Regulation of Na+,K(+)-ATPase activity by dopamine in cultured rat aortic smooth muscle cells.

We investigated the effect of dopamine on Na+,K(+)-ATPase activity in cultured aortic smooth muscle cells. Na+,K(+)- ATPase activity was measured by a coupled enzyme assay. Our results demonstrate that dopamine and dopamine receptor agonists, SKF-38393 (a D1 receptor agonist) and quinpirole (a D2 receptor agonist) produced 62%, 50% and 49% inhibition of Na+,K(+)-ATPase activity in aortic smooth muscle cells, respectively. The combination of the two agonists produced inhibition similar to that of dopamine. Dopamine- and the agonist-induced Na+,K(+)-ATPase inhibition was blocked by selective receptor antagonists. The Na+,K(+)-ATPase inhibition by SKF-38393 but not by quinpirole was abolished by pertussis toxin. Na+,K(+)-ATPase inhibition was also achieved by guanosine triphosphate analog GTP-gamma-S. SKF-38393 but not quinpirole stimulated phosphoinositide hydrolysis rate in rat aortic slices. SKF-38393-induced phosphoinositide hydrolysis stimulation was reversed by SCH-23390, a dopamine D1 receptor antagonist, and attenuated by pertussis toxin. In conclusion, our observations indicate that dopamine and dopamine receptor agonists inhibit Na+,K(+)-ATPase activity through specific vascular receptors. Dopamine D1 receptors are linked to pertussis toxin sensitive-mechanism(s) and a GTP-binding protein appears to be coupled to the enzyme inhibition. Finally, the inhibition of Na+,K(+)-ATPase activity in response to dopamine D1 receptor activation may be mediated by the phospholipase C signaling pathway.

Regulation of Na(+)-pump activity by dopamine in rat tail arteries.

We investigated the effect of dopamine on the vascular Na+-pump activity in isolated rat tail artery sections. Effect of dopamine on vascular tone was also assessed using a perfused tail artery preparation. Dopamine inhibited the Na+-pump activity in isolated rat tail arteries in a dose-dependent manner. Both SKF-38393 HCl, a selective dopamine D1 receptor agonist, and quinpirole HCl, a selective dopamine D2 receptor agonist inhibited the Na+-pump activity. The inhibition of the Na+-pump activity. The inhibition of the Na+-pump by dopamine was accompanied with a transient increase in the vascular tone. SKF-38393, but not quinpirole produced a sustained increase in the vascular tone. Tissues preincubated simultaneously with SCH-23390 HCl, a selective dopamine D1 receptor antagonist, and sulpiride, a selective dopamine D2 receptor antagonist, prevented the dopamine inhibition of the Na+-pump activity. Pertussis toxin blocked the Na+-pump inhibition produced by the dopamine D1 receptor agonist but not by the dopamine D2 agonist. Similarly, the dopamine D1 receptor but not dopamine D2 agonist increased the rate of phosphoinositide hydrolysis in rat tail artery sections. Our results indicate that dopamine inhibition of the Na+-pump is mediated by a pertussis toxin-sensitive mechanism and may be coupled to the activation of the phospholipase C system in rat tail arteries. The modulation of the Na+-pump by dopamine may contribute to the vascular tone.

Ouabain amplifies contractile responses to phenylephrine in rat tail arteries in hypertension.

Ouabain, a cardiac glycoside, binds to the alpha-subunits of Na+, K(+)-ATPase and inhibits Na+ pump activity. It has been proposed that endogenous ouabain, by inhibiting vascular Na+, K(+)-ATPase, can increase vascular resistance and thus may contribute to hypertension. One of the consequences of inhibition of the membrane Na+ pump is enhanced responsiveness of vascular smooth muscle to vasopressor substances. The purpose of the present study was to determine whether ouabain can enhance the responsiveness of the vasculature in hypertension. In the present study 100 microM ouabain enhanced the contractile response elicited by phenylephrine in isolated, perfused tail arteries from spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats. The enhanced contractile response was more pronounced in the arteries of the SHR. We demonstrated that this concentration of ouabain inhibits the Na+ pump activity, measured as ouabain-sensitive 86Rb uptake, by about 65%, in isolated tail arteries. We conclude that ouabain can sensitize the vascular smooth muscle to the effects of vasopressor substances and this effect is more pronounced in genetically hypertensive rats. Endogenous ouabain may contribute to the pathophysiology of hypertension by enhancing vascular tone.

Rat vascular tissues express all three alpha-isoforms of Na(+)-K(+)-ATPase.

The catalytic alpha- and smaller glycosylated beta-subunits of the membrane transport enzyme Na(+)-K(+)-adenosinetriphosphatase (ATPase) occur in different molecular forms, alpha 1, alpha 2, alpha 3, beta 1, and beta 2. The catalytic alpha 1-, alpha 2-, and alpha 3-subunits of the enzyme have varying affinities for digitalis and exist in different tissues with unique distribution patterns. In this report we document for the first time the existence of alpha 1-, alpha 2-, alpha 3-subunit proteins (all approximately 97.5 kDa) in cultured rat aortic smooth muscle cells and rat tail arteries. In addition to the three molecular forms of the alpha-protein we detected a minor band at approximately 68-kDa position in aortic smooth muscle cells, which may correspond to the truncated alpha 1-protein reported earlier.

Regulation of hepatic energy metabolism by epidermal growth factor.

Employing the non-recirculating perfused rat liver preparation, we have investigated the regulation of hepatic gluconeogenesis, and metabolic fluxes through the tricarboxylic acid cycle and 2-oxoglutarate dehydrogenase reaction by epidermal growth factor (EGF) which mimics the actions of both insulin and Ca(2+)-mobilizing hormones (e.g. vasopressin). As monitored by the rate of 14CO2 production from [2-14C]pyruvate (0.5 mM), EGF (10 nM) transiently stimulated the activity of the tricarboxylic acid cycle. EGF also transiently stimulated hepatic gluconeogenesis from pyruvate. The transient stimulation of tricarboxylic acid cycle activity and gluconeogenesis were accompanied by an increase in perfusate Ca2+ content indicating that EGF also altered hepatic Ca2+ fluxes. EGF-elicited stimulation of gluconeogenesis was, at least in part, the result of a transient (50%) inhibition of pyruvate kinase activity. Likewise, EGF-mediated stimulation of tricarboxylic acid cycle activity can, in part, be attributed to EGF-elicited stimulation of metabolic flux through the mitochondrial, Ca(2+)-sensitive, 2-oxoglutarate dehydrogenase reaction. The regulation of hepatic metabolism by EGF appears to be the manifestation of alteration in cellular Ca2+ content since in experiments performed under conditions known to abolish the ability of EGF to alter cytosolic free-Ca2+ concentrations, i.e. in livers of pertussis-toxin-treated rats, EGF did not alter either perfusate Ca2+ content or any of the metabolic parameters monitored. Additionally, experiments involving pulsatile infusion of either EGF or phenylephrine into livers demonstrated that, unlike the alpha 1-adrenergic receptor, homologous desensitization of the EGF receptor occurs. Such a homologous desensitization of the EGF receptor can explain the transient nature of EGF-elicited stimulation of various metabolic processes. Since protein kinase C activation by EGF can lead to receptor desensitization, experiments were performed with phorbol esters which either activate or do not alter protein kinase C activity. While the inactive phorbol ester 4 alpha-phorbol 12,13-didecanoate did not modulate the hepatic actions of EGF, activation of protein kinase C by 4 beta-phorbol 12-myristate 13-acetate (70 nM) abolished the ability of EGF to stimulate gluconeogenesis, tricarboxylic acid cycle activity and metabolic flux through the 2-oxoglutarate dehydrogenase complex.

Humoral and cellular immune response in schistosomiasis pre and post praziquantel therapy.

Humoral and cellular immune response in schistosomiasis was studied pre and post praziquantel therapy. After treatment the mean anti SEA IgM and IgG and anti SWAP IgM levels in all cases showed significant reduction. In patients with high eosinophilic count anti SEA IgE and IgA were statistically decreased. Other specific antibodies showed negligible changes Cellular immune response was not affected.

Animals as reservoir hosts for Leishmania in Qualyobia Governorate, Egypt.

A total of 239 rodents were collected from El-Khanka, Shebin El-Kanater, El-Kanater, Shoubra El Khima, Qualiob, Tokh, Benha and Kafr-Shokr and identified as Mus musculus (30), Rattus rattus (78), Rattus norvegicus (35), Arvicanthus niloticus (62) and Acomys cahirinus (34). Examination of these rodents showed the presence of cutaneous lesions in two R. rattus, three R. norvegicus and one A. cahirinus which showed no Leishmania parasites neither by smear nor by culture. On examination of the liver, spleen and bone marrow parasitologically, the spleen of two R. norvegicus grew promastigotes, one was lost and the other was typed. Serological examination of rodents revealed antileishmanial antibodies in one A. niloticus and in two R. norvegicus by IHAT and in one R. rattus by Dot-ELISA. A total of 33 stray dogs trapped from El-Khanka Shebin El-Kanater and Qualiob were free from natural Leishmania infection as indicated clinically, parasitologically and serologically.

Comparison between parasitological and serological techniques in assessment of schistosomiasis prevalence.

The prevalence of schistosomiasis serologically based on detection of anti-soluble egg antigen (SEA)--IgM and/or IgG by ELISA technique was 68% of 380 cases, and 52.7% of 148 cases by stool examination. The serological technique seems to be more sensitive and able to detect early infection as well as detection of ectopic infection.

Correlation between circulating schistosomal antigen, schistosomal complement C3 and intensity of infection.

53.7% of the already parasitologically proved schistosomiasis cases showed circulating schistosomal antigen (C.S.A.) in their sera with significantly higher levels than the controls, with no correlation between the level of C.S.A. and the foecal egg count. Significant higher levels of schistosomal complement C3 were found in schistosomiasis patients as compared to the control group, with no significant difference in the mean level of C3 between patients with positive and negative C.S.A.

The effect of some drugs on acute toxoplasmosis in mice.

The effect of some chemotherapeutics, on the course of acute toxoplasmosis in experimentally infected mice was studied. Obtained results showed that, praziquantel, levamisole had no effect on acute toxoplasmosis, while trimethoprim-sulphamethoxazole and clindamycin showed some prophylactic effect on acute toxoplasmosis in mice.

Effect of ambient temperature changes on chronic toxoplasmosis in rats.

The effect of excess heat and cold on chronic toxoplasmosis was studied on rats. That was evident from the average increase in body weight, the effect on blood picture, deleterious effect of the pathology recorded in various organs, increased Toxoplasma brain cyst count, long persistence of parasites in the viscera, high antibody titre by I.H.A.T. in infected animals exposed to excess heat and its decrease in animals exposed to excess cold.

Schistosomiasis and transient nephritis in children.

Transient nephritis, manifested by albuminuria may be caused by the deposition of the circulating schistosomal antigen in the kidney glomeruli.

Four methods in diagnosing protozoal parasites in stool.

Stool examination by 4 different methods showed that zinc sulphate floatation technique was more or less the best.