluid of the phenylephrine-treated but not control myocytes. In conclusion, during α-adrenergic activation cardiac myocytes release a factor, probably angiotensin II, that stimulates the vascular production of endothelin. Although the physiological implications of this mechanism are not obvious, this may represent a protective mechanism that integrates neuronal vasoconstrictor mechanisms with myocardial metabolism, which minimizes periods of both coronary underperfusion and overperfusion.

Analysis of NaCl transport in thin ascending limb of Henle's loop in CLC-K1 null mice

To characterize the nature of NaCl transport in the thin ascending limb (tAL), we examined the transport properties of Na+ and Cl− using in vitro microperfusion of the tAL in CLC-K1 null mice. In the presence of a transmural NaCl concentration gradient (100 mM higher in the lumen), the transepithelial diffusion voltage ( V d) was 15.5 ± 1.0 and −7.6 ± 1.4 mV in CLC-K1+/+ and CLC-K1−/− mice, respectively. Neither Cl−transport inhibitor 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) nor acidification of the bathing fluid changed the V d values in CLC-K1−/−mice. The addition of 300 μg/ml protamine, a selective blocker of paracellular conductance, to the bath increased the V d values by 5.6 ± 0.7 and 12.6 ± 1.5 mV ( P < 0.001) in CLC-K1+/+ and CLC-K1−/− mice, respectively. Although efflux coefficients of 36Cl were significantly decreased in CLC-K1−/− mice (188.3 ± 25.6 in 4 tubules vs. 17.2 ± 7.0 × 10−5 cm/s in 6 tubules), those of22Na were not different between CLC-K1+/+ and CLC-K1−/− mice. These results clearly indicate that the major component of Cl− transport sensitive to NPPB or pH is mediated by CLC-K1 in the tAL.

Spread of synaptic potentials through electrical synapses in Retzius neurones of the leech

SUMMARYWe studied the spread of excitatory postsynaptic potentials (EPSPs) through electrical synapses in Retzius neurones of the leech Haementeria officinalis. The pair of Retzius neurones in each ganglion is coupled by a non-rectifying electrical synapse. Both neurones displayed synchronous EPSPs of varying amplitudes and rise times. The kinetics of synchronous EPSPs was similar in 79 % of the EPSP pairs. In the remaining 21 %, one EPSP was smaller and slower than the other, suggesting its passive spread from the other neurone. The proportion of these events increased to 75 % in the presence of Mg2+ in the bathing fluid. This spread of EPSPs from one neurone to another was tested by producing artificial EPSPs by current injection into the soma of one Retzius neurone. The artificial EPSPs were smaller and arrived more slowly at the soma of the coupled neurone. The coupling ratios for the EPSPs were proportional to the coupling ratio for long steady-state pulses in different neuronal pairs. Our results showed that EPSPs spread from one Retzius neurone to the other and support the idea that EPSP spread between electrically coupled neurones may contribute to the integration processes of neurones.

Myogenic and neurogenic mechanisms and arachidonate metabolites in bronchial muscle response to allergen

We investigated allergen-induced airway hyperresponsiveness (AH) in bronchial tissues obtained from dogs that inhaled Ascaris suum leading to AH (RESP) in vivo or that exhibited no change (NON-RESP) as well as from dogs that inhaled saline (SHAM). RESP tissues were not hyperresponsive to KCl or to carbachol, whereas contractions to electrical field stimulation (EFS) were reduced. This reduction was reversed partially by indomethacin and completely by replacement of the bathing fluid. Radioimmunoassay revealed marked elevation of prostaglandin (PG) E2 generation in RESP tissues compared with SHAM and NON-RESP tissues. EFS-evoked contractions were often followed by a slowly developing secondary contraction in RESP tissues but not in SHAM or NON-RESP tissues. However, indomethacin unmasked such secondary contractions in many SHAM and NON-RESP tissues and markedly enhanced those in RESP tissues, whereas L-655,240 (thromboxane A2/PGD2receptor antagonist) abolished such contractions in all groups. We were unable to detect thromboxane using radioimmunoassay. We conclude that allergen-induced AH involves altered generation of cyclooxygenase metabolites of arachidonic acid (particularly PGE2) as well as of a nonprostanoid inhibitory factor; as such, the responsiveness of the tissue in vitro is dependent on the relative levels of inhibitory and excitatory metabolites.

Effects of PTH, calcitonin, and cAMP on calcium transport in rabbit distal nephron segments

Distal nephron segments are heterogenous with respect to adenylate cyclase responses to stimulation with parathyroid hormone (PTH) or calcitonin (CT). We examined effects of these hormones and of 8-(p-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (CPTcAMP) on net Ca absorption (Jnet Ca2+, pmol.min-1.mm-1) in rabbit distal nephron segments by in vitro microperfusion technique. We studied three segments, including distal convoluted tubule (DCT), connecting tubule (CNT), and cortical collecting duct (CCD). PTH (1 nM) in bath significantly increased Jnet Ca2+ from 2.28 +/- 0.35 to 9.44 +/- 1.13 in CNT, but did not affect Jnet Ca2+ in DCT or CCD. CT (1 nM) in bath significantly increased Jnet Ca2+ from 1.58 +/- 0.29 to 4.45 +/- 1.01 in DCT, whereas it did not affect Jnet Ca2+ either in CNT or in CCD. CPTcAMP (30 microM) in bath significantly increased Jnet Ca2+ from 2.29 +/- 0.42 to 3.97 +/- 0.43 in DCT and from 2.43 +/- 0.18 to 5.83 +/- 0.37 in CNT, but it did not affect Jnet Ca2+ in CCD. When Na+ was removed from bathing fluid or when 0.1 mM ouabain was added to bath, Jnet Ca2+ in both DCT and CNT significantly decreased. Furthermore, stimulatory effects of PTH and CT on Ca2+ absorption in the respective segments were abolished under these conditions. These results suggest that PTH and CT increase Ca2+ absorption in CNT and DCT, respectively, through cAMP-mediated mechanisms. Presence of a basolateral Na(+)-Ca2+ exchange process seems to be a prerequisite for effects of these hormones. However, exact intracellular mechanisms remain uncertain.

Effect of Ca2+ on Cl- transport in thin ascending limb of Henle's loop

Effects of ambient Ca2+ concentration on Cl- transport across the thin ascending limb of Henle's loop (TAL) were examined by the in vitro microperfusion technique. When Ca2+ concentration in the bathing fluid was decreased from 1.5 mM to nominally 0 mM at 37 degrees C, the relative permeability of Cl- to Na+ (PCl/PNa) estimated from the NaCl diffusion voltage changed from 2.44 +/- 0.20 to 1.27 +/- 0.16 (n = 7, P less than 0.01). When Ca2+ concentration of the luminal fluid was reduced, PCl/PNa was unchanged. When Ca2+ concentration in the bathing fluid was changed from 4.5 to nominally 0 mM, the lumen-to-bath flux coefficient for 36Cl (K36Cl(l----b)) was decreased, whereas the value for 22Na was unchanged, indicating that the reduction of Ca2+ concentration in the bathing fluid selectively inhibits Cl- transport without affecting Na+ transport. By contrast, at 23 degrees C, the elimination of Ca2+ from the bathing fluid caused only a small reduction of PCl/PNa. Although at 23 degrees C acidification of the bathing fluid caused only little or no decrease in Cl- permeability, the elimination of Ca2+ from the bathing fluid under acid pH markedly suppressed the (K36Cl(l----b)) (10(-7) cm2/s). The pH titration curves of relative Cl- permeability examined at three different Ca2+ concentrations at 37 degrees C revealed that the interaction between proton and Ca2+ was noncompetitive. Addition of quin 2-AM, which reduced intracellular Ca2+ concentration, to the bath caused an irreversible suppression of Cl- permeability, suggesting that the decrease in intracellular Ca2+ concentration also inhibits the Cl- transport across the TAL.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of pH on Cl- transport in TAL of Henle's loop

To further characterize the mechanism of Cl- transport across the hamster thin ascending limb (TAL) of Henle's loop, we examined effects of pH on Cl- permeability as determined by either the choline chloride diffusion voltage or the lumen-to-bath 36Cl flux in the isolated segments perfused in vitro. When pH of the bathing fluid or the perfusate was reduced from 7.4 to 5.8, the Cl(-)-Na+ permeability ratio (PCl/PNa) was reduced from 2.77 +/- 0.21 to 0.48 +/- 0.02 (n = 7, P less than 0.01) or from 2.55 +/- 0.15 to 0.81 +/- 0.11 (n = 6, P less than 0.01), respectively. At 37 degrees C, when the pH of the bathing fluid was reduced from 7.4 to 6.2, the lumen-to-bath flux coefficient for 36Cl (X10(-7) cm2/s) was reduced from 84.8 +/- 7.5 to 20.4 +/- 3.2 (n = 7, P less than 0.01), whereas the value for 22Na was unchanged (27.3 +/- 2.9 vs. 25.3 +/- 2.5, n = 5). From the pH titration curves for PCl/PNa, pKa values for proton binding were 6.31 and 5.78, and Hill's coefficients were 2.1 and 2.3 on the basolateral side and on the luminal side, respectively. Alkalinization had little or no effect on the Cl- permeability. At room temperature, the acid pH did not affect the Cl- permeability. Intracellular acidification with o-nitrophenylacetate also decreased the Cl- permeability.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium modulates vasopressin effect in rabbit cortical collecting tubule

The calcium ion has been proposed to be an important mediator of the hydroosmotic response to arginine vasopressin (AVP). We examined the effect of reducing basolateral calcium activity on hydraulic conductivity (Lp) in response to AVP in rabbit cortical collecting tubules (CCT) perfused in vitro. Each tubule served as its own control. Reducing bathing fluid calcium from 0.94 mM to 4.6 microM reduced Lp in each tubule (mean decrease from 146 +/- 13 to 106 +/- 7 cm X s-1 X atm X 10(-7), n = 11, P less than 0.025). To determine whether this inhibitory effect was due to a decrease in cellular calcium uptake, we measured the effect of adding 10(-4) M lanthanum to bathing fluid on AVP-stimulated Lp. Lanthanum decreased Lp (from 109 +/- 13 to 80 +/- 10 cm X s-1 X atm X 10(-7), P less than 0.05) in each tubule. To examine the site at which low peritubular calcium activity regulates AVP action, we measured the effect of decreasing bathing fluid calcium on 8-[p-chlorophenylthio]-adenosine 3',5'-cyclic monophosphate (ClPheS-cAMP)-stimulated Lp (n = 5). Decreasing bathing fluid calcium significantly decreases (P less than 0.025) Lp response to ClPheS-cAMP. Since these results suggest that cellular calcium uptake can exert a post-cAMP effect to modulate AVP action, we examined the effect of the calcium ionophore A23187 (10(-7) M) on AVP- and ClPheS-cAMP-stimulated Lp A23187 reversibly potentiates (25-30%, P less than 0.025) the Lp response to both AVP and ClPheS-cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)