Circadian pacemaker coupling by multi-peptidergic neurons in the cockroach Leucophaea maderae

Lesion and transplantation studies in the cockroach, Leucophaea maderae, have located its bilaterally symmetric circadian pacemakers necessary for driving circadian locomotor activity rhythms to the accessory medulla of the optic lobes. The accessory medulla comprises a network of peptidergic neurons, including pigment-dispersing factor (PDF)-expressing presumptive circadian pacemaker cells. At least three of the PDF-expressing neurons directly connect the two accessory medullae, apparently as a circadian coupling pathway. Here, the PDF-expressing circadian coupling pathways were examined for peptide colocalization by tracer experiments and double-label immunohistochemistry with antisera against PDF, FMRFamide, and Asn13-orcokinin. A fourth group of contralaterally projecting medulla neurons was identified, additional to the three known groups. Group one of the contralaterally projecting medulla neurons contained up to four PDF-expressing cells. Of these, three medium-sized PDF-immunoreactive neurons coexpressed FMRFamide and Asn13-orcokinin immunoreactivity. However, the contralaterally projecting largest PDF neuron showed no further peptide colocalization, as was also the case for the other large PDF-expressing medulla cells, allowing the easy identification of this cell group. Although two-thirds of all PDF-expressing medulla neurons coexpressed FMRFamide and orcokinin immunoreactivity in their somata, colocalization of PDF and FMRFamide immunoreactivity was observed in only a few termination sites. Colocalization of PDF and orcokinin immunoreactivity was never observed in any of the terminals or optic commissures. We suggest that circadian pacemaker cells employ axonal peptide sorting to phase-control physiological processes at specific times of the day

Effect of angiotensin II-induced changes in perfusion flow rate on chlorothiazide transport in the isolated perfused rat kidney

Angiotensin II was used as a probe to study the effect of changes in perfusate flow rate on the renal clearance parameters of chlorothiazide in the isolated perfused rat kidney. Perfusion studies were performed in five rats with no angiotensin II present in the perfusate and in five rats with a 1–4 ng/min infusion of angiotensin II into the perfusate. Angiotensin II had a dramatic effect on the renal hemodynamics, resulting in a 43% decrease in perfusate flow, a 16% decrease in glomerular filtration rate (GFR), and a 45% increase in filtration fraction. Values for the fractional excretion of glucose were low and consistent, with or without angiotensin II. Although the unbound fraction (fu) of chlorothiazide was unchanged between treatments, the renal (CL r ) and the secretion clearances were reduced by about 50% in the presence of angiotensin II; the excretion ratio [ER=CL r /(fu·GFR)] was reduced by 38% with angiotensin II present in the perfusate. Analysis of the data was complicated by the presence of a capacity-limited transport for renal tubular secretion. Transport parameters (±SD) were obtained and the corrected intrinsic secretory clearance [(V max /GFR)/K m ] of chlorothiazide was 123 ± 18 without angiotensin II vs. 72.8 ± 30.0 with angiotensin II. These results demonstrate that alterations in organ perfusion can significantly reduce the clearance parameters of chlorothiazide in the rat IPK. These flow-induced changes in intrinsic secretory transport may reflect perturbations other than that of perfusion flow rate alone .Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45047/1/10928_2005_Article_BF01071001.pd

Disposition of quinapril and quinaprilat in the isolated perfused rat kidney

An isolated perfused rat kidney model was used to probe the renal disposition of quinapril and quinaprilat after separate administration of each drug species. Control studies were performed with drug-free perfusate ( n=8 ) and perfusate containing quinapril ( n=9 ) quinaprilat ( n=7 ) at initial drug concentrations of 1000 ng/ml (including corresponding tracer levels of tritiated drug). Physiologic parameters were within the normal range of values for this technique and were stable for the duration of each experiment. Quinapril and quinaprilat concentrations were determined in perfusate, urine, and perfusate ultrafiltrate using a specific and sensitive reversed-phase HPLC procedure with radiochemical detection, coupled to liquid scintillation spectrometry. Perfusate protein binding was determined using an ultrafiltration method at 37°C. The total renal learance of quinapril ( CLr ) was calculated as Dose/AUC (0-∞), and is represented by the sum of its urinary and metabolic clearances. The urinary clearances ( CLe ) of quinapril and quinaprilat were calculated as urinary excretion rate divided by midpoint perfusate concentration for each respective species. Of the total renal clearance for quinapril ( CLr =4.49 ml/min), less than 0.1% was cleared as unchanged drug ( CLe =0.004 ml/min); over 99% of the drug was cleared as quinaprilat formed in the kidney. The clearance ratio of quinapril [ CR=CLr/(fu·GFR )] was 41.0, a value representing extensive tubular secretion into the renal cells. Following quinaprilat administration, the clearance ratio of metabolite [ CR=CLe/(fu β GFR) ] was 3.85, indicating a net secretion process for renal elimination.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45050/1/10928_2006_Article_BF02354286.pd

Renal transport kinetics of furosemide in the isolated perfused rat kidney

Direct quantitative data and corresponding theory are provided for the effect of protein binding on the renal transport of furosemide. Drug studies were performed with various combinations of bovine serum albumin and dextran. This resulted in a percent unbound ( fu ) of furosemide ranging from 0.785 to 85.8%. The corrected renal ( CLr/GFR ) and secretion ( CLs/GFR ) clearances of furosemide were observed to increase with percent free, but in a nonproportional manner. Plots of CLr/GFR or CLs/GFR vs. fu appeared to have a prominent y intercept as well as a convex ascending curve. In addition, the excretion ratio [ ER=CLr/ (fu · GFR) ] was reduced from 60.8 to 8.72 as fu increased. Overall, the data were best fitted to a model in which two Michaelis-Menten terms wre used to describe renal tubular transport, and secretion was dependent upon free drug concentrations in the perfusate. The results demonstrate that the renal mechanisms of furosemide excretion are more complex than previously reported and that active secretion may involve two different transport systems over the concentration range studied.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45036/1/10928_2005_Article_BF01065259.pd

Tubular transport mechanisms of quinapril and quinaprilat in the isolated perfused rat kidney: Effect of organic anions and cations

The clearance mechanisms of quinapril and quinaprilat were probed using an isolated perfused rat kidney model. Sixty-four experiments were performed with drug in the absence and presence of classic inhibitors of the organic acid (i.e., probenecid and p-aminohippurate) and organic base (i.e., tetraethylammonium and quinine) transport systems of the proximal tubule. Initial perfusate concentrations of quinapril and quinaprilat were approximately 2.36 μM (or 1000 ng/ml), and transport inhibitors were coperfused at 100–10,000 times the drugs' initial μM concentrations. Quinapril and quinaprilat concentrations were determined in perfusate, urine, and perfusate ultrafiltrate using a reversed-phase HPLC procedure with radiochemical detection, coupled to liquid scintillation spectrometry. Perfusate protein binding was determined using an ultrafiltration method at 37°C. Overall, the clearance ratios of quinapril (total renal clearance divided by fu·GFR ) and quinaprilat (urinary clearance divided by fu·GFR ) were significantly reduced, and in a dose-dependent manner, by the coperfusion of organic acids but not organic bases. The data demonstrate that the organic anionic secretory system is the primary mechanism by which quinapril and quinaprilat are transported into and across renal proximal cells.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45053/1/10928_2006_Article_BF02353517.pd

STUDIES ON THE ROLE OF THE CORPUS ALLATUM IN THE ERI-SILKWORM, PHILOSAMIA CYNTHIA RICINI

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