EVALUATION OF MODEL-BASED ITERATIVE RECONSTRUCTION IN ABDOMINAL COMPUTED TOMOGRAPHY IMAGING AT TWO DIFFERENT DOSE LEVELS.

The purpose of this study was to qualitatively evaluate recently introduced Model-based iterative reconstruction method (IMR) and routinely used iterative reconstruction algorithm iDose4 to investigate future dose reduction possibilities for abdominal CT exams. The study contained data from 34 patients who underwent abdominal CT in SkåneUniversityHospital Lund, Sweden. A low-dose scan (CTDIvol3.4 mGy) reconstructed with both iDose4 and IMR and a standard-dose scan (CTDIvol 5.3 mG) reconstructed with iDose4 alone were visually graded in ViewDEX v2.0 by four radiologists using modified EU image criteria. The visual grading characteristics analysis for the evaluation comparing iDose4 standard dose with IMR low dose did not show any statistically significant difference in five of six criteria. In one of the criteria, iDose4 was superior to IMR. The result show promising possibilities are introduced for substantial radiation dose reduction (35%) in abdominal CT imaging when replacing iDose4 with IMR. Still, care should be taken when considering the reproduction of adrenal glands.

Minimizing contrast medium doses to diagnose pulmonary embolism with 80-kVp multidetector computed tomography in azotemic patients.

BACKGROUND: In diagnosing acute pulmonary embolism (PE) in azotemic patients, scintigraphy and magnetic resonance imaging are frequently inconclusive or not available in many hospitals. Computed tomography is readily available, but relatively high doses (30-50 g I) of potentially nephrotoxic iodine contrast media (CM) are used. PURPOSE: To report on the diagnostic quality and possible contrast-induced nephropathy (CIN) after substantially reduced CM doses to diagnose PE in azotemic patients using 80-peak kilovoltage (kVp) 16-row multidetector computed tomography (MDCT) combined with CM doses tailored to body weight, fixed injection duration adapted to scan time, automatic bolus tracking, and saline chaser. MATERIAL AND METHODS: Patients with estimated glomerular filtration rate (eGFR) <50 ml/min were scheduled to undergo 80-kVp MDCT using 200 mg I/kg, and those with eGFR >or=50 ml/min, 120-kVp MDCT with 320 mg I/kg. Both protocols used an 80-kg maximum dose weight and a fixed 15-s injection time. Pulmonary artery density and contrast-to-noise ratio were measured assuming 70 Hounsfield units (HU) for a fresh clot. CIN was defined as a plasma creatinine rise >44.2 micromol/l from baseline. RESULTS: 89/148 patients (63/68 females) underwent 80-/120-kVp protocols, respectively, with 95% of the examinations being subjectively excellent or adequate. Mean values in the 80-/120-kVp cohorts regarding age were 82/65 years, body weight 66/78 kg, effective mAs 277/117, CM dose 13/23 g I, pulmonary artery density 359/345 HU, image noise (1 standard deviation) 24/21 HU, contrast-to-noise ratio 13/13, and dose-length product 173/258 mGy x cm. Only 1/65 and 2/119 patients in the 80- and 120-kVp cohorts, respectively, with negative CT and no anticoagulation suffered non-fatal thromboembolism during 3-month follow-up. No patient developed CIN. CONCLUSION: 80-kVp 16-row MDCT with optimization of injection parameters may be performed with preserved diagnostic quality, using markedly reduced CM doses compared with common routine practice, which should be to the benefit of patients at risk of CIN.

Some pre- and postjunctional effects of castration in rabbit isolated corpus cavernosum and urethra.

Pre- and postjunctional effects of castration were investigated in isolated corpus cavernosum (CC) and prostatic and preprostatic urethral preparations obtained from rabbits that had been castrated surgically 14 days before investigation. Preparations obtained from untreated animals were used as controls. Castration did not change the relaxing effects of SIN-1 (NO donor) or papaverine in CC preparations contracted by noradrenaline (NA). Electrical field stimulation of CC preparations contracted by NA or endothelin-1 produced frequency-dependent and tetrodotoxin-sensitive relaxations. As compared with controls, the electrically induced relaxations were increased in preparations from castrated animals. Pretreatment with prazosin increased the electrically induced relaxations in CC from untreated rabbits, but had no effect on preparations from castrated animals. In CC preparations incubated with 3H-NA, castration significantly reduced the electrically evoked release of 3H. L-NOARG, an inhibitor of NO synthase, had no effect on 3H-efflux. In prostatic, but not preprostatic, urethral preparations contracted by NA, the relaxant effects of SIN-1 and vasoactive intestinal polypeptide were significantly smaller following castration. Furthermore, castration significantly reduced electrically evoked relaxations in prostatic urethral preparations contracted by NA, while in preprostatic urethra, no such effect was seen. Castration or L-NOARG had no effect on the electrically induced release of 3H-NA in either of the urethral tissues. The results suggest that the hormonal changes caused by castration may modulate the functional effects in vitro of some parts of the urogenital tract. In penile erectile tissue, the relaxations induced by electrical field stimulation are increased, probably for the most part through a decrease in the neuronal release of NA. In prostatic urethra, on the other hand, electrically evoked relaxations are decreased, possibly as a result of an impaired ability of the smooth muscle itself to respond to relaxant agents. In preprostatic urethra, castration has no obvious functional effects. The physiological consequences of these findings in the in vivo situation remain to be established.

Effects of nicorandil on human isolated corpus cavernosum and cavernous artery.

Nitric oxide (NO) released from nonadrenergic-noncholinergic (NANC) nerves seems to be a principal mediator of the relaxation of penile erectile tissue necessary for erection, and drugs acting by release of NO have been shown to produce erection when injected intracorporeally into impotent patients. By producing hyperpolarization, K+ channel openers are effective in relaxing isolated penile erectile tissue from rabbit and man, and can produce tumescence and erection when injected intracorporeally into animals. Nicorandil is classified as a K+ channel opener, but it also acts as a donor of NO. In the present study, the effects of nicorandil on isolated preparations from human corpus cavernosum (CC) and deep cavernous artery (Acc) were compared with those of cromakalim (K+ channel opener) and SIN-1 (NO donor). Nicorandil produced a concentration-dependent relaxation of CC and Acc preparations. The relaxations obtained at the highest nicorandil concentration used (10(-4) M.) were 75 +/- 3% and 66 +/- 4% in CC preparations contracted by noradrenaline and endothelin-1, respectively. The corresponding effects in Acc preparations were 70 +/- 14% and 73 +/- 5%. Glibenclamide (blocking ATP-dependent K+ channels) significantly reduced the nicorandil-induced relaxation in CC, but not in Acc. Methylene blue (believed to block soluble guanylate cyclase) reduced nicorandil's relaxant effect in CC, although statistical significance was not obtained. NG-nitro-L-arginine 10(-4) M. (NO synthase inhibitor) did not significantly influence the effect of nicorandil on precontracted preparations in either tissue. In CC preparations contracted by electrical field stimulation, nicorandil and cromakalim concentration dependently inhibited the responses. This effect was significantly counteracted by glibenclamide. It is concluded that nicorandil is effective in relaxing human CC chiefly by its K+ channel opening action, and to some extent by its ability to release NO. For nicorandil's relaxing effect on Acc, ATP dependent K+ channels seem to be of limited importance. If effective in impotent patients, the drug may represent a new, interesting approach to the treatment of erectile dysfunction.

Regulation of tone in penile cavernous smooth muscle. Established concepts and new findings.

Since Benson, in 1983, reported on a potent nonadrenergic, noncholinergic (NANC) transmitter postulated to relax penile vessels and the corpus cavernosum, much new information on the mechanisms of contraction and relaxation of corporeal smooth muscle and penile vasculature has been obtained. The information currently available suggests that NANC transmitters may be involved in both contractile and relaxant responses of penile erectile tissues. There is good experimental evidence to allow the assumption that neurogenic nitric oxide (NO) is a mediator of penile erection, but even if NO probably is the most important factor for relaxation of penile vessels and the corpus cavernosum, this does not exclude the possibility that other agents released from nerves may have a modulatory function in this process. However, the roles of, for example, vasoactive intestinal polypeptide and related peptides as neurotransmitters and/or neuromodulators in the nervous control of penile erection have yet to be established. The restricted availability of human penile erectile tissues has led to the use of cavernous tissue and penile vessels from animals, both for screening and for detailed analysis of mechanisms previously demonstrated to exist also in human tissues. When interpreting the results obtained, it is important to stress that there may be important differences between human and animal tissues, that each of the tissues only gives a piece of information on the complex process of penile erection, and that the physiological and clinical importance of results from such experiments may be limited. The differing responses in different parts of the vasculature within the penis and the multiplicity of putative transmitters present in the corpus cavernosum and in perivascular nerves make further investigations necessary, as do the interactions between transmitters and neuromodulators at the neuromuscular junction, and between the neural and endothelial control of vascular tone.

Actions of 3-morpholinosydnonimin (SIN-1) on rabbit isolated penile erectile tissue.

The effects of the NO-donor 3-morpholinosydnonimin (SIN-1) on isometric tension, cyclic guanosine 3',5'-monophosphate (cyclic GMP) accumulation and neuronal release of 3H-noradrenaline were investigated in rabbit isolated corpus cavernosum (CC), and compared to the actions of sodium nitroprusside (SNP) and the cyclic GMP-specific phosphodiesterase inhibitor zaprinast. SIN-1, zaprinast and SNP concentration dependently relaxed rabbit CC preparations contracted by 1 microM. phenylephrine. All the drugs were highly effective, and the order of potency was SNP > zaprinast > SIN-1. SIN-1 had a biphasic effect on contractions evoked by electrical field stimulation of nerves: at low concentrations (1 and 10 microM.), SIN-1 inhibited the contractions, while at concentrations > or = 100 microM., the contractions were again increased. There were no changes in baseline tension. Electrically evoked contractions were inhibited by zaprinast in a concentration-dependent manner. Compared with controls, 1 mM. SIN-1 caused a significant (p < 0.05) increase in both the basal efflux and in the electrically induced release of 3H from CC preparations incubated with 3H-noradrenaline. SIN-1, zaprinast and SNP increased tissue levels of cyclic GMP. There was no positive correlation between cyclic GMP accumulation and the relaxant effects of the drugs. The effects of SIN-1 and SNP on the tissue content of cyclic GMP were not significantly affected by methylene blue, an inhibitor of soluble guanylate cyclase. It may be concluded that SIN-1, zaprinast and SNP are effective in relaxing isolated penile erectile tissue, and this effect is associated with an increase in the tissue content of cyclic GMP via pathways not sensitive to methylene blue. However, additional mechanisms beside stimulation of adrenergic neurotransmission and activation of guanylate cyclase in the smooth muscle cell seem to participate in the action of SIN-1 on rabbit penile erectile tissue.

Endothelin-1-induced phosphoinositide hydrolysis and contraction in isolated rabbit detrusor and urethral smooth muscle.

1. Endothelin-1 (ET-1) caused a concentration-dependent increase in the formation of inositol phosphates (IPs) in isolated rabbit detrusor and urethral smooth muscle preparations prelabelled with myo-[3H]inositol. 2. The increase in accumulation of IPs was slow in onset in both detrusor and urethra, with no significant accumulation demonstrable during the first 30 min. The increase in IPs accumulation found after exposure of detrusor tissue to ET-1 (10(-7) M) for 2 hr (250 +/- 38%, n = 7) was not significantly different from that found in the urethra (279 +/- 40%, n = 6), when expressed as per cent of corresponding control values. 3. Pretreatment with nifedipine (10(-6) M) did not reduce IPs formation. In contrast, no increase in IPs formation was demonstrated in Ca(2+)-free medium. 4. ET-1 (10(-11)-10(-7) M) produced concentration-dependent, slowly developing contractions in both detrusor and urethral preparations. Pretreatment with H-7 (3 x 10(-5) M) for 30 min before ET-1 application resulted in a non-parallel shift of the ET-1 concentration-response curve with significant reductions in maximal responses in both tissues. 5. ET-1-induced contractions in urethral preparations were markedly inhibited by Ni2+ (3 x 10(-4) M), whereas the effect of Ni2+ in the detrusor was less pronounced. 6. The results suggest that ET-1 stimulates phosphoinositide hydrolysis in the rabbit detrusor and urethra. Both IPs formation and contractile activation evoked by ET-1 are dependent on extracellular Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Preliminary results with the nitric oxide donor linsidomine chlorhydrate in the treatment of human erectile dysfunction.

Recent experimental studies showed an important role of endothelium derived relaxing factor for cavernous smooth muscle relaxation. Since nitric oxide seems to account for the biological actions of endothelium derived relaxing factor, a study was done to examine a possible role of the nitric oxide donor linsidomine chlorhydrate (SIN-1) in the treatment of erectile dysfunction. To determine a therapeutically useful dose 0.1, 0.2, 0.5 and 1 mg. SIN-1 were injected intracavernously in patients with erectile dysfunction. Each dose was given to 2 patients. Then, 63 patients received 1 mg. SIN-1, including 7 who had prolonged erections to minimal doses of papaverine plus phentolamine and 4 who did not respond with a full erection to other pharmacological agents. Intracavernous injection of SIN-1 induced a dose-dependent erectile response by increasing the arterial inflow and relaxing cavernous smooth muscles. Of the patients 29 had a full, 21 an almost full and 13 a moderate erection to 1 mg. SIN-1. There were no systemic or local side effects. In the patients with prolonged erections to papaverine plus phentolamine the mean duration of a full erectile response to SIN-1 was 57 minutes. Compared to the responses to a papaverine (15 mg./ml.) and phentolamine (0.5 mg./ml.) mixture, the erection induced by SIN-1 was superior in 10, comparable in 47 and inferior in 6 patients. Our data suggest a possible role for SIN-1 in the treatment of erectile dysfunction. Possible advantages may be that erection is induced by a mechanism similar to that occurring physiologically, a decreased risk of inducing prolonged erections and low therapy costs.

Phospholipase C activation by endothelin-1 and noradrenaline in isolated penile erectile tissue from rabbit.

The effects of endothelin-1 and noradrenaline on phospholipase C activity in the rabbit isolated corpus cavernosum were investigated by measuring the accumulation of inositol phosphates. Both endothelin-1 and noradrenaline caused a time- and concentration-dependent increase in the accumulation of 3H-inositol phosphates in preparations prelabelled with 3H-myo-inositol. The reaction was slow in onset with no significant accumulation of 3H-inositol phosphates, including inositol trisphosphate, demonstrable during the first 15 minutes. At 60 minutes, the mean increases in 3H-inositol inositol phosphates induced by 3 x 10(-7) M endothelin-1 and 10(-3) M noradrenaline amounted to 341 and 530% of time-matched controls, respectively. However, when given at concentrations having the same contractile amplitude on rabbit corpus cavernosum, there was no difference in the amounts of 3H-inositol phosphates generated by endothelin-1 and noradrenaline. Prazosin (10(-6) M) significantly inhibited the stimulatory effect of noradrenaline on phosphoinositide hydrolysis. Pretreatment with 10(-6) M nimodipine did not reduce the increases in 3H-inositol phosphates induced by 3 x 10(-7) M endothelin-1 and 10(-3)M noradrenaline. Also in Ca(2+)-free medium, both agonists had significant stimulatory effects on phosphoinositide turnover, although under this condition, the responses were greatly reduced. The results suggest that exogenous endothelin-1 and noradrenaline activate phospholipase C in corpus cavernosum, and that this mechanism is partly independent of extracellular Ca2+. Considering the slow onset of action, phospholipase C activation is probably not directly involved in rapid contractile events, but may be of importance in the long-term regulation of penile smooth muscle tone.

Endothelin-1-induced contractions of isolated pig detrusor and vesical arterial smooth muscle: calcium dependence and phosphoinositide hydrolysis.

1. In isolated pig detrusor and vesical arterial smooth muscle preparations, endothelin-1 (ET-1) caused concentration-dependent contractions. Nifedipine (10(-6) M) did not significantly affect the action of ET-1 in the vessels, but almost abolished its effect in the detrusor. Incubation for 30 min in Ca(2+)-free solution markedly reduced the ET-1-induced contractions in both detrusor and vesical arteries. 2. The protein kinase C inhibitor H-7 (3 x 10(-5) M), reduced the response to ET-1 in detrusor muscle as well as in vessels, and abolished the contractions evoked by ET-1 in Ca(2+)-free solution. 3. ET-1 caused an increase in the accumulation of inositol phosphates (IPs) in preparations prelabelled with myo-[3H]inositol. After exposure to ET-1 (10(-7) M) for 60 min, an approx. 4-fold increase in IPs levels were demonstrated, compared to untreated controls, in both detrusor and vessel preparations. Pretreatment with nifedipine (10(-6) M) did not reduce IPs formation. In contrast, no increase in IPs formation was demonstrated in Ca(2+)-free medium. 4. The increase in accumulation of IPs was slow in onset in both detrusor and vesical arteries, with no significant accumulation demonstrable during the first 30 min. Time-course studies of tension development for ET-1 revealed that maximum tension was reached before significant levels of IPs could be detected.

Functional effects, binding sites and immunolocalization of endothelin-1 in isolated penile tissues from man and rabbit.

Functional effects of endothelin-1 (ET-1) were investigated in isolated preparations of human and rabbit corpus cavernosum (CC) and human penile circumflex veins (CV). In all preparations, ET-1 induced slowly developing, concentration-dependent contractions. The threshold concentration of ET-1 in CV was approximately 10 and 112 times lower than the threshold concentrations in human and rabbit CC, respectively. Furthermore, the contractions in CV reached a defined maximum at 10(-7) M ET-1 (-log EC50 = 9.12 +/- 0.17), whereas no maximum was obtained in CC preparations within the concentration range used (less than or equal to 3 x 10(-7) M). Pretreatment with the Ca++ channel blocker nimodipine partly reduced the ET-1-induced contractions in human and rabbit CC, but had no significant effect on CV preparations. In a Ca(++)-free medium containing the chelator ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetra-acetic acid, the contractions induced by ET-1 were reduced, but not abolished, in all preparations. The contractions induced by ET-1 are thus mediated mainly by influx of Ca++, although there seem to exist differences in the relative contribution of L-type Ca++ channels in CC and CV. Furthermore, additional mechanisms beside Ca++ influx are likely to be involved in both tissues. A high density of [125I]ET-1 binding sites was observed throughout the stroma and in the muscle layer of the deep penile artery in both human and rabbit CC. In the human CV, numerous binding sites were observed, but no clear difference between the various structures of the vessel wall could be detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of inhibitory neurotransmission in the isolated corpus cavernosum from rabbit and man.

1. NG-nitro-L-arginine (L-NOARG, 10(-4) M), an inhibitor of nitric oxide (NO) synthesis, had no contractile effect on isolated preparations of rabbit and human corpus cavernosum at baseline tension, but increased tension in preparations contracted by noradrenaline (rabbit 10(-5) M, man 3 x 10(-7)-3 x 10(-6) M) or K+ (rabbit 60 mM). 2. Electrical field stimulation (supramaximal voltage, 0.8 ms pulses, 5 s train duration, 0.5-35 Hz) of rabbit and human corpus cavernosum preparations contracted by noradrenaline (rabbit 10(-5) M, man 3 x 10(-6) M) or endothelin-1 (rabbit 10(-8) M) produced relaxations that were sensitive to tetrodotoxin (10(-6) M), and dependent on the frequency and number of pulses delivered. L-NOARG (10(-6)-10(-4) M), but not NG-nitro-D-arginine (D-NOARG, 10(-6)-10(-4) M), inhibited electrically induced relaxations in a concentration-dependent manner, and at 10(-4) M the relaxations were virtually abolished. L-Arginine (10(-3) M), but not D-arginine (10(-3) M), partly reversed the inhibitory effect of L-NOARG (10(-4) M). In rabbit corpus cavernosum preparations, as with Methylene Blue (3 x 10(-5) M), an inhibitor of the soluble guanylate cyclase, and haemoglobin (10(-5) M), sequestering NO in the extracellular space, significantly reduced electrically evoked relaxations. Scopolamine (10(-6) M) had little or no effect on relaxations induced by electrical field stimulation. 3. Preparations of rabbit and human corpus cavernosum contracted by noradrenaline (rabbit 10(-5) M, man 3 x 10(-6) M) were relaxed by carbachol (10(-9)-10(-4) M) in a concentration-dependent manner. Scopolamine (10(-6) M) and L-NOARG (10(-4) M) abolished, and Methylene Blue (3 x 10(-5) M) and haemoglobin (10(-5) M) greatly reduced, the carbachol-induced relaxation, while D-NOARG (10(-4) M) had no significant effect. 4. In rabbit corpus cavernosum preparations contracted by noradrenaline (10(-5) M), L-NOARG (10(-4) M) had no significant effect on relaxations induced by vasoactive intestinal polypeptide (10(-6) M). 5. SIN-1 (3-morpholino-sydnonimin hydrochloride, 10(-8)-3 x 10(-4) M), which spontaneously liberates NO, relaxed preparations of rabbit and human corpus cavernosum contracted by noradrenaline (rabbit 10(-5) M, man 3 x 10(-6) M) or endothelin-1 (rabbit 10(-8) M, man 3 x 10(-9) M) in a concentration-dependent way.(ABSTRACT TRUNCATED AT 400 WORDS)

Vasoactive intestinal polypeptide (VIP) and peptide histidine methionine (PHM) in human penile corpus cavernosum tissue and circumflex veins: localization and in vitro effects.

Localization and functional effects of vasoactive intestinal polypeptide (VIP) and peptide histidine methionine (PHM), two peptides derived from a common precursor molecule, were investigated in isolated preparations from human penile corpus cavernosum (CC) and circumflex vein (CV). VIP- and PHM-immunoreactivity (IR) was demonstrated in both CC and CV. The concentrations of VIP-IR and PHM-IR in CC tissue were 54.4 +/- 15.3, and 42.0 +/- 7.5 pmol g-1 wet weight respectively with a VIP/PHM ratio of 1.5 +/- 0.4 (mean +/- SEM). The corresponding values for CV tissues were 28.0 +/- 7.7 and 9.6 +/- 2.6 pmol g-1 wet weight with a VIP/PHM ratio of 3.1 +/- 0.4. CC and CV displayed VIP- and PHM-IR confined to nerve fibres in close relation to bundles of smooth muscle cells and blood vessels in both tissues. In vitro, VIP and PHM had no effects in unstimulated tissue preparations. Both peptides concentration-dependently (10(-9)-10(-6) M) relaxed CC and CV preparations precontracted with 3 x 10(-6) M noradrenaline. In CC the maximum relaxant effect of VIP and PHM was 22 +/- 11% and 9 +/- 9% and in CV the corresponding values were 82 +/- 8% and 93 +/- 3% respectively. The present study supports the hypothesis of VIP and PHM as neurotransmitters and/or neuromodulators in the nervous control of penile erection.

Effects of the nitric oxide synthase inhibitor NG-nitro-L-arginine on the erectile response to cavernous nerve stimulation in the rabbit.

Using a rabbit model, the involvement of the L-arginine/nitric oxide pathway in penile erection was investigated. The mean basal intracavernous pressure was 21 cm H2O. Cavernous nerve stimulation (4-8 V, 20-30 Hz) increased the pressure to approximately 130 cm H2O. This response was highly reproducible and usually associated with full penile erection. The pressure increase could be quantified in terms of: (1) the slope of the initial, ascending part of the pressure increase; (2) delta P, which was defined as the maximal pressure obtained by the stimulation minus the basal pressure before the stimulation; (3) T90, which was defined as the time to reach 90 per cent of delta P. Intrapenile administration of the L-arginine/nitric oxide synthesis inhibitor NG-nitro-L-arginine had no effect on systemic arterial blood pressure. However, NG-nitro-L-arginine (0.22 and 2.19 mg), administered via the same route, abolished the erectile response induced by cavernous nerve stimulation; T90 increased and slope and delta P decreased significantly. NG-nitro-D-arginine (2.19), on the other hand, had no inhibitory effect. L-arginine (21.07 mg), given either directly or after NG-nitro-L-arginine had no consistent effect on the functional response to cavernous nerve stimulation. The results suggest that pharmacologically induced effects on intracavernous pressure in the rabbit can be described quantitatively, and that this model may be useful to study the mechanisms controlling penile erection in vivo. The pronounced inhibitory action of NG-nitro-L-arginine demonstrates the important role of the arginine/nitric oxide pathway in mediating relaxation of penile smooth muscles necessary for erection.

Studies on binding sites, contents, and effects of AVP in isolated bladder and urethra from rabbits and humans.

The binding sites, contents, and effects of arginine vasopressin (AVP) were studied in isolated bladder and urethral preparations from rabbits and humans. In all tissues, higher levels of AVP-like immunoreactivity (AVP-LI) were detected than those normally found in plasma. Radioligand membrane binding studies using [3H]AVP as the ligand revealed the existence of a single population of binding sites in the rabbit bladder, and displacement experiments indicated that the receptor was of the V1 subtype. By autoradiography, [3H]AVP binding sites in the rabbit bladder were shown to be located on both circularly and longitudinally oriented smooth muscle cells, as well as in the submucosa at the part adjacent to the urothelium. In the rabbit urethra, the binding sites were confined mainly to the circular smooth muscle layer. Neither radioligand membrane binding studies nor autoradiography revealed any specific [3H]AVP binding sites in the human bladder. AVP contracted rabbit bladder and urethral preparations concentration dependently. The contractions were inhibited by the V1-receptor selective antagonist A16 in a noncompetitive manner. However, A16 had no effects on contractions elicited by electrical-field stimulation. In preparations of the human bladder and urethra, AVP in concentrations up to 10(-5) M did not have any contractile effects. These results suggest that in the rabbit and human lower urinary tract, AVP-LI is synthesized locally and/or extracted from the circulation. It is unlikely that AVP is directly involved in the neurotransmission in these tissues, although in the rabbit bladder and urethra a modulatory role cannot be excluded.

Muscarinic receptor stimulation of phosphoinositide hydrolysis in the human isolated urinary bladder.

The stimulatory action of carbachol and acetylcholine (ACh) on phosphoinositide turnover, as well as their contractile effects, were investigated in human isolated detrusor muscle. Carbachol, and ACh in combination with 10(-7) M physostigmine, induced increases in phosphoinositide turnover. However, at all the concentrations tested, carbachol was more effective than ACh (plus physostigmine), and at the highest concentration used (10(-4) M), the difference was significant (p less than 0.05). Also in a Ca(2+)-free medium containing the chelator EGTA (10(-4) M), both agonists (10(-4) M) induced small but distinct increases in phosphoinositide breakdown. Carbachol and ACh contracted the detrusor preparations concentration-dependently, and the responses were almost identical when ACh was combined with 10(-7) M physostigmine. In Ca(2+)-free medium the agonists elicited a moderate but concentration-dependent contractile response at high concentrations. The results show that muscarinic receptor agonists stimulate phosphoinositide turnover in the human bladder. Possibly, this effect is coupled to multiple muscarinic receptor subtypes. More studies are required to elucidate to what extent phosphoinositide breakdown participates in the contractile activation of this tissue.

Pre- and postjunctional effects of some prostanoids in human isolated vas deferens.

The effects of prostaglandin (PG) E1, PGE2, the thromboxane A2 analogue U-44069, and the prostacyclin derivative iloprost were studied on isometric contractions induced by norepinephrine (NE) and by electrical field stimulation of nerves in isolated preparations of the human vas deferens. The effects of these agents on the electrically induced release of 3H from preparations preincubated with [3H]NE were also investigated. PGE1 and PGE2 inhibited the electrically induced contractions concentration dependently. U-44069 augmented the contractions without affecting baseline tension, and in preparations where the contractions had been inhibited by PGE1 or PGE2, U-44069 restored the contractions almost to starting levels. The thromboxane A2-receptor antagonist BM 13505, having no effect or inhibitory effects on electrically induced contractions, abolished the stimulatory effect of U-44069. Contractions induced by exogenous NE were augmented by U-44069, whereas PGE1 and BM 13505 were without effects. The electrically induced release of 3H was inhibited by PGE1 and PGE2 in a concentration-dependent manner, whereas U-44069 and BM 13505 increased the release of 3H. Furthermore, the inhibitory effect of PGE1 on 3H release was partly counteracted by U-44069. Iloprost had no significant effect on electrically induced contractions or on 3H release. These results suggest that, in the human vas deferens, thromboxane A2 augments contractions predominantly through a postjunctional site of action, whereas PGs of the E type have a prejunctional inhibitory effect. In addition, the pre- and post-junctional effect profiles of U-44069 and BM 13505 suggest that there may be more than one thromboxane receptor.