Role of leptin in the control of postprandial pancreatic enzyme secretion.

Leptin released by adipocytes has been implicated in the control of food intake but recent detection of specific leptin receptors in the pancreas suggests that this peptide may also play some role in the modulation of pancreatic function. This study was undertaken to examine the effect of exogenous leptin on pancreatic enzyme secretion in vitro using isolated pancreatic acini, or in vivo in conscious rats with chronic pancreatic fistulae. Leptin plasma level was measured by radioimmunoassay following leptin administration to the animals. Intraperitoneal (i.p.) administration of leptin (0.1, 1, 5, 10, 20 or 50 microg/kg), failed to affect significantly basal secretion of pancreatic protein, but markedly reduced that stimulated by feeding. The strongest inhibition has been observed at dose of 10 microg/kg of leptin. Under basal conditions plasma leptin level averaged about 0.15 +/- 0.04 ng/ml and was increased by feeding up to 1.8 +/- 0.4 ng/ml. Administration of leptin dose-dependently augmented this plasma leptin level, reaching about 0.65 +/- 0.04 ng/ml at dose of 10 microg/kg of leptin. This dose of leptin completely abolished increase of pancreatic protein output produced by ordinary feeding, sham feeding or by diversion of pancreatic juice to the exterior. Leptin (10(-10)-10(-7) M) also dose-dependently attenuated caerulein-induced amylase release from isolated pancreatic acini, whereas basal enzyme secretion was unaffected. We conclude that leptin could take a part in the inhibition of postprandial pancreatic secretion and this effect could be related, at least in part, to the direct action of this peptide on pancreatic acini.

The effects of ammonia on pancreatic enzyme secretion in vivo and in vitro.

BACKGROUND: Recent studies clearly demonstrate that Helicobacter pylori (H. pylori) infection of the stomach causes persistent elevation of ammonia (NH3) in gastric juice leading to hypergastrinemia and enhanced pancreatic enzyme secretion. METHODS: The aim of this study is to evaluate the influence of NH4OH on plasma gastrin level and exocrine pancreatic secretion in vivo in conscious dogs equipped with chronic pancreatic fistulas and on secretory activity of in vitro isolated acini obtained from the rat pancreas by collagenase digestion. The effects of NH4OH on amylase release from pancreatic acini were compared with those produced by simple alkalization of these acini with NaOH. RESULTS: NH4OH given intraduodenally (i.d.) in increasing concentrations (0.5, 1.0, 2.0, 4.0, or 8.0 mM/L) resulted in an increase of pancreatic protein output, reaching respectively 9%, 10%, 19%, 16% and 17% of caerulein maximum in these animals and in a marked increase in plasma gastrin level. NH4OH (8 x 0 mM/L, i.d.) given during intravenous (i.v.) infusion of secretin (50 pmol/kg-h) and cholecystokinin (50 pmol/kg-h) reduced the HCO3 and protein outputs by 35% and 37% respectively, as compared to control obtained with infusion of secretin plus cholecystokinin alone. When pancreatic secretion was stimulated by ordinary feeding the same amount of NH4OH administered i.d. decreased the HCO3- and protein responses by 78% and 47% respectively, and had no significant effect on postprandial plasma gastrin. In isolated pancreatic acini, increasing concentrations of NH4OH (10(-7)-10(-4) M) produced a concentration-dependent stimulation of amylase release, reaching about 43% of caerulein-induced maximum. When various concentrations of NH4OH were added to submaximal concentration of caerulein (10(-12) M) or urecholine (10(-5) M), the enzyme secretion was reduced at a dose 10(-5) M of NH4OH by 38% or 40%, respectively. Simple alkalization with NaOH of the incubation medium up to pH 8.5 markedly stimulated basal amylase secretion from isolated pancreatic acini, whereas the secretory response of these acini to pancreatic secretagogues was significantly diminished by about 30%. LDH release into the incubation medium was not significantly changed in all tests indicating that NH4OH did not produce any apparent damage of pancreatic acini and this was confirmed by histological examination of these acini. CONCLUSIONS: 1. NH4OH affects basal and stimulated pancreatic secretion. 2. The excessive release of gastrin may be responsible for the stimulation of basal pancreatic enzyme secretion in conscious animals, and 3. The inhibitory effects of NH4OH on stimulated secretion might be mediated, at least in part, by its direct action on the isolated pancreatic acini possibly due to the alkalization of these acini.

Evaluation of the role of neurolinins and urecholine hypersensitivity in an animal model of infravesical outflow obstruction.

OBJECTIVES: To determine whether detrusor muscle strips from a male rat with infravesical outflow obstruction model demonstrate supersensitivity to parasympathomimetic and neurokinin NK-1 and NK-2 selective agonists. METHODS: Bladder instability developed after 6 weeks of partial urethral obstruction. The micturition frequency and voided volume were determined in unanesthetized animals. Detrusor hypertrophy was confirmed by evaluation of bladder weight. In vitro organ bath was used to compare the affinity and maximal activity of bethanechol and neurokinin NK-1 and NK-2 selective agonists on strips from the detrusor muscle of sham and obstructed rats. Bethanechol, N-Ac[Arg6, Sar9, Met(O2)]-SP(6-11), and [beta-Ala8]-NKA(4-10) were used to characterize cholinergic muscarinic, neurokinin NK-1 and NK-2 receptors. Results. No significant differences in affinities and maximal responses were found using 10-mg detrusor muscle strips with each of the three agonists. CONCLUSIONS: Bladder instability produced by outlet obstruction does not involve changes in the affinity or maximal activity of cholinergic muscarinic, neurokinin NK-1 and NK-2 receptors. Furthermore, detrusor supersensitivity to neurokinins or bethanechol was not seen. This suggests that bladder instability is not due to an increased affinity or maximal response to neurokinins or parasympathomimetics.

The role of CGRP and afferent nerves in the modulation of pancreatic enzyme secretion in the rat.

CONCLUSION: Stimulation of pancreatic sensory nerves by capsaicin produced secretory effects probably caused, at least in part, by the release of CGRP. BACKGROUND: In the pancreas calcitonin gene-related peptide (CGRP) has been localized in the sensory nerves, but its physiological role is unknown. This study was undertaken to compare the changes of pancreatic enzyme secretion produced by CGRP and by stimulation or destruction of sensory nerves. METHODS: To stimulate sensory nerves, low doses of capsaicin (0.25-0.5 mg/kg) were given intraduodenally to the conscious rats with chronic pancreatic fistula. To inactivate sensory nerves high doses of capsaicin (100 mg/kg) were given subcutaneously 10 d before tests. For the in vitro experiments pancreatic slices and isolated pancreatic acini were prepared from intact and capsaicin-denervated rats. RESULTS: In conscious rats, CGRP given subcutaneously (5-10 micrograms/kg) and low doses of capsaicin given intraduodenally reduced basal pancreatic secretion. In isolated pancreatic acini, CGRP (10(-10)-10(-6) M), but not capsaicin, increased basal or secretagog-stimulated amylase release. In pancreatic slices (containing nerve fibers) capsaicin (10(-10)-10(-6) M) increased enzyme secretion, and this secretion was abolished by previous inactivation of sensory nerves by this neurotoxin. Capsaicin deactivation did not affect the secretory response of pancreatic acini to CGRP, cerulein, or urecholine. Sensory denervation by capsaicin did not change basal protein secretion, but reduced that produced by feeding or diversion of pancreatic juice to the exterior during first 2 h of the tests.

Potentiation by baclofen of gastric acid secretion stimulated by secretagogues in vagotomized rats under anesthesia.

The effect of intravenous administration of baclofen, a GABA(B) receptor agonist, on gastric acid secretion from perfused stomach was studied in vagotomized rats anesthetized with urethane. Baclofen did not stimulate acid secretion by itself. In contrast, baclofen dose-dependently potentiated acid secretion induced by pentagastrin, bethanechol and direct vagal stimulation, but not by histamine. Baclofen-potentiated acid secretion induced by pentagastrin and bethanechol was not influenced by pretreatment with atropine or cimetidine, respectively. Baclofen-potentiated acid secretion evoked by direct vagal stimulation was prevented by pretreatment with proglumide which is a gastrin receptor antagonist. Baclofen-potentiated acid secretion evoked by bethanechol was partly prevented by bicuculline methiodide which is a GABA(A) receptor antagonist, but not by phaclofen which is a GABA(B) receptor antagonist, suggesting an involvement of peripheral GABA(A) receptors. Baclofen-potentiated acid secretion induced by direct vagal stimulation was not affected by the change of body temperature. These results suggest that baclofen stimulates acid secretion under certain conditions, and that two mechanisms are involved in this effect. The effects of baclofen on acid secretion may be mediated by increasing the release of histamine by pentagastrin, bethanechol and direct vagal stimulation. In addition, baclofen would also be effective if muscarinic agents were already occupying muscarinic acetylcholine receptors on parietal cells.

Role of endogenous nitric oxide in the control of exocrine and endocrine pancreatic secretion.

L-Arginine (L-Arg), that is a substrate for nitric oxide (NO) synthase, stimulates the release of pancreatic islet hormones but the mechanism of this stimulation is unknown. The aim of this study was to determine the role of NO in the control of endocrine and exocrine pancreatic secretion in response to sham feeding (SF), ordinary meat feeding (F), duodenal perfusion with nutrients and i.v. infusion of gastrin releasing peptide (GRP) or urecholine in conscious dogs with chronic pancreatic fistulas. SF1 F, duodenal nutrient and GRP and urecholine resulted in the stimulation of pancreatic secretion reaching, respectively, 50%, 50%, 40%, 85% and 20% of maximal response to caerulein (200 pmol/kg-h i.v.). Infusion of L-Arg (50 mg/kg + 5 mg/kg-h i.v.) almost doubled the basal pancreatic protein secretion and significantly increased the secretory response to SF, F, and duodenal nutrient. After i.v. administration of L-NNA (2.5 mg/kg + 0.5 mg/kg-h), an inhibitor of NO synthase, the pancreatic secretory responses to SF, F, duodenal nutrient, GRP and urecholine were significantly inhibited by about 74%, 70%, 70%, 80% and 30%, respectively. When L-Arg was combined with L-NNA, the reduction in pancreatic secretion induced by L-NNA was significantly attenuated. SF resulted in a marked rise in plasma insulin and glucagon and this response was completely abolished by L-NNA infusion. Insulin and glucagon levels were 2-3 folds increased by F and L-NNA infusion inhibited these responses while the addition of L-Arg partly reversed this inhibition. Duodenal nutrient produced several fold increase in plasma insulin and glucagon levels that were significantly reduced by L-NNA and this reduction was partially reversed by L-Arg. GRP also caused moderate rise in plasma insulin and glucagon levels which were significantly reduced by L-NNA and this was partially restored by L-Arg. We conclude that SF, F, duodenal nutrient, GRP or urecholine stimulate both the exocrine and endocrine pancreatic secretion and that these effects are mediated, at least in part, through the NO pathway.

Influence of strip size and location on contractile responses of rat urinary bladder body strips.

1. We investigated the influence of strip length and dorsal or ventral location of rat urinary bladder strips on contractile responsiveness. 2. No differences occurred in the contractile responses of 0.5, 1.0 and 2.0 cm strips to field stimulation, carbachol, ATP, substance P or to KCl when the data were expressed as either absolute tension or as tension per cross-sectional area. However, correction for strip mass resulted in significant decreases in the contractile responses of the 2.0-cm strips compared with the 0.5-cm strips. 3. No differences occurred in length-tension curves for ventral and dorsal bladder strips, even though the strips from the dorsal surface appeared thinner than those from the ventral surface. 4. Strips from the ventral surface exhibited more variability in response to field stimulation and were less sensitive to atropine pre-treatment than were those from the dorsal surface. They were also less sensitive to the contractile effects of carbachol than dorsal strips. Dorsal and ventral strips were equally responsive to ATP, substance P and KCl. 5. Our data indicate that the contractile responsiveness of rat urinary bladder strips is independent of strip length. Although there are some differences between the cholinergic responsiveness of strips from the ventral and dorsal surfaces of the bladder, the differences are so small that for most studies they will probably have no influence on data interpretation.

The involvement of endogenous nitric oxide in vagal-cholinergic stimulation of exocrine and endocrine pancreas in dogs.

Previous studies showed that nitric oxide (NO), synthesized from L-arginine (L-arg) by NO synthase (NOS) in vascular epithelium and nerve terminals, affects exocrine pancreatic secretion, but its role in control of endocrine pancreas has not been studied. In this study, the role of NO in the control of pancreatic secretion in response to vagal-cholinergic stimulation and duodenal infusion of nutrients was determined in conscious dogs with chronic pancreatic fistulas. Sham feeding (SF), urecholine iv infusion, and duodenal perfusion with nutrients were used to stimulate the pancreatic protein secretion, and insulin and glucagon release in tests without and with iv infusion of NG-nitro-L-arginine (L-NNA), an inhibitor of NO synthase, L-arg, a substrate of NOS, or their combination was used. SF, urecholine, and duodenal nutrient resulted in the stimulation of pancreatic protein secretion reaching, respectively, 50, 20, and 42% of cerulein maximum. Infusion of L-arg almost doubled the basal protein secretion and tended to increase the secretory response to SF and duodenal nutrient. After infusion of L-NNA, the pancreatic secretory responses to SF, urecholine, and duodenal nutrient were inhibited by about 70, 30, and 75%, respectively. When L-arg was combined with L-NNA, the reduction in pancreatic secretion by L-NNA was significantly attenuated. SF resulted in a significant rise in plasma insulin and glucagon, and this response was completely abolished by L-NNA infusion. Urecholine and duodenal nutrient also resulted in a marked increment in plasma insulin and glucagon, the insulin (but not glucagon) increment being abolished by the pretreatment with L-NNA and reversed by the addition of L-arg.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of CGRP antagonist, alpha-CGRP 8-37, on acid secretion in the dog.

The recently synthesized calcitonin gene-related peptide (CGRP) antagonist, human alpha-CGRP 8-37, was used to study its effects on gastric acid secretion. Four dogs with gastric fistula were used to measure the antagonist's physiologic effects in the stomach. All dogs received a bactopeptone dextrose meal (intragastric titration to pH 5.5) with either continuous CGRP 8-37 (1000 pmol/kg/hr) or saline (control). Additionally, intravenous bombesin (75-600 ng/kg/hr) and bethanechol (12.5-100 micrograms/kg/hr) was tested in the presence of the antagonist. Plasma gastrin levels also were measured via radioimmunoassay (RIA) in control and CGRP 8-37-stimulated animals. Gastric acid secretion increased by 100% with infusion of 1000 pmol/kg/hr CGRP 8-37 when compared to the control. Acid output increased 98% with both intravenous antagonist and 600 ng/kg/hr bombesin when compared to bombesin alone. However, no augmentation of acid secretion by CGRP 8-37 was shown with 25 micrograms/kg/hr bethanechol. RIA of plasma gastrin demonstrated no effect with the antagonist when given alone and did not increase bombesin-stimulated gastrin release. We conclude that CGRP 8-37 blocks native CGRP inhibitory effects on gastric acid secretion. Our findings of potentiation of acid secretion by bombesin as well as no change in gastrin levels in the presence of the antagonist is likely due to a blockage in a noncholinergic neuron to the somatostatin cell. Furthermore, CGRP 8-37 did not increase bethanechol-stimulated acid secretion, most likely due to bethanechol's (acetylcholine) nearly ubiquitous positive effects on acid secretion.

A clinical trial of bethanechol in patients with xerostomia after radiation therapy. A pilot study.

The effects of bethanechol in the treatment of dry mouth were assessed in patients with xerostomia after radiation therapy to the head and neck. Bethanechol possesses muscarinic and nicotinic-cholinergic activity that likely accounts for its mode of action. Bethanechol (25 mg, three times daily) was not associated with significant side effects. Statistically significant increases in whole resting saliva (p = 0.003) and whole stimulated saliva (p = 0.001) were seen. In patients with pretreatment stimulated saliva volumes greater than resting saliva volumes, a positive response to subsequent use of the sialagogue was seen.

Differential effects of Na+, K(+)-ATPase inhibition by ouabain on acid secretory responses to histamine and bethanechol in the mouse isolated stomach.

1. The effect of Na+,K(+)-ATPase inhibition by ouabain on gastric acid secretion was studied in the mouse isolated whole stomach preparation. 2. Ouabain caused a transient enhancement of histamine-induced gastric acid secretion followed by an inhibitory phase. On the other hand, ouabain caused a rapid reduction of bethanechol-stimulated acid secretion without an enhancement phase. 3. In dibutyryl cyclic AMP-induced acid secretion, ouabain led to a transient increase in acid secretion followed by a fall, as was seen with the histamine stimulation. Ouabain caused a rapid reduction of A23187-induced acid secretion. 4. Ouabain by itself increased basal acid secretion, and thereafter slowly suppressed the acid secretion. 5. Atropine inhibited both the ouabain-induced enhancement of the stimulated gastric acid secretion and the ouabain-induced stimulation of basal acid secretion. 6. The present study showed that Na+,K(+)-ATPase inhibition by ouabain caused a phasic enhancement of the stimulated gastric acid secretion through release of endogenous acetylcholine when the secretagogues act via an intracellular cyclic AMP pathway. It also inhibited the stimulated acid secretion irrespective of secretagogues, probably through its inhibitory effect on Na+,K(+)-ATPase in the gastric parietal cell.

Ventricular arrhythmias induced by chemically modified intrinsic cardiac neurones.

OBJECTIVE: The aim was to investigate whether intrinsic cardiac neurones can be involved in the genesis of ventricular arrhythmias. METHODS: Nicotinic, muscarinic, beta adrenergic, peptidergic, and amino acidergic agonists, as well as purinergic compounds, were individually administered in microliter quantities adjacent to spontaneously active in situ right atrial neurones in 57 anaesthetised dogs before and after acute decentralisation. RESULTS: Ventricular arrhythmias were induced in one third of the dogs following neurochemical administration. Ventricular arrhythmias are induced much less frequently when intrathoracic extracardiac neurones are modified chemically. Salvos of ventricular premature contractions or ventricular tachycardias were elicited when intrinsic cardiac neurones were modified locally applied nicotine, bethanechol, isoprenaline, angiotensin II, bradykinin, substance P, vasoactive intestinal polypeptide, glutamate, or adenosine. In 60% of those instances in which intrinsic cardiac neuronal activity was modified by a neurochemical, ventricular arrhythmias were elicited. When arrhythmias were induced, activity generated by chemically modified intrinsic cardiac neurones increased from 0.7(SD 0.2) to 2.2(0.4) impulses.s-1 (p < 0.05). Following decentralisation of the intrinsic cardiac nervous system, repeat administration of the same neurochemicals into the same loci elicited ventricular arrhythmias in 42% of those dogs in which ventricular arrhythmias had been elicited previously. Neuronal activity increased [0.8(0.5) to 2.1(0.6) impulses.s-1; p < 0.05] in 86% of these instances. CONCLUSIONS: Intrinsic cardiac neurones can be involved in the genesis of ventricular arrhythmias.

Pharmacological profile of (R)-1-[2,3-dihydro-1-(2'-methylphenacyl)-2-oxo- 5-phenyl-1H-1,4-benzodiazepin-3-yl]-3-(3-methylphenyl)urea (YM022), a new potent and selective gastrin/cholecystokinin-B receptor antagonist, in vitro and in vivo.

(R)-1-[2,3-dihydro-1-(2'-methylphenacyl)-2-oxo-5-phenyl-1H-1,4- benzodiazepin-3-yl]-3-(3-methylphenyl)urea (YM022) is an extremely potent and highly selective gastrin/cholecystokinin (CCK)-B receptor antagonist. We compared the gastrin/CCK-B receptor-blocking properties of this compound with those of the racemate (mixture of YM022 and its S-form), its enantiomer (S-form), L-365, 260 and Cl-988 in vitro and in vivo. YM022 replaced specific binding of [125I]CCK-8 to rat brain gastrin/CCK-B receptors in a stereoselective and competitive manner. The Ki value of YM022 for gastrin/CCK-B receptors in brain were estimated to be 0.068 nM. The racemate, the S-form of YM022, L-365,260 and Cl-988 also replaced gastrin/CCK-B receptor binding, with Ki values of 0.11, 140, 19 and 6.3 nM, respectively. The affinity of YM022 for gastrin/CCK-B receptor was more than 2 orders of magnitude higher than that for rat pancreatic CCK-A receptor and various other receptors, such as benzodiazepine. In vivo, intravenous (i.v.) administration of YM022 inhibited pentagastrin-induced gastric acid secretion in anesthetized rats, with an ED50 value of 0.0078 mumol/kg. Inhibition by the S-form of YM022 was only 33.8% even at the relatively high dose of 1 mumol/kg i.v. L-365,260 (1-10 mumol/kg i.v.) and Cl-988 (0.3-3 mumol/kg i.v.) also antagonized acid secretion induced by pentagastrin, with ED50 values of 4.23 and 1.01 mumol/kg, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cholinergic stimulation and aldosterone administration on salivary parotid secretion in the brushtail possum, Trichosurus vulpecula.

Parotid salivation was stimulated by infusion of bethanechol chloride into anaesthetized brushtail possums to ascertain maximal flow rates, salivary composition and dietary adaptations of salivary function. Secretion rates for one gland ranged from 5.3 +/- 0.16 to 84.3 +/- 3.20 microliters/min (2.4 +/- 0.07 to 37.8 +/- 1.43 microliters/min per kg body weight). Salivary osmolality (160.8 +/- 15.39 to 248.2 +/- 8.70 mosmol/kg) and the concentrations of Na (63.1 +/- 10.93 to 124.1 +/- 5.52 mmol/l) and HCO3 (19.5 +/- 3.41 to 89.0 +/- 3.19 mmol/l) were positively correlated with flow rate. The concentrations of urea (7.8 +/- 0.64 to 4.6 +/- 0.33 mmol/l), PO4 (2.6 +/- 0.25 to 0.96 +/- 0.10 mmol/l), H+ (46.2 +/- 16.30 to 9.0 +/- 1.51 nequiv/l), K (21.4 +/- 3.73 to 13.7 +/- 2.33 mmol/l), Ca (3.7 +/- 0.53 to 2.2 +/- 0.27 mmol/l) and Mg (0.3 +/- 0.07 to 0.04 +/- 0.007 mmol/l) fell with increasing flow rate. The relations between flow rate and amylase activity (22.6 +/- 10.47 to 10.5 +/- 3.68 mu kat/l), protein concentration (2.7 +/- 0.61 to 1.3 +/- 0.28 g/l), and Cl concentration (62.1 +/- 6.88 to 50.6 +/- 6.37 mmol/l) were inconsistent between experiments. Salivary Na/K ratios were not decreased by infusion of aldosterone (2.2-22.2 nmol/h for 5 h), showing that the gland of Na-replete possums is unresponsive to short-term increases in mineralocorticoids. The low salivary amylase activity, less than that of kangaroos, presumably reflects the interaction of evolutionary history of the possum with its natural low-starch diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative pharmacology of the male and female rabbit bladder neck and urethra: involvement of nitric oxide.

The present study compared the contractile and relaxant responses of male and female rabbit bladder neck and urethra to field stimulation (FS) and various contractile and relaxant agents, with special attention paid to the involvement of nitric oxide (NO) in the mediation of field-stimulated relaxation. FS at basal tension elicited a frequency-dependent contractile response in all preparations. The maximal response to high frequency FS was significantly greater in the bladder neck strips isolated from male rabbits than in those from female rabbits. There were no significant differences in the response to bethanechol or phenylephrine between strips isolated from males and females. Field-stimulated responses of the strips from male bladder neck and urethra were greater than the response to phenylephrine. The responses of all strips to FS were greater than those to bethanechol. In addition, the response to phenylephrine was generally greater than that to bethanechol. Phentolamine was a significantly more effective inhibitor of the response of the female bladder neck and urethral strips to FS than of the response of the male strips. The contractile response of all strips to phenylephrine was generally greater than that to bethanechol for both sexes and for both bladder neck and urethral strips. NG-nitro-L-arginine methylester (L-NAME) inhibited totally the field-stimulated relaxation of all strips. Isoproterenol stimulated a slowly developing but significant inhibition of phenylephrine prestimulated contractions. In conclusion, significant differences exist in the magnitude of field-stimulated relaxation between the bladder neck and urethra of both male and female rabbits, and, for all tissues, field-stimulated relaxation could be completely inhibited by pretreatment with L-NAME, an NO synthesis inhibitor.

Comparative studies on the ontogeny and autonomic responses of the fetal calf bladder at different stages of development: involvement of nitric oxide on field stimulated relaxation.

This initial study correlates the passive length-tension relationship, contractile and relaxant responses to field stimulation and contractile responses to specific autonomic agonists and antagonists with gestational age. Fetal bovine bladders were separated into three groups based on the head-rump length (FL): 30 to 45 cm. (early gestation), 50 to 65 cm. (middle gestation) and 70 to 85 cm. (late gestation). Each bladder was separated into upper and lower bladder segments; longitudinal strips of smooth muscle were isolated and placed in individual muscle baths. Passive length-tension studies demonstrated that compliance was greatest in the bladder of late gestation and lowest in the bladder of early gestation period. Field stimulation (FS) elicited frequency-dependent contractile responses in all strips. In the upper bladder, the maximal response and maximal rate of tension generation to FS was lowest in the youngest fetuses and increased in proportion to the gestational age. In the lower bladders, there were no gestational age-related differences in the maximal response or maximal rate of tension generation in response to field stimulation. The maximal response of the upper bladder to bethanechol increased significantly from the youngest gestational age to mid-gestation, with no further changes between mid- and late gestation. The maximal response to field stimulation and bethanechol were equal between upper and lower bladder segments for the youngest gestational bladders, whereas for the oldest gestational ages, the maximal response of the upper bladder to FS and bethanechol were significantly greater than the responses of the lower bladder. In the presence of maximal precontraction with bethanechol, FS induced a rapid and marked decrease in tension. The magnitude of the relaxation was substantially greater for the strips of lower bladder than for the strips of upper bladder at late gestation. In lower bladders, the magnitude of the field stimulated relaxation was greater in the strips from the older fetuses than in the strips from younger fetuses. In all strips, field stimulated relaxations were completely inhibited by pretreatment with L-NAME (an inhibitor of nitric oxide synthesis), indicating that the FS-induced relaxation was due to nitric oxide. In addition to nitric oxide-induced relaxation, beta adrenergic stimulation also induced a significant relaxation of the isolated strips. In summary, these data suggest that, in the tubular shaped fetal bovine bladder, there were distinct differences in the autonomic responses between the upper bladder segment and the lower bladder segment in the late gestation period.

Parasympathetic innervation of rat peri-orbital smooth muscle: prejunctional cholinergic inhibition of sympathetic neurotransmission without direct postjunctional actions.

The role of parasympathetic neurotransmission in regulating periorbital smooth muscle function was investigated in urethane-anesthetized rats. Parasympathetic nerves were activated by stereotaxic electrical stimulation (20 Hz, < or = 2.0 V) of the ipsilateral superior salivatory nucleus, which gives rise to preganglionic innervation to the pterygopalatine ganglion and hence to the orbital targets. This approach permits selective parasympathetic activation that cannot be attained at more peripheral sites. Target responses were measured by recording changes in tarsal smooth muscle tension from the superior eyelid. Parasympathetic stimulation caused a small decrease in resting tension (-73 +/- 4 mg) that was not altered when the muscle was partially contracted with methoxamine. However, adrenoceptor-mediated contraction induced by cervical sympathetic nerve stimulation was attenuated in a frequency-dependent manner, with inhibition greatest at higher sympathetic stimulation frequencies (-338 +/- 35 mg at 8 Hz). This attenuation was blocked by the muscarinic receptor antagonist atropine methyl nitrate. Administration of the muscarinic agonist bethanechol increased resting tarsal muscle tension (655 +/- 34 mg). However, sympathetically mediated contraction at 2 Hz (1295 +/- 53 mg) was decreased by bethanechol administration to a value (710 +/- 37 mg) not significantly different from the contraction caused by bethanechol alone. We conclude that muscarinic receptors are present on tarsal smooth muscle, where they elicit contractions, and on sympathetic nerves, where they inhibit neurotransmission presumably by depressing noradrenaline release.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of direct and indirect acetylcholine receptor agonists on growth hormone secretion in humans.

Cholinergic pathways in the central nervous system positively influence growth hormone (GH) secretion. In fact pyridostigmine, a cholinesterase inhibitor, enhances both basal and GH-releasing hormone (GHRH)-induced GH secretion while, conversely, pirenzepine, an antagonist of muscarinic M1 receptors, inhibits the GH response to GHRH and to other physiological and pharmacological stimuli. The effect of the cholinergic system on GH secretion probably takes place via inhibition of the release of endogenous somatostatin. In this study in 36 normal adults (26 males and 10 females, age 22-35 years) we compared the effects of three cholinesterase inhibitors (pyridostigmine, 120 mg p.o., n = 19; neostigmine, 10 micrograms/kg i.v., n = 6; physostigmine, 12.5 micrograms/kg i.v., n = 6) and bethanechol, a direct muscarinic receptor agonist that is mainly active on muscarinic M3 receptors (25 micrograms/kg i.v., n = 5), on both basal and GHRH (1 microgram/kg i.v.)-stimulated GH secretion. Pyridostigmine, neostigmine and physostigmine induced a significant GH increase (peak vs. basal levels, mean +/- S.E.: 10.4 +/- 1.6 vs. 0.6 +/- 0.2 micrograms/l, P = 0.0001; 13.3 +/- 1.2 vs. 0.5 +/- 1.1 micrograms/l, P = 0.004; and 14.9 +/- 3.1 vs. 2.7 +/- 1.1 micrograms/l, P = 0.025;, respectively). These drugs also induced a similar potentiation of the GH response to GHRH (peak: 48.3 +/- 5.6 vs. 16.2 +/- 2.2 micrograms/l, P = 0.0001; 49.2 +/- 2.2 vs. 19.9 +/- 5.1 micrograms/l, P = 0.006; and 76.9 +/- 12.4 vs. 18.1 +/- 5.3 micrograms/l, P = 0.001, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)