A symmetrical 1,4-dihydropyridine with opposite actions on K(+)-induced contractions in guinea-pig ileum.

The effects of 1,4-dihydro-2,6-dimethyl-4-phenyl-pyridine-3,5-dicarboxylic acid dimethyl ester (DHMP) on Ca2(+)-evoked contractions in potassium-depolarized guinea-pig ileum longitudinal muscle were evaluated. DHMP (1-10 nM) potentiated Ca2(+)-evoked contractions; maximum enhancement was seen at 1 nM. A concentration-dependent inhibition of Ca2(+)-induced contractility was observed at higher concentrations. Racemic BAY K 8644 (1 nM - 1 microM), on the other hand, enhanced ileum responses to Ca2+ with a maximum effect at 3 nM. BAY K 8644, but not DHMP, directly elicited concentration-dependent contractions. The results provide further support for the hypothesis that dihydropyridines can act as both Ca2+ agonists and antagonists.

The anticholinergic activity of agents indicated for urinary incontinence is an important property for effective control of bladder dysfunction.

The anticholinergic, antispasmodic and local anesthetic properties of agents indicated for the treatment of neurogenic bladder disorders were compared with known reference drugs in vitro and in cystometric studies in vivo in the guinea pig. Highly significant correlations (P = .0001) were found among the potencies of drugs to inhibit carbachol-induced isolated guinea pig detrusor muscle contraction in vitro and peak intravesical bladder pressure in vivo in the guinea pig cystometrogram, a test that provides the integrated micturition response in the intact animal. In contrast, there was no significant correlation (P greater than .5) among the potencies of the drugs to depress bladder contractile responses (in vitro and in vivo in the cystometrogram) and their potencies as antispasmodic or local anesthetic agents. Based on these correlations, we suggest that the anticholinergic component of the drugs' action is important in current effective therapies of bladder dysfunction. However, the possibility that other ancillary activities may also contribute to the specific mechanism of action of these agents in the urinary bladder is not ruled out.

In vivo cystometrogram studies in urethane-anesthetized and conscious guinea pigs.

Urinary bladder cystometry using urethral catheters is described in vivo in a urethane-anesthetized guinea pig preparation and compared to an awake-animal preparation in which surgically implanted catheters were used. Anticholinergic drugs dose-dependently inhibited the peak intravesical pressure (PvesP) to a maximum of approximately 80% but had no effect on other cystometrogram (CMG) parameters (threshold pressure, bladder capacity). Stereoselectivity was evident; dexetimide but not levetimide potently depressed PvesP. Oxybutynin was equipotent (ID50 approximately 0.15 mg/kg) in both preparations and showed a similar duration of action (t1/2 = 48-53 min). The data suggests that CMG parameters and the effects of oxybutynin were not affected by urethane anesthesia, making the in vivo urethane-anesthetized guinea pig preparation a valuable tool to evaluate both the filling and voiding phases of cystometry.

R and S enantiomers of oxybutynin: pharmacological effects in guinea pig bladder and intestine.

Oxybutynin (Ditropan) is widely utilized in treatment of incontinence due to neurogenic bladder dysfunction. We prepared its R and S enantiomers and evaluated their antimuscarinic, Ca++-channel antagonistic and spasmolytic effects in guinea pig detrusor strips and ileal longitudinal muscle. Ussing chambers were used to assess inhibition of carbachol-induced mucosal Cl-secretion in vitro. The enantiomers and the racemate were also tested in in vivo preparations for local anesthetic activity and for antimuscarinic activity in the slow filling cystometrogram. Stereoselective antimuscarinic effects [R)OXY:(R/S)OXY:(S)OXY) were evident for isolated ileal longitudinal (0.12:1.0:4.5) and bladder detrusor muscle (0.5:1.0:13) isolated ileal mucosa (0.2:1:8.9) and acetylcholine stimulated phosphoinositide turn-over in vitro (0.24:1.0:39). Stereoselectivity was also evident for the volume-induced contractions of the cystometrogram in vivo (0.7:1:15). In contrast, no stereoselectivity was observed for Ca++-channel antagonism, spasmolytic and local anesthetic properties of (R/S)OXY and its enantiomers.

Cocaine inhibits muscarinic cholinergic receptors in heart and brain.

(-)-Cocaine inhibits M2 muscarinic cholinergic binding measured with [3H]quinuclidinyl benzilate in heart and brain with a Ki of 18.8 microM. The cyclic nucleotide 5'-guanylylimidodiphosphate does not shift the competition curve, suggesting that (-)-cocaine is an antagonist. (-)-Cocaine also reverses the methacholine-induced inhibition of guinea pig atrial contractions at a similar concentration. Although (+)-cocaine is about 8-fold more potent than (-)-cocaine, (+)-cocaine is not present in extracts of the coca plant. Of the many compounds tested, only (-)-cocaine and lidocaine have a higher affinity at M2 muscarinic receptors than at M1 receptors; other compounds such as (+)-cocaine, norcocaine, procaine and dimethocaine are equipotent at the M1 and M2 subtypes. These results indicate that cocaine can act as an antimuscarinic agent, particularly at higher, toxic doses.

Pharmacology of BMY 20064, a potent Ca2+ entry blocker and selective alpha 1-adrenoceptor antagonist.

BMY 20064 is a dihydropyridine Ca2+ entry blocker with potent and selective alpha 1-adrenoceptor antagonist properties. The drug was equal in potency to nifedipine as a Ca2+ entry blocker in depolarized smooth muscle preparations. It was less active than nifedipine in antagonizing Ca2+-induced contractions of isolated guinea pig papillary muscles paced at 0.2, 1.0, or 2 Hz. BMY 20064 was a potent (0.1-0.2 X prazosin) and selective alpha 1-adrenoceptor antagonist in radioligand binding assays and in ganglion-blocked anesthetized rats challenged with phenylephrine. BMY 20064 blocked both the K+ and alpha 1-adrenergic agonist-induced increases in 45Ca uptake into rabbit aortic rings. The drug was more effective than nifedipine, prazosin, or combinations of the drugs in preventing ATP depletion of the rat heart during global ischemia. BMY 20064 was a potent antihypertensive agent in normotensive rats and in SHR. BMY 20064 administered intraarterially (i.a.) dilated both femoral and coronary arterial beds of the dog. Hemodynamic changes elicited by BMY 20064 in anesthetized dogs were similar to those induced by nifedipine. BMY 20064 appears to be a more effective myocardial antiischemic agent than nifedipine, prazosin, or combinations of nifedipine and prazosin. A drug of this type may be more efficacious than dihydropyridines in the management of ischemic episodes.

Heterogeneity of muscarinic receptors coupled to phosphoinositide breakdown in guinea pig brain and peripheral tissues.

Muscarinic receptors coupled to phosphoinositide hydrolysis (PI) are present in guinea pig bladder and colon. Compared to rat cerebral cortex, an extensively studied muscarinic/PI turnover system, all agonists were more potent and efficacious in both bladder and colon. The "M1-selective antagonists", pirenzepine and dicyclomine, were much more potent (Ki = 1-5 nM) and selective (300 to 500-fold) at both rat and guinea pig brain and guinea pig colon receptors, compared to PI-coupled receptors in guinea pig bladder. In contrast, "M2-selective antagonists", AF-DX 116 and HHSiD, were 2-6 fold more potent in bladder than in brain, while HHSiD was very potent in the colon (50 times more potent than in brain). These results suggest a pharmacological heterogeneity of PI-linked muscarinic receptors. If muscarinic receptors with a low affinity for pirenzepine are defined as M2, these results show that the guinea pig bladder contains PI-linked M2 muscarinic receptors, whereas the guinea pig colon contains PI-linked M1 receptors.

Cardiovascular and renal effects of buspirone in several animal models.

Intravenous administration (0.3 or 3 mg/kg) of buspirone to anesthetized rats elicited a transient pressor response (14 +/- 2 mmHg) and sustained bradycardia. However, oral administration (30 mg/kg) reduced the blood pressure and heart rate of conscious normotensive (-14 +/- 4 mmHg) and DOCA-salt hypertensive rats (-22 +/- 5 mmHg). Buspirone (3-100 mg/kg, p.o.) elicited increases in urinary volume and electrolyte excretion of conscious normotensive rats and decreased these parameters in conscious mice. Buspirone was observed to possess alpha 1-adrenoceptor agonist activity in ganglion-blocked anesthetized rats. Buspirone (0.3-3 mg/kg, i.v.) elicited transient elevations in the blood pressure of open-chest anesthetized dogs. There was a sustained increase in total peripheral resistance and a decrease in aortic blood flow, heart rate, right ventricular contractile force and left ventricular dp/dt max. Intravenous and oral administration to anesthetized and conscious dogs elevated urinary volume and electrolyte excretion. However, the doses used to elicit the observed alterations in hemodynamic/renal function are considerably greater than those which produce anxiolytic effects. Thus, it is doubtful that anxiolytic doses of buspirone will produce cardiovascular alterations in patients.

Differential cardioprotective properties of the l- and d- enantiomers of bucindolol in a canine model of heart failure.

In previous studies racemic bucindolol was found to reverse the effects of pentobarbital-induced heart failure in anesthetized dogs. Reductions of right ventricular contractile force (RVCF), left ventricular (LV) dp/dt, and aortic blood flow (ABF) serve as indicators of depressed cardiac function in this model. In this study, racemic bucindolol (0.25 mumol/kg +0.25 mumol/kg/hr) again evoked pronounced and sustained stimulant effects on these depressed parameters. l-Bucindolol (0.125 mumol/kg +0.125 mumol/kg/hr) was a more effective stimulator of cardiac function than d-bucindolol in this model. l-Bucindolol elicited maximal increases in RVCF, ABF, LV dp/dt and heart rate of 66, 19, 30 and 11%, respectively. In comparison, d-bucindolol maximally increased these parameters only 20, 14, 12 and 4%, respectively. Total peripheral resistance was reduced 29% by l-bucindolol and 19% by d-bucindolol. The responses to l-bucindolol and racemic bucindolol were essentially the same. The myocardial stimulation and vasodilation profile derived from l-bucindolol (at one-half the molar dose of bucindolol) suggests the possible preference for its use in clinical management of congestive heart failure over bucindolol, the racemic compound. The results further suggest that l-bucindolol could also be used to treat hypertensive patients with depressed cardiac function.

Acute and chronic diuretic-induced alterations in urinary sodium and calcium excretion in the conscious rat.

The acute and chronic (5-day) effects of three low-ceiling diuretics (hydrochlorothiazide, indapamide or xipamide) and two high-ceiling diuretics (furosemide or muzolimine) on urinary volume and electrolyte excretion were examined in the saline-loaded conscious rat. The three low-ceiling agents produced qualitatively similar alterations in both acute and chronic volume and electrolyte excretion patterns. Each of these agents produced an acute disassociation between urinary sodium and calcium excretion and hypocalciuria after chronic administration. It is suggested that indapamide and xipamide, like hydrochlorothiazide, inhibit sodium but not calcium reabsorption in the distal nephron. Acute as well as chronic treatment with either furosemide or muzolimine produced dose-dependent increases in urinary volume and electrolyte excretion. A generally parallel response was observed on sodium and calcium excretion with these agents. It is suggested that muzolimine, like furosemide, inhibits both sodium and calcium reabsorption in the ascending limb of Henle's loop.

Incidence and pathophysiological changes in chronic two-kidney hypertension in the dog.

Unilateral renal artery plication in dogs reduced renal blood flow by 80% and produced a sustained elevation in arterial pressure whereas plasma renin activity increased for only 4 days. Sodium was retained for 3 days after plication, but this response is similar to that after a sham operation. Of seven dogs studied chronically, elevated arterial pressure was sustained for 27 days or longer in six animals. In three dogs hypertension continued for 2 mo before collateral vessels developed and arterial pressure fell; ligation of these collaterals restored hypertension. Arterial pressure was unaffected by an infusion of [1-sarcosine, 8-alanine] angiotensin II in chronic hypertensive dogs on a normal sodium intake. This angiotensin antagonist lowered arterial pressure after sodium depletion, but became ineffective following rapid sodium repletion. Chronic hypertensive dogs showed normal responses to deoxycorticosterone acetate. These findings suggest that the renin-angiotensin system is not critically involved in maintenace of chronic two-kidney renovascular hypertension in the dog. The data also show that the homeostatic role played by the renin-angiotensin system in the maintenance of arterial pressure remained intact in chronic hypertension.

Effects of propranolol on renin release during chronic thoracic caval constriction or acute renal artery stenosis in dogs.

Dogs were given d,1-propranolol before and after thoracic inferior vena cava constriction (TIVCC) or renal artery constriction (RAC) to determine if the increase in plasma renin activity (PRA) and associated biological activity could be suppressed. Oral propranolol administration (240 mg twice daily) was begun at least 2 days prior to TIVCC in six dogs; heart rate was reduced from 133 to 95 beats/min but PRA did not change with propranolol administration. After TIVCC and during continued propranolol administration, daily renal sodium excretion fell from an average value of 50 to less than 3 mEq sodium/day and PRA was elevated two- to fourfold. With prolonged propranolol administration during TIVCC, PRA returned toward normal levels but renal sodium excretion remained low. At this time, hourly measurements of sodium excretion showed no change after a 240-mg oral dose or propranolol although very high plasma levels of propranolol were achieved; also, PRA was unchanged and low. The effects of RAC were studied before and during an intravenous propranolol infusion (0.2 mg/kg/hour) in conscious animals. Before propranolol administration, arterial pressure increased during RAC from 120 to 136 mm Hg and PRA doubled. Propranolol infusion lowered heart rate from 110 to 84 beats/min, but arterial pressure and PRA were not attentuated by propranolol during RAC. The data indicate that non-beta-adrenergic mechanisms are involved in renin release during TIVCC and RAC.

Mercury detection by means of thin gold films.

The adsorption of elemental mercury vapor on a thin (several hundred angstroms) gold film produces resistance changes in the film. An instrument for the detection of mercury based on this phenomenon is simple and rapid and requires no chemical separations other than passage of the vapor sample through a few standard dry filters. The instrument is portable, and the technique is directly applicable to environmental problems and geochemical prospecting. The limit of detection of the prototype instrument is 0.05 nanogram of mercury.