PubMed Health⌕ Search

Biomedical subjects

J J Helwig

Publications and source records attributed to J J Helwig.

At least 55 records · Page 3Linked to original sources
PubMed1989

[Renal vasodilator effect of parathormone].

Parathyroid hormone (PTH) has been shown to decrease blood pressure in several animal species and to increase blood flow in different vascular beds. The aim of this work was to characterize and quantify the renal vasodilator effect of PTH on the isolated perfused kidney of the rat. The rat kidney was isolated and perfused in a closed circuit with a modified Krebs-Henseleit solution under non filtering conditions (BSA 10 g/100 ml, ligature of the ureter and perfusion pressure set on 70 mmHg). These conditions have been shown to avoid both glomerular filtration and PTH degradation. Vascular tone of the isolated kidney was restored by a continuous perfusion of prostaglandin F2 alpha (2 x 10(-8) mol/mn). The vasodilator responses to PTH were expressed as a percentage of the relaxation induced on each kidney preparation by 4.4 x 10(-4) M papaverine. PTH fragments [bovine PTH (1-34), NLe8.18Tyr34bPTH (1-34) amide and rat PTH (1-34)] induced concentration-dependent renal vasodilation. When tested at increasing cumulative concentrations, EC50 values ranged from 1 to 2 nM for all PTH fragments; maximal relaxation was obtained at 10(-8) M and only approached 40 p. 100 of the response induced by papaverine. Moreover, at concentrations higher than 10(-8) M, all three peptides induced lower vasodilator responses. Neither indomethacin nor phentolamine modified rPTH (1-34) induced renal response. When rPTH (1-34) was tested as a single concentration on each kidney preparation, a higher maximal response (60 p. 100 relaxation) was obtained. This suggested tachyphylaxis of the renal vasculature to repeated PTH administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Effect of prostaglandin E2 on adenylate cyclase activity in isolated glomeruli and tubules during postnatal maturation of rat renal cortex.

To examine the effect of prostaglandins on adenylate cyclase during the postnatal maturation of kidney, the prostaglandin E2 (PGE2) responsiveness of adenylate cyclase in the absence and presence of exogenous GTP was investigated in glomeruli and tubules isolated from renal cortex of 14-, 21- and 30-day-old rats. In the absence of GTP, the adenylate cyclase response to PGE2 in glomeruli of 14-day-old rats was about fourfold higher than that in 21- and 30-day-old rats. In the tubules there was an about 30-35% decrease in the enzyme response to the prostaglandin between 14 and 21 days as well as between 21 and 30 days. When GTP was present, the PGE2 responsiveness of adenylate cyclase was of the same order of magnitude in glomeruli at 14 and 21 days and lower at 30 days. Under the same conditions, no significant changes were observed in the cortical tubules throughout the period studied. Thus association of PGE2 plus GTP suggests that during the postnatal maturation of rat kidney, the response of adenylate cyclase to PGE2 remains unchanged in cortical tubules and slightly decreases in glomeruli.

Adenylyl Cyclases↗
PubMed1987

Structure-activity relationship of parathyroid hormone: relative sensitivity of rabbit renal microvessel and tubule adenylate cyclases to oxidized PTH and PTH inhibitors.

It has been shown previously that secondary structural changes of bPTH-(1-34) (synthetic amino-terminal (1-34) fragment of bovine parathyroid hormone), obtained by oxidation of the methionines 8 and 18, abolished its hypotensive but not its hypercalcemic action. Hence, it has been postulated that the various physiological effects of the hormone are mediated by different receptors that require different regions or configurations of the peptide. To further examine this hypothesis the relative sensitivity of the PTH-responsive adenylate cyclase of microvessels and tubules isolated from rabbit kidney cortex, to oxidized PTH and PTH inhibitors, was examined. In the presence of GTP, bPTH-(1-34) stimulated both microvessel and tubule adenylate cyclase in a dose-dependent fashion and with analogous affinities (ED50 = 52 nM in the microvessels and 85 nM in the tubules). Hydrogen peroxide treatment of bPTH-(1-34) resulted in the loss of the adenylate cyclase stimulating potency in the microvessels while there was substantial enzyme activation (ED50 = 900 nM) in the tubules. Oxidized PTH inhibited the untreated PTH-stimulated adenylate cyclase, suggesting that oxidized PTH still retains an affinity for vascular receptor sites. Similar treatment of the sulfur-free PTH analog [Nle8,18, Tyr34]bPTH-(1-34)NH2, where methionines have been replaced by norleucine, had little or no effect in both fractions. In the microvessels the synthetic PTH antagonist analogs [Nle8,18, Tyr34]bPTH-(3-34)NH2 and [Tyr34]bPTH-(7-34)NH2, strongly inhibited the adenylate cyclase responses to bPTH-(1-34). No inhibition was seen in the tubules with the same molar ratios of inhibitor to native PTH. Together, these results suggest strongly that the differences in the adenylate cyclase response to various PTH fragments most likely represent a difference in the structural requirements for PTH actions between microvessels and tubules.

Adenylyl Cyclases↗
PubMed1987

Parathyroid hormone stimulation of renal adenylate cyclase in various vertebrate species: evidence for an effect in the frog.

The effect of [Nle8,18,Tyr34]bPTH-(1-34)amide on renal plasma membrane adenylate cyclase, in the presence of 0.1 mM guanylylimidodiphosphate was measured in rat, chicken, frog and trout. All species showed an enrichment of at least 8-fold (relative to homogenate) in the marker enzyme Na+,K+-ATPase. A significant dose-dependent adenylate cyclase stimulation was found in frog, with affinity values similar to those of rat and chicken (ED50=8, 10 and 3 nM, respectively), but not in trout. The frog response was specific since [Nle8,18,Tyr34]bPTH-(3-34)amide strongly inhibited the agonist-stimulated enzyme. These results suggest the existence of a PTH-like substance in anurans acting via cyclic AMP formation in the kidney.

Adenylyl Cyclases↗
PubMed1985

Glutamic acid decarboxylase in tubules and glomeruli isolated from rat kidney cortex.

4-Aminobutyric acid (GABA) synthesis was examined in purified glomeruli and tubules of rat kidney cortex that were incubated in the presence of [2,3-3H2]glutamate. The GABA that was formed was separated from glutamate using anion-exchange resin, and identified by means of an automatic amino acid analyser. In the renal cortex only the tubules were able to form GABA (35.0 nmol mg-1 h-1); the remaining GABA synthesis found in the glomerular preparations can most probably be attributed to a contamination by cortical tubules (9%), as shown by determination of a known tubular marker enzyme (L-gamma-glutamyltransferase). Hydroxylamine (1 mM) and ethanolamine-O-sulfate (10 mM), well-known inhibitors of cerebral GABA formation and GABA catabolism respectively, inhibited renal tubular GABA formation at 100% and 44% respectively.

Animals↗
PubMed1985

Activity of phosphatases and cellular contents in glomeruli and tubules isolated from growing rat renal cortex.

The activity of acid and alkaline phosphatases was determined in glomeruli and tubules isolated from 14-day old to adult rat renal cortex. Within a nephron fraction, each phosphatase activity produced a specific pattern which was not similar to that in other fractions. In the glomeruli the acid phosphatase activity increased between 14 and 21 days of life and was always higher than in the tubules where it did not significantly change with age. By using tartrate sodium and formaldehyde it was shown that the acid phosphatase isoenzymes are distributed according to a specific pattern which does not change during maturation. The alkaline phosphatase activity in glomeruli and in tubules increases with age but is always lower in the former fraction than in the latter. Furthermore, in young as well as in adult rats, glomeruli were characterized by a higher DNA content and lower RNA and protein/DNA ratios than the corresponding tubular fragments.

Acid Phosphatase↗
PubMed1985

Isoproterenol-sensitive adenylate cyclase in glomeruli isolated from young and adult rat renal cortex.

The stimulation of the adenylate cyclase activity of isolated rat renal glomeruli by isoproterenol decreased during kidney maturation. A potentiation of the isoproterenol response by GTP was demonstrated in young and adult animals. Both KF and GPP(NH)P enhanced the enzyme activity under basal conditions in young and adult glomeruli. GTP had no significant effect upon the basal activity of the adenylate cyclase in glomeruli of 14-day old rat kidney while it had one in 21-day old and adult kidneys.

Adenylyl Cyclases↗
PubMed1984

Distribution of parathyroid hormone-sensitive adenylate cyclase in isolated rabbit renal cortex microvessels and glomeruli.

The effect of the synthetic amino-terminal fragment of bovine parathyroid hormone, bPTH-(1-34), on the adenylate cyclase of microvessels and glomeruli isolated from rabbit kidney cortex was studied in the presence and absence of guanosine triphosphate (GTP). bPTH-(1-34) stimulated the vascular and glomerular adenylate cyclase in a dose-dependent manner with apparent ED50 values of 11.5 nM and 64 nM respectively, in the absence of GTP. 10(-4)M GTP greatly amplified the vascular response to bPTH-(1-34) while, in the glomeruli, both GTP and bPTH-(1-34) had only additive effects. In the presence of GTP, vascular and glomerular apparent ED50 were 190 nM and 64 nM respectively. [Nle8, Nle18, Tyr34] -bPTH-(3-34) amide, described as a PTH antagonist, inhibited the action of bPTH-(1-34) in the microvessels and to a lesser extent in the glomeruli. PTH is therefore a potent stimulator of adenylate cyclase in rabbit renal microvessels and glomeruli, and may play a role in the regulation of renal blood flow and glomerulo-tubular feedback control.

Adenylyl Cyclases↗
PubMed1984

[Distribution of various sites of hormonal action between microvessels, glomeruli and tubules isolated from the renal cortex of rabbits].

Collagenase dispersion of rabbit kidney cortex followed by centrifugation on discontinuous sucrose gradient, allowed the simultaneous obtention of microvascular, glomerular and tubular fractions. Microscopic studies and the measurements of cellular renin activity and the muscle-specific-enzyme creatine kinase showed that these vessels were arteriolar in nature and that they contained the preglomerular arterioles. The glomerular or tubular contamination rates were assessed by means of enzymatic markers. AVP stimulated only the tubular fraction whether GTP was present or not. In the absence of GTP, beta-isoproterenol stimulated only the tubular enzyme while in the presence of GTP, the microvascular and especially the glomerular AC were also stimulated. GTP enhanced considerably the microvascular response to bPTH-(1-34) while, in the glomeruli and tubules the effects of GTP and hormones were only additive. The possible physiological significance of these results are discussed.

Animals↗
PubMed1983

Early changes of guanylate cyclase and cGMP phosphodiesterase activities in glomeruli and tubules isolated from the remaining kidney after unilateral nephrectomy in the rabbit.

Guanylate cyclase (GCase) and cyclic guanosine 3'5'-monophosphate-phosphodiesterase (cGMP-PDE) activities were measured in the medulla, glomeruli and cortical tubules isolated from the remaining kidney 5-120 min after unilateral nephrectomy. The results showed that cGMP-PDE-specific activities were unchanged in all the fractions isolated from the contralateral kidney when compared with the nephrectomized control kidney. The GCase-specific activity in the cortical and medullary tubules isolated from the remaining kidney reached a maximum by 10 min after unilateral nephrectomy and then returned to control values. On the other hand the glomerular GCase activity decreased for 10 min after unilateral nephrectomy, then rebound activity reached a maximum by 30 min and after 120 min had returned to the control value. The possible physiological signification of such variations is discussed.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1982

[Proposal for a technic for demonstrating T lymphocytes on a frozen section. Marking by membrane fragments of sheep red blood cells].

T lymphocytes may be identified in the blood and in suspensions derived from lymphoid tissue, by their tendency to form rosettes with sheeps' red blood cells. Some authors have described a method of obtaining the E rosettes in histological sections (Whiteside and Rowlands, 1977; Brubaker and Whiteside, 1977, 1979; Sakamoto and Oda, 1979). We demonstrate that it is possible to fix fragments of the membrane of sheep's red blood cells obtained by thermal shock. This fixation may be demonstrated by fluorescent or electron microscopy. It is possible to demonstrate T lymphocytes in sections by using membrane from fragmented sheeps' red blood cells.

Animals↗