We have recently shown that hydrolysis of labeled angiotensin I in canine brainstem homogenate causes a rapid accumulation of the heptapeptide aniotensin-l-7) [Ang-(1-7)]. Although this angiotensin fragment has no vasopressor activity its consistent generation in brain homogenate led us to study its potential neirosecretory effects in the rat hypothalamo-neurohypophysial system (INS) in vitro. Ang-(1-7) or angiotensin U (Ang II) was added to HNS perifusate in concentrations of 0.04, 0.4, and 4 pLM, and release of arginire vasopressin (AVP) during each treatment was quantified as a percentage of the AVP release detected in the preceding collection period. Base-line release of AVP averaged 281' ±47 pg per 15 min (mean SEM) in HNS explants (five experiments, five explants per chamber) perifused in Krebs solution at 37C, after a 1-hr equilibration period. At 0.04 pM, Ang'II-or Ang-(1-7) did-not stimulate AVP release. Ang II increased AVP release over the control value by 172% ± 44% and 268% ± 66% at 0.4 and 4 pM, respectively; the same concentrations of Ang-(1-7) increased AVP release by 134% ± 12% and 216% ± 45%. The responses to Ang I and Ang-(1-7) at the highest concentration were both s cant (P < 0.05), and comparison by two-way analysis of variance indicated that Ang II and Ang-(1-7) were equipotent in stimulating AVP release over the range of concentrations studied. In the presence of the competitive Aug II antagonist [Sar',Thr'JAng 11 (20 pzM), the release of AVP increased '2-fold. Neither Ang U nor Ang-(1-7) (4 pAM) caused a further enhancement of AVP release in the presence of [Sarl,ThrJAng UI. These d.ata suggest that a hydrophobic residue in position 8 of the angiotensin peptide is not essential for activation of angiotensin receptors in the rat HNS. Moreover, the equipotence of Ang U and Ang-(1-7) indicates that Ang-(1-7) may participate in the control of AVP release.Angiotensin II (Ang II) plays an important role in the control ofcardiovascular function and body fluid regulation by acting on blood vessels, renal hemodynamics, and the endocrine system. There is also evidence that Ang II may function as a paracrine hormone, since a number of studies showed that this peptide may be synthesized and released by a variety of tissues, including the brain (1). In the central nervous system, Ang II may participate in the central regulation of blood pressure by augmenting sympathetic and parasympathetic efferent discharges (2,3), by the release of arginine vasopressin (AVP) (4, 5) and corticotropin releasing factor (6), and by stimulating thirst (7,8 (17). Since this heptapeptide fragment was generated even in the presence of the angiotensin-converting enzyme inhibitor MK-422, the results suggested that a direct pathway may exist for endogenous generation of Ang-(1-7) in the brain. Although Ang-(1-7) has been shown to possess minimal pressor activity when administered into the peripheral circulation (18,19) and may have no dipsogenic effects when administered intracerebroventricularly (20), the consist...

No abstract

A model of BMD was developed in the present study. Because overexpression of wt bestrophin shifted luminance response but did not alter the range of LP response amplitudes, the authors conclude that the rate-limiting step for generating LP amplitude occurs before activation of bestrophin or that bestrophin does not directly generate the LP conductance.

Novel spray reactors are described that employ immobilized biocatalyst (carbonic anhydrase), enabling concentration and solubilization of emitted CO(2) by allowing catalytic contact with water spray. The reactors were fed with simulated emission gas. The performance of the reactors was investigated with respect to operation variable: emission flow rate; gas composition in the emission stream; water flow rate; area-to-volume ratio of immobilized reactor core; and the enzyme load within the core. The reactors were also investigated for pressure drop and extractability of CO(2) from the emission with single vs. multiple reactors (of combined equal volume). The biotechnological process of solubilization and concentration of CO(2) from emission exhausts or streams occurring in the spray reactors could be coupled for further biochemical/chemical conversion of the concentrated CO(2).

The enzyme carbonic anhydrase (isoform II) from bovine and human erythrocytes was immobilized using different covalent coupling methods on inert matrices. Immobilized carbonic anhydrase may enable concentration of CO2 for Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase)-catalysed fixation in bioreactors. In the present study the activity of carbonic anhydrase with respect to hydration of CO2 using soluble and immobilized enzymes was determined. The stability of the immobilization matrix, the properties of the immobilized enzymes subjected to a variation in operation variables and the activity profile with respect to storage are reported. Immobilization imparted greater thermal and storage stability and enhanced reusability.

The secretory effect of muscarine was studied in the perfused adrenal gland of the cat. During perfusion of the adrenal gland with Krebs‐bicarbonate solution containing muscarine 480 μm, the rate of catecholamine (CA) secretion was 2.02 ± 0.43 μg/2 min in the first 2 min; thereafter, CA output declined only moderately, to reach about 70% of the initial value after 10 min. Secretory responses to brief infusions of muscarine remained reproducible for at least the first 3 infusions. When the adrenal gland was perfused with muscarine (480 μm), infusions of high K+, nicotine, or veratridine produced their usual responses. A 100 fold lower dose of muscarine also failed to modify these responses. During perfusion with high K+, muscarine evoked a secretory response that was only slightly smaller than the response to muscarine alone. It is concluded that muscarine and nicotine activate CA secretion in the cat adrenal gland by independent mechanisms and that the muscarinic response, unlike the nicotinic response, is not readily desensitized.

No abstract

(1968) showed that high K+ evokes secretion of noradrenaline (NA) from the sympathetic nerves of the cat spleen in a calciumdependent manner. It has also been reported that agents which increase the duration of the action potential, such as tetraethylammonium (TEA) and 4-aminopyridine (4-AP), markedly potentiate the release evoked by nerve stimulation (Thoenen, Haefely & Staehelin, 1967;Gillespie & Tilmisany, 1976;Wakade, 1980) Wakade (1981aWakade ( , 1982 further extended these observations in the guinea-pig heart, showing that TEA (20 mM) enhanced the response to 35 and 70 mM K+ i) The Macmillan Press Ltd 1983 278 S.M. KIRPEKAR, J.C. PRAT & M.T. SCHIAVONE by 5 fold and 1.5 fold, respectively, and that TTX blocked this potentiation. They suggested that a part of the release induced by high K+ is due to regenerative activity, since the response was partially blocked by TTX and potentiated by TEA.The primary purpose of this study was to reassess the secretory response to excess K+ in the cat spleen. Our previous investigations of K+-evoked NA release in the cat spleen focused on responses to very high K+ concentrations (bolus injection of 3.7 M K+ or prolonged application of 140 mM K+) (Kirpekar & Wakade, 1968;Kirpekar et al., 1976; Kirpekar etal., 1977;Garcia, Kirpekar & Pascual, 1978). In the present study, we have used intermediate concentrations of K+ to re-examine the role of regenerative depolarization in K+-evoked secretion and the mechanisms of muscarinic inhibition and aautoinhibition in the splenic nerve terminals. Methods Spleen slicesCats were anaesthetized with ether. The abdomen was opened by a midline incision, then the spleen was quickly removed and cut into transverse sections (0.5 to 0.7 mm thick), using a tissue slicer. To label the NA stores of the splenic nerve, the slices were incubated for 30 min with 10 ml of Krebs solution containing 10 pCi of (±)-[3H]-NA (specific activity 7.5 Ci/mmol), then washed 3 times in 20 ml of Krebs solution over a 30 min period. In each experiment, a number of slices (approximately 100 mg) were incubated in 10 ml of Krebs solution for 5 min to determine the background release, then transferred to 10 ml of a test solution for 5 min. The incubation temperature was 37°C. Perfused adrenal glandLeft and right adrenal glands were prepared for retrograde perfusion at room temperature according to the procedure of Garcia, Hernandez, Horga & Sanchez-Garcia (1980). The perfusion rate was about 1 ml/min. Glands were perfused for about 30 min before the start of each experiment. Perfusion and incubation solutionsKrebs bicarbonate buffer consisted of (mM): NaCl 118, KCl 4.7, CaCl2 2.5, MgSO4-7H2O 1.2, KH2PO4 1.2, NaHCO3 25, and glucose 10. When excess K+ (as K2SO4) was added, an osmotic equivalent of NaCl was concomitantly removed. For studies with La3", 2+or 10mMNa, a Tris-buffered solution was used, consisting of (mM): NaCl 143, KCl 6.7, CaC12 2.5, MgSO4-7H20, 2.4, Tris (hydroxymethyl)-aminomethane (Tris) 5.0, and glucose 10. When NaCl was decreased to 10 mM, 266 mM su...