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K J Martin

Publications and source records attributed to K J Martin.

At least 91 records · Page 5Linked to original sources
PubMed1987

Equilibrium DNA-binding of AraC protein. Compensation for displaced ions.

Experiments on the AraC regulatory protein of Escherichia coli suggest a mechanism that DNA-binding proteins can use to reduce potentially drastic alterations in their affinity for DNA resulting from changes in salt concentration. Measurement of the net number of ions apparently displaced as AraC protein binds DNA and of fluorescence changes in the protein lead to the following picture. About 14 ions are displaced from the DNA as the protein binds the araI site. As the protein binds the DNA, however, it undergoes a conformational change and binds about ten ions. Consequently, the net order of the reaction is reduced from 15th to about fourth order in salt concentration.

AraC Transcription Factor↗
PubMed1987

Differences in the response to intact b-PTH I-84 and synthetic b-PTH I-34 in isolated perfused bones from young and adult dogs.

Controversy exists over the relative effects of intact b-PTH I-84 and synthetic b-PTH I-34 on the generation of cyclic-AMP (cAMP) by the skeleton. Some experimental models demonstrate that these parathyroid hormone (PTH) peptides are equipotent while other systems show that the synthetic amino-terminal PTH fragment is more potent. The present studies examine the release of cAMP by isolated perfused bone from adult and young dogs in response to intact PTH I-84 and synthetic b-PTH I-34 in order to examine if age is important in determining the response of bone to PTH peptides. The results show that there is a remarkable difference in the release of cAMP between bones from adult and young animals. The release of cAMP in response to synthetic b-PTH I-34 is greater in bones from puppies than in bones from adult dogs. The release of cAMP in response to b-PTH I-84 is minimal in bones from adult dogs which is in agreement with previous studies from our laboratory. In puppies, however, there is a definite response to b-PTH I-84 albeit less than that of synthetic b-PTH I-34.

Aging↗
PubMed1987

Role of 1,25-dihydroxyvitamin D on the skeletal resistance to parathyroid hormone.

Hypocalcemia in chronic renal failure (CRF) has been attributed in part to a skeletal resistance (S.R.) to the calcemic action of parathyroid hormone (PTH) as a consequence of low levels of 1,25(OH)2D3. To further elucidate the role of 1,25(OH)2D3 in the genesis of S.R., the calcemic effect of infusion of synthetic b-PTH 1-34 was examined in dogs before and after 7, 90 and 180 days of CRF. The maximum increment in ionized calcium after the infusion of PTH in the normal dogs was 1.15 +/- 0.13 mg/dl, decreased to 0.84 +/- 0.09 after 7 days, 0.68 +/- 0.1 after 90 days and to 0.66 +/- 0.11 mg/dl after 180 days of CRF. Thereafter, the dogs received 1,25(OH)2D3, 0.5 microgram daily for seven days and the studies were repeated. No improvement in the calcemic response to PTH was observed (0.57 +/- 0.26 mg/100 ml). Subsequently, a parathyroidectomy (PTX) was performed and 24 hours later the studies were repeated. After the infusion of PTH the calcemic response returned to normal (0.93 +/- 0.14 mg/dl). Further studies were performed in a group of four uremic dogs receiving no 1,25(OH)2D3, in which a PTX was performed 24 hours prior to the infusion of PTH. For this group, the increase in serum ionized calcium was 0.99 +/- 0.11 mg/dl. These values were not statistically different from normal dogs. In summary: (1) renal insufficiency was characterized by an abnormal calcemic response to PTH; (2) the administration of 1,25(OH)2D3 did not correct the S.R. to PTH; and (3) PTX performed 24 hours before the infusion of PTH restored the calcemic response to normal. These data suggest that high levels of endogenous parathyroid hormone desensitized the skeleton to the administration of exogenous PTH. These studies indicate that low values of 1,25(OH)2D3 are not directly responsible for the skeletal resistance to PTH in chronic renal failure.

Animals↗
PubMed1987

Effect of biological activity of PTH on its peripheral metabolism in the rat.

Previous studies from our laboratory have characterized the peripheral metabolism of parathyroid hormone (PTH) in the dog using radioimmunoassay techniques following injection or infusion of biologically active, bovine PTH preparations. Other investigators have used biologically-inactive labelled PTH and interpreted their results as representative of the normal physiological processes. Since oxidized inactive PTH does not bind to PTH receptors and since we have found substantial differences between the tissue uptake of active and inactive PTH preparations, it is possible that results obtained with inactive PTH preparations may not totally represent the normal metabolism of PTH. Therefore, we performed studies in rats to compare the disappearance of immunoreactive PTH (i-PTH) from plasma following injection of active or inactive syn b-PTH 1-34. The maneuvers of bilateral ureteral ligation and bilateral nephrectomy were utilized to characterize the sites of tissue uptake of i-PTH. The results obtained indicate that inactive syn b-PTH 1-34 has a significantly slower disappearance from plasma than biologically active syn b-PTH 1-34. Reduction of glomerular filtration by acute bilateral ureteral ligation decreased the disappearance of oxidized PTH more than active PTH. Thus, the results indicate a major dependence on glomerular filtration for the removal of inactive syn b-PTH 1-34. The demonstration that the peripheral metabolism of active and inactive syn b-PTH 1-34 is not identical suggests that studies of the metabolism of inactive PTH preparations do not accurately reflect that of biologically active PTH.

Animals↗
PubMed1987

WR-2721 inhibits parathyroid adenylate cyclase.

WR-2721 [S-2-(3-aminopropylamino)ethylphosphorothioic acid] is a chemoprotective and radioprotective agent that has been shown to lower serum calcium in dogs and in humans. This is secondary both to impaired release of Ca2+ from bone and diminished secretion of parathyroid hormone (PTH) from parathyroid glands. Because cAMP plays a role in the regulation of PTH secretion and WR-2721 has been shown to lower cAMP levels in radiated mouse spleen, we investigated the effects of WR-2721 on cAMP production in dispersed bovine parathyroid cells. Additionally, we studied the adenylate cyclase in plasma membranes from normal bovine parathyroid glands after exposure to WR-2721. With parathyroid cells incubated at 0.5 mM Ca2+, addition of WR-2721 in concentrations ranging from 0.02 to 2.0 mM resulted in a progressive decrease in intracellular cAMP (42-50%, respectively). In plasma membranes of bovine parathyroid cells a dose-dependent decrease in adenylate cyclase activity was noted. Inhibition of the cyclase was seen over a wide range of Mg2+ concentrations (2.5-40 mM). WR-2721 inhibited both basal and NaF, Gpp(NH)p, forskolin, and pertussin toxin-stimulated adenylate cyclase. These data suggest that WR-2721 inhibits the activity of parathyroid adenylate cyclase.

Adenylyl Cyclase Inhibitors↗
PubMed1986

The effects of discontinuation of aluminum exposure on aluminum-induced osteomalacia.

Studies in patients on dialysis have shown that aluminum (Al) accumulation in bone plays a major role in the pathogenesis of osteomalacia. It has been suggested that deferoxamine (DFO) may be beneficial in the treatment of aluminum-induced osteomalacia. The present studies were performed in four groups of uremic rats to determine if DFO and/or discontinuation of Al administration have an effect on bone histomorphometry and blood chemistries. The groups were: 1) uremic control 2) aluminum (0.75 to 1.0 mg/rat i.p., five times a week for twelve weeks): 3) aluminum + DFO, after twelve weeks Al was discontinued and the rats received DFO (75 mg/rat two times a week for nine weeks); 4) aluminum + time, after twelve weeks Al was discontinued and the rats were sacrificed after nine weeks. High levels of Al in serum and bone and low levels of PTH were seen in rats receiving Al. Bone histology revealed Al at the mineralization front, abnormal tetracycline uptake, and an increase in osteoid. DFO treatment did not significantly change the level of Al in bone, however both DFO treatment and discontinuation of Al reversed towards normal the above described lesions. In conclusion, these studies suggest that DFO and/or discontinuation of Al administration to rats with approximately 30% of renal function greatly improve aluminum-induced osteomalacia.

Aluminum↗
PubMed1986

Atriopeptin III increases cGMP in glomeruli but not in proximal tubules of dog kidney.

Atriopeptin III is natriuretic, diuretic, and phosphaturic in the intact dog and relaxes vascular and nonvascular smooth muscle in vitro. The mechanism of the renal effects of atriopeptin remains ill defined but may include hemodynamic alterations and/or direct tubular effects. Since many peptide hormones act through changes in cyclic nucleotide formation, we examined the effect of synthetic atriopeptins on cAMP and cGMP accumulation in isolated glomeruli and proximal tubules from normal dog kidney. Synthetic atriopeptin produced a dose-related increase in cGMP in glomeruli with a Kact of 200 +/- 19 nM and a maximal activity of 64.1 +/- 6.3 pmol cGMP X mg prot-1 X 5 min-1. In the presence of 4 mM Mn2+ Kact was reduced to 19 +/- 2 nM with no change in maximal cGMP production (66.2 +/- 11.8 pmol cGMP X mg prot-1 X 5 min-1). Atriopeptin (1 microM) did not increase cGMP accumulation above basal levels in proximal tubule segments. The cAMP production of neither glomeruli nor proximal tubules was stimulated by atriopeptin. These studies demonstrate a dose-dependent stimulation of guanylate cyclase by atriopeptin in glomeruli but not in proximal tubule segments. In addition, atriopeptin neither stimulates nor inhibits cAMP accumulation in glomeruli or proximal tubules. These data suggest a major role for the renal effects of atriopeptin at the glomerular level, possibly through hemodynamic effects or changes in the glomerular ultrafiltration coefficient.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Thromboxane synthesis and blood pressure in spontaneously hypertensive rats.

The present study examines effects of administration of OKY 046, an inhibitor of thromboxane synthesis, for 100 days on systemic blood pressure and renal function in spontaneously hypertensive rats and in normotensive control rats. Untreated spontaneously hypertensive rats had higher values for thromboxane excretion in the urine and higher values for blood pressure than did normotensive control rats. Administration of OKY 046 decreased systolic and mean arterial blood pressure and urinary excretion of thromboxane and protein in spontaneously hypertensive rats. Administration of OKY 046 decreased thromboxane excretion in the urine of normotensive control rats but had no effect on blood pressure or protein excretion. Renal function, as assessed by the clearances of inulin and p-aminohippuric acid, was greater in spontaneously hypertensive rats treated with OKY 046 than in those receiving vehicle alone. In normotensive control rats, OKY 046 administration did not affect renal function. These results suggest that increased renal synthesis of thromboxane may play a role in the pathogenesis of the elevated blood pressure of spontaneously hypertensive rats.

Acrylates↗
PubMed1986

Hypocalcemia may not be essential for the development of secondary hyperparathyroidism in chronic renal failure.

Hypocalcemia is the main factor responsible for the genesis of secondary hyperparathyroidism in chronic renal disease. Studies with parathyroid cells obtained from uremic patients indicate that there is a shift in the set point for calcium-regulated hormone (parathyroid hormone [PTH] secretion. Studies were performed in dogs to further clarify this new potential mechanism. Hypocalcemia was prevented in uremic dogs by the administration of a high calcium diet. Initially, ionized calcium was 4.79 +/- 0.09 mg/dl and gradually increased up to 5.30 +/- 0.05 mg/dl. Despite a moderate increase in ionized calcium, immunoreactive PTH (iPTH) increased from 64 +/- 7.7 to 118 +/- 21 pg/ml. Serum 1,25(OH)2D3 decreased from 25.4 +/- 3.8 to 12.2 +/- 3.6 pg/ml. Further studies were performed in two other groups of dogs. One group received 150-200 ng and the second group 75-100 ng of 1,25(OH)2D3 twice daily. The levels of 1,25(OH)2D3 increased from 32.8 +/- 3.5 to a maximum of 69.6 +/- 4.4 pg/ml. In the second group the levels of serum 1,25(OH)2D3 after nephrectomy remained normal during the study. Amino-terminal iPTH did not increase in either of the two groups treated with 1,25(OH)2D3. In summary, the dogs at no time developed hypocalcemia; however, there was an 84% increase in iPTH levels, suggesting that hypocalcemia, per se, may not be the only factor responsible for the genesis of secondary hyperparathyroidism.

Amino Acid Sequence↗
PubMed1985

Effects of benzyl alcohol on PTH receptor-adenylate cyclase system of canine kidney.

In many systems, perturbations of membrane architecture by changes of lipid and phospholipid composition have been shown to alter the activity of membrane-bound enzymes. The present studies examined the effect of benzyl alcohol, an agent that has been shown to increase membrane fluidity, on the parathyroid hormone (PTH)-sensitive adenylate cyclase system of canine kidney. Benzyl alcohol progressively increased basal adenylate cyclase activity up to fourfold and maximal enzyme activity in the presence of PTH, GTP, guanylimidodiphosphate, and sodium fluoride by four- to sixfold. In the presence of 20 mM Mn2+ (no Mg2+), conditions under which enzyme activity is devoid of influence of guanine nucleotides or hormones, benzyl alcohol was without effect. PTH binding was increased by 25% in the presence of benzyl alcohol without a change in binding affinity. Fluorescent polarization studies using diphenylhexatriene showed a decrease in fluorescence anisotropy in the presence of benzyl alcohol. The results suggest that benzyl alcohol facilitates the interaction of the components of the adenylate cyclase system, presumably by increasing membrane fluidity. Alterations of membrane fluidity may be a potent means of regulating hormone sensitive adenylate cyclase activity.

Adenylyl Cyclases↗
PubMed1985

Impaired parathyroid hormone receptor-adenylate cyclase system in the postobstructed canine kidney.

The present studies examine the initial events in the action of PTH, namely receptor binding and adenylate cyclase activation in the postobstructed canine kidney. Both kidneys were removed from five mongrel dogs 2 h after relief of unilateral ureteral obstruction (UUO) of 42 h duration. Basolateral membranes (BLM) were prepared from both the UUO and contralateral (control) kidneys. Maximal activation of adenylate cyclase by PTH was 35% lower (P less than 0.01) in BLM from UUO than control kidneys (3869 +/- 200 vs. 5978 +/- 425 pmol cAMP/mg protein X 30 min). The concentration of PTH required for half-maximal activation of the enzyme was unchanged. Addition of 1 mM GTP failed to correct the decreased enzyme activity in response to PTH of BLM from kidneys with UUO. NaF activation, a measure of interaction of the nucleotide regulatory component (G/F) with the catalytic unit of the adenylate cyclase was similar in BLM from UUO and control kidneys. Similarly, activation of the catalytic unit of the enzyme by Mn2+ was not different. Specific binding of [125I]Nle8, Nle8, Tyr34-bovine PTH NH2 was markedly reduced (P less than 0.01) in BLM from UUO vs. control (6.37 +/- 1.20 vs. 2.43 +/- 0.09 fmole bound/microgram protein). There was no change in hormone affinity for the binding site. These data indicate that there is decreased activation of adenylate cyclase by PTH as a consequence of apparent loss of receptors for the hormone in the BLMs of renal tubular cells of postobstructed kidneys. These abnormalities may play a role in the abnormal regulation of phosphorus excretion after ureteral obstruction.

Adenylyl Cyclases↗
PubMed1985

Effects of aluminum on bovine parathyroid adenylate cyclase.

It is known that the secretion of PTH is often impaired in association with aluminum (Al3+) accumulation in patients with renal failure. The mechanisms involved remain ill defined. Since adenylate cyclase plays a role in the regulation of PTH secretion, these studies examine the effects of Al3+ on parathyroid adenylate cyclase. In membranes from normal bovine parathyroid glands, basal adenylate cyclase activity, in the presence of 0.2 mM ATP and 20 mM Mg2+, increased by 22% as Al3+ was raised from 0-10 microM. Higher Al3+ concentrations caused a progressive decrease in adenylate cyclase activity, reaching 68% inhibition of control activity at 2 mM Al3+. Since adenylate cyclase activation is influenced by the interaction of multiple sites within the adenylate cyclase complex, the nature of the inhibition by Al3+ was explored by examining the interaction of Al3+ with substrate ATP and with Mg2+, an allosteric activating metal ion. In the presence of 20 mM Mg2+, Al3+ concentrations of 1-2 mM resulted in noncompetitive inhibition with respect to ATP [decrease in maximum velocity (Vmax) from 4176 in the absence of Al3+ to 1106 pmol cAMP/mg protein X 15 min; Michaelis Menten constant (Km) for ATP was unchanged]. In contrast, at fixed ATP (0.2 mM), 0.5 mM resulted in competitive inhibition of adenylate cyclase with respect to Mg2+, whereas at higher Al3+ concentrations the inhibition was noncompetitive. When Mg2+ was replaced by Mn2+ (enzyme activity reflects the activity of the catalytic unit), the inhibitory effect of Al3+ on adenylate cyclase activity was abolished. These data suggest that the inhibition of parathyroid adenylate cyclase by Al3+ occurs at the level of the allosteric metal activating site. These data provide a potential mechanism for the inhibition of PTH secretion by Al3+.

Adenosine Triphosphate↗
PubMed1984

Parathyroid hormone receptors in circulating human mononuclear leukocytes.

In this article we demonstrate receptors for parathyroid hormone in circulating mononuclear leukocytes using the radioiodinated analogue (8,18 norleucine, 34 tyrosine) bPTH 1-34 (bovine parathyroid hormone 1-34). Specific binding, which is reversible and saturable, equilibrates within 5 min at 0-4 degrees C with a calculated KD of 8.9 X 10(-11) M. This binding has a pH maximum of 7.0, is magnesium-dependent, and is inversely related to medium calcium concentration. Such binding is completely inhibited by simultaneous addition of 4 ng/ml of bovine parathyroid hormone 1-34, 5 ng/ml of bovine parathyroid hormone 1-84, or 5 ng/ml (8,18 norleucine, 34 Tyr) of 3-34 bPTH, but is unaffected by a biologically inactive parathyroid hormone fragment or other unrelated peptide hormones. Cyclic AMP accumulation increases 3-fold after 5 min exposure of mononuclear leukocytes to bPTH 1-34 in concentrations as low as 1 X 10(-9) M. Lymphocytes appear to be the circulating cells which interact with PTH as indicated by the observations that: 1) lymphocyte-enriched preparations bind three times as much radioligand/cell as do mixed mononuclear leukocytes, 2) monocytes, platelets, granulocytes, and erythrocytes do not bind PTH, and 3) monocytes, but not lymphocytes, degrade the hormone.

Cell Separation↗
PubMed1984

Marked suppression of secondary hyperparathyroidism by intravenous administration of 1,25-dihydroxy-cholecalciferol in uremic patients.

Current evidence suggests that administration of 1,25(OH)2D3 to patients with chronic renal insufficiency results in suppression of secondary hyperparathyroidism only if hypercalcemia occurs. However, since the parathyroid glands possess specific receptors for 1,25(OH)2D3 and a calcium binding protein, there is considerable interest in a possible direct effect of 1,25(OH)2D3 on parathyroid hormone (PTH) secretion independent of changes in serum calcium. Recent findings indicate substantial degradation of 1,25(OH)2D3 in the intestine, therefore, it is possible that while oral administration of the vitamin D metabolite increases intestinal calcium absorption, the delivery of 1,25(OH)2D3 to peripheral target organs may be limited. We therefore compared the effects of orally or intravenously administered 1,25(OH)2D3 on the plasma levels of 1,25(OH)2D3 and the effects of these two modes of treatment on PTH secretion. Whereas oral administration of 1,25(OH)2D3 in doses adequate to maintain serum calcium at the upper limits of normal did not alter PTH levels, a marked suppression (70.1 +/- 3.2%) of PTH levels was seen in all 20 patients given intravenous 1,25(OH)2D3. Temporal studies suggested a 20.1 +/- 5.2% decrease in PTH without a significant change in serum calcium with intravenous 1,25(OH)2D3. In five patients the serum calcium was increased by the oral administration of calcium carbonate, the decrement in serum i-PTH was only 25 +/- 6.65% when compared with 73.5 +/- 5.08% (P less than 0.001) obtained by the administration of intravenous 1,25(OH)2D3. Thus, a similar serum calcium achieved by intravenous 1,25(OH)2D3 rather than calcium carbonate has a greater suppressive effect in the release of PTH. These studies indicate that 1,25(OH)2D3 administered intravenously rather than orally may result in a greater delivery of the vitamin D metabolite to peripheral target tissues other than the intestine and allow a greater expression of biological effects of 1,25(OH)2D3 in peripheral tissues. The use of intravenous 1,25(OH)2D3 thus provides a simple and extremely effective way to suppress secondary hyperparathyroidism in dialysis patients.

Administration, Oral↗
PubMed1984

Uncoupling of the parathyroid hormone receptor-adenylate cyclase system of canine kidney during dietary phosphorus deprivation.

The mechanisms involved in the renal resistance to the phosphaturic action of PTH during dietary phosphorus deprivation remain ill defined. Previous studies in dogs from our laboratory demonstrated that baseline excretion of cAMP and the increment after administration of parathyroid extract were markedly reduced during dietary phosphorus deprivation. The present studies examine the initial events in the actions of PTH, namely receptor binding and adenylate cyclase activation, in renal cortical membranes from normal and phosphorus-deprived animals. Mongrel dogs were fed a diet deficient in phosphorus for 4-6 weeks. Plasma phosphorus fell from 4.2 +/- 0.4 to 1.4 +/- 0.3 mg/dl. In renal cortical membranes from these animals, basal adenylate cyclase activity was not different from that in control normal animals. However, PTH-stimulated enzyme activity was markedly reduced (5785 +/- 303 pmol cAMP/mg protein X 30 min in controls vs. 2612 +/- 406 pmol cAMP/mg protein X 30 min; P less than 0.01). Kact (PTH concentration for half-maximal enzyme activation) was unchanged. PTH receptor binding assessed with [Nle8,Nle18,Tyr34]bovine PTH-(1-34) NH2 was not different in the two groups. The decreased PTH-stimulated adenylate cyclase activity was not corrected by GTP. Activation of adenylate cyclase by NaF was reduced in membranes from the phosphorus-deprived animals, whereas enzyme activation by guanylylimidodiphosphate was similar in both groups. Enzyme activity in the presence of Mn++ was not different from the control value. These data indicate that during dietary phosphorus deprivation there is uncoupling of the PTH receptor-adenylate system of canine kidney. This abnormality may play a role in the renal resistance to PTH during dietary phosphorus deprivation.

Adenylyl Cyclases↗
PubMed1984

Influence of forskolin on the parathyroid hormone dependent adenylate cyclase system of canine kidney: evidence for noncatalytic effects of forskolin.

The present studies examined the effects of forskolin on the PTH responsive adenylate cyclase system of canine basolateral renal cortical membranes. This agent is a potent activator of adenylate cyclase in a wide variety of intact cells and broken cell preparations. Initially forskolin was believed to activate adenylate cyclase by direct stimulation of the catalytic unit of the enzyme. Several observations, however, have suggested that there may be additional noncatalytic sites of action. In the present studies, forskolin was found to increase PTH-stimulated adenylate cyclase activity by 4-fold associated with a 2-fold decrease in the Kact for PTH (dose of PTH required for half-maximal enzyme stimulation). Studies of the interaction of forskolin with magnesium revealed that forskolin resulted in a dose dependent increase in the affinity of adenylate cyclase for magnesium. A short lag was observed in the onset of enzyme activation by forskolin. The lag was decreased as Mg++ concentration was increased. The forskolin-induced increase in the affinity for Mg++ was similar to that produced by other activators of adenylate cyclase such as NaF and GTP, which interact with the nucleotide regulatory protein. Magnesium also markedly affected the affinity of the enzyme system for forskolin. Kact for forskolin was reduced from 10 microM to 0.1 microM as Mg++ concentration was raised from 0.5 mM to 40 mM. Since previous studies have shown that the allosteric effects of Mg++ are at, or closely related to, the nucleotide regulatory protein, these findings suggest that forskolin may also affect this site. In summary, in basolateral renal cortical membrane of canine kidney the effects of forskolin to increase the affinity of adenylate cyclase for PTH and to alter the allosteric effects of Mg++ on enzyme activity are indicative of noncatalytic effects of forskolin. The interpretation of action of forskolin on adenylate cyclase activity should not be restricted to direct stimulation of the catalytic unit.

Adenylyl Cyclases↗
PubMed1984

Absence of biological effects of oxidized parathyroid hormone-(1-34) in dogs and rats.

Recent studies have shown that oxidation of bovine PTH-(1-34) [bPTH-(1-34)] with H2O2 abolished the vascular effects of PTH in rats and dogs, but the hypercalcemic effect of the oxidized PTH was preserved in the Japanese quail in vivo. These observations seem at variance with previous studies from our laboratory in the isolated perfused canine tibia preparation in which no uptake of immunoreactive PTH or stimulation of cAMP release was demonstrated during infusion of oxidized bPTH-(1-34). The present studies examine the skeletal and renal effects of oxidized PTH-(1-34) in rats and dogs in vivo. Oxidation of PTH with H2O2 reduced its activation of adenylate cyclase by 95% in dog renal cortical membrane. Awake normal dogs were studied before and during the infusion of bPTH-(1-34) or oxidized PTH-(1-34) (4 U/kg X h). With active PTH, ionized Ca+2 rose in each dog (range, 0.7-1.5 mg/dl), while with oxidized PTH, Ca+2 remained within 0.1 mg/dl of the baseline values. Fractional excretion of PO4 rose from 1.58 +/- 0.6% to 29.5 +/- 2.5% with active PTH and from 1.4 +/- 0.4% to 5.7 +/- 1% with oxidized PTH. The latter did not differ from the value in vehicle-infused dogs. Further studies were performed in 30 acutely parathyroidectomized rats. Plasma Ca+2 rose from 8.2 +/- 0.1 to 9.0 +/- 0.3 mg/dl with active PTH (20 micrograms/kg), fell to 7.7 +/- 0.2 with oxidized PTH, and fell to 7.3 +/- 0.3 mg/dl with vehicle. In parathyroid-intact rats plasma Ca+2 increased by 0.9 mg/dl whether given active PTH, oxidized PTH, or vehicle. We conclude that oxidation of bPTH-(1-34) results in loss of both the renal and skeletal effects of PTH in vivo in rats and dogs.

Adenylyl Cyclases↗