Influence of ketamine and propranolol on plasma renin activity (PRA) in female rabbits and guinea pigs.

1. Plasma renin activity was measured in non pregnant rabbits and guinea pigs under Ketamine-induced general anesthesia after pretreatment either with Propranolol or with a Placebo. Study was performed using a radio-immunoassay for angiotensin I. 2. Twenty minutes after the beginning of the observation period, renin activity in rabbits who had received Placebo alone (11.47 +/- 2.35 ng/ml/h) or associated with Ketamine (11.36 +/- 2.54 ng/ml/h) was similar. However, enzyme activity was significantly lower (P less than 0.001) when Propranolol was associated with Ketamine (3.97 +/- 0.58 ng/ml/h) or with Placebo (4.10 +/- 0.55 ng/ml/h). 3. In the same way, renin activity was significantly higher (P less than 0.001) in guinea pigs without Propranolol than in those who had received this drug. 4. These findings indicate that stress induced by general anesthesia with Ketamine or by simple manipulation of animals (Placebo) was accompanied by an excessive increase in plasma renin activity. Propranolol maintained the level of this enzyme activity within normal limits.     

Circadian variations of plasma renin activity (PRA), aldosterone and electrolyte concentrations in plasma in pregnant and non-pregnant goats

The aim of this study was to estimate and analyse circadian variations of the renin-angiotensin-aldosterone system (RAA) activity in blood of goats and the influence of late pregnancy on the circadian variations of RAA system. The study was carried out on a group of 17 non-pregnant and 9 pregnant goats. The animals were kept in uniform environmental conditions, (9 h light/15 h darkness). Blood samples were collected seven times over a period of 24 h, every 4 h. Plasma renin activity (PRA), plasma aldosterone (PA), sodium, potassium and chloride concentrations were determined. PRA and PA of both groups changed during 24 h, with the highest values in the dark phase and with higher RAA system activity (especially during the night) in the pregnant goats. In the non-pregnant goats, no circadian changes in PRA and PA were observed. The circadian changes in PRA and PA found in pregnant goats had acrophases at 06:27 h and 01:13 h, respectively. Plasma electrolyte concentrations in both groups of goats also changed during 24 h. These results suggest that circadian changes of potassium concentration in plasma of goats during late pregnancy may be one of the main factors affecting the RAA system.     

电刺激延髓最后区对血浆肾素活性及肾交感神经...

68 urethan-anesthetized rabbits were prepared for registration of changes of respiration, arterial blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) due to stimulation of area postrema (AP) by rectangular pulse trains each lasting for 4 s for every 30 s. During 40 min of such a stimulation paradigm the venous blood samples were collected for radioimmunoassay of plasma renin activity (PRA) (both pre- and post-stimulation), RSNA registered and processed by a computer. Animals were divided into three groups: (1) with AP stimulation only (n = 47); (2) AP stimulation after bilateral renal denervation (n = 13); (3) AP stimulation after propranolol injection (n = 8). In Group I, a 91% increase in PRA, an augmentation of RSNA, a rise of BP and a decrease of HR were observed, while respiration did not show obvious change. In Group II, hemodynamic and RSNA response was similar to that in Group I, but PRA was not changed significantly. In Group III, the effects on BP, HR, respiration and RSNA showed no remarkable changes compared with Group I, but significant inhibition of the response of PRA [from 0.65 +/- 0.07 ng/(ml.h-1) to 0.72 +/- 0.10 ng/(ml.h-1), P > 0.05] was observed. The results mentioned above suggested that electrical stimulation of AP may induce an increase in renin release and renal sympathetic nerve activity and hemodynamic changes in rabbits.     

Effects of water intake on variations of plasma renin activity (PRA) and blood aldosterone during physical exercise in man]

In man, increase of renin and aldosterone levels in sera resulting from a brief and heavy muscular exercise on bicyle ergometer is notably reduced but not abolished by massive hydration.     

Cell permeability as a rate limiting factor in the microbial reduction of sulfonated azo dyes

Summary Permeabilization of cells of B. cereus and other bacterial strains by toluene treatment significantly increased the passage of sulfonated and carboxylated azo dyes from the external medium into the cells with a concomittant increase of the reduction rate of the dyes. Dyes which are not reduced at all by intact cells were readily decolorized. The reduction rate of sulfonated compounds was consistently larger than of their carboxylated analogues, once the dyes had entered the cells.     

Calcium as a limiting factor in the biology of Biomphalaria pfeifferi (Krauss), (Gastropoda: Planorbidae)

The minimum calcium requirements, relative importance of buffering and optimum ratio of calcium to magnesium, calcium to sodium, and calcium to potassium ions were determined for laboratory populations ofBiomphalaria pfeifferi and related to suggested limiting factors for the natural distribution of this species. Snails were reared in a range of concentrations of both calcium bicarbonate and unbuffered calcium sulphate from 0.5 to 20 mg/l as Ca⁺⁺ and also in a series of media with a constant concentration of 2 mg/l as Ca⁺⁺ but with a range of Ca/Mg, Ca/Na and Ca/K ratios of 4.0 to 0.1. Shell growth, survivorship, fecundity, egg fertility, and the net reproductive rate were compared. In calcium bicarbonate cultures a concentration of 2mg/l Ca⁺⁺ appeared to be the lower limit for the survival of laboratory populations but a concentration of 4 mg/l Ca⁺⁺ was needed for a population to thrive. The calcium sulphate salt gave much poorer results, emphasizing the importance of the bicarbonate buffer. In the cationic ratio experiments the low Ca/Mg ratios proved to have the most damaging effects on snail populations but the effects of very low Ca/Na and Ca/K ratios could also be measured. A parallel experiment on the hatching rate of snail eggs, using similar experimental solutions, gave comparable results. The significance of these findings to snail ecology is discussed.     

Role of plasma renin activity and the renal nerves in the natriuresis of L-NMMA infusion in rats

The objective of this study was to determine the effect of N(G)-monomethyl-L-arginine (L-NMMA) infusion on plasma renin activity (PRA) in the presence or absence of the renal nerves in normotensive Wistar-Kyoto (WKY) rats and Okamoto spontaneously hypertensive rats (SHR). All rats were unilaterally nephrectomized two weeks before the acute experiment. On the day of the experiment, acute renal denervation (Dnx) of the remaining kidney was performed in one group of WKY rats (Dnx-WKY; n= 10) and one group of SHRs (Dnx-SHR: n=7). The renal nerves were left intact in a group of WKY rats (Inn-WKY; n=8) and SHRs (Inn-SHR; n=9). After a control clearance period, L-NMMA was administered i.v. (15 mg/kg bolus followed by 500 microg/kg/min infusion) and another clearance period of 20 min was taken. In all experimental groups L-NMMA infusion resulted in a significant natriuresis. L-NMMA infusion increased fractional excretion of sodium (FE(Na)) to a greater extent in the Inn-SHR than in the Inn-WKY (delta FE(Na) = 5.23+/-0.87% vs delta FE(Na) = 2.87+/-0.73% respectively; P=0.05), PRA did not change in the SHR with the infusion of L-NMMA. However, in the Inn-WKY group, the natriuresis of L-NMMA infusion was associated with a tendency for lower PRA levels as compared to a group of time control Inn-WKY rats. In Dnx-WKY, the natriuresis of L-NMMA infusion (delta FE(Na) = 4.60+/-0.52%) was associated with a significantly lower level of PRA (4.26+/-1.18 ng AI/ml/hr) as compared to a group of time control Dnx-WKY rats (9.83+/-1.32 ng AI/ml/hr; P<0.05). In the Dnx-SHR, the natriuretic response to L-NMMA infusion was significantly attenuated by renal denervation (delta FE(Na) = 2.36+/-0.34%) and PRA was unchanged. In conclusion, the natriuretic effect of systemic inhibition of nitric oxide (NO) synthesis was associated with decreased PRA in the Dnx-WKY suggesting that a potential interaction exists between NO and the renal nerves in the modulation of PRA in the normotensive WKY rat. Whereas, the natriuretic effect of L-NMMA infusion in the SHR in the presence and absence of the renal nerves, were independent of changes in PRA.     

Response of plasma renin activity to postural change in vasovagal syncope in children, with observations on syncope

37 children aged 7-14 years with a history of repetitive fainting (vasovagal syncope) were studied. Plasma renin activity (PRA), blood pressure and heart rate were measured before and after standing for 15 min. Standing PRA was significantly higher in cases of fainting (n = 14) than in cases of nonfainting (n = 23). A significant positive correlation was observed between PRA and fall in systolic blood pressure on standing in cases of fainting, but not in cases of nonfainting. These findings suggest that the renin-angiotensin system may respond to the fall in blood pressure in children subject to fainting, unlike their adult counterparts previously reported.     

Effect on maternal and fetal renal function and plasma renin activity of a high salt intake by the ewe

The effect on renal function of replacing maternal drinking water with a solution containing 0.17 M NaCl was studied in 9 ewes and their chronically catheterised fetuses over a period of 9 days. Maternal sodium intake increased from control values of 2.19 +/- 0.09 mmol/h to 44.3 +/- 7.4 (P less than 0.001) and 46.3 +/- 6.5 mmol/h (P less than 0.001) on the 3rd and 6th days of salt ingestion. Maternal plasma sodium levels were not affected, but the urinary sodium/potassium ratio increased from 0.15 +/- 0.07 to 2.26 +/- 0.34 (P less than 0.001) after 6 days and plasma renin activity fell from 2.87 +/- 0.76 to 1.00 +/- 0.25 ng/ml per h (P less than 0.05). The changes in maternal sodium intake had no effect on fetal plasma sodium levels nor on fetal plasma renin activity. Sodium excretion and fetal urinary sodium/potassium ratio did not change. However, 3 days after the ewes returned to drinking water fetal plasma renin activity was significantly higher than it was prior to maternal ingestion of 0.17 M NaCl. Fetal plasma renin activity was inversely related to fetal plasma sodium levels (P less than 0.01). The results show that changes in maternal sodium intake had no long term effect on fetal plasma sodium levels nor on fetal renal sodium excretion. The fall in maternal plasma renin activity in the absence of any change in the fetal renin activity, indicates that the fetal renin angiotensin system is controlled by factors other than those influencing the maternal renin angiotensin system. Since fetal urinary sodium/potassium ratios remained unchanged it would suggest that fetal sodium excretion is not influenced by maternal levels of aldosterone.     

Arthropod-borne disease as a possible factor limiting the distribution of birds

Warner found that arthropod-borne disease in the Hawaiian islands (bird malaria and avian pox in particular) is a factor limiting the distribution of the Drepaniidae. Rowan considers it conceivable that the present distribution of certain African birds (and perhaps some other vertebrates showing similar patterns of occurrence) may have been determined in the same way. This suggestion is supported by the observations of the author in southern Africa in regard to bird malaria and avian pox.     

Nitrogen as a limiting factor in the development of beech forests in the Sierra de la Demanda (Spain)

The leaf nitrogen contents of beech growing in the Sierra de la Demanda are studied, relating the contents with other structural population characteristics. For this, different experiments were conducted: (a) To analyze of nitrogen levels in shed leaves, in leaf biomass and in leaves decomposing on a test plot in the Tres Aguas beech forest. (b) To study leaf nitrogen contents over a vegetative cycle in the above beech forest. (c) To study the leaf nitrogen contents of thirty beech stands in the Sierra de la Demanda located at different altitudes and corresponding to three beech budding isophenes. Annual nitrogen accumulation in leaf biomass was 79.4 kg ha^-1yr^-1, of which 22.9 kg ha^-1yr^-1 return to the soil substrate through shedding and 2.1 kg ha^-1yr^-1 are actually incorporated into the soil. Nitrogen cannot be a limiting factor for the development of the beech stands studied because all of them surpassed the leaf deficiency threshold. Only other factors such as those of the soil or silvicultural treatment have a decisive effect on the production of the stands studied. Study of the correlations for leaf nitrogen contents and the structural population characteristics explored reveals that leaf nitrogen was only slightly correlated with the mean height of the trees at the plot.