Role of the renin-angiotensin system in tubuloglomerular feedback

The link between the renal tubule and glomerular vasculature comprised of the juxtaglomerular apparatus appears to serve two functions: the regulation of filtration rate and of renin secretion. Elevation of macula densa NaCl concentration stimulates a vasoconstrictor response, which results in a fall in filtration rate, a response that has been termed tubuloglomerular feedback (TGF). Simultaneously, renin secretion is suppressed. The two responses appear to be initiated by a furosemide-sensitive transport step probably located in the macula densa. Both show a pattern of anion specificity identical to Na/K/Cl cotransport mechanisms. An increase in intracellular calcium in the effector cells, the vascular smooth muscle, and the renin-containing granular cells is a likely effector mechanism for both reactions. Angiotensin probably does not mediate the vasoconstrictive feedback response, because changes in local (intracellular) angiotensin concentration would have to be opposite from systemic changes. However, acute changes in angiotensin levels appear to be an important modulator of the magnitude of the TGF response.

Tubuloglomerular feedback responses with native and artificial tubular fluid

Experiments were performed to compare the tubuloglomerular feedback response to native and artificial tubular fluid. The change in early proximal flow rate produced by changes in loop of Henle flow rate was measured in anesthetized rats using micropuncture techniques. Loop perfusion fluid was either an artificial solution with an electrolyte composition similar to that of proximal fluid (ATF) or native tubular fluid (NTF) collected from the late proximal tubule. In control rats, in rats on a low NaCl diet, in rats on restricted food intake, and in acutely saline-expanded rats no differences were detected between ATF- and NTF-perfused nephrons. In rats receiving 10 g NaCl/100 g, diet, responses with ATF and NTF to a flow change from 0 to 15 nl/min did not differ significantly; maximum feedback responses (flow change from 0 to 40 nl/min) were, however, significantly greater with ATF (-25.4%) than NTF (-12.9%). Chloride absorption was not different with the two perfusates. With both ATF and NTF a significant negative correlation was found between maximum responses and NaCl intake, with the slope being steeper with NTF. We conclude that some unidentified constituent of tubular fluid affects maximum feedback responses during very high NaCl intake, but feedback responses to physiological flow rate changes appear to be independent of luminal factors.

Fiber optic probe cytometer

An optical fiber probe is used to both excite and collect fluorescence from a suspension of cells. The configuration of the probe is such that one or a few cells are sensed at a time, with a convenient cell concentration. With fluorescently labeled antibodies to cellular antigens, the fiber optic cytometer is able to identify the presence of a specific set of cells with high sensitivity.

Experimental examination of cavity ionisation theory applied to alpha-particle fields

The form of a general theory of cavity ionisation is outlined and its applications to alpha-particle fields considered. The attenuation of the alpha particles within the cavity, which gives rise to the weighting factor in general cavity theory, is considered in detail and an appropriate treatment for alpha-particle fields developed. Apparatus, consisting of an ionisation chamber composed of electrodes emitting alpha rays, was constructed in order to impose a rigorous test on the theory in the most critical region of cavity size. The general theory of cavity ionisation as applied to alpha-particle fields is shown to be in close agreement with the experimental results. As in the case of photon and electron fields, it is possible to characterise a cavity by a single chord length (path length) but the charged particle energy spectrum and the variation of stopping power with energy must be considered in detail.

High concentrations of p-Glu-His-Pro-NH2 (thyrotropin-releasing hormone) occur in rat prostate

Thyrotropin-releasing hormone (TRH) immunoreactivity occurs in high concentration within the rat prostate. Previous studies have shown that the immunoreactive species consists of more than one TRH-like tripeptide which cross-reacts in the TRH radioimmunoassay. The component which was highly retained during cation exchange chromatography was subjected to a preparative scale isolation, purification and structural analysis. The methods used included methanol extraction, water-ethyl ether partitioning, cation exchange chromatography, affinity chromatography, high pressure liquid chromatography, TRH radioimmunoassay, in vitro pituitary bioassay, TRH receptor assay, and amino acid analysis. The mean concentration of the predominant amino acids (Glu, His, Pro), 344 pmoles/ml, and the TRH concentration measured by TRH radioimmunoassay prior to acid hydrolysis, 372 pmoles/ml, were nearly identical. Because the material analyzed cochromatographed with synthetic TRH in several chromatographic systems, had a radioreceptor potency which was indistinguishable from that for synthetic TRH, and released TSH and prolactin but not growth hormone from rat pituitaries in vitro, it is concluded that pGlu-His-Pro-NH2 is one of the TRH-like peptides in the rat vental prostate.

Psychiatric hospital versus community treatment: the results of a randomised trial

One hundred and twenty patients presenting for admission were randomly allocated into two groups. Controls received standard hospital care and after-care. Projects were not admitted if this could be avoided; instead they and their relatives were provided with comprehensive community treatment and a 24-hour crisis service. Patients with a primary diagnosis of alcohol or drug dependence, organic brain disorder or mental retardation were excluded. During the 12 months study period, 96% of controls were admitted, 51% more than once. Of the projects, 60% were not admitted at all and only 8% were admitted more than once. Controls spent an average of 53.5 days in psychiatric hospitals; projects spent an average of 8.4 days. Community treatment did not increase the burden upon the community, was considered to be significantly more satisfactory and helpful by patients and their relatives, achieved a clinically superior outcome, and cost less than standard care and after-care.

Fluorescence fluctuation immunoassay

The homogeneous fluorescent immunoassay described above allows one to measure the brightness of fluorescently tagged carrier particles that are suspended in a background of free, unbound fluorescent sources. We have demonstrated the feasibility of our technique using a gentamicin competitive assay as well as idealized model systems. We have seen that the fluctuation-correlation method is able to discriminate against free background sources because each fluorescing particle in solution contributes to the correlation peak [Eq. (4)] with a weighting equal to the square of its respective intensity. Hence, a few very bright sources contribute disproportionately to the "signal" relative to many weak ones. To take advantage of this property, one would therefore design an assay that uses relatively larger carrier particles, each of which is capable of binding on the order of 10(3) to 10(4) tagged antibodies or antigens. Unfortunately, the nonlinear dependence of the correlation peak on the brightness of the fluorescing species causes the technique to be perturbed by carrier particle aggregation; the apparent bound fluorescence intensity increases with the extent of aggregation. The latter may be an unavoidable consequence of performing assays using raw blood serum, for example. The ultimate usefulness of this method will depend on its sensitivity and speed when applied to "real" assays of clinical significance. These characteristics will be influenced by a number of technical details. Given our limited experience with the method thus far, it would appear that its principal drawback is its relatively slow speed. In order to decrease the time needed for a reliable measurement, one must average the random fluctuations in the fluorescent intensity to zero more quickly. In principle, this can be accomplished by decreasing the shot noise by collecting a larger fraction of the fluorescent light, and increasing the sampling rate. The method requires rather complicated instrumentation; it is by no means clear that this level of complexity is justified given the realistic level of sensitivity that will be obtained by this technique.

A simple steady-state model for feedback control of glomerular filtration rate

Repeat measurements of SNGFR during different rates of microperfusion of the loop of Henle have demonstrated that the alterations of SNGFR were greatest between perfusion rates of 10 and 20 nl/min, but that changes also occurred below 10 nl/min and above 20 nl/min. By a simple curve-fitting procedure, yielding parameter estimates for single nephrons, we determined that the half-maximum response was achieved at a perfusion rate of 16.3 nl/min and that at that flow the slope of the relationship between VLP and SNGFR was 1.84. From the curve describing the perfusion response and from measurements of the proximal transport rate, we estimated that, at the operating point of the feedback loop, VLP and SNGFR should be approximately 18 and 35 nl/min, respectively. Measurements made without interruption of the feedback pathway confirmed this prediction, suggesting that perfusion adequately mimics the free-flow state. We conclude, that under the experimental conditions studied, the operating point of the feedback mechanism is located within the flow range in which the mechanism is most sensitive, so that both increases and decreases in tubular flow from the normal values should produce changes in filtration rate.

Concentration-dependent sodium chloride transport as the signal in feedback control of glomerular filtration rate

There is good evidence that the initial step leading to a feedback response is the concentration-dependent active transport of sodium chloride across the macula densa cells. This may lead to changes in sodium chloride concentration or tonicity in the small and relatively unstirred compartment of the juxtaglomerular interstitium or to changes in the concentration of transport-related compounds or metabolites. We assume that the Goormaghtigh cells act as receptor cells that transform such compositional changes into a signal propagating to the glomerular vascular elements.

Indicator dilution using a fluorescent indicator

In vitro and in vivo indicator-dilution measurements are made with a fluorescent indicator and a novel detection system using a catheter containing a single optical fiber that carries both the exciting and returning fluorescent light. These fluorescent-dilution measurements are compared with simultaneous green dye-dilution measurements. The double-indicator-dilution measurement of extravascular lung water using heat and fluorescence is compared with gravimetric measurements. Also investigated is the sensitivity of the fluorescent measurement to changes in O2 saturation and hematocrit of the blood. An example of the measurement of a right-to-left heart shunt with this new indicator is given.

Further evidence for an inverse relationship between macula densa NaCl concentration and filtration rate

It has been concluded that tubulo-glomerular feedback mechanism is triggered by changes in NaCl concentration ([NaCl]) at the macula densa. This conclusion is based on the demonstration that changes in filtration rate produced during retrograde perfusion of the loop of Henle depend upon the perfusate [NaCl]. Experiments were performed to evaluate whether the effect on glomerular function of orthograde perfusion of the loop of Henle is consistent with this conclusion. Early proximal flow rate (VEP), stop-flow pressure (PSF), early distal chloride concentration ([C]), and flow rate were measured during perfusion of the loop of Henle with mannitol solution (300 mosm kg-1), 30mM NaCl + mannitol (300 mosm kg-1), 140 mM Na isethionate and artificial tubular fluid. When distal flow exceeded 10 nl min-1, the magnitude of the glomerular response was predictable from the [Cl]. The linear regression line, delta VEP = -0.27 [Cl] + 4.3, did not differ from that obtained previously with the retrograde technique. Retrograde perfusion with 140 mM Na isethionate was without effect on VEP. We conclude that the effect on glomerular function of perfusion of the loop of Henle in either an orthograde or a retrograde direction with these solutions depends upon the chloride concentration at the macula densa.

A controlled study of psychiatric hospital versus community treatment - the effect on relatives

One hundred and twenty patients presenting at Macquarie Hospital for admission were randomly allocated into two groups. The control group patients received standard hospital care and follow-up. The project group patients were not admitted if this could be avoided; instead they were taken back to the community by the project team who provided them and their relatives with comprehensive, assertive and prolonged follow-up treatment backed by a 24-hour crisis service. The majority (63%) of the project group had no admission during the 10 month study period. Initially, the burden on the relatives of the project group was higher, but by one month it was somewhat lower and by four months it was significantly lower than the burden on the control group relatives. Relatives of the project group patients were significantly more satisfied with the treatment than control group relatives. It is clearly feasible to treat most psychiatric patients in the community without increasing the burden on their relatives.

Feedback-mediated reduction of glomerular filtration rate during infusion of hypertonic saline

An acute rise in plasma sodium concentration from 146 +/- 2.6 to 155 +/- 1.7 was produced in rats by the intraarterial infusion of 0.6 M sodium chloride (0.25 ml/min for 4 min followed by 0.25 ml/hr). A parallel fall in whole kidney GFR (from 0.45 +/- 0.02 to 0.36 +/- 0.04 ml/min per 100 g of body wt) and SNGFR measured in the distal tubule (31.4 +/- 3.01 to 27.9 +/- 2.40 nl/min) was observed. In contrast, proximally measured SNGFR (with feedback interrupted) rose from 32.7 +/- 2.73 to 37.1 +/- 2.84 nl/min. The loop of Henle flow, determined from distal SNGFR and (TF/P) inulin in late proximal fluid collected without interrupting tubular flow, rose from 13.7 +/- 1.50 to 17.0 +/- 1.42 nl/min as a consequence of a fall in proximal reabsorptive rate from 15.8 +/- 1.87 to 11.0 +/- 1.37 nl/min. Intraarterial infusion of hypertonic sodium bicarbonate resulted in comparable increases in plasma sodium concentration and inhibition of proximal reabsorption but did not produce a fall in filtration rate. We conclude (1) acute infusion of hypertonic sodium chloride results in an inhibition of proximal reabsorption and therefore in an increased rate of loop of Henle flow, (2) this increase in flow causes a fall in GFR through the tubuloglomerular feedback mechanism, and (3) acute infusion of hypertonic sodium bicarbonate does not result in a feedback-mediated fall in GFR, presumably because increased delivery of bicarbonate-rich fluid does not activate the feedback mechanism.

The role of opiates and endogenous opioid peptides in the regulation of rat TSH secretion

The administration of morphine to rats at room temperature is reported to suppress serum thyrotropin (TSH) levels by a hypothalamic mechanism. However, it is unknown whether endogenous opioid peptides (EOP) are involved in the control of TSH secretion. The present studies show that naloxone (10 mg/kg, i.p.) an opiate-receptor antagonist, prevented the decline in rat serum TSH which occurs with heat exposure. Morphine sulfate (20 mg/kg, i.p.) treatment prevented the cold-induced elevation in serum TSH and pretreatment with haloperidol (0.3 mg/kg, i.p.) eliminated morphine's influence. Medial-basal hypothalamic thyrotropin-releasing hormone (TRH) content, measured by RIA, increased in the morphine-treated rats which were exposed to 4 degrees C. A submaximal intravenous dose of TRH (300 ng/100 g) was given to determine whether morphine suppresses serum TSH through the release of hypothalamic thyrotropic inhibitors. Morphine pretreatment did not alter TSH stimulation by TRH. Morphine alone or combined with TRH did not alter basal or stimulated TSH secretion in vitro. These studies strongly suggest that, in rats, the EOP modulate TSH secretion under conditions such as acute heat exposure which was associated with a decline in serum TSH. Under specific circumstances, the suppression of serum TSH by morphine may be dopamine-dependent.

Homogeneous fluorescent immunoassay

A fluorescent immunoassay based on the correlation of fluctuations in particle number measures the amount of tagged species bound to micrometer-sized beads and is insensitive to background fluorescence. Without separation steps, a competitive assay can resolve I nanogram of gentamicin per milliliter from a total sample volume of only 10 microliters.

The macula densa sensing mechanism for tubuloglomerular feedback

A series of studies on the signal responsible for initiating the tubuloglomerular feedback (TGF)-mediated changes in SNGFR have utilized a retrograde perfusion technique that permits close control of macula densa segment tubular fluid composition. The feedback response has been demonstrated to be an approximately linear function of luminal NaCl concentration between 15 and 60 mM, with increasing NaCl concentration resulting in lower nephron filtration rate. Feedback responses could be initiated by NaCl and NaBr solutions but not by NaI, NaNO3, NaF, NaHCO3, NaSCN, or Na acetate. All chloride salts tested, in which chloride was accompanied by a univalent cation, elicited a response. The feedback mechanism thus shows a special requirement for chloride or bromide and not for sodium. With the chloride salts the response varied in magnitude depending on the accompanying cation with the following order of decreasing response, Rb+, Na+, Cs+, NH4+, K+, choline+, and Li+, CaCl2 and MgCl2 did not elicit a feedback response. The feedback response was not influenced by large changes in luminal osmolarity by addition of urea, suggesting either that the feedback sensing site is water impermeable or that water movement does not influence the signal. When electrolyte-free solutions are perfused through the loop of Henle in an orthograde direction, sufficient electrolyte may enter the luminal fluid to transiently influence the feedback mechanism.

Fluorescence immunoassay based on long time correlations of number fluctuations

We report the development of a fluorescence-based immunoassay technique relying on the physical phenomena of random number fluctuations and diffusion, which we review. By determining the autocorrelation of the fluctuations in the fluorescent intensity, this methid is able to measure the amount of labeled antigen or antibody that is bound to micrometer-sized carrier particles in solution. The principal advantage of this technique is its insensitivity to small, fast-diffusing sources. It also discriminates against weakly fluorescent contaminants of size comparable to the carrier particles. We demonstrate these attributes by using two model systems: a human IgG assay and an idealized system consisting of polystyrene fluorescent spheres and rhodamine dye.

Autofeedback of prolactin in cultured prolactin-secreting pituitary cells

Cultured GH3 rat pituitary tumor cells which secrete prolactin (PRL) were used to study autoregulation of rat PRL (rPRL) secretion. Acute (1 h) release of rPRL by cells in monolayer culture was inhibited by ovine PRL (oPRL; 10(-7) and 10(-8) M). Intracellular rPRL accumulation was not inhibited by exogenous oPRL. No effect of oPRL was seen during long-term (12-day) incubation of cells with oPRL (10(-7) to 10(-9) M). oPRL exerts an acute suppressive effect on rPRL release at the cellular level, but does not inhibit rPRL synthesis or long-term release.

Alterations in the pyruvate dehydrogenase complex during adaptation to glucose by Neurospora

A 20-fold induction of the pyruvate dehydrogenase complex, pyruvate dehydrogenase (EC 1.2.4.1) plus dihydrolipoate S-acetyltransferase, (lipoyltransacetylase) (EC 2.3.1.12) plus dihydrolipoyl dehydrogenase, NADH : lipoamide oxidoreductase, (EC 1.6.4.3), from a specific activity of 3.5-65.0 was observed in mitochondrial extracts during adaptation of Neurospora to glucose from acetate media. The extent of ATP-dependent, time-dependent inactivation of the pyruvate dehydrogenase complex was approximately the same in both acetate- and glucose-grown cells, thereby indicating that the low pyruvate dehydrogenase complex activities in acetate-grown cells did not represent phosphorylated pyruvate dehydrogenase complex molecules. High levels of dihydrolipoyl transacetylase (EC 2.3.1.12) were observed in mitochondrial extracts from acetate-grown cells; this lipoyltransacetylase was analyzed on sucrose density gradients and found to be associated with the pyruvate dehydrogenase complex. Digitonin fractionation of mitochondria revealed that both the pyruvate dehydrogenase complex and lipoyltransacetylase were primarily associated with the mitochondrial outer membrane.

Below- and through-knee amputations in ischaemic disease

Fifty-three below-knee amputations and 22 through-knee amputations were done for ischaemic disease at St. Thomas's Hospital over the past 5 years. It was found that 36 of the below-knee amputations healed satisfactorily, 27 by first intention, 9 after infection. Eleven of the through-knee amputations healed, 4 after infection. The healing was unaffected by the presence or absence of peripheral gangrene. It is suggested that is suggested that in ischaemic disease of the lower limbs a below-knee amputation should be considered as it has a 70 per cent chance of healing, but if it is felt that this amputation is not suitable then an above-knee amputation should be done in preference to a through-knee amputation.

Pulmonary veno-occlusive disease

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