Influence of the Beta-Adrenergic Antagonists Propranolol, Practolol and Oxprenolol On the Proliferation of Rat Jejunal Crypt Cells

Abstract. Beta-adrenergic blockade by quite large doses of propranolol, practolol and oxprenolol, once or continuously applied, does not influence jejunal crypt-cell proliferation in the rat. After a single i.p. injection of 20 mg/kg propranolol or practolol and even of 100 mg/kg practolol, the mitotic index, the labelling index and the duration of the S phase do not differ between treated and untreated control animals nor between animals treated with the different drugs. Continuous application of 30 mg/kg/d propranolol, practolol or oxprenolol for 7 or 14 days does not affect the mitotic and labelling indices either, nor does it change the duration of the cycle of the jejunal crypt cells and its phases as determined by the percent labelled mitoses method. These results are in contrast to those reported previously by Tutton & Helme (1974).     

Re-examination of the effect of beta-adrenergic blocking agents on the proliferation of rat jejunal crypt cells using the stathmokinetic method

Reports of the effects of beta-adrenergic receptor blocking agents on the proliferative activity of rat jejunal crypt cells are contradictory. According to Tutton and Helme (1974) a single injection of propranolol or practolol (10 mg/kg) increased the mitotic index twofold and shortened the duration of the cell cycle of the crypt cells. However, upon repeating the experiments with double the dose of propranolol, Maurer-Schultze et al. (1986) observed no such effects using cell kinetic methods with 3H-thymidine instead of the stathmokinetic method applied by Tutton and Helme. Since the discrepancy in the results may have been due to methodological differences the same stathmokinetic method used by Tutton and Helme has been applied in the present work. However, the results obtained with this method indicate no influence by propranolol on the proliferation of jejunal crypt cells even with a dose of 20 mg/kg. Consequently we were unable to confirm the stimulant effect of propranolol on crypt cell proliferation. The possible causes of the discrepancy between the present results and those of Tutton and Helme are discussed.     

Effect of practolol on experimental hypertension in dogs]

In the dog, the intra-venous injection of practolol (1 to 3 mg/kg) reduces the hypertension provoked by vagotomy and sino-aortic nerves section, or by intra-venous administration of potassium cyanide. But practolol differs from propranolol ; he does not modify hypertension observed after electrical stimulation of central end of saphene, laryngeal superior, or vagus nerf.     

Effect of beta adrenergic receptor agonists and blockaders on the action of bradykinin

A study was made of the effect of beta-adrenomimetics (isoprenaline, orciprenaline, inoline) and beta-adrenoblockers (propranolol, pindolol, oxprenolol, atenolol and practolol) on changes in the tone of smooth muscles of an isolate ileum of guinea-pigs, increase in microvascular permeability and depressor reaction in rats induced by bradykinin. beta-Adrenomimetics decreased spasmogenic and microcirculatory effects of bradykinin. Depending on the selectivity and presence of partial agonistic activity, beta-adrenoblockers exerted different influence on changes in the tone of extravasal muscles and permeability induced by bradykinin. In doses of 0.1, 0.5 and 1 mg/kg (intravenously) beta-adrenoblockers potentiated and prolonged the depressor effect of bradykinin.     

Double-blind comparison of tolamolol,propranolol, practolol,and placebo in the treatment of angina pectoris.

Forty-two patients with angina pectoris have completed a randomized, double-blind trial comparing tolamolol 100 mg and 200 mg with propranolol 80 mg, practolol 100 mg, and placebo, all given three times a day. Tolamolol 200 mg thrice daily was found to be equivalent to propranolol 80 mg thrice daily in anti-anginal efficacy. Anginal attack rates and trinitrin consumption were significantly reduced by all active treatments as compared with the placebo but tolamolol and propranolol were the most effective. Tolamolol 200 mg thrice daily was most effective in reducing blood pressure, while propranolol was most effective in reducing the resting heart rate. All treatments except the placebo significantly increased the amount of exercise which could be performed before angina appeared (exercise work), while tolamolol 200 mg thrice daily significantly reduced Robinson''s index when compared with all other active agents. The degree of S-T segment depression induced by exercise was significantly lessened by both tolamolol and propranolol but not by practolol or placebo. There was no difference in patient preference between tolamolol and propranolol but tolamolol at both dose levels was preferred to practolol. Both tolamolol and propranolol are potent adrenergic beta-receptor antagonists and equal in anti-anginal efficacy but tolamolol has the advantage of being cardioselective. It is superior to practolol.     

The effect of single and of multiple doses of prednisolone tertiary butyl acetate on cell population kinetics in the small bowel mucosa of the rat.

The effect of single and of multiple doses of prednisolone upon cell population kinetics in the rat jejunal crypt was investigated, using autoradiography and stathmokinetic techniques with vincristine. Single injections of prednisolone (2.5 mg/kg body weight) induced a depression both flash thymidine labelling and mitotic indices; this change was shown to be due to a decreased cell production rate. Recovery of these proliferative indices occurred over seven days after injection; measurement of crypt size parameters showed a transient decrease in crypt population. Multiple daily injections of prednisolone (1 mg/kg body weight) produced a more sustained decrease in labelling and mitotic indices, which lasted as long as injections were continued (7 days); stathmokinetic techniques showed decreases in cell production rates, and the crypt population was also depressed throughout this period. It is concluded that prednisolone depresses cell proliferative rates in rat jejunal mucosa.     

THE INFLUENCE OF ADRENORECEPTOR ACTIVITY ON CRYPT CELL PROLIFERATION IN THE RAT JEJUNUM

The influence of adrenergic stimulation, adrenergic blockade and sympathectomy on crypt cell cycle time and mitotic time in rat jejunum was studied. Alpha adrenergic stimulation by noradrenaline was found to shorten both cell cycle and mitotic times, whereas beta adrenergic stimulation by adrenaline or isoprenaline was found to prolong both cell cycle and mitotic times. Conversely, alpha adrenergic blockade by phentolamine prolonged cell cycle time and beta adrenergic blockade by propranolol or practolol shortened cell cycle time but not mitotic time. Both chemical and surgical sympathectomy inhibited crypt cell proliferation. Chemically sympathectomized animals manifested supersensitivity to exogenous noradrenaline.     

Clinical Evaluation of Practolol,a New Cardioselective Beta-blocking Agent in Angina Pectoris

In a controlled double-blind study practolol, a new cardioselective beta-blocking drug, was given to 15 patients with angina pectoris, and compared with propranolol 80 mg. q.d.s. The dose of practolol ranged from 200 to 600 mg.b.d. and was decided by initial open titration in individual patients. Though practolol did not influence the incidence of angina or glyceryl trinitrate consumption, it increased the duration of exercise possible in exercise tests and reduced the amount of ischaemic S—T depression in the radiocardiogram during exercise. Propranolol reduced the incidence of angina and, in the exercise tests, increased the amount and duration of exercise but did not affect the degree of S—T depression. Unlike propranolol, practolol did not produce any adverse effects on bronchial smooth muscle. Hence it is concluded that practolol is an effective drug in treating angina, and in the dosage used is of potential value in patients with asthmatic bronchitis and angina. It should, however, be used cautiously in anginal patients with heart failure.     

Atenolol,sustained-release oxprenolol,and long-acting propranolol in hypertension.

The effect of once-daily atenolol, sustained-release oxprenolol (a new formulation of oxprenolol presented as a compressed tablet in a waxed matrix), and long-acting propranolol (a new formulation presented as spheriods in a capsule) was studied in a double-blind crossover trial in 23 carefully selected hypertensive outpatients. After a run-in period with matching placebo each patient received atenolol (100 mg/day), sustained-release oxprenolol (160 mg/day), long-acting propranolol (160 mg/day), and placebo according to a randomised sequence. After four weeks'' treatment with sustained-release oxprenolol blood pressure in the two to four hours before the next dose was not significantly lower than after placebo. The effectiveness of atenolol and of the new formulation of propranolol in reducing blood pressure was confirmed. These results suggest that the present formulation of sustained-release oxprenolol should be reconsidered.     

AUTORADIOGRAPHIC CONFIRMATION OF THE MITOTIC DIVISION OF EVERY MOUSE JEJUNAL CRYPT CELL LABELLED WITH 3H-THYMIDINE

The question was investigated of whether for crypt epithelia of the jejunum of the mouse all cells labelled after a single injection of ³H-TdR subsequently divide or whether cells exist in the crypt which synthesize metabolic DNA and, therefore, do not undergo division after labelling.
A double labelling experiment was performed with a first injection of ³H-TdR followed 1 hr later by an injection of ¹⁴C-TdR. Then from double emulsion autoradiographs of isolated squashed crypts the number of ³H-only, ¹⁴C-only and double labelled cells and mitoses were counted.
The double labelling produced a narrow, 1 hr wide sub-population of ³H-only labelled cells. This subpopulation of S cells completed its division before labelled cells were lost from the crypts by migration onto the villi. The results showed that this subpopulation of ³H-only cells completely doubled within 3 hr and then remained constant through 6 hr. From this result it was concluded that every cell labelled after a single injection of ³H-TdR divides.
From the same autoradiographs the flow rate through the end of mitosis was measured. From the flow rate and the mitotic index a mitotic duration of 0·5 hr was determined. The agreement of this measured mitotic time with the value calculated from the labelling index, mitotic index and S duration is also strong evidence that every labelled cell divides.
Both experiments show that the intestinal crypt does not contain cells synthesizing metabolic DNA.     

Methyldopa and propranolol or practolol in moderate hypertension.

The effect of a low dose of methyldopa combined with (a) a non-selective and (b) a selective beta-adrenoceptor antagonist was studied in a double-blind crossover trial in 24 carefully selected patients with moderate hypertension (mean initial lying blood pressure 189/117 mm Hg). Each patient received methyldopa 750 mg/day, propranolol 240 mg/day, practolol 600 mg/day, methyldopa 750 mg/day combined with propranolol 240 mg/day, methyldopa 750 mg/day combined with practolol 600 mg/day, and placebo for four weeks each according to a random sequence. After four weeks of therapy the most effective treatment, methyldopa combined with propranolol, reduced lying and standing blood pressures by 36-5/21-4 mm Hg and 44-7/25 mm Hg respectively. Thic combination had similar effects to those of the combination of methyldopa with the cardioselective agent practolol except that it reduced lying diastolic pressure further. The combination was more effective than either treatment alone. No significant differences were found between the effects of propranolol, practolol, or methyldopa at the doses used.     

Role of adrenergic mechanisms in the development of cardiac hypertrophy.

This experiment was designed to study the role of cardiac beta-adrenergic mechanisms in the development of hypertrophy in rats. The suprarenal abdominal aorta was banded, resulting in an increase in cardiac wt-body wt ratio. A group of rats received a sham operation. Half of the banded rats were treated with practolol, 2.0 mg/kg intraperitoneally every 12 hr for the 6 days after banding. The effectiveness of cardiac beta-adrenergic blockade was confirmed by absence of an increase in heart rate following intravenous isoproterenol at various times between practolol injections. Practolol did not affect the gradient in the banded groups. Six animals in each banded group were sacrificed daily for 6 days. The right and left ventricles were dissected separately and weighed. RV-body weight ratios increased similarly in both banded groups. LV-body weight ratio (g/kg) was 2.17 +/- 0.043 in sham rats, and it attained maximal levels of 3.03 +/- 0.10 within 6 days in banded untreated rats and 2.96 +/- 0.14 in banded rats receiving practolol. Therefore, beta-adrenergic mechanisms were not involved in the development of hypertrophy due to increased afterload. Also, these findings are not consistent with the Meerson hypothesis, since hypertrophy occurred despite the reduction in myocardial O2 consumption due to practolol.     

Hemodynamic effects of procainamide and quinidine and the influence of beta-blockade before and after experimental myocardial infarction.

The use of antiarrhythmie drugs in combination has been limited because of possible side effects secondary to myocardial depression in the acute myocardial infarction patient. Therefore, we investigated in intact dogs (group I) the hemodynamic interaction of propranolol plus procainamide (subgroup A) or quinidine (subgroup B) and in dogs after experimental myocardial infarction produced by coronary artery ligation (group II). Infusion of procainamide (30 mg/kg over 5 min) in animals of group IA produced a significant (P less than 0.05) decrease of 30% in mean aortic pressure, a decrease of 40% in left ventricular dp/dt and 29% in cardiac output. When procainamide was reinfuse after propranolol (1 mg/kg), its hemodynamic effects were not significantly different from those observed before propranolol in both groups IA and IIA. Infusion of quinidine (10 mg/kg over 5 min) in animals of group IB (intact dogs) also produced significant decreases of 24% in mean aortic pressure and 38% in dp/dt while cardiac output was unchanged. However, these hemodynamic changes were seen only after beta-blockade and were significantly different from those obtained before propranolol, where heart rate increased by 14%, dp/dt by 30%, and cardiac output by 35%. These changes occurred despite a similar reduction in mean aortic pressure. This drug combination produced similar response in animals after coronary artery ligation (group IIB). In conclusion, we feel that the administration of propranolol does not prevent the depressive circulatory effects of procainamide. The combined use of quinidine and propranolol also has a negative circulatory effect although not as marked as the effects observed after procainamide with propranolol.     

Induction of micronuclei in mouse bone-marrow erythrocytes in association with hypothermia after administration of the sigma receptor ligand E-5842

Oral administration of E-5842, a new sigma1 receptor ligand being developed as an antipsychotic drug, to male mice at single doses of 50, 100, 200 and 400 mg/kg produced marked and sustained decreases in rectal temperature. Both the intensity and the duration of the hypothermic effect increased with dose. Maximum decreases from the mean pre-administration temperature (36.2 degrees C) ranged from 7.5 to 12.9 degrees C for animals receiving 50 and 400 mg/kg doses, respectively. Examination of bone-marrow smears obtained 24, 48 and 72 h after administration revealed a slight but statistically significant (p < 0.05) increase in the frequency of micronucleated polychromatic erythrocytes (MNPCE) at the 48 h sampling for animals receiving the 200 mg/kg dose. These animals showed decreases from pre-administration temperature of approximately 12 degrees C, with recovery being observed 24 h after administration. When the hypothermic effect of E-5842 administration was avoided by housing treated animals under conditions of increased environmental temperature (30 degrees C) for 24 h, MNPCE frequency reverted to vehicle control values. Further, in E-5842-treated animals with an increased MNPCE frequency there was a shift in the distribution of the relative areas of micronuclei in MNPCE towards higher values. In addition, there was a statistically significant increase (p < 0.001) in the number of relatively large micronuclei (micronucleus diameter > or = 1/4 cytoplasm diameter) similar to that produced by administration of the mitotic spindle inhibitor colchicine (1 mg/kg), suggesting disturbance of mitotic apparatus as the possible underlying mechanism. The results suggest that the slight increase in MNPCE frequency observed 48 h after administration of a 200 mg/kg dose of E-5842 is due to a hypothermic effect and not to a direct effect of E-5842 on DNA.     

Diuretic effects on renal brush border membrane transport and metabolism

Previous studies have indicated that the thiazide diuretics exert effects on proximal electrolyte transport. To determine whether the locus of these effects is at the brush border membrane (BBM) and if renal metabolism is affected, adult female Sprague-Dawley rats were acutely treated with either 1 mg/kg metolazone, 20 mg/kg chlorothiazide followed by a 20 mg/kg/hr maintenance infusion, 10 mg/kg acetazolamide followed by a 10 mg/kg/hr maintenance infusion, or the vehicles only. Administration of these agents resulted in an approximately tenfold increase in sodium excretion. Neither urinary phosphate nor inulin excretion changed significantly in any group. Sodium dependent BBM vesicle phosphate transport was examined at 0.15, 0.5, and 1 and 120 minute incubation periods in the diuretic treated groups and their respective control groups. Decreased uptake was seen in all pre-equilibrium time points in rats treated with metolazone: 0.15 minutes: 221 +/- 24 pmoles/mg protein (pmol/mg prot) in control rats versus (vs) 185 +/- 23 pmoles/mg prot in metolazone-treated animals (P less than .05) ; 0.5 minutes: 463 +/- 54 vs 369 +/- 49 pmol/mg prot (P less than .005); 1 minute: 549 +/- 74 vs 460 +/- 61 pmol/mg prot (P less than .05); no significant difference in phosphate transport was noted at the two hour equilibrium time point. No significant differences in sodium dependent phosphate transport existed between chlorothiazide or acetazolamide treated rats and control animals. Substrate-stimulated renal gluconeogenesis did not differ between metolazone treated and control animals. We therefore conclude that metolazone inhibits phosphate transport through an effect on the BBM and does not affect renal gluconeogenesis in the rat.     

Cell population kinetic profile of the mouse thymus, and the changes induced by prednisolone.

The cell population kinetic parameters of the thymus in BALB/c mice have been estimated using stathmokinetic and [3H]TdR techniques in both control animals and animals treated with prednisolone. FLM data were analysed by computer using the Gilbert program. The study showed that prednisolone had an inhibitory effect mainly in the DNA synthesis phase and in G1. Stathmokinetic data also showed a decrease in the cell birth rate and an increase in the apparent cell cycle time (or potential doubling time) after treatment. The labelling index, the mitotic index and the growth fraction were also decreased. The study also shows a good agreement between the data obtained by stathmokinetic and [3H]TdR techniques.     

Antimutagenic potential of curcumin on chromosomal aberrations in Wistar rats

Curcumin, a yellow pigment commonly used as a spice and food coloring agent is obtained from rhizomes of Curcuma longa and is a major chemopreventive component of turmeric. In the present set of investigations the antimutagenic potential of curcumin has been evaluated using in vivo chromosomal aberration assay in Wistar rats. Cyclophosphamide (CP), a well-known mutagen was given by intraperitoneal (i.p.) injection at the dose of 40 mg/kg body weight (b.w.). Curcumin was given at the dose of 100 and 200 mg/kg b.w. through gastric intubation for seven consecutive days prior to CP treatment. The animals were sacrificed at the sampling time of 24 h after treatment and their bone marrow tissue was analyzed for chromosomal damage and mitotic index. In CP treated animals a significant induction of chromosomal aberration was recorded with decrease in mitotic index. However, in curcumin-supplemented animals, no significant induction in chromosomal damage or change in mitotic index was recorded. In different curcumin-supplemented groups, a dose dependent significant decrease in CP induced clastogenicity was recorded. The incidence of aberrant cells was found to be reduced by both the doses of curcumin when compared to CP treated group. The anticytotoxic potential of curcumin towards CP was also evident as the status of mitotic index was found to show increment. The study revealed the antigenotoxic potential of curcumin against CP induced chromosomal mutations.     

Cell population kinetics and DNA content during thyroid carcinogenesis

The proliferation kinetics and DNA content of thyroid follicular cells in rats were studied by autoradiography and cytophotometry. Continuous treatment of animals with methylthiouracil (MTU) results in hyperplasia followed by tumour growth in the thyroid gland. The mitotic index (MI) increases from 0.006 +/- 0.002% in controls to 0.13 +/- 0.06% in hyperplasia and to 0.09 +/- 0.03% in malignant cells. The same is true for the labelling index (LI) which rises from 0.08 +/- 0.003% in controls to 1.4 +/- 1.1% in hyperplasia and to 1.0 +/- 0.6% in follicular adenomas. The S-phase duration (TS) is shortened from 8.0 +/- 1.2 hr in controls to 6.0 +/- 1.4 hr in animals treated for 9 months with MTU and prolonged to 15.4 +/- 2.1 hr in papillary carcinomas. In all MTU-treated animals a decrease in the value of the potential population doubling time (TPD) and thyroid weight doubling time (TD) was observed. The cell loss factor (phi) decreases in animals treated for 3 months with MTU and increases during the stage of tumour growth in the gland (animals treated 12-15 months with MTU). DNA measurements in the nuclei of hyperplastic and neoplastic thyroid tissues reveal cells with values exceeding that in control animals. However, no difference was found in the DNA content between thyroid adenomas and carcinomas, nor between thyroid hyperplasia and neoplasia.     

Effects of propranolol and indomethacin on muscarinic airway reactivity in unanesthetized guinea pigs

To investigate whether endogenous beta-adrenergic stimulation or cyclooxygenase products normally affect muscarinic reactivity in conscious, spontaneously breathing guinea pigs, we measured specific airway resistance (SRaw) during acetylcholine (ACh) infusion before and after treatment with propranolol (10 mg/kg ip) or indomethacin (30 mg/kg ip). Airway reactivity was assessed by measuring changes in SRaw upon increasing ACh infusion. We found that propranolol treatment increased reactivity to parenteral ACh, but did not change baseline SRaw. Furthermore, propranolol reduced the range in muscarinic reactivity for the group, and it enhanced thr reproducibility of measurements in individual animals. In contrast, indomethacin had no effect on either baseline SRaw or muscarinic reactivity. Our results suggest that beta-blockade of endogenous adrenergic stimulation increases the muscarinic reactivity of guinea pig airways, but does not influence resting airway tone. It appears that propranolol treatment allows a more reproducible assessment of muscarinic reactivity in the guinea pig. In contrast, cyclooxygenase products do not seem to significantly affect baseline airway resistance, reactivity, or reproducibility in the guinea pig.     

Mechanism of action of βadrenergic receptor blocking agents in angina pectoris: Comparison of action of propranolol with dexpropranolol and practolol

The effect on exercise tolerance of racemic propranolol has been assessed in eight angina pectoris patients and compared with that of dexpropranolol (the dextro isomer of propranolol), practolol (I.C.I. 50172), and saline. Dexpropranolol has the same local anaesthetic action as propranolol with negligible β-adrenergic receptor blocking activity, while practolol is a cardio-selective β-adrenergic blocking agent which does not have local anaesthetic activity.Saline and dexpropranolol had no significant effect on exercise time; racemic propranolol and practolol improved exercise tolerance in six subjects, the response to the two drugs being very similar in individual patients. It was concluded that the beneficial effect of propranolol in angina pectoris results from its action as a β-adrenergic receptor blocking agent and is not due to its local anaesthetic, or quinidine-like, activity.