Measurement of the effects of cadmium stress on protozoan grazing of bacteria (bacterivory) in activated sludge by fluorescence microscopy.

The effect of cadmium stress on protozoan bacterivory in sewage sludge was measured by experimentally exposing sludge communities to 0 to 150 mg of Cd per liter for up to 6 h and then determining the rates of protozoan grazing on bacteria, using a double-staining technique and epifluorescence microscopy. Bacterivory was measured by incubating the sludge with fluorescently labeled bacterium-sized latex beads and directly observing ingestion of the beads and bacterial cells in the sludge by epifluorescence microscopy of preserved samples. Staining with 4',6-diamidino-2-phenylindole and acridine orange permitted the simultaneous determination of protozoan numbers and bacterivory activity as estimated by the number of bacterial cells and bacterium-sized latex beads ingested by the representative ciliate Aspidisca costata. Enumeration with latex beads proved to be an effective way of estimating bacterivory in sludges subjected to heavy-metal stress. This technique should prove useful for determining the effects of other chemical stresses on protozoan numbers and bacterivory in organic-rich environments. Although the number of protozoa declined significantly only after exposure to 100 mg of Cd per liter for 4 h, grazing, as indicated by bead ingestion, was significantly inhibited by Cd concentrations of greater than 25 mg/liter in less than 1 h, and exposure to 100 mg of Cd per liter effectively stopped protozoan grazing within 1 h of exposure. Protozoan ingestion of latex beads and bacteria was inversely correlated to Cd concentration and exposure time. The reduction of protozoan bacterivory by Cd provides a possible explanation for the increase in suspended bacteria in the effluents of metal-stressed treatment facilities.     

Response of microbial populations to environmental disturbance

Taxonomic and genetic diversities of microbial communities disturbed by chemical pollutants were lower than in undisturbed reference communities. The dominant populations within the disturbed communities had enhanced physiological tolerances and substrate utilization capabilities, indicating that generalized physiological versatility is an adaptive characteristic of populations that successfully compete within disturbed communities.     

Effect of introducing genetically engineered microorganisms on soil microbial community diversity

Abstract Introducing the genetically engineered microorganism Pseudomonas cepacia AC1100 into soil microcosms resulted in elevated taxonomic diversity determined by phenotypic analyses of culturable isolates and genetic diversity determined by analysis of the heterogeneity of total microbial community DNA reannealing kinetics. The greatest impact occurred when P. cepacia AC1100 was introduced along with the herbicide 2,4,5-T, which P. cepacia AC1100 can degrade. The data suggests that both changes in the balance of populations and genetic recombination contributed to the increased diversity.     

Effects of atrial natriuretic factor on urinary concentration of catecholamines and renin secretion in dogs

This study evaluated the effects of synthetic atrial natriuretic factor (ANF) on renal hemodynamics, urinary excretion of electrolytes, norepinephrine (NE), and dopamine (DA); and renal production of renin in anesthetized dogs. Following a bolus (1 micrograms/kg body weight) and infusion (0.1 microgram/kg/min) for 30 min, there was significant increase in urine flow (220 +/- 41%), glomerular filtration rate (72 +/- 14%), and urinary sodium excretion (170 +/- 34%). There was a decrease in renin secretory rate and the concentration ratio of urine NE to DA following ANF was decreased (p less than 0.05). These data suggest that ANF decreases renal production of NE and renin.     

The effect of ovarian steroidogenesis on ovulation and fertilizability in the in vitro perfused rabbit ovary

The effects of aminoglutethimide phosphate (AGP) on ovulation, ovum maturation, fertilizability, and steroid production were studied with the use of an isolated perfused rabbit ovary preparation. AGP (10(-3) or 10(-4) M) was added to the perfusate of one ovary. The contralateral control ovary was perfused in medium alone. Thirty minutes later human chorionic gonadotropin (hCG) (50 IU) was added to the perfusate of all ovaries. No difference was observed in time of ovulation or ovulatory efficiency between controls and AGP-treated ovaries. The degree of ovum maturity and degeneration was also comparable in the two groups. Progesterone and estradiol production were significantly reduced by AGP treatment. A second experiment examined fertilizability of ova ovulated in vitro after perfusion with 10(-3) M AGP. AGP significantly reduced the rate of normal fertilization as observed 12 h after insemination. The percentage of inseminated ova with evidence of degeneration was greater in ova from AGP-treated ovaries than in those from controls, however, this difference was not significant. The study indicates that AGP affects neither hCG-induced ovulation nor meiotic resumption; however, fertilizability of ova from ovaries treated with AGP is impaired. These data suggest that the intrafollicular steroid environment may participate in cytoplasmic maturation of ovulated ova.     

Effects of atrial natriuretic factor on blood pressure and the renin-angiotensin-aldosterone system

Atrial natriuretic factor (ANF) antagonizes vasoconstriction induced by numerous smooth muscle agonists and also lowers blood pressure in intact animals. ANF has particularly marked relaxant effects on angiotensin II-contracted vessels in vitro. Sensitivity to the blood pressure-lowering effect of ANF in vivo appears to be enhanced in renin-dependent models of renovascular hypertension compared with other experimental hypertensive models. The depressor action of low, possibly physiological doses of ANF in two-kidney, one-clip Goldblatt rats is due to a decrease in total peripheral resistance. On the other hand, high doses of ANF can lower cardiac output, particularly in volume-expanded models such as deoxycorticosterone-salt hypertension. ANF markedly inhibits renin secretion in intact animals, probably via increased glomerular filtration rate and load of sodium chloride to the macula densa. This effect is masked when renal perfusion is impaired (e.g., via unilateral renal artery constriction), in which case ANF may stimulate renin secretion slightly. ANF also reduces plasma aldosterone in vivo and inhibits basal and agonist-induced aldosterone release from isolated adrenal cortical cells. This effect appears to be especially marked for angiotensin-induced aldosterone production in vivo and in vitro. These findings indicate that ANF has potentially important interactions with the renin-angiotensin-aldosterone system and suggest a role for ANF in the homeostatic control of blood pressure as well as of extracellular fluid volume.     

Renal hemodynamic and natriuretic effects of atrial natriuretic factor

In this article we review the renal hemodynamic and excretory actions of atrial natriuretic factor (ANF) and consider some of the mechanisms of its vascular and natriuretic effects. ANF leads to a marked, sustained, and parallel increase in whole-organ and superficial single-nephron glomerular filtration rate (GFR) while mean blood pressure is decreased and renal blood flow (RBF) is unchanged or even decreased. The increase in GFR is caused by an efferent arteriolar vasoconstriction or by a combination of afferent vasodilation and efferent vasoconstriction. ANF also leads to a decrease in the hypertonicity of the innermedullary interstitium. Together with the increase in GFR, this phenomenon accounts wholly or in great part for the ANF-induced natriuresis. The overall renal vascular effects of ANF are complex and may tentatively be conceptualized as a behavior of a functional partial agonist: slight vasoconstriction in vasodilated kidneys, no sustained effects on the vascular resistance in normal kidneys, and vasodilation in vasoconstricted kidneys. The vasoconstrictor effect of ANF may be direct or indirect and depends on extracellular calcium whereas the antagonist effect likely results from alterations in intracellular calcium homeostasis. The data raise the perspective that ANF is not only a powerful natriuretic substance but has the potential of being an important modulator of GFR and RBF in intact animals.     

An endogenous brain substance, CDS (clonidine-displacing-substance), inhibits the twitch response of rat vas deferens

The effect of CDS, an endogenous brain substance that specifically displaces bound [3H]clonidine and [3H]rauwolscine in rat brain membranes and human platelets, has been tested in isolated, field-stimulated rat vas deferens. CDS, obtained after an extensive purification procedure as a single peak from an HPLC sizing column, inhibited the electrically stimulated rat vas deferens similarly to the inhibitory action of clonidine, an alpha 2-agonist. The effective dose of CDS as an inhibitor of the vas deferens is equivalent to its effective dose in displacing specifically bound [3H]-clonidine in rat brain membranes. Furthermore, the CDS inhibition of the twitch response is reversed by two alpha 2-adrenergic antagonists, yohimbine and phentolamine. From these results, it is suggested that CDS extracted from brain, with affinity for clonidine sites, may be involved in the nonadrenergic fast response of the sympathetic transmission of the vas deferens.     

Effects of atrial natriuretic factor on human platelet function

We examined the hypothesis that atrial natriuretic factor (ANF), a substance with known vasorelaxant activities, shares with other vasodilators the property of inhibiting platelet function. Aggregation of citrated platelet-rich plasma (PRP) from 23 healthy volunteers induced by ADP, adrenaline, arachidonic acid, collagen, gamma-thrombin, the endoperoxide analogue U-44069, serotonin, the calcium ionophore A-23187 or platelet aggregating factor was measured after incubation of PRP with ANF for 3 minutes at concentrations of 4 X 10(-9), 4 X 10(-8) and 4 X 10(-7) M or vehicle as control. ANF decreased ADP-induced aggregation significantly (P less than 0.02), but only at the highest concentration used and to a minor extent (control: 73.6 +/- 11.2%; after ANF 4 X 10(-7) M: 60.0 +/- 17.1%, mean +/- S.D., n = 39) by a selective inhibitory effect on the secondary wave; neither aggregation by all other agents tested nor thromboxane B2 generation induced by ADP and adrenaline was altered by incubation with ANF. Although ANF thus has detectable effects on ADP-induced platelet aggregation in vitro, these data suggest that ANF is unlikely to be a physiologically significant modulator of platelet function.