Impact of anabolic androgenic steroids on sexual function

Background

To describe the impact of supra-physiologic anabolic-androgenic steroid (AAS) use, including agent, dosage, and duration of therapy, on sexual function.

Methods

We reviewed data from an online survey of AAS users to evaluate their sexual function on and off AAS. The online survey consisted of questions addressing demographics, anabolic steroid use and patterns, ancillary medications, testosterone (T)-related symptoms while on and off of therapy, as well as sexual function which was assessed using the 5-item, International Index of Erectile Function (IIEF-5).

Results

A total of 321 men responded to the survey, of which 90 failed to meet inclusion criteria, for a final cohort of 231 AAS users. The majority of men were Caucasian (85%), employed (62%), and younger than 35 years (58%), while an equal mix were single (47%) or married (46%). The mean IIEF-5 was 22.5, with higher scores associated with increased T dosages (>600 mg/week), use of 17-alpha alkylated hormones and anti-estrogens, and absence of concurrent medical conditions. Lower mean IIEF scores were associated with current and pre-AAS low T symptoms, self-reported angry or violent tendencies, self-reported erectile dysfunction (ED), decreased libido, decreased energy, and depression. After controlling for age, low T symptoms and decreased energy remained significantly associated with lower IIEF scores. Among 127 men reporting de novo decreased libido when not taking AAS, several factors were significantly associated including frequency and duration of T and use of adjunctive therapies, while post-cycle therapies were protective. Men who reported any other de novo symptom (decreased energy, libido, muscle mass or depression) after discontinuing T were also more likely to report de novo ED, as well as those using >10 years or for >40 weeks per year.

Conclusions

The long-term impact of high dose AAS use on sexual function remains poorly defined. Although high T dosages appeared to be protective of erectile function during use, de novo symptoms such as decreased libido and ED occurred more frequently after discontinuing T, particularly among those using more frequently and for longer durations. Given the importance of these findings, long-term studies evaluating the impacts of discontinuing T on sexual dysfunction are indicated.

Assessment of blood measures of n-3 polyunsaturated fatty acids with acute fish oil supplementation and washout in men and women

Changes in n-3 highly unsaturated fatty acids (HUFA, > or =20 carbons and > or =3 carbon-carbon double bonds) at baseline, during fish oil supplementation (4 weeks) and during washout (8 weeks) were compared in venous plasma, erythrocytes, whole blood and fingertip prick blood (weeks 0, 4, 8 and 12) with additional weekly fingertip prick samples. Correlations between the various blood fractions were slightly stronger when n-3 HUFA status was expressed as the percentage of n-3 HUFA in total HUFA as compared with the sum of EPA and DHA. Increases and decreases in n-3 HUFA were more dramatic in plasma, and EPA responded rapidly (within 1 week) with fish oil supplementation and cessation. Sex differences in the proportions of n-3 HUFA in blood were also apparent at baseline with females (n=7) having a tendency for higher docosahexaenoic acid (DHA, 22:6n-3) relative to eicosapentaenoic acid (EPA, 20:5n-3) and n-3 docosapentaenoic acid (DPAn-3, 22:5n-3) as compared with males (n=9). Further n-3 biomarker research in larger populations is required.

Apparently anomalous sedimentation behavior in mixed solvent systems with strong interactions between solution components: analysis of nonideal behavior by bovine serum albumin in 7 M urea at pH 3.3

The use of the analytical ultracentrifuge to study nonideal behavior of macromolecules in multicomponent systems is discussed, noting the value of interference optics to extend the range of concentrations of macromolecule that may be studied. The choice of appropriate theory in the treatment of experimental data is examined, using a study of bovine serum albumin (BSA) in 7 M urea at pH 3.3 as an example. Under these conditions BSA undergoes extensive unfolding and exhibits marked nonideality, with the binding of approximately 200 molecules of urea per molecule of BSA.

Gene dose effect reveals no Gs-coupled A2A adenosine receptor reserve in murine T-lymphocytes: studies of cells from A2A-receptor-gene-deficient mice

Agonist binding to extracellular A2A adenosine receptors (A2ARs) inhibits the activation of virtually all tested functions of T-cells and can induce apoptosis in thymocytes. The evaluation of levels of expression of these immunosuppressive receptors is expected to clarify whether the absence of spare A2ARs (no 'receptor reserve') might be one of the mechanisms of attenuation of the effects of extracellular adenosine on T-cells. A2A transcript is found in T-cells and functional receptors can be demonstrated, but the density of receptor on T-cells is too low to be detected by radioligand binding. Studies of direct radioligand binding to murine brain with the selective A2AR agonist [3H]CGS21680 (2-(4-[(2-carboxyethyl)-phenyl]ethylamino)-5'-N-ethylcarboxamidoadenosine) established that striata levels of A2AR are virtually absent from A2A knock-out mice. Mice that are heterozygous (A2AR+/-) for the A2AR express significantly decreased levels of A2AR. To test for the presence of spare receptors in T-cells we took advantage of this gene dose effect and examined whether the decrease in the number of receptors in thymocytes from A2AR+/- mice was proportionately reflected in a decrease in the functional cAMP response of T-cells to adenosine. cAMP accumulation and apoptosis induced by adenosine and by A2AR agonist are of a lower magnitude in T-cells from A2AR+/- heterozygous mice than in T-cells from A2AR+/+ littermate control mice. These results indicate that there is no A2AR reserve in murine T-cells. Strongly decreased adenosine-triggered cAMP increases were detected in thymocytes from A2AR-/- mice, suggesting that A2B adenosine receptors cannot fully compensate for the loss of A2ARs in murine T-cells. We conclude that the number of A2ARs is the limiting factor in determining the maximal cAMP response of T-lymphocytes to extracellular adenosine, thereby minimizing the immunosuppressive effects of extracellular adenosine.

Metabolism-dependent stimulation of reactive oxygen species and DNA synthesis by cyclosporin A in rat smooth muscle cells

The clinical use of the immunosuppressive drug cyclosporin A (CsA) is limited by its side effects, namely hypertension and nephrotoxicity. It has been proposed that reactive oxygen species (ROS) could be involved as mediators of the toxic effects of CsA. Here, we have studied the possible interrelationship between CsA metabolism and production of ROS. Using cultures of rat aortic smooth muscle cells (RASMC), CsA (1 microM) produced a rapid (within 10 min) increase in reactive oxygen species, detected by oxidation of the fluorescent probes 2,7-dichlorofluorescin and dihydrorhodamine-123. DNA synthesis was increased in the presence of CsA as assessed by [3H]thymidine incorporation. The superoxide dismutase inhibitor diethyldithiocarbamate (1 mM) and the iron chelator desferal (5 microM), as well as ketoconazole (1 microM) and troleandomycin (10 microM), inhibitors of the cytochrome P-450 3A, were able to block both effects. High-performance liquid chromatography analysis revealed that RASMC were capable to metabolize CsA to its primary metabolites (AM1, AM9 and AM4N), and that their formation was inhibited by ketoconazole and troleandomycin. Furthermore, mRNAs encoding cytochrome P-450 3A1 and 3A2 were detected in RASMC by reverse transcriptase-polymerase chain reaction. Our data suggest that CsA is metabolized by cytochrome P-450 3A in RASMC producing reactive oxygen species, most likely superoxide and the hydroxyl radical, known to damage lipids and DNA.

Synthesis of acetyl,docosahexaenoyl-glycerophosphocholine and its characterization using nuclear magnetic resonance

Docosahexaenoic acid (DHA) circulates in mammals in lipoproteins and bound to serum albumin as a nonesterified fatty acid as well as esterified in lysophosphatidylcholine (lysoPC). 1-Lyso,2-DHA-glycerophosphocholine (GPC) is an unstable isomer because of a primary alcohol at the sn-1 position. To keep DHA at the sn-2 position of lysoPC, its usual position for the corresponding lysoPC to be acylated into PC in tissues, we synthesized 1-acetyl,2-DHA-GPC and confirmed its structure by use of nuclear magnetic resonance (NMR) spectroscopy in comparison with its positional isomer, 1-DHA,2-acetyl-GPC. 1-Lyso,2-DHA-GPC was prepared from 1-stearoyl,2-DHA-GPC by enzymatic hydrolysis and purified by high-performance liquid chromatography. The isomerization of 1-lyso,2-DHA-GPC into 1-DHA,2-lyso-GPC was obtained by keeping the former overnight at room temperature under nitrogen. Both lysoPC isomers were acetylated by acetic anhydride into 1-acetyl,2-DHA-GPC and 1-DHA,2-acetyl-GPC, respectively, and the resulting phospholipids were fully characterized by NMR. In particular, the 1,2 substitution pattern of the acetyl and DHA chains could be easily detected by 2D heteronuclear multibond correlation. We conclude that 1-acetyl,2-DHA-GPC might be considered as a stable form of 1-lyso,2-DHA-GPC for its delivery to tissues, if the latter exhibits acetyl hydrolase activity.

Thermodynamic analysis of the stabilisation of pig heart mitochondrial malate dehydrogenase and maize leaf phosphoenolpyruvate carboxylase by different salts, amino acids and polyols

As part of our investigations into the inactivation of pig heart mitochondrial malate dehydrogenase (phm-MDH) and maize leaf phosphoenolpyruvate carboxylase (ml-PEPC) in the presence of various cosolvents, the denaturation kinetics as a function of temperature have been determined based on Arrhenius plots derived from transition state theory analysis over the temperature range from 3.5 degrees C to 65 degrees C. The experimental data for phm-MDH were obtained in the presence of 1 M concentrations of various salts of monovalent and polyvalent anions, 1 M amino acids or 1 M sucrose and 6.1 M glycerol. Similarly, Arrhenius plot data were obtained for ml-PEPC in the presence of 2.5 M NaOAc and 0.8 M sodium glutamate. Distinct regimes of inactivation corresponding to high and low values of inactivation enthalpy were identified for the phm-MDH in the presence of all cosolvents and for the ml-PEPC in the presence of 2.5 M NaOAc, but not in the presence of 0.8 M sodium glutamate. A significant temperature-dependent effect dominated the inactivation of phm-MDH and ml-PEPC at elevated temperatures (e.g., > or = 45 degrees C), whilst the inactivation of these enzymes over a lower temperature range (< or = 25 degrees C) was dominated by temperature-independent phenomenon. The corresponding thermodynamic activation parameters (deltaG++, deltaH++ and deltaS++) associated with the transition state complexes involved in the inactivation of phm-MDH and ml-PEPC in the presence of the various cosolvents have been determined. The results indicate that the transition states associated with the inactivation of these two enzymes at elevated temperatures are characterised by large, positive enthalpic and entropic changes. In contrast, the inactivation process observed for phm-MDH at low temperatures in the presence of various cosolvents was marked by a large, negative entropic contribution and a small, positive enthalpic contribution. The results obtained in this study indicate that more than one mechanism of inactivation can occur with these two multimeric enzymes depending on the selected temperature range and the type of cosolvent. The relationship of these results to stabilisation models for phm-MDH and ml-PEPC in the presence of various cosolvents, as well as the application of Arrhenius plot data to extrapolate the long term solution stability of these enzymes at lower temperatures from the pseudo-first order rate constants of inactivation experimentally derived over a range of temperatures, are discussed.

Emotional control in adulthood

Although it is widely believed that emotions vary with age, there is a dearth of information on emotional experiences in later adulthood. Several researchers think that older adults experience less emotional intensity than younger people while others have suggested that aging is accompanied by a decrease in positive affect and an increase in negative emotions. Sex similarities and differences in emotionality have also been documented. This study focuses on age and sex similarities and differences in emotional control. Three hundred and twenty seven men and women aged 19 to 92 years were administered two emotion measures. The results support previous research which suggests that the control of emotions increases with age. In evaluating sex differences in emotional control, women scored as more emotionally expressive than men, a finding which is consistent with previous research. Results are discussed in relation to socioemotional selectivity theory.

Effects of K+ channel inhibitors and antagonists on NS-004 evoked relaxations in guinea-pig isolated trachea

The smooth muscle relaxant responses to NS-004, an activator of charybdotoxin-sensitive, large conductance Ca(2+)-dependent K+ channels (BKCa) were studied on the basal spontaneous tone in guinea-pig trachea in vitro. The sensitivity of these responses to a range of K+ channel inhibitors and antagonists were also evaluated. NS-004 (0.1-30 microM) evoked concentration-related relaxations (pIC50 5.48 +/- 0.13) on the spontaneous tone in guinea-pig tracheal rings, suspended in Krebs bicarbonate solution, with a maximum response not different to that to aminophylline (1 microM). Charybdotoxin (0.03 and 0.1 microM) or iberiotoxin (0.1 microM) significantly displaced the NS-004 concentration-response curve to the right of control with no change in maximum response. In contrast, glibenclamide (1.0 microM) apamin (0.1 microM) and dofetilide (1.0 microM) each failed to modify the responses to NS-004 on spontaneous tone in guinea-pig trachea. These results suggest that relaxations in guinea-pig tracheal smooth muscle to the substituted benzimidazolone, NS-004, involve the activation of BKCa channels.

The roles of Fas and perforin in LAK T-cell/bispecific antibody-mediated killing of the murine B-lymphoma cells, BCL1

The aim of this study was to construct bispecific F(ab')2 [anti-CD3 x anti-BCL1 idiotype (Id)] Abs (BsAbs) which would enable lymphokine-activated killer (LAK) T cells to kill Id+ mouse BCL1 lymphoma cells, and to determine the mechanism(s) underlying cell death. Using 4-day activated LAK T cells from either perforin-knockout mice or FasL-deficient gld mice, we show that the Fas pathway, but not perforin, is required for BsAb-mediated LAK T-cell-induced killing of BCL1 cells.

Stability studies on pig heart mitochondrial malate dehydrogenase: the effect of salts and amino acids

The effect of different salts and amino acids on the thermal stability and quaternary conformation of pig heart mitochondrial malate dehydrogenase (phm-MDH) in solution has been determined. The effectiveness of salts of anions in the stabilisation of phm-MDH followed the order: Citrate > SO(4)2- > or = Tartrate > Phosphate > F-, CH3COO- > Cl- > Br-. Anions above and including Cl- in this series were increasingly effective in stabilising phm-MDH with a rise in salt concentration from 0.05-2 M, whilst Br- was destabilising under similar conditions. The effect of potassium salts of acetate, chloride and bromide at a concentration of 1 M on the quaternary conformation of phm-MDH correlated also with the relative order of anion stabilisation above, with the anions higher in the series increasingly promoting the formation of the dimeric conformation of the enzyme. The cations of the corresponding salts had a relatively neutral (Cs+, K+, Na+, (CH3)4N+, NH4+) to a destabilising ((CH3)4N+, NH4+, Li+) effect on phm-MDH. Potassium ferrocyanide and potassium ferricyanide conferred complex, concentration dependent effects on the stability of phm-MDH, unlike the salts described above. Salts of amino acids were effective in the stabilisation of phm-MDH against temperature induced changes, following the order: NaGlutamatec = NaAspartate > NaGlycinate > lysine. HCl > arginine. HCl. The magnitudes and trends of the effects of these salts and amino acids on the stability and quaternary structure of phm-MDH were observed to correlate well with considerations based on the Hofmeister series of anions and solvophobic concepts as they apply to the influence of co-solvents at intermediate to higher concentrations. Other, more specific effects were also evident in the stabilisation and destabilisation of phm-MDH by low concentrations of the salts, as noted most particularly in the presence of potassium ferrocyanide and potassium ferricyanide.

Neuroprotective efficacy of lifarizine (RS-87476) in a simplified rat survival model of 2 vessel occlusion

1. A new, modified rat two vessel occlusion model (with hypotension) was established and the neuroprotective efficacy of the novel agent lifarizine (RS-87476) was examined. 2. The two vessel occlusion model used in the study was a modification of the model described in the literature, whereby we have obviated the need to use a muscle relaxant and intubate the trachea to provide ventilatory support by providing a tight fitting face mask attached to the ventilator. Furthermore, the need to combine exsanguination and additional pharmacological means of inducing the mandatory hypotension (50 mmHg), required to decrease brain blood perfusion pressure, has been removed by simply manipulating the concentration of the already present halothane anaesthetic. 3. The appropriate level of hypotension having been reached, microvascular clips were applied to bilaterally occlude the common carotid arteries for 12 min. This resulted in a loss of the cortical EEG activity. Local cerebral blood flow was measured 6 min into the occlusion period, using the fully quantitative [14C]-iodoantipyrine autoradiographic technique, in a separate group of rats (n = 5). This illustrated the lack of any blood flow, in the areas under study, during the period when there was an isoelectric cortical EEG pattern. 4. The high grade global ischaemic lesion which occurred gave quantifiable neuronal damage in several vulnerable regions of the brain, namely, the hippocampal CA1 sub-field, cortex, thalamus, striatum, and cerebellar brain stem (Purkinje cells). 5. Following the global ischaemic insult the rats were allowed to recover for 72 h before assessment of the damage, during which time one group of rats (n = 11) received 100 micrograms kg-1 lifarizine i.a. 5 min post-occlusion, 500 micrograms kg-1 lifarizine i.p. 15 min post-occlusion, and 500 micrograms kg-1 lifarizine i.p. twice daily for 72 h. A second group of rats (n = 12) was treated with appropriate volumes of vehicle (0.4 ml kg-1 i.a. and 2 ml kg-1 i.p.) at identical time points. 6. Histopathological damage was assessed, from cresyl violet and haematoxyline/eosin stained sections, using a scoring system of 0-6 (no damage-complete neuronal death). The dosing regimen of lifarizine gave reduced damage in the hippocampal CA1 sub-field (4.1 +/- 0.3 to 2.8 +/- 0.6) and striatum (1.7 +/- 0.3 to 1.2 +/- 0.3) and significant neuroprotection in the anterior cortex (2.0 +/- 0.2 to 1.2 +/- 0.2; p < 0.05), thalamus (1.5 +/- 0.2 to 0.8 +/- 0.2; p < 0.01), posterior cortex (1.5 +/- 0.2 to 1.0 +/- 0.2; p < 0.05) and cerebellar brain stem (0.9 +/- 0.2 to 0.4 +/- 0.1; p < 0.01). The overall mean brain score was significantly reduced (from 1.5 +/- 0.1 to 0.9 +/- 0.2). 7. These data show that the newly modified 2 vessel occlusion model produced a quantifiable level of ischaemic damage and that the novel agent lifarizine is neuroprotective in the model.

Reduction by lifarizine of the neuronal damage induced by cerebral ischaemia in rodents

1. The objective of this study was to evaluate the broad neurocytoprotective potential of the novel sodium-calcium ion channel modulator, lifarizine (RS-87476), in two rodent 72 h survival models of forebrain ischaemia. 2. Under fluothane anaesthesia, rats were subjected to 10 min four vessel occlusion and gerbils to either (i) 5 or (ii) 10 min bilateral carotid artery occlusion. 3. Rats were dosed parenterally solely post-ischaemia (reperfusion) in a series of five studies covering a range of intra-arterial/intraperitoneal (i.a./i.p.) combination doses from 2/10, 5/20, 20/100, 50/200 and 100/500 micrograms kg-1, where the initial loading dose was injected i.a. at 5 min. An i.p. dose was given at 15 min and repeated twice daily. In a sixth study, treatment at 50/200 micrograms kg-1 was deferred for 1 h. 4. Gerbils were treated (i) 15 min pre-ischaemia with either (a) 250, (b) 500 micrograms kg-1 i.p., or (c) 5 mg kg-1 by gavage (p.o.) for 3 days then at 1 h pre-ischaemia. Animals treated as (ii) received 500 micrograms kg-1 i.p. 15 min pre-ischaemia. The above doses were repeated twice daily for 3 days post-ischaemia for the respective groups. 5. In rats, the protective effect of lifarizine was regionally and cumulatively assessed in six brain regions (anterior and posterior neocortex, hippocampal CA1 subfield, thalamus, striatum, cerebellar Purkinje cells-brain stem) at each dose level. Cumulative (total) means +/-s.e.mean neurohistopathological scores(0-4) of 1.16+/-0.09 (n=5), 1.02+/-0.10 (n=5), 0.93+/-0.06 (n=6), 0.79+/-0.09 (n=9) and 0.45+/-0.16(n = 7), respectively, were obtained for the above treatment groups compared to the control (2.01 +/- 0.17,n = 16) group (P<0.0035). The score for the 1 h deferred treatment group was also significant at 0.77 +/- 0.10, n =5 (P< 0.0035). The normal group without ischaemia showed a score of 0.52 +/- 0.09 (n = 6).6. In gerbils, (i) percentage delayed neuronal death (DND) of hippocampal pyramidal cells in the CA1subfield was prevented at 250 (a) and 500 microg kg-' i.p. (b) (27.2+/- 14.6, n=6 and 26.9+/- 10.4%, n= 10 respectively, P<0.02) compared to controls (78.3+/-8.5%, n= 12) and by 5 mg kg-1 p.o. (c) (2.9+/-0.8%,n =l1, P <0.002). Mean +/- s.e.mean total brain scores (0-4) for each of 4 different features denoting cerebral 'oedema' were lower for normal brains (1.60 +/-0.34, n =6) and reduced in animals dosed at 250(a) (3.00+/-0.79, n=6) and 500 microg kg-1 i.p. (b) (3.75 0.36, n= 10) compared to controls (6.58+/-1.00,n = 12) (P< 0.02 -0.03). There was a linear relationship (r = 0.97) between the 'oedema' scores and percentage CA1 DND. Percentage CA1 DND in response to 10 min ischaemia (ii) was reduced(53.0+/-21.0%, n=6, P<0.05) compared to controls (100.0+/-0.0%, n=7).7 The significant neuroprotection shown by lifarizine in rodents substantiates findings in other species.These observations, together with its effect on ion channels and efficacy at extremely low doses offers novelty and suggests a broad spectrum of activity in ischaemia.

Stability studies on maize leaf phosphoenolpyruvate carboxylase: the effect of salts

The solution stability of phosphoenolpyruvate carboxylase (PEPC) has been determined in the presence of various salts by temperature-accelerated enzyme inactivation and also by using high-performance size-exclusion chromatography. Kosmotropic (water structuring) anions in the Hofmeister series (HPO(4)2-, citrate3-, SO(4)2-, F-, OAc-) and glutamate stabilized the enzyme most effectively, while Cl- (a borderline Hofmeister anion) and Br- (a chaotropic anion) were destabilizing. The effects of the cations on PEPC stability ranged from relatively inert (Na+, K+) to destabilizing ((CH3)4N+, NH4+, Li+). The observed stabilization of PEPC by specific salts has been interpreted in terms of the positive surface tension increment and the water-structuring effects conferred on the solution by the specific stabilizing reagents. Both these effects enhance hydrophobic interactions of proteins and increase the energy required to enlarge the surface area of the solvent cavity in which the protein resides. The destabilization of PEPC by some salts at a concentration of 0.5 M was associated with the dissociation of the tetrameric enzyme into its dimeric and monomeric forms, a process most probably occurring as a result of ion-peptide dipole binding, which promotes protein-solvent interaction and a subsequent reduction in the free energy of cavity formation. The stabilization of enzyme activity by kosmotropic salts depended on the salt concentration with maximum stabilization of PEPC in solution at 52 degrees C observed with 0.6-0.8 M sodium glutamate, 2 M KF, and 2.2 M KOAc. Higher concentrations of these salts resulted in decreased activity. This reduction in activity of PEPC in the presence of high concentrations of kosmotropic salts appears to be associated with irreversible conformational changes of the tetrameric enzyme.

Effects of ATP-dependent K+ channel modulators on an ischemia-reperfusion rabbit isolated heart model with programmed electrical stimulation

The effects of glibenclamide and BRL-38227 were studied in isolated rabbit hearts subjected to ischemia and programmed electrical stimulation. Coronary artery occlusion over 24 min decreased the ventricular effective refractory period in the ischemic zone. BRL-38227 (0.1 microM) showed significant coronary vasodilator effects, but failed to modify the ventricular effective refractory period under these conditions. A higher concentration (5 microM) of BRL-38227 potentiated the ischemia induced ventricular effective refractory period shortening effects. Glibenclamide (0.1 and 1 microM) delayed the onset of the ischemia-induced ventricular effective refractory period shortening. Glibenclamide (1 microM) inhibited the potentiated ventricular effective refractory period shortening effects of BRL-38227 (5 microM) during ischemia, but failed to antagonise the coronary vasodilator effects of BRL-38227 (5 microM). A higher incidence of ventricular fibrillation was inducible when an extra beat was applied in the ischemic zone through programmed electrical stimulation. The incidence of programmed electrical stimulation induced ventricular fibrillation was increased by BRL-38227 (5 microM) and antagonised by glibenclamide (1 microM). The results suggest that high concentrations of KATP-activators can accentuate ischemia-induced decreases in refractory period and increase the susceptibility of hearts to ventricular fibrillation when an extra beat is applied to the ischemic myocardium. These effects did not occur at lower coronary vasodilating concentrations of BRL-38227.

An in vitro method for the evaluation of antiarrhythmic and antiischemic agents by using programmed electrical stimulation of rabbit heart

A new model using isolated rabbit hearts perfused at constant flow in the Langendorff mode with the sinus node destroyed and under constant (2 Hz) pacing is described. Ventricular ischemia (24 min) was induced by ligation of the left ventricular branch of the coronary artery (LVB), followed by reperfusion (15 min). The programmed electrical stimulation (PES) technique was used to induce arrhythmias in the ischemic zone (IZ). Three agents with different mechanisms of action were tested to validate this model: dl-sotalol (10(-6) and 10(-5) M), oxfenicine (10(-6) M), and lidocaine (10(-5) M). These compounds were administered 15 min before the ligature and maintained until the end of the experiment. Ventricular effective refractory period (VERP), PES-induced ventricular fibrillation (VF), and coronary perfusion pressure (CPP) were monitored. PES-induced VF was only observed in ischemic tissue. Sotalol slightly reduced VF incidence only during reperfusion. Oxfenicine prevented PES-induced VF during the ischemia, but not during reperfusion, while lidocaine prevented VF during ischemia and throughout the reperfusion period. In conclusion, the rabbit heart model where PES is applied to normal and ischemic myocardium, appears useful to discern different mechanisms involved in ventricular arrhythmias. In addition, this model is considerably cheaper than equivalent dog models.

Haemodynamic effects of the calcium facilitator Bay K-8644 in rats following vascular calcium overload

1. The haemodynamic effects of the Ca2+ facilitator Bay K-8644 (Bay) were studied in a model of calcinosis induced by acute treatment with vitamin D3 and nicotine administration over 4 days with 13 days of recovery. 2. Calcium content of the left ventricular myocardium increased 8-9 fold, while aortic Ca2+ levels increased up to 12-fold in treated animals. There were minimal changes in the ECG and no change in the level of plasma alpha-hydroxy-butyrate-dehydrogenase, a cardiac specific enzyme which increases during ischaemia. Significant increases in pulse pressure (PP) were seen in anaesthetized and conscious calcinotic rats, with no increase in cardiac output index (DABF) or systemic vascular resistance. However, aortic rigidity (AORI) was significantly elevated in the calcinotic group under anaesthesia. 3. In both control and calcinotic rats, pressor responses to i.v. Bay were exclusively mediated by an increase in aortic blood flow (DABF) as lower body vascular resistance (TLBVR) did not change. The increase in DABF at low doses (0.1-1 microgram kg-1) of Bay probably resulted from an increase in venous return induced by the agonist, as Bay had little effect on cardiac contractility over this dose range (as estimated by left ventricular dp/dtmax) and did not cause tachycardia. At higher doses (10-1000 micrograms kg-1), Bay significantly increased LV dp/dt. Bay caused dose-related increases in AORI in pithed calcinotic rats, but a decrease in AORI in control animals. 4. The calcinosis model, which incorporates a recovery period to obviate the acute effects of nicotine and/or vitamin D3 treatment, results in long-term tissue calcium accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of endothelin-1 on the vasorelaxant properties of benzopyran and non-benzopyran potassium channel openers

1. The effects of endothelin-1 (ET-1) on the vasorelaxant properties of structurally different potassium channel openers (PCOs), BRL-38227, Ro 31-6930, SDZ PCO 400, EMD-52692, RP-49356 and pinacidil, were studied. 2. All PCOs evoked concentration-related relaxations of ET-1 (10 nM) or KCl (20 mM) contracted rat isolated aortic rings denuded of endothelium. BRL-38227, EMD 52692, SDZ PCO 400 and Ro 31-6930 were 11-42 times less potent in relaxing contractions to ET-1 than KCl. In contrast, this differential potency was not observed with RP-49356 or pinacidil. 3. BRL-38227 (0.06-3.0 microM), RP-49356 (0.3-3.0 microM) and pinacidil (0.3-3.0 microM) displaced KCl concentration-response curves to the right of controls, without modifying the maximum response. A subcontractile concentration of ET-1 (0.1 nM) prevented the inhibitory effects of low concentrations of BRL-38227 (0.06-0.1 microM) on KCl responses, but failed to modify those to RP-49356, pinacidil or high concentrations of BRL-38227 (0.3-3.0 microM). The inhibitory effects of BRL-38227 (0.1 microM) were also not changed by ET-3 (1.0 nM) or angiotensin II (0.1 nM). 4. In anaesthetized spontaneously hypertensive rats (SHR), cumulative bolus intravenous administrations of BRL-38227 (1-1000 micrograms kg-1, i.v.), Ro 31-6930 (1-1000 micrograms kg-1, i.v.), RP-49356 (10-1000 micrograms kg-1, i.v.) or nitrendipine (0.1-30 micrograms kg-1, i.v.) produced dose-dependent falls in diastolic blood pressure (DBP).ET-1 (i.v.) evoked a transient fall in DBP (1 pg kg- = 58 + 1 mmHg) which returnedto pre-administration levels within 4 min.5. Pretreatment of anaesthetized SHR with ET-l (1 pg kg-', i.v.) significantly increased the ED,5 (dose to evoke a 15% fall in DBP) values for BRL-38227 and Ro 31-6930. However, ET-l failed to modify the ED,5 values for RP-49356 or nitrendipine. The ED50 values for all of the vasodilators studied were not modified by ET-1.6. Infusion of BRL-38227 (2 pgkg-'min-', i.v.) or RP-49356 (4 pgkg-'min', i.v.) to anaesthetized SHR evoked dose-related falls in DBP, with a corresponding increase in descending aortic blood flow (DABF) and a decrease in total lower body vascular resistance (TLBVR). Pretreatment with ET-1 (1 ptg kg-', i.v.) significantly attenuated the decreases in DBP and TLBVR observed with low doses of BRL-38227, but not RP-49356 or high doses of BRL-38227. In contrast, ET-3 (3 pig kg-, i.v.) failed to modify the effects of BRL-38227 on DBP or TLBVR.7. In conscious SHR, the fall in DBP to BRL-38227 (30 pgkg-', p.o.) was significantly reduced following ET-1 (1 pig kg-', i.a.) treatment. ET-1 (1 pg kg-', i.a.) pretreatment, however, failed to modify the decrease in DBP induced by an equieffective oral dose of RP-49356 (1001pgkg-1).8. In conclusion, ET-1 selectively attenuated the vasorelaxant effects of the potassium channel opener,BRL-38227 and other substituted benzopyrans. The results are compatible with the hypothesis that benzopyran PCOs and ET-1 have affinity for a site that does not recognise RP-49356 or pinacidil. Thus,ET-l can differentiate between structurally unrelated potassium channel openers. The cardiovascular effects of some, but not all, PCOs might be radically modified in the clinical setting by elevated endogenous levels of ET-1 associated with certain diseased states.

An industrial approach to drug discovery: a pharmacologist's eyeview

1. The pressures on the pharmaceutical industry to produce novel, safe and effective therapeutic agents have provoked management to rethink the way in which drug discovery is undertaken. 2. Advances in drug therapy are likely to come from the application of new technologies and leading-edge science, perhaps in collaboration with academia. 3. Close collaboration between biologists and medicinal chemists is a proven way to discover new products. 4. The complexity of the modern industrial discovery process, due to the interaction of many disciplines, requires matrix-style management. 5. The early demonstration of efficacy in human subjects is considered essential for providing feedback to the basic scientists about the validity of hypotheses, and the relevance of the methods utilized, as well as whether a decision should be allowed to advance to full development.

Inhibitory autoantibody to a conformational epitope of the pyruvate dehydrogenase complex, the major autoantigen in primary biliary cirrhosis

The mitochondrial autoantibodies present in primary biliary cirrhosis (PBC) react with the 2-oxoacid dehydrogenase enzymes that include the pyruvate dehydrogenase complex (PDC). All epitopes so far demonstrable, including the inner lipoyl domain of PDC-E2, have been revealed by immunoblotting. To identify other epitopes, advantage was taken of the capacity of PBC sera to inhibit in vitro the catalytic function of the PDC enzyme. PBC sera were analyzed by affinity chromatography, using columns containing either recombinant PDC-E2 or intact PDC. Fractions that bound to the column (B) and nonbinding effluent fractions (NB) were tested by immunoblotting and ELISA and for their capacity to inhibit enzyme function. After separation on the PDC-E2 column the B fractions were reactive with PDC-E2 and intact PDC, whereas the NB fractions did not react by immunoblotting or ELISA with PDC-E2 but did react strongly by ELISA with PDC and did strongly inhibit the enzyme function. After separation of sera on the PDC column, the B fractions reacted more strongly with PDC than PDC-E2 by ELISA and strongly inhibited the enzyme function, whereas the NB fractions were nonreactive. Thus we describe a hitherto undetected population of autoantibodies in PBC sera that react only with intact PDC but not with the recombinant PDC-E2 subunit that contains the lipoyl epitope, are demonstrable by ELISA but not by immunoblotting, and notably, inhibit enzyme function. These nonblotting inhibitory autoantibodies in PBC are presumed to react with an exclusively conformational determinant perhaps presented by the tertiary structure of the entire enzyme complex.

Pentafraction-Du Pont versus albumin for resuscitation of a lethal intestinal ischemic shock in rats

This study compares the effect of pentafraction-Du Pont 6% (PF), albumin 5% (ALB), and Ringer's lactate (RL) on plasma volume (PV) expansion and survival in a lethal intestinal ischemic shock model. Shock was induced by exteriorizing the small intestines and occluding the mesenteric vessels for 75 min. Changes in PV were estimated using hematocrit (Hct). The solutions were administered continuously for 6 hr in volumes to maintain a stable Hct, or 15 ml/100 g body weight (bwt) for PF and ALB and 44 ml/100 g bwt for RL. Hct and bwt were measured hourly during the infusion and at 24 h. Untreated animals in shock developed hemoconcentration (Hct 62%) corresponding to a PV of 41% of baseline preshock level, with 9% (3/35) of the animals surviving 72 hr. RL expanded PV to 87% of preshock level, with a 57% (20/35) 72 hr survival rate and 46% (16/35) surviving greater than 7 days. Only 34% as much ALB was needed to induce a greater PV expansion of 101% with a 72 hr survival rate of 51% (18/35) and 46% (16/35) surviving greater than 7 days. When PF was used, PV expanded to 109% of preshock level with survival rates improving to 80% (28/35) at 72 hr and 71% (25/35) greater than 7 days compared to RL and ALB (P less than 0.05). There were no significant differences in survival rates between RL and ALB treated animals. We conclude that PF improves survival following intestinal ischemic shock compared to ALB and RL. PF is a safe and effective alternative to albumin for resuscitation in this shock model.

Alpha-adrenoceptor subtypes in dog saphenous vein that mediate contraction and inositol phosphate production

1. Studies have been made of the contractile responses to the alpha-adrenoceptor agonists phenylephrine (Phen), cirazoline (Cir) or BHT-920 (BHT) in dog isolated saphenous vein (DSV) rings, using the antagonists yohimbine (Yoh), idazoxan (Idaz), prazosin (Praz), WB-4101 (WB) and nitrendipine or zero Ca2+ medium. 2. Contractile concentration-response curves to Phen or BHT were displaced to the right of controls by Yoh (0.01-3 microM) with mean apparent antagonist dissociation constants (pKBs) of 7.9 and 8.6 respectively. Yoh did not show simple competitive antagonism against either agonist, since the Schild plot slopes were significantly less than unity. Neither the antagonist affinity of Yoh against Phen, nor the slope of the Schild plot was modified in the presence of catecholamine uptake inhibitors, nor in the presence of alpha,beta-methylene ATP, which desensitizes P2-purinoceptors, suggesting that Phen does not release ATP, or noradrenaline to cause contraction in DSV. In the presence of Praz (0.3 microM) the antagonist potency of Yoh (mean pKB 7.4) against Phen was slightly decreased. Yoh had low potency against responses induced by Cir (pKB 6.3). 3. WB (0.001-1.0 microM) was a very potent antagonist of Phen-induced contractions, however, the biphasic Schild plot against Phen could be separated into two affinity sites, a high pKB of 9.3 (equivalent to that obtained using Cir as the agonist; pKB 9.6) and a lower affinity (pKB 8.6). WB showed an even lower antagonist affinity (pKB 7.4) against BHT-induced contractions, suggesting that these effects might be mediated by alpha 2A-adrenoceptors. Praz also appeared to identify two sites using Phen-induced contractions, a high pKB of 8.4 was equivalent to that obtained with Cir (pKB 8.2) and a lower affinity site (pKB 7.7; pA2 7.6; slope 1.1) at which Praz showed competitive antagonism. Higher concentrations of Praz were required to antagonize contractions to BHT (pKB 5.9). 4. Idaz was a weak partial agonist in this tissue with threshold contractile effects at concentrations in excess of 3 microM. Idaz (0.1-1 microM) competitively antagonized the contractile effects of BHT, but showed low antagonist affinity against Phen at these concentrations. 5. Contractions to Phen were slightly antagonized by nitrendipine (1 microM), with a 36% decrease in Emax. Contractions to Phen and Cir were also markedly attenuated in zero calcium medium (with EGTA), but maximum responses of 4.2 +/- 0.1 and 3.6 +/- 0.1 g, could be obtained with these agonists respectively. Only part of the contractile effects to Phen or Cir are therefore due to calcium influx (but L-type channels are not totally implicated), while the contractile effects of BHT were abolished in zero Ca2 + medium. Yoh (0.1 microm) retained its antagonist effects on Phen-induced responses in zero Ca2 + medium. 6. The formation of inositol phosphates (InsPs) in the presence of lithium (10mM) was measured after incubation of intact DSV strips with myo-2-[3H]-inositol. Phen (1-1OO0 microM) and Cir (O.O1-1O microm) induced concentration-dependent increases in total labelled InsP1_3, but BHT showed minimal InsP stimulation. InsPs were recovered after Phen (100,M) stimulation (10min) as labelled InsP1 (71%), InsP2 (25%) and InsP3 (4%). Phen (100 microM)-stimulated InsP1-3 formation was significantly antagonized by Praz (10nM), but was not fully inhibited even after Praz 1 microM. Yoh and Praz (0.1 and 1.0 microM) were equipotent inhibitors of this response, while Idaz (0.3 microM) showed no effects. 7. The receptors in DSV which are stimulated by Phen to cause contraction show characteristics of the alpha lA-adrenoceptor (high pM antagonist affinity for WB-4101 and extracellular calcium sensitivity) and the alpha lB-adrenoceptor (contraction in calcium-free medium, increase in InsP and low nm antagonist affinity of WB). The paradoxical results obtained with Yoh (potent antagonist effects on Phen-stimulated PI and pKB 7.9 on contraction) and Praz (low affinity competitive antagonist of Phen-induced contraction, pKB 7.7 and failure to inhibit completely the PI response at 1 microM), cannot fully exclude an alpha 2B-subtype characterization of these responses. These pharmacological differences suggest that the adrenoceptor involved in the contractile and in particular the second messenger effects of Phen in DSV is not typically an alpha lB-adrenoceptor.

Pulmonary and systemic haemodynamic effects of cromakalim in conditions of normoxia and hypoxia in dogs

1. In anaesthetized-closed chest dogs, exposure to hypoxia (60 min) caused a sustained increase in arterial pulmonary pressures (diastolic: DPP, mean: MPP and effective capillary: EPCP by 132, 66 and 104% respectively) and increased total pulmonary vascular resistance (TPVR, 143%) with minimal changes in systemic haemodynamics. 2. Under normoxia, cromakalim infusion (2 micrograms kg-1 min-1 for 30 min) progressively decreased diastolic systemic arterial pressure (DBP, 30%) and total systemic vascular resistance (TSVR, 54%). In contrast, DPP was increased by 45%, due to an increase in cardiac output (CO: 55%), while TPVR was essentially unchanged. 3. Under hypoxic conditions, cromakalim (2 micrograms kg-1 min-1 for 30 min) induced changes in systemic haemodynamics comparable to those seen under normoxia. However, DPP was decreased by 37% at the end of infusion. The compound progressively decreased TPVR in a dose-related manner and PaO2 (55.9 mmHg) was maintained since cardiac output was increased. 4. Thus, under normoxia, cromakalim induced haemodynamic effects on the pulmonary circulation which were directly related to an increase in CO, but were clearly different from those observed under hypoxia. In the hypoxia-induced constricted pulmonary vascular bed, cromakalim effectively reduced the elevated pulmonary vascular resistance at low doses but showed comparable vasodilator effects on the systemic circulation under both conditions. The findings suggest that a vasodilator agent like cromakalim may be useful in patients with respiratory conditions associated with elevated pulmonary vascular resistance.

Inhibition of enzyme function by human autoantibodies to an autoantigen pyruvate dehydrogenase E2: different epitope for spontaneous human and induced rabbit autoantibodies

Antibodies to the mitochondrial autoantigen M2, characteristic of the autoimmune liver disease primary biliary cirrhosis (PBC), react with the E2 subunit of the pyruvate dehydrogenase enzyme (PDH-E2). We examined the effect of disease sera on the enzyme activation catalysed by the PDH complex. Inhibition of enzyme activity was observed in 19 of 24 sera of patients with PBC with a level of greater than 90% inhibition in 14 at a serum dilution of 1/50. The onset of inhibition by serum was rapid, within the time of mixing, and the inhibitory activity was shown to reside in the immunoglobulin fraction of the serum. The immunoglobulin fraction of control sera from patients with other liver diseases (n = 26) and healthy persons (n = 8) failed to produce inhibitory activity. In addition sera from four rabbits, intensively immunized with a recombinant human M2 autoantigen, gave anti-M2 reactions by fluorescence, ELISA and immunoblotting, but did not inhibit the activity of PDH. The failure of experimentally induced M2 antibodies in rabbits to inhibit is interesting in view of the reactivity of the natural M2 autoantibodies of PBC with the highly conserved site on the enzyme which carries the essential lipoic acid cofactor.

Electrophysiologic, antiarrhythmic, and cardioprotective effects of N-[3,5 dichlorophenyl] 4-[4-hydroxy-2-methoxy-phenyl] piperazine carboxamidine dihydrochloride (RS-87337)

N-[3,5-Dichlorophenyl] 4-[4-hydroxy-2-methoxy-phenyl] piperazine carboxamidine dihydrochloride (RS-87337) is a chemically novel antiarrhythmic agent with an electrophysiologic profile characteristic of both class III and class Ia compounds as defined by Vaughan-Williams and Campbell. In isolated superfused guinea pig papillary muscles, RS-87337 (0.1-10 microM) prolonged the duration of the action potential (class III effect) and at higher concentrations (10-30 microM) reduced the maximum rate of membrane depolarisation (class I effect). The rate of onset and of recovery from the latter activity was similar to that of disopyramide, between that of lignocaine and flecainide, which allowed its placement in subclass Ia. When perfused into isolated working rat hearts, RS-87337 (10-1,000 nM) reduced the incidence of ventricular fibrillation that followed coronary artery reperfusion and in anaesthetised rats [RS-87337, 1-5 mg/kg intravenously (i.v.)] enabled more animals to survive the tachycardia, fibrillation, and mortality produced by a similar procedure. In conscious dogs, i.v. (3-10 mg/kg) and oral (15-60 mg/kg) doses of RS-87337 reduced the number of the ectopic electrocardiogram (ECG) complexes observed 24 h after a two-stage coronary ligation. In anaesthetised dogs with paced hearts, i.v. doses of RS-87337 (0.02-5.0 mg/kg) reduced the elevated ECG S-T segment evoked by brief coronary artery occlusion without altering baseline haemodynamic values. We assume that the class III and Ia effects of RS-87337 made an important contribution to the compound's antiarrhythmic and cardioprotective effects.

Pulmonary vascular and renal effects of cromakalim in anaesthetized dogs

1) CROM reduced hypoxia-induced pulmonary vasoconstriction and maintained PaO2 with an increase in cardiac output. 2) Low doses of CROM infused into the kidney caused pronounced renal vasodilation, marked natriuresis and a significant increase in cardiac output with minor changes in blood pressure. In addition to its previously described systemic antihypertensive effects, CROM also reduces hypoxia-induced pulmonary hypertension and shows marked renal vasodilation with natriuresis in anaesthetized dogs.

Studies on the mode of action for thyroid gland tumor promotion in rats by phenobarbital

A study was conducted to determine the mode of action for phenobarbital promotion of thyroid follicular cell neoplasia in rats using an initiation-promotion model established by Hiasa et al. (Y. Hiasa, Y. Kitahori, M. Ohshima, T. Fujita, T. Yuasa, N. Konishi, and A. Miyashiro, 1982a, Carcinogenesis 3, 1187-1190). Seven groups of Charles River Crl: CD(SD)BR rats (20/sex/group) were treated with either saline or 700 mg/kg DHPN [N-bis(2-hydroxypropyl)nitrosamine] administered subcutaneously once a week for 5 weeks (Initiation Phase) followed by 15 weeks of treatment with control diet or diets containing 500 ppm of phenobarbital (Promotion Phase). Groups of rats were also treated with L-thyroxine (50 micrograms/kg/day) in the diet to determine its effect on thyroid gland tumor promotion by phenobarbital. The incidence of thyroid follicular adenomas in DHPN male rats treated with phenobarbital was markedly increased [83% (15/18 rats)] as compared to rats receiving DHPN alone [37% (6/16 rats)]. Thyroxine treatment completely blocked the tumor promoting effect of phenobarbital in that the tumor incidence [25% (5/20 rats)] was reduced back to or somewhat less than that observed with DHPN alone. In female rats no tumors were observed with DHPN nor was a promoting effect of phenobarbital observed. These results demonstrate the potential for a microsomal enzyme inducer such as phenobarbital to alter the incidence of thyroid gland neoplasia in the male rat. The inhibitory effect of L-thyroxine on tumor promotion by phenobarbital supports the hypothesis that the promoting effect of phenobarbital is mediated via increased pituitary secretion of thyroid stimulating hormone as a compensatory response to the known effects of phenobarbital on peripheral thyroxine metabolism and excretion.

Greater vasodepressor sensitivity to nicardipine in spontaneously hypertensive rats (SHR) compared to normotensive rats

Differences in the degree of attenuation by the calcium entry blocker, nicardipine, of the pressor responses to alpha-1 (phenylephrine) and alpha-2 (UK 14.304) adrenoceptor agonists was investigated in pentobarbital-anesthetized, normotensive Sprague-Dawley (SD) or Wistar Kyoto (WKY) rats, and spontaneously hypertensive rats (SHR), treated with the ganglionic blocking agent, pentolinium. Following administration of the ganglionic blocking agent, pentolinium, nicardipine produced a significant fall in blood pressure in SHR but not in SD or WKY rats. Nicardipine had no effect on the basal blood pressure of pithed SHR. In rats treated with the ganglionic blocking agent, pentolinium, nicardipine produced parallel shifts to the right in the dose-response curves for phenylephrine but had no effect on maximal responses to phenylephrine. The decrease in the ED50 of phenylephrine was greater in the SHR than in normotensive rats. Nicardipine produced a decrease in both the ED50 and the maximal response to the alpha-2 adrenoceptor agonist, UK 14.304. The decrease in the maximal response was greater in SHR than in WKY normotensive rats but the change in ED50 for UK 14.304 was greater in WKY than in SHR. SD normotensive rats gave intermediate results. We conclude that the inhibition of alpha-adrenoceptor-mediated pressor responses by nicardipine is generally more pronounced in SHR than in normotensive rats. This suggests that hypertension may be accompanied by an increase in the sensitivity of peripheral resistance beds to calcium entry blockers.

Hexose phosphates as regulators of hepatic glycogen synthase phosphatases

The activity of glycogen synthase phosphatase from smooth endoplasmic reticulum of liver was stimulated markedly by galactose-6- and fructose-6-phosphates and to a lesser extent by glucose-1- and 2-deoxyglucose-6-phosphates. The synthase phosphatase of liver cytosol showed strong activation by glucose-1-, glucose-6- and fructose-6-phosphates and smaller activation by galactose-6- and 2-deoxyglucose-6-phosphates. Kinetic analysis showed that the activators did not affect the Km for glycogen synthase D, for either enzyme. The mechanism of activation of the two phosphatases by hexose phosphates appears to be by combination of the activator at a specific activator site on the enzyme rather than by substrate modulation. It is concluded that certain hexose phosphates, particularly fructose-6-phosphate and glucose-1-phosphate, can function as regulators of hepatic synthase phosphatase activity, and that this may explain the ability of elevated blood glucose to increase both glycogen synthase I activity and glycogen synthesis in the liver.

Activation of phosphoprotein phosphatases by growth hormone sequences with insulin-like activity

The N-terminal part sequences of pituitary growth hormone, N alpha-acetyl-hGH 7-13 and hGH 6-13, promoted conversion of glycogen synthase b to glycogen synthase a in skeletal muscle and adipose tissue when injected intravenously. The peptides also caused conversion of phosphorylase a to phosphorylase b in liver and adipose tissue, but not in muscle, where the peptides antagonised activation of phosphorylase. Synthase phosphatase activity in muscle and phosphorylase phosphatase activity in liver increased after injection of peptide, with time courses of change similar to those seen for muscle synthase and liver phosphorylase activities. Injection of peptide also decreased both the cyclic AMP dependent and independent synthase kinase activities in muscle. These results show that the insulin-like activities of these peptides on glycogen synthase and phosphorylase involve both increases in protein phosphatase activities and inhibition of protein kinase activities. These results are discussed in relation to the insulin-like activities of growth hormone.

Retardation of spermiation following short-term treatment of rats with theobromine

Groups of 4-6 Fü-albino rats were examined 24 h after 3 daily doses of 500 mg/kg bw of theobromine administered orally by gavage as well as 1, 2, 4, 6, and 10 weeks after 5 daily doses. Controls received the standard solvent vehicle (SSV) only. A variety of parameters were assessed including body and organ weights, serum clinical chemistry, hematological parameters, epididymal sperm motility and LDH-X fraction in seminal plasma, serum gonadotropins and testosterone, and the morphology of various organs. Testes were perfused with 5% glutaraldehyde and semi-thin sections were evaluated. The most striking morphological observation was a retarded release of late spermatids into the tubular lumen mainly 2 weeks post treatment. This partial disruption of the rigid spermatogenic synchronization was not followed by substantial germ cell death. The other parameters investigated remained relatively normal throughout the study. These observations suggest that theobromine at the dose tested rather selectively interferes with germ cell kinetics. Sertoli cell toxicity could account for these early and subtle effects as well as for the late and severe effects of subchronic exposure of rats to theobromine as reported in the literature.

Assay of insulin mediator activity with soluble pyruvate dehydrogenase phosphatase

The putative mediator of intracellular insulin action has been assayed quantitatively by its ability to increase the activity of solubilized pyruvate dehydrogenase (PDH) phosphatase. Conversion of soluble beef heart PDH b to PDH a by PDH phosphatase increased when incubation was carried out in the presence of a crude insulin mediator fraction generated from insulin-treated adipose tissue or liver plasma membranes. Increased PDH phosphatase activity was proportional to the concentration of added insulin mediator. Mediator generation was rapid, with a half-time of approximately 45 sec and was insulin dose dependent. Half-maximal mediator activity was produced at 0.3 nM added insulin, with maximal activity being generated at approximately 3 nM insulin. Mediator activity was significantly decreased at 7 nM insulin, but was increased 4-fold after ethanol extraction. Mediator behaved as an activator of PDH phosphatase, apparently by abolishing the inhibitory effects of ATP on phosphatase activity, but had no effect on PDH kinase activity. The assay of insulin mediator activity described here can be carried out under standardized conditions, in contrast to previously described methods using particulate mitochondrial preparations.

A simple, rapid method for the preparation of plasma membranes from liver

A method for the preparation of plasma membrane fractions from liver is described. A crude membrane fraction, substantially free of mitochondria and nuclei, is collected by centrifuging liver homogenate over a pad of 1.45 M sucrose. This interfacial fraction is further purified by isopycnic centrifugation in a self-generating density gradient of Percoll. All steps are carried out in buffered, isotonic solutions. Membrane prepared in this way is enriched in marker enzymes associated with plasma membrane, while marker enzymes for cellular components other than plasma membrane are diminished. Contamination by mitochondrial components is very much less than for membrane prepared from hypotonic liver homogenates. The membrane fraction also shows specific insulin binding, and negligible degradation of insulin. The procedure is rapid, uses simple equipment, and can be completed within 3 h.

A study on the ocular and extraocular pharmacology of metipranolol

Metipranolol (Betamann) is a clinically efficacious ocular hypotensive drug and preclinical experiments were undertaken to characterize this beta-adrenoceptor antagonist. In vitro beta1- and beta2-adrenoceptor antagonism was evaluated using the guinea pig atrium and the rat uterus, respectively. The respective pA2 values were 8.3 and 8.4. Topical metipranolol, 0.3% and 0.6%, blocked both the hypotension (beta2-mediated) and the tachycardia (beta1-mediated) elicited in ganglion-blocked, conscious rabbits by isoproterenol, 0.5 microgram/kg, i.v. The Ki for displacement of 3H-dihydroalprenolol binding to rabbit iris + ciliary body homogenates was 34 nM. The effect of metipranolol, 0.3% and 0.6%, was not particularly striking on the intraocular pressure (IOP) of conscious, normotensive rabbits. However, the elevated IOP of the alpha-chymotrypsinized rabbit eye was significantly decreased (maximum reduction of 5.8 mm Hg) following the instillation of metipranolol, 0.3%. IOP recovery in conscious rabbits following hyperosmotic challenge (i.v. infusion of a 20% NaCl solution) was not decreased by a 1-h pretreatment with a 0.3% solution. In contrast, a significant reduction of 41% was elicited by a 0.6% solution. Hence, the ocular hypotensive effect of metipranolol may result from decreased aqueous humor inflow. Metipranolol, 0.6%, was devoid of effect on rabbit pupil diameter. However, corneal local anesthesia was elicited in the rabbit by both 0.3% and 0.6% solutions of the drug, the effect being more marked with the higher concentration.

Regulation of glycogen synthase activity in muscle by a C-terminal part sequence of human growth hormone

The synthetic peptide hGH 177-191, corresponding to the last 15 residues at the carboxyl terminus of human pituitary growth hormone, promotes the conversion of glycogen synthase a to glycogen synthase b in muscle. When injected, the peptide was found to produce inactivation of glycogen synthase phosphatase activity in rat skeletal muscle. The time course of phosphatase inactivation was closely correlated with that for glycogen synthase. The peptide had no effect either on muscle 3',5'-cyclic AMP levels or on synthase kinase activity. These results can be explained in terms of a dynamic cycle of interconversion of synthase between active and inactive forms, by the simultaneous action of synthase kinases and synthase phosphatases. A decrease in the ratio of phosphatase to kinase activity would result in a decrease in the steady-state level of synthase a activity.

Parallel insulin-like actions of human growth hormone and its part sequence hGH 7-13

The insulin-like effects of human growth hormone and the synthetic part sequence, N alpha-acetyl-hGH 7-13, on glycogen synthase and phosphorylase have been compared in an in vivo system using 16--18-day-old rats. Both the hormone and its part sequences had similar effects, increasing muscle glycogen synthase a activity and decreasing liver phosphorylase a activity, without affecting phosphorylase activity in muscle or synthase activity in liver. Insulin had similar effects, but also increased liver synthase a activity. The effects of all three substances could be abolished by prior treatment of the animals with anti-insulin serum, showing that the effects of growth hormone and its part sequences were insulin-dependent. Both growth hormone and the synthetic peptide increased the binding of insulin to liver plasma membrane. It is concluded that the insulin-like activity of human growth hormone is associated with a region containing residues 7 to 13 of the hormone molecule, and that this activity is insulin-dependent. It is suggested that both growth hormone and the synthetic peptide produce insulin-like activity by enhancing the binding of circulating insulin to its receptor.

Urethane inhibits cardiovascular responses mediated by the stimulation of alpha-2 adrenoceptors in the rat

Clonidine and oxymetazoline (4.0 microgram/kg i.v. or i.a.) evoked a marked bradycardia in either methylatropine-pretreated conscious or pentobarbital-anesthetized (55 mg/kg i.p.), vagotomized rats. Urethane (1.2 g/kg i.p.) inhibited by more than 50% this effect which is mediated through the stimulation of peripheral and/or central neuronal alpha-2 adrenoceptors. However, in adrenalectomized rats only the inhibition of oxymetazoline by urethane was significantly less pronounced. In pithed rats in which the adrenal glands were either left untouched or surgically removed, urethane significantly attenuated the clonidine or oxymetazoline-induced decreases in experimental neural sympathetic tachycardia although it neither changed the base-line nor the experimentally elevated heart rate. Urethane, in contrast to pentobarbital, increased plasma epinephrine concentrations in intact but not in adrenalectomized or in pithed rats. Elevation of plasma epinephrine did not result from the low arterial pressure level associated with urethane anesthesia since the increase of this parameter with vasopressin did not abolish the effect of urethane. Furthermore, guanethidine-pretreated rats, when anesthetized with urethane, exhibited a higher heart rate and plasma adrenaline value than those anesthetized with pentobarbital. The elevated heart rate was decreased by either propranolol or adrenalectomy. The bradycardia produced by injecting clonidine into the lateral cerebral ventricles of either intact or adrenalectomized rats was markedly less in urethane- than in pentobarbital-anesthetized animals. Whereas in pentobarbital-anesthetized rats the peak heart rate effects of i.v. or i.c.v. clonidine were similar, in urethane-anesthetized animals the effects of clonidine were more inhibited when it was given centrally than when it was given peripherally. In pithed rats, the cumulative dose-pressor response curves elicited by the relatively selective alpha-2 adrenoceptor agonists, B-HT 930 and M-7, were depressed by urethane significantly more than those produced by the relatively selective alpha-1 adrenoceptor agonists, phenylephrine and cirazoline, or by angiotensin II. Urethane also decreased the pressor responses evoked by clonidine, oxymetazoline and norepinephrine which stimulate both alpha-1 and alpha-2 adrenoceptors. However, the extent of this inhibition was less than that of B-HT 920 and M-7 but greater than that of cirazoline and phenylephrine. These results show that urethane inhibits cardiovascular responses that are mediated by peripheral and central alpha-2 adrenoceptors. Furthermore, urethane increases the central drive to the adrenal medulla and this leads to the secretion of epinephrine. This may be partly responsible for the inhibitory activity of urethane on oxymetazoline-induced bradycardia. Although the basic mechanism by which urethane impairs responses mediated by alpha-2 adrenoceptors remains to be determined, it is advised that urethane anesthesia should be avoided, particularly for cardiovascular studies.

Effects of part sequences of human growth hormone on in vivo hepatic glycogen metabolism in the rat

Acute effects of two part sequences of human growth hormone on the in vivo activity levels of hepatic glycogen synthase and glycogen phosphorylase were examined. The peptide corresponding to residues 6 to 13 of the hormone (hGH 6--13) decreased the percentage of phosphorylase in the active form without affecting synthase activity. This action was indirect and dependent upon insulin. The peptide hGH 177--191 decreased the level of the active form of synthase without affecting phosphorylase activity. This effect was also observed with analogous peptides containing the sequence hGH 178--191 (i.e., hGH 172--191 and hGH 178--191), whereas the peptide hGH 179--191 was inert. The onset of these effects was rapid, and maximum changes in activity were produced in 5 min by both peptides. The effect for hGH 177--191 was short-lived, and synthase activity had returned to normal levels by 15 min, whereas the action of hGH 6--13 was of longer duration and was still quite marked at 60 min. Both peptides showed a linear dependence of response to the log dose of peptide injected over the range 0.1--250 microgram hGH 6--13 per kg body weight and 0.05--25 microgram hGH 177--191 per kg body weight. Hepatic 3',5'-cyclicadenylic acid levels were not affected by either peptide. Incorporation of glycerol carbon into liver glycogen was increased by hGH 6--13 and decreased by hGH carbon into liver glycogen was increased by hGH 6--13 and decreased by hGH 177--191. This is discussed in terms of a futile cycle between glycogen and hexose phosphate in the liver, as the basis for a control mechanism for hepatic glycogen metabolism. The present observations are consistent with other in vivo and in vitro actions of these and related peptides.

On the activities of glycogen phosphorylase and glycogen synthase in the liver of the rat

A procedure was developed for determination of glycogen synthase and phosphorylase activities in liver after various in vivo physiological treatments. Liver samples were obtained from anaesthetised rats by freeze-clamping in situ. Other procedures were shown to stimulate the activity of phosphorylase and depress the activity of glycogen in the liver. The direction of glycogen metabolism appears to be regulated by the relative proportions of the two enzymes, as shown by a strong positive correlation between total activities and active forms of phosphorylase and synthase. The enzyme activities responded as expected to stimuli such as insulin and glucose, which depressed phosphorylase and increased synthase activity, and glucagon, which increased phosphorylase and decreased synthase activity. In fasted animals approximately 50% of each enzyme was in the active form, which suggests the existence of a potential futile cycle for glycogen metabolism. The role for such a cycle in the regulation of glycogen synthesis and degradation is discussed.

Comparison of the vasodepressor effects of prostacyclin and 6-oxo-prostaglandin F1alpha with those of prostaglandin E2 in rats and rabbits

1 Vasodepressor effects of prostacyclin (5z-5,6-didehydro-9-deoxy-6,9alpha-epoxyprostaglandin F1) and its decomposition product 6-oxo-prostaglandin F1alpha (6-oxo-PGF1alpha) have been compared with those of prostaglandin E2 (PGE2) in anaesthetized rats and rabbits. 2 In rats intravenous prostacyclin produced hypotension and was 4--8 times more potent than PGE2 and about 128 times more potent than 6-oxo-PGF1alpha. 3 In rabbits also, intravenous prostacyclin (less than 2 microgram/kg) produced hypotension and was twice as active as PGE2 and approximately 250 times more active than 6-oxo-PGF1alpha. 4 In rats and rabbits vasodepressor responses induced by prostacyclin were similar in magnitude after either intravenous or intra-aortic administration. 5 Thus, in both species prostacyclin resembles PGE2 in producing vasodepression but does not lose activity on passage through the lungs. The results emphasize the need to consider prostacyclin in addition to PGE2 as a major determinant influencing blood pressure.

Contribution of prostaglandins to the renal vascular supersensitivity to vasoconstrictor agents exhibited by New Zealand genetic hypertensive rats

1. Studies were made of the effects on responses to vasoconstrictor agents of prostaglandins released from Krebs perfused isolated kidneys of genetic hypertensive and normotensive rats. 2. Prostaglandin E-like activity, detected by bioassay, was released from kidneys of both groups of rats during the vasoconstriction produced by noradrenaline, angiotensin or prostaglandin F2alpha. 3. In preparations obtained from hypertensive rats, responses to higher doses of noradrenaline or angiotensin were initially greater than those from normotensive rats and these were then reduced to a greater extent by infusion of indomethacin, which abolished release of prostaglandin E-like activity. Thereafter, in kidneys of either group, vasoconstriction to noradrenaline was potentiated by infusion of prostaglandin E2. 4. We conclude that, in rats, renal prostaglandins released in response to vasoconstrictor agents could augment the effect of such agents and in genetic hypertensive rats release of renal prostaglandins could contribute to the disease.

The reactions of D-glyceraldehyde 3-phosphate with thiols and the holoenzyme of D-glyceraldehyde 3-phosphate dehydrogenase and of inorganic phosphate with the acyl-holoenzyme

D-Glyceraldehyde 3-phosphate forms adducts with thiols. These adducts, which are presumed to be hemithioacetals, equilibrate rapidly with the unhydrated form of the aldehyde, which is the subtrate for D-glyceraldehyde 3-phosphate dehydrogenase. The adduct provides a substrate buffer system whereby a constant low free aldehyde concentration can be maintained during the oxidation of aldehyde by the enzyme and NAD+. With this system, the kinetics of the association of the aldehyde with the enzyme were examined. The rate profile for this reaction is a single exponential process, showing that all four active sites of the enzyme have equivalent and independent reactivity towards the aldehyde, with an apparent second-order rate constant of 5 X 10(7)M-1-S-1 at pH8.0 and 21 degrees C. The second-order rate constant becomes 8 X 10(7)M-1-S-1 when account is taken of the forward and reverse catalytic rate constants of the dehydrogenase. The pH-dependence of the observed rate constant is consistent with a requirement for the unprotonated form of a group of pK 6.1, which is the pK observed for second ionization of glyceraldehyde 3-phosphate. The rate of phosphorolysis of the acyl-enzyme intermediate during the steady-state oxidative phosphorylation of the aldehyde was studied, and is proportional to the total Pi concentration up to at least 1 mM-Pi at pH 7.5. The pH-dependence of the rate of NADH generation under these conditions can be explained by the rate law d[NADA]/dt = k[acy] holoenzyme][PO4(3-)-A1, where thioester bond, although kinetically indistinguishable rate equations for the reaction are possible. The rates of the phosphorolysis reaction and of the aldehyde-association reaction decrease with increasing ionic strength, suggesting that the active site of the enzyme has cationic groups which are involved in the reaction of the enzyme with anionic substrates.