Changes In Adenylate Cyclase Activity Research Articles

Onset Mechanisms and Prognosis of Neurally Mediated Syncope

Neurally mediated syncope (NMS) is associated with a sudden loss of consciousness. However, the diagnostic tools and measures for prognosis management are limited. To overcome these limitations, the differences in the binding energies of Giα-protein-coupled receptors to the Glu9 and Glu12 residues on the α2B-AR gene were elucidated through the analysis of α2B-AR gene polymorphism. The suppression of the activity of adenylate cyclase (AC), which is involved in vasoconstriction, may be related to the onset of NMS. The head-up tilt (HUT) test results indicated differences in systolic blood pressure (SBP) and AC activity between patients with vasodepressor (VT)-NMS and healthy volunteers. Patients with VT-NMS had increased AC activity and decreased SBP. Conversely, in healthy volunteers, no changes in AC activity or SBP were found. These findings suggest that a high SBP and elevated AC activity at rest are likely to cause syncope. A high incidence of cardiovascular events is found in patients with negative HUT test results, highlighting the importance of investigating the cause of syncope in cases where the HUT test results are negative. Overall, our results may provide a means of assessing the risk of NMS development within healthy populations and underscore the importance of subsequent treatments for NMS.

Diagnosis and prevention of the vasodepressor type of neurally mediated syncope in Japanese patients.

We investigated circulatory dynamics in patients with vasodepressor type neurally mediated syncope (VT-NMS) by performing high-resolution Holter electrocardiography and a correlation analysis of changes in adenylate cyclase activity, blood pressure, and pulse during the head-up tilt test. Holter electrocardiography was performed for 30 patients. Adenylate cyclase activity was evaluated in lymphocytes from blood samples taken at rest and during the head-up tilt test. There was no change in autonomic nerve fluctuation during electrocardiography in VT-NMS patients, but our results showed a significant difference in blood pressure and adenylate cyclase activity between VT-NMS patients and healthy volunteers; the systolic blood pressure of VT-NMS patients decreased after 5 min, while at 10 min, the adenylate cyclase activity was the highest (0.53%) and the systolic blood pressure was the lowest (111.8 mm Hg). Pulse rates increased after 10 min. VT-NMS patients showed higher blood pressure, pulse rate, and adenylate cyclase activity during the tilt test than did healthy volunteers. In patients with syncope, standing for longer than 10 minutes may increase the risk of VT-NMS. From our results, we consider it likely that high systolic blood pressure and adenylate cyclase activity at rest cause fainting in VT-NMS patients. Our findings may be helpful for identifying individuals with a high risk of developing NMS in the healthy population.

Оценка активности аденилатциклазы в тромбоцитах овец после внешнего воздействия гамма-излучения в различных дозах

The paper presents results of study of adenylate cyclase activity in the platelets after external whole-body gamma-irradiation of 32 tsigai rams (Ovis aries) with 2, 4 and 6 Gy, at the dose rate of 1 Gy/hour. The irradiation caused the development of acute radiation damage of a different degree of severity. To detect changes in the basal and prostoglandin E1 stimulated (PGE1-stimulated) adenylate cyclase activity thin-layer chromatography (TLC) was carried out during the first 30 days of the damage development. After external -irradiation directly proportional effect of dose on changes in the basal adenylate cyclase activity in the platelets was registered on the 1 and the 7 days of the damage development, the changes in the PGE1-stimulated activity was registered on the 7 day. The study results allow making the suggestion that detected changes in the adenyl-ate cyclase activity in the platelets of irradiated rams may be resulted from the modification of cy-toplasmic cell membranes and impaired functioning of membrane-bound cAMP-sensitive signal-ing pathway. It may be also caused by new cells with qualitatively new properties released from the bone marrow megakaryocytes pool into the bloodstream.

Neurally mediated syncope diagnosis based on adenylate cyclase activity in Japanese patients.

The study aims to clarify the mechanism in patients with neurally mediated syncope (NMS), focusing on the adenylate cyclase (AC) activity level in lymphocytes. This study included 40 subjects: 22 healthy volunteers and 18 NMS patients. We investigated the changes in AC activity that occur during of syncope at rest and during the head-up tilt (HUT) test. We obtained 8 mL of blood at rest time and four times during the HUT test. Then, we measured the AC activity and the test reagent was added to the lymphocytes (10,000) and reacted for 30 min at room temperature. We were able to determine the standard value of AC activity when adrenaline (AD) and isoproterenol (IP) were added to lymphocytes. The results of our study showed one of the causes of NMS has a difference in AC activity level and classification of the patients into two different types of NMS was possible: either the vasodepressor type (VT) or mixed type (MT). At rest time, VT patients showed significantly higher AC activity (AD; 100 μM: p = 0.005, IP; 50 μM: p = 0.02) and MT patients showed significantly lower AC activity (AD; 10 μM: p = 0.02, IP; 50 μM: p = 0.004) than the average AC activity in healthy volunteers. Moreover, VT patients had significantly higher AC activity than healthy volunteers at the four points of the HUT test. MT patients had significantly lower AC activity (AD: p = 0.04 and IP: p = 0.04) than healthy volunteers at the rest time of HUT. Our study showed a significant difference in AC activities between NMS patients and healthy volunteers at rest. Therefore, a detailed NMS diagnosis can be made by examining AC activity levels in blood taken at rest time.

Differential Pharmacological Actions of Methadone and Buprenorphine in Human Embryonic Kidney 293 Cells Coexpressing Human μ-Opioid and Opioid Receptor-Like 1 Receptors

Methadone and buprenorphine are used in maintenance therapy for heroin addicts. In this study, we compared their effects on adenylate cyclase (AC) activity in human embryonic kidney (HEK) 293 cells stably overexpressing human μ-opioid receptor (MOR) and nociceptin/opioid receptor-like 1 receptor (ORL1) simultaneously. After acute exposure, methadone inhibited AC activity; however, buprenorphine induced compromised AC inhibition. When naloxone was introduced after 30 min incubation with methadone, the AC activity was enhanced. This was not observed in the case of buprenorphine. Enhancement of the AC activity was more significant when the incubation lasted for 4 h, and prolonged exposure to buprenorphine elevated the AC activity as well. The removal of methadone and buprenorphine by washing also obtained similar AC superactivation as that revealed by naloxone challenge. The study demonstrated that methadone and buprenorphine exert initially different yet eventually convergent adaptive changes of AC activity in cells coexpressing human MOR and ORL1 receptors.

Iloprost-induced desensitization of the prostacyclin receptor in isolated rabbit lungs

BackgroundThe rapid desensitization of the human prostacyclin (IP) in response to agonist binding has been shown in cell culture. Phosphorylation of the IP receptor by protein kinase C (PKC) has been suggested to be involved in this process.Methods and resultsIn this study we investigated the vasodilatory effects of iloprost, a stable prostacyclin analogue, in perfused rabbit lungs. Continuous infusion of the thromboxane mimetic U46619 was employed to establish stable pulmonary hypertension. A complete loss of the vasodilatory response to iloprost was observed in experiments with continuous iloprost perfusion, maintaining the intravascular concentration of this prostanoid over a 180 min period. When lungs under chronic iloprost infusion were acutely challenged with inhaled iloprost, a corresponding complete loss of vasoreactivity was observed. This desensitization was not dependent on upregulation of cAMP-specific phosphodiesterases or changes in adenylate cyclase activity, as suggested by unaltered dose-response curves to agents directly affecting these enzymes. Application of a prostaglandin E1 receptor antagonist 6-isopropoxy-9-oxoxanthene-2-carboxylic acid (AH 6809) or the PKC inhibitor bisindolylmaleimide I (BIM) enhanced the vasodilatory response to infused iloprost and partially prevented tachyphylaxis.ConclusionA three-hour infusion of iloprost in pulmonary hypertensive rabbit lungs results in complete loss of the lung vasodilatory response to this prostanoid. This rapid desensitization is apparently not linked to changes in adenylate cyclase and phosphodiesterase activation, but may involve PKC function and co-stimulation of the EP1 receptor in addition to the IP receptor by this prostacyclin analogue.

Impaired beta-adrenergic response and decreased L-type calcium current of hypertrophied left ventricular myocytes in postinfarction heart failure

Infarct-induced heart failure is usually associated with cardiac hypertrophy and decreased -adrenergic responsiveness. However, conflicting results have been reported concerning the density of L-type calcium current (I Ca(L)), and the mechanisms underlying the decreased -adrenergic inotropic response. We determined I Ca(L) density, cytoplasmic calcium ([Ca2+]i) transients, and the effects of -adrenergic stimulation (isoproterenol) in a model of postinfarction heart failure in rats. Left ventricular myocytes were obtained by enzymatic digestion 8-10 weeks after infarction. Electrophysiological recordings were obtained using the patch-clamp technique. [Ca2+]i transients were investigated via fura-2 fluorescence. -Adrenergic receptor density was determined by [ H]-dihydroalprenolol binding to left ventricle homogenates. Postinfarction myocytes showed a significant 25% reduction in mean I Ca(L) density (5.7 0.28 vs 7.6 0.32 pA/pF) and a 19% reduction in mean peak [Ca2+]i transients (0.13 0.007 vs 0.16 0.009) compared to sham myocytes. The isoproterenol-stimulated increase in I Ca(L) was significantly smaller in postinfarction myocytes (Emax: 63.6 4.3 vs 123.3 0.9% in sham myocytes), but EC50 was not altered. The isoproterenol-stimulated peak amplitude of [Ca2+]i transients was also blunted in postinfarction myocytes. Adenylate cyclase activation through forskolin produced similar I Ca(L) increases in both groups. -Adrenergic receptor density was significantly reduced in homogenates from infarcted hearts (Bmax: 93.89 20.22 vs 271.5 31.43 fmol/mg protein in sham myocytes), while Kd values were similar. We conclude that postinfarction myocytes from large infarcts display reduced I Ca(L) density and peak [Ca2+]i transients. The response to -adrenergic stimulation was also reduced and was probably related to -adrenergic receptor down-regulation and not to changes in adenylate cyclase activity.

Circadian change of adenylate cyclase activity in rabbit ciliary processes

Purpose. To characterize in vivo changes of adenylate cyclase activity in rabbit ciliary processes during the circadian cycle. Methods. After removal of vitreous, lens, retina and choroid from freshly enucleated rabbit eyes, the anterior segment and attached sclera was chilled in cold buffer containing the non-selective phosphodiesterase (PDE) inhibitor, 3-isobutyl-1-methylxanthine (IBMX). Then ciliary processes were excised and homogenized in ice cold trichloro-acetic acid (TCA) 2.5 min after IBMX treatment. Increased cyclic AMP in response to PDE inhibition was measured in ciliary processes at six times during the circadian cycle, after preganglionic section of the cervical sympathetic trunk (decentralization, DX), and after topical instillation of hydroxyamphetamine, timolol, brimonidine, rauwolscine or a soluble derivative of forskolin. Results. The increase of rabbit ciliary process cyclic AMP levels in response to PDE inhibition with IBMX was enhanced at night. Much of the enhanced nocturnal increase persisted in constant dark and was blunted by DX. Topical instillation of hydroxyamphetamine enhanced the increase during the day; whereas, timolol, a ß-adrenergic antagonist, or brimonidine, an a 2 -adrenergic agonist, blunted the IBMX induced increase. Neither instillation of rauwolscine, an a 2 -adrenergic antagonist, nor the soluble forskolin derivative enhanced the increase of cyclic AMP after IBMX. Conclusions. The technique reported here can be used to estimate ciliary process adenylate cyclase activity in vivo. There is a circadian rhythm of adenylate cyclase activity in rabbit ciliary processes that is driven in part by ocular sympathetic input and stimulation of ß-adrenergic receptors.

Changes in expression of adenyl cyclase activity in human endometrium during hormone replacement therapy and ovarian stimulation.

We have investigated membrane fractions prepared from human endometrium for activity of the signalling adenyl cyclase (AC). We characterized the AC guanine nucleotide-binding proteins (G proteins) and examined the changes in AC activity during evaluation cycles of oestrogen and progesterone replacement therapy as well during ovarian stimulation cycles. AC activity was determined by the conversion of substrate ATP into cyclic AMP under basal conditions and in the presence of guanine nucleotide or forskolin. G proteins were determined by Western Blot using specific polyclonal antibodies against Gsalpha, Gi1,2alpha and Gi3alpha. Our results indicate that endometrial AC was highly responsive to activation by both guanine nucleotide and forskolin and its rate of cyclic AMP production was highly pronounced. Mean activity reached 920 pmol/l/min/mg membrane protein in the presence of forskolin, a value approximately 5-fold higher than those detected in corpus luteum. Hormonal induction of AC activities increased Gsalpha protein, which couples with and stimulates the catalytic component of AC. We conclude that human endometrium is rich in AC and that enzyme activity is induced by oestrogen and progesterone treatment. These data strongly support the concept that the transmembrane signalling AC system and its messenger cyclic AMP are major regulators of endometrial function in the human.

Effect of asphyxia on adenylate cyclase activity in cat brain cortex

Effect of 1–5-min asphyxia on adenylate cyclase activity in cat brain cortex is studied. Adenylate cyclase activity is measured in cortex specimens obtainedex vivo after 1, 2.5, and 5 min of asphyxia, and 30 and 60 min of reoxygenation by radioassay. Stimulating effects of norepinephrine and NaF on adenylate cyclase activity are assessed. Five-min asphyxia induces phasic changes in adenylate cyclase activity: on the 1st min basal activity of the enzyme increases by 97%, after 2.5 min it returns to the initial level, and increases again by 55% on the 5th min of asphyxia. On the 30th and 60th min of reoxygenation after 2.5- and 5-min asphyxia, basal adenylate cyclase activity does not differ from the initial activity. The stimulating effect of norepinephrine and NaF on enzyme activity is weakened after 5 min of asphyxia and 30 min of reoxygenation after 2.5- and 5-min asphyxia. Even short-term asphyxia affects adenylate cyclase activity and modifies the mechanisms of adrenergic signal transduction in the brain cortex in response to oxygen deficiency and probably to hypercapnia as well as during the early reoxygenation period.

Temporal effects of cytokines on neonatal cardiac myocyte Ca2+ transients and adenylate cyclase activity.

This study investigates the hypothesis that inflammatory cytokines, interleukin (IL)-1alpha IL-1beta, and tumor necrosis factor (TNF), influence cardiac function by affecting calcium homeostasis and that this effect is mediated by the beta-adrenergic-adenylate cyclase system. After 4 days in culture, neonatal rat ventricular myocytes were treated with cytokines (10 ng/ml) for short (2 h) or longer (18 h) times. Myocyte calcium, contractility, and adenylate cyclase were measured under each condition. Anticipated stepwise increases in adenylate cyclase and intracellular calcium were found in controls (non-cytokine-treated) with 10(-7) M isoproterenol, 10(-7) M isoproterenol + 0.1 mM guanosine triphosphate, and 10(-9) M forskolin. Cells in the presence of cytokine for 2 h show increased basal calcium levels but no changes in adenylate cyclase activities, and isoproterenol fails to elevate adenylate cyclase levels or affect contractile shortening. After long-term treatment with IL-1beta or TNF, but not IL-1alpha, the significantly elevated levels of basal systolic calcium remain, and isoproterenol increases adenylate cyclase activity, unlike after short exposure. Forskolin maximally activates adenylate cyclase following both short- and long-term incubation, but the stepwise increase in activity is blunted following prolonged exposure. Thus short-term cytokine treatment blocks the adrenergic receptor-mediated increases in adenosine 3',5'-cyclic monophosphate, dissociating adenylate cyclase activation from cytokine-mediated increases in cell calcium, whereas longer treatment apparently produces direct affects on adenylate cyclase. Time-dependent differences in contractile response were found with IL-1alpha at 2 h and TNF at 18 h, implying that myofibrillar responsiveness to increased cytoplasmic calcium is dependent on both cytokine species and exposure time.

Changes in adenylate cyclase activity during chondrogenesis in cultured limb mesenchyme

An in vitro assay to examine the effects of forskolin on adenylate cyclase (AC) activity and chondrogenesis in micromass cultures of mesenchymal cells derived from the distal tip of stage 25 chick limb buds is described. Forskolin activation of AC increased 6 fold in prechondrogenic cells cultured for 48 hours relative to uncultured cells at the time of cell dissociation (Day 0) and remained elevated and unchanged in differentiated cells during the remaining four days of culture. Equivalent increases occurred in cyclic AMP (cAMP) concentrations over the six day period examined. Forskolin also accelerated chondrogenesis in these cultures. Quantitative analysis of Alcian green binding to cartilage matrix showed approximately 2 fold increases in forskolin-treated cultures relative to controls on each of days 2–4 of culture. These results demonstrate that dramatic increases in the total pool of AC activity occur in prechondrogenic mesenchyme prior to overt chondrogenesis which, through increases in cAMP, may play an important role in cartilage differentiation.

Changes of Adenylate Cyclase Activity in AH-130 Ascites Hepatoma of Yoshida Induced by Enrichment with Fatty Acids

Enrichment of hepatoma cells with arachidonic acid increases fluidity of plasma membranes, unstimulated lipid peroxidation and basal adenylate cyclase activity, whereas enrichment with stearic acid decreases fluidity and does not cause any variation in lipid peroxidation or adenylate cyclase. The increase in adenylate cyclase activity may be due to the increase not only in fluidity, but also in lipid peroxidation products. Indeed, adenylate cyclase is stimulated by 4-hydroxynonenal, one important product of lipid peroxidation, when added to plasma membranes. 4-hydroxynonenal increases adenylate cyclase two-fold in unenriched plasma membranes and three-fold in plasma membranes enriched with arachidonic acid in comparison with basal activity.

Mu-Opioid receptor-mediated reduction of neuronal calcium current occurs via a G(o)-type GTP-binding protein

It has recently been shown that the activation of mu-opioid receptors inhibits several components of calcium channel current in rat DRG sensory neurons. mu-Opioid receptors, acting through the pertussis toxin (PTX)-sensitive substrate Gi, also reduce the activity of neuronal adenylate cyclase, but the relationship of this effect to changes in calcium channel activity has yet to be determined. Using whole-cell recordings from acutely isolated rat DRG neurons, we examined the ability of the mu-opioid-selective agonist Tyr-Pro-NMe-Phe-D-Pro-NH2 (PLO17) to reduce calcium current after treatment with PTX and in the presence of the nonhydrolyzable GTP analog guanosine 5'-[-thio]triphosphate (GTP gamma S), to assess the role of G-proteins in the coupling of mu-opioid receptors to calcium channels. Inhibition of current by PLO17 was mimicked or rendered irreversible by intracellular administration of GTP gamma S, an activator of G-proteins, and was blocked by pretreatment of neurons with PTX. In contrast, when the catalytic subunit of cAMP-dependent protein kinase was included in the recording pipette, calcium currents increased in magnitude throughout the recording without attenuation of responses to PLO17. Thus, the mu-opioid-induced inhibition of calcium current occurs through activation of a Gi- or G(o)-type G-protein, but independent of changes in adenylate cyclase activity. As a first step in identifying this G-protein, we compared the ability of several antisera directed against specific regions of Gi and G(o)alpha subunits to block the inhibition in current by PLO17. Intracellular dialysis with an antiserum specific for G(o) (GC/2) attenuated calcium current inhibition by PLO17 in five of six neurons by an average of 75%. In contrast, there was no attenuation in the response to PLO17 when neurons were dialyzed with an anti-Gi1 alpha/Gi2 alpha antiserum (AS/7) or antibodies specific for alpha subunits of Gi proteins (Gi1/Gi2 or Gi3) in an identical manner. These results suggest that in rat DRG neurons mu-opioid receptors couple to calcium channels via the PTX-sensitive G(o) subclass of GTP-binding proteins.

Effect of reversal of diet-induced changes in acyl group composition of cardiac membrane lipids on adenylate cyclase activity in rats

The purpose of the present investigation was to determine if the diet-induced changes in cardiac adenylate cyclase activity and membrane lipids can be reversed. Three groups of male weanling Sprague-Dawley rats were fed purified diets containing different fats: 9% butter (Btr) + 1% corn oil (CO) (group 1), 10% CO (group II), and 9% ethyl ester concentrate of n-3 fatty acids (EEC) + 1% CO (group III). After 5 weeks of feeding, rats from each group were killed. Cardiac membranes were prepared and assayed for adenylate cyclase activity. The fatty acid composition of membrane total phospholipids was also determined. The remaining rats in group I were divided into four subgroups and fed the following diets for the reversal study: 9% Btr + 1% CO (group Ia), 9% EEC + 1% CO (group 1b), 10% CO (group Ic), and 7% Btr + 2% EEC + 1% CO (group Id). Rats in groups II and III were maintained on their original diets. Rats were killed 5 weeks after changing the dietary regimes, and membranes were prepared from heart and analyzed for their fatty acid composition of total phospholipids. Adenylate cyclase activity (basal, fluoride- and forskolin-stimulated) was also measured. The enzyme activity was lower in membranes of rats in group Ia than those in groups II or III. Whereas the diet-induced changes in fatty acid composition were essentially reversed by dietary modification (groups Ib and Ic), the changes in adenylate cyclase activity were only partially reversed.

Effects of prostaglandins E 1, E 2 and F 2α on changes in adenylate cyclase activity in rabbit urinary bladder

Effects of prostaglandins E 1, E 2 and F 2α on changes in adenylate cyclase activity in rabbit urinary bladder

Modulation of neuropeptide Y expression in rat brain neuronal cultures

Neuropeptide Y (NPY) and its encoding mRNA were measured in neurons co-cultured from rat basal forebrain and cerebral cortex. NPY was synthesized and released in a manner consistent with secretion-synthesis coupling; depolarization increased each in a calcium-dependent manner. The accumulation of NPY encoding mRNA was elevated by a muscarinic receptor blocker, without changes in transmitter release or peptide synthesis, thereby consistent with a membrane potential-independent mechanism. Changes in intrinsic muscarinic transmission could nonetheless be expressed rapidly as an elevation in NPY levels by depolarizing the neurons subsequent to muscarinic receptor blockade. This depolarization-induced elevation of NPY subsequent to muscarinic receptor blockade was dependent on the presence of extracellular calcium ions. Forskolin and pertussis toxin also increased NPY encoding mRNA levels in a manner that was not additive with muscarinic receptor blockade. These results suggest that one or more muscarinic receptors may tonically modulate NPY synthesis via changes in adenylate cyclase activity, providing a model for the non-homeostatic modulation of neuropeptide turnover.

Reversal of diet-induced changes in adenylate cyclase activity and fatty acid composition of rat submandibular salivary gland lipids

This study sought to determine if the diet-induced changes in submandibular salivary glands can be reversed. Two groups of male weanling Sprague-Dawley rats were fed purified diets containing 9% butter + 1% corn oil (group I, control) or 9% ethyl ester concentrate of n-3 fatty acids + 1% corn oil (group II, experimental). After 5 weeks of feeding the respective diets, rats in group I were divided into two subgroups: Ia, which was maintained on the control diet, and Ib, which was shifted to the experimental diet for the reversal study. The rats in the experimental group were kept on their original diet. After five further weeks of feeding, the rats were killed, and membranes from submandibular glands were prepared and assayed for adenylate cyclase activity and for the fatty acid composition of total phospholipids. Changes characteristic of feeding n-3 fatty acids, including a significant increase in membrane fluidity as measured by the degree of unsaturation of fatty acids, were observed in the total phospholipids of membranes from the experimental group. The adenylate cyclase activity was two- to three-fold higher in membranes of rats fed the experimental diet (group II) than the control diet (group Ia). Whereas the diet-induced changes in fatty acid composition and membrane fluidity were largely reversed (group Ib, reversal study), changes in adenylate cyclase activity were only partially reversed. The results suggest that, in addition to the fatty acid composition and membrane fluidity, other factors may also be important in modifying adenylate cyclase activity.

Effects of prostaglandin E1, E2 and F2 alpha on the changes in the adenylate cyclase activities of rabbit urinary tract tissues

Effects of prostaglandin E1, E2 and F2 alpha (PGE1, PGE2 and PGF2 alpha) on the changes in the adenylate cyclase (AC) activities of rabbit urinary tract tissues were studied in order to clarify whether the PGs' actions are mediated by cAMP in the urinary tract. AC activities were measured by the method of Salomon et al. The three PGs studied were all found to increase the AC activities dose-dependently in the renal pelvis, ureter, bladder dome and bladder base. Among the changes in AC activities, PGE1 and PGE2 significantly increased the AC activities of the renal pelvis and ureter. PGE1 significantly increased the AC activities of the bladder dome. It was reported that Ca2+ influx plays an important role in the PGs' action on the urinary tract. Our data suggest that the PGs act on the urinary tract via cAMP as well as Ca2+ influx.

Effects of beta-agonists on the changes in adenylate cyclase activity and cAMP content of rabbit renal pelvis

Effects of beta-agonists on the changes in adenylate cyclase activity and cAMP content of rabbit renal pelvis