Growth hormone and prolactin secretion after metoclopramide administration (DA2 receptor blockade) in fertile women.

In this report, we will describe the results of a cross-sectional study to assess PRL and GH secretion during the early follicular phase in 22 fertile patients after metoclopramide administration in order to achieve a dopaminergic DA2 receptor blockade. Blood samples were collected at - 15, 0, 15, 30, 45 and 60 minutes. PRL, GH, estradiol, IGF-I, TSH, glucose, and insulin were measured in the samples taken at - 15 and 0 minutes. The existence of a correlation between GH and PRL secretion was investigated. All patients presented normal serum levels of estradiol, prolactin, insulin, fasting glucose and IGF-I. Serum GH levels were not changed after metoclopramide infusion (p = 0.302), but there was a significant alteration in serum PRL (p = 0.0001) with the highest levels after 30 (mean: 237.20 ng/ml +/- 95.86) and 45 (mean: 211.80 ng/ml +/- 83.24) minutes. Serum GH levels did not correlate with serum PRL levels after the dopaminergic DA2 blockade. We conclude that GH secretion was not modulated by a direct effect of type 2 dopamine receptor.     

Responses of growth hormone to metoclopramide in normal women and amenorrheic women with or without hyperprolactinemia

Response of growth hormone (GH) release to metoclopramide (MCP), a dopamine antagonist, was evaluated in normal women, hyperprolactinemic-amenorrheic patients with pituitary microadenoma and normoprolactinemic-amenorrheic patients. Mean basal concentrations of serum GH and prolactin (PRL) in amenorrheic patients were not significantly different from those in normal women except PRL concentrations in hyperprolactinemic patients. Serum GH concentrations significantly increased after MCP administration in normal women and normoprolactinemic-amenorrheic patients, but not in hyperprolactinemic patients. Dopamine causes modest and transient GH secretion in some subjects. Therefore MCP is not likely to stimulate GH secretion through its effect as a dopamine antagonist, and the mechanism of action of MCP on GH secretion is not known. Although the cause of the absence of GH response to MCP in hyperprolactinemic patients is unclear, it may be related to the increased hypothalamic dopaminergic tone which is operative in such patients or it may reflect a direct action of PRL on hypothalamic-pituitary GH regulation.     

Difference in effects of pirenzepine and atropine on carbachol-induced pepsinogen secretion from isolated gastric glands

The effect of pirenzepine on carbamylcholine (carbachol)-stimulated pepsinogen secretion was compared with that of atropine in the isolated guinea pig gastric glands. Pirenzepine and atropine caused a dose dependent inhibition of carbachol-stimulated pepsinogen secretion. Moreover, pirenzepine as well as atropine produced a rightward shift in the dose response curve of carbachol-stimulated pepsinogen secretion but did not alter the maximum increase in pepsinogen secretion. Results therefore demonstrate that pirenzepine acts as a specific receptor antagonist in the interaction of carbachol with its receptor on gastric chief cells. However, pirenzepine was 50 times less potent than atropine in inhibiting pepsinogen secretion. Half maximal inhibitory concentration of pirenzepine was 2 X 10(-5) M when a maximally effective concentration of carbachol was used, while that of atropine was 4 X 10(-7) M. Results, therefore, suggest that muscarinic receptor on gastric chief cells to which pirenzepine binds may be an intermediate affinity type.     

Enhanced response of plasma prolactin to metoclopramide during chronic converting enzyme inhibition

The effect of chronic converting enzyme inhibition with enalapril on the PRA, PRL and plasma aldosterone responses to metoclopramide was studied in 10 patients with mild to moderate essential hypertension. Enalapril reduced supine blood pressure and increased heart rate significantly. PRA and urinary sodium excretion rose significantly. PRA levels did not change after metoclopramide neither during placebo nor during enalapril. The aldosterone response to metoclopramide was not altered by enalapril, indicating that this response is independent of the renin-angiotensin system. The PRL response to metoclopramide was considerably enhanced after 4 weeks of treatment with enalapril. It is proposed that enalapril, by decreasing the formation of angiotensin II, increases the prolactin reserve.     

Timing of Atropine and Neostigmine in the Reversal of Muscle Relaxants

The antimuscarinic effects of atropine were studied in 46 patients to whom neostigmine had been given after operation to reverse the action of a muscle relaxant. Neostigmine was given to alternate patients three minutes after, or together with, atropine, and the effects of the two procedures were compared by measuring the secretions which collected in the buccal and oropharyngeal cavities and observing the heart rate.It was found that the glands of the oral cavity were stimulated to a greater extent when neostigmine was given with atropine than after atropine. Any dose of atropine sufficient to inhibit peristaltic movements of the bowel is more than enough to block completely secretion by the salivary glands, and the appearance of some secretion in all cases after the administration of neostigmine suggests that the bowel was at liberty to react to the neostigmine in every case, but perhaps particularly so when atropine and neostigmine were given mixed. The integrity of an anastomosis of the bowel could be endangered by vigorous peristalsis in the early postoperative period.Electrocardiograms in about half the patients from each group confirmed earlier work that the muscarinic effects of neostigmine on the heart can be prevented by giving the atropine either before or together with the neostigmine.     

Muscarinic receptor subtypes: M1 and M2 biochemical and functional characterization

The heterogeneity of muscarinic receptors was examined in sympathetic ganglia and atria by “in vitro” binding techniques and functional studies. As tools we have used the classical antagonist atropine, the selective antagonist pirenzepine and the unique muscarinic agonist McN-A-343. In binding studies atropine showed similar affinities to muscarinic sites in ganglionic and atrial membranes with dissociation constants of 1.1 and 3.2 nM, respectively. In contrast, pirenzepine displayed a distinctly different binding profile. In atria it bound to an homogenous population of low affinity sites (diss. const. 620 nM) while in ganglia it revealed the presence of two sites: a major population of high affinity sites (diss. const. 11 nM) and a minor one of lower affinity (diss. const. 280 nM). The functional correlate of the receptor properties in the two tissues was studied in the pithed rat by measuring A) the increase of arterial pressure evoked by McN-A-343 through selective activation of muscarinic receptors in ganglia and B) the bradycardia elicited by acetylcholine release in the heart through vagal stimulation. Mirroring the “in vitro” binding data atropine inhibited both muscarinic responses in the same narrow range of doses (2–30 μg/kg i.v.) whereas pirenzepine showed similar potency to atropine in inhibiting ganglionic stimulation (ED50 4.1 μg/kg i.v.) but was almost two orders of magnitude weaker in blocking vagal bradycardia (ED50 172 μg/kg i.v.). These data suggest that McN-A-343 and pirenzepine act selectively on a common muscarinic receptor subtype, a finding which agrees with the view that muscarinic receptors are heterogenous and that excitatory ganglionic receptors (Ml) are distinguishable from those (M2) present in effector organs like smooth muscle and heart.     

Mechanism of tachycardia caused by intracarotid PGE2 in conscious ewes

Conscious adult ewes prepared with nonocclusive indwelling vascular catheters were used to determine the mechanism by which heart rate increases during central administration of prostaglandin E2 (PGE2). Heart rate increased 14 bpm during steady-state intracarotid infusion of PGE2, 10 ng/kg/min (P less than 0.05). Intravenous atropine methyl bromide, 1 mg/kg, increased heart rate 26 bpm (P less than 0.05) 5 min after injection. Heart rate remained elevated 30 min after injection. The heart rate response to PGE2 plus atropine was greater than the heart rate response to either atropine or PGE2 alone (P less than 0.05). Propranolol, 1 mg/kg bolus plus intravenous infusion, 0.025 mg/kg/min, did not change resting heart rate. Propranolol attenuated but did not abolish the increase in heart rate caused by intracarotid PGE2. Although heart rate increased in response to PGE2 after administration of either propranolol or atropine alone, the combination of propranolol and atropine prevented any further increase in heart rate during subsequent PGE2 infusion. The increase in heart rate when all three drugs were given together was not different from the increase observed during atropine alone. Thus, both beta-adrenergic activation and muscarinic deactivation contribute to the PGE2-induced tachycardia.     

A comparison of the antimuscarinic effects of pirenzepine and N-methylatropine on ganglionic and vascular muscarinic receptors in the rat

The antimuscarinic properties of pirenzepine and N-methylatropine were evaluated in two intact preparations by measuring A) the inhibition of increase in mean arterial pressure evoked by McN-A-343 in pithed rats through activation of ganglionic muscarinic receptors and B) the inhibition of fall in arterial pressure evoked by methacholine in anaesthetized rats through activation of vascular muscarinic receptors. To characterize the antimuscarinic potencies of pirenzepine and N-methylatropine, for both antagonists doses were calculated that produce a 10-fold shift to the right of the dose-response curves for A) the pressor response to McN-A-343 (i.v. administration) in pithed rats (D10-p.r.) and B) for the depressor effect to methacholine (i.v. administration) in anaesthetized rats (D10-an.r.), respectively. Whereas N-methylatropine was virtually equieffective in blocking both muscarinic responses (D10-an.r./D10-p.r. approximately equal to 1), pirenzepine, however, was considerably more potent at ganglionic than at vascular muscarinic receptors (D10-an.r./D10-p.r. approximately equal to 16). These data confirm the existence of excitatory ganglionic muscarinic receptors with high affinity for pirenzepine (M1) and provide evidence for the presence of M2 receptors - receptors which show a low sensitivity to pirenzepine - on vascular smooth muscle cells. To further characterize the anticholinergic properties of pirenzepine, its effect on the pressor response to DMPP, a nicotinic ganglionic stimulant, was investigated in pithed rats. A high dose of pirenzepine (1.13 mumol/kg), given i.v., did not affect nicotinic ganglionic transmission.     

Variations of prolactin content in human cerebrospinal fluid after metoclopramide and morphine

Serum and cerebrospinal fluid (CSF) prolactin (PRL) concentrations were determined in fourteen patients of both sexes suffering from hydrocephalus, in basal conditions and after i.m. administration of 10 mg metoclopramide or 10 mg morphine. A significant increase in both serum and CSF hormone values was found after administration of both drugs. Serum and CSF PRL values after metoclopramide administration increased earlier and to a greater extent than after morphine. Furthermore, the metoclopramide induced CSF PRL increase immediately followed the serum peak, whereas after morphine administration an evident delay in the CSF hormone peak with respect to the serum increase was found. These data suggest that PRL entry in the CSF compartment is subject to a controlling mechanism which acts at the blood/brain barrier.     

Characterization of muscarinic receptor subtypes in human tissues

The affinities of selective, pirenzepine and AF-DX 116, and classical, N-methylscopolamine and atropine, muscarinic cholinergic receptor antagonists were investigated in displacement binding experiments with [3H]Pirenzepine and [3H]N-methylscopolamine in membranes from human autoptic tissues (forebrain, cerebellum, atria, ventricle and submaxillary salivary glands). Affinity estimates of N-methylscopolamine and atropine indicated a non-selective profile. Pirenzepine showed differentiation between the M1 neuronal receptor of the forebrain and the receptors in other tissues while AF-DX 116 clearly discriminated between muscarinic receptors of heart and glands. The results in human tissues confirm the previously described selectivity profiles of pirenzepine and AF-DX 116 in rat tissues. These findings thus reveal the presence also in man of three distinct muscarinic receptor subtypes: the neuronal M1, the cardiac M2 and the glandular M3.     

Effect of the antimuscarinic agent pirenzepine on the in vivo biliary secretion of dogs in response to various stimuli

Pirenzepine is known to be an antiulcer drug with antimuscarinic activity. The present work shows the effect of pirenzepine dihydrochloride on biliary secretion in dogs under normal conditions and after the application of different nervous and humoral stimuli. Pirenzepine (3 mg/kg) was orally administered to unanaesthetized dogs one hour before feeding. This treatment diminished the increase in biliary secretion as well as the intracholedochal pressure that usually followed feeding. On the other hand, a 0.75 mg/kg dose of the antimuscarinic drug intravenously administered to anaesthetized dogs, significantly reduced the increase in intracholedochal pressure produced after the injection of acetylcholine or cholecystokinin (CCK-PZ). Finally, the same dose of pirenzepine eliminated the effect of vagal electrical stimulation on intracholedochal pressure. These results suggest that the effect of pirenzepine on biliary secretion is mainly due to its action on the emptying of the gallbladder.     

Cholinergic mediation in dermorphin-induced growth hormone secretion in man

The effects of pirenzepine (P), a cholinergic muscarinic antagonist, on growth hormone (GH) and prolactin (PRL) response to dermorphin (D) were studied in a group of 7 healthy men. D produced clear elevations in GH and PRL levels. P completely blocked the GH-releasing activity of D, whereas it did not alter the PRL-releasing activity. These results indicate that GH-releasing action of D is mediated via the central cholinergic nervous system in man.     

The autonomic nervous control of heart rate in ducks during voluntary diving

Autonomic nervous control of heart rate was studied in voluntarily diving ducks (Aythya affinis). Ducks were injected with the muscarinic blocker atropine, the beta-adrenergic blocker nadolol, the beta-adrenergic agonist isoproterenol, and a combination of both atropine and nadolol. Saline injection was used as a control treatment. The reduction in heart rate (from the predive level) normally seen during a dive was abolished by atropine. Nadolol reduced heart rate during all phases of diving activity-predive, dive, and postdive-indicating that sympathetic output to the heart was not withdrawn during diving. Isoproterenol increased heart rate before, during, and after the dive, although the proportional increase in heart rate was not as high during the dive as compared with the increase in routine heart rate or heart rate during the predive or postdive phase. The parasympathetic system predominates in the control of heart rate during diving despite the maintenance of efferent sympathetic influences to the heart, perhaps due to accentuated antagonism between the two branches of the autonomic nervous system.     

Clinical use of metoclopramide test in the diagnosis of women with hyperprolactinemia

14 women with elevated prolactin (PRL) serum levels (greater than 25 ng/ml) were given 2.5 mg of metoclopramide, by bolus intravenous injection, to evaluate its diagnosic potential as a stimulus for PRL release. Following metoclopramide injection there was a prompt increase in serum PRL in normal subjects and in patients with moderate PRL elevations associated with galactorrhea-oligomenorrhea. The women with amenorrhea-galactorrhea regardless of the presence of absence of a pituitary tumor, showed a blunted response. Metoclopramide failed to induce TSH secretion in all cases. In conclusion: the use of the metoclopramide test provides no additional clinical information to that furnished by the basal serum PRL concentration for the hyperprolactinemic patient.     

Vagal cardiac function and arterial blood pressure stability

This study was designed to investigate the importance of vagal cardiac modulation in arterial blood pressure (ABP) stability before and after glycopyrrolate or atropine treatment. Changes in R-R interval (RRI) and ABP were assessed in 10 healthy young (age, 22 +/- 1.8 yr) volunteers during graded lower body negative pressure (LBNP) before and after muscarinic cholinergic (MC) blockade. Transient hypertension was induced by phenylephrine (1 microg/kg body wt), whereas systemic hypotension was induced by bilateral thigh cuff deflation after a 3-min suprasystolic occlusion. Power spectral densities of systolic [systolic blood pressure (SBP)] and diastolic ABP variability were examined. Both antimuscarinic agents elicited tachycardia similarly without significantly affecting baseline ABP. The increase in SBP after phenylephrine injection (+14 +/- 2 mmHg) was significantly augmented with atropine (+26 +/- 2 mmHg) or glycopyrrolate (+27 +/- 3 mmHg) and associated with a diminished reflex bradycardia. The decrease in SBP after cuff deflation (-9.2 +/- 1.2 mmHg) was significantly greater after atropine (-15 +/- 1 mmHg) or glycopyrrolate (-14 +/- 1 mmHg), with abolished reflex tachycardia. LBNP significantly decreased both SBP and RRI. However, after antimuscarinic agents, the reduction in SBP was greater (P < 0.05) and was associated with less tachycardia. Antimuscarinic agents reduced (P < 0.05) the low-frequency (LF; 0.04-0.12 Hz) power of ABP variability at rest. The LF SBP oscillation was significantly augmented during LBNP, which was accentuated (P < 0.05) after antimuscarinic agents and was correlated (r = -0.79) with the decrease in SBP. We conclude that antimuscarinic agents compromised ABP stability by diminishing baroreflex sensitivity, reflecting the importance of vagal cardiac function in hemodynamic homeostasis. The difference between atropine and glycopyrrolate was not significant.     

Effects of corticotropin releasing factor and growth hormone releasing factor on pituitary hormone secretion in patients with congenital thyrotropin deficiency. Abnormal response of growth hormone to corticotropin releasing factor

Blood concentrations of anterior pituitary hormones, ACTH, GH, TSH, PRL, LH, and FSH were determined in corticotropin releasing factor (CRF) test (synthetic ovine CRF 1.0 microgram per kg body weight) and growth hormone releasing factor (GRF) test (synthetic human pancreatic GRF-44 100 micrograms) in 2 female sibling patients with congenital isolated TSH deficiency, in their mother, in 2 patients with congenital primary hypothyroidism and in 8 normal controls. The patients with isolated TSH deficiency showed normally increased plasma ACTH and serum GH after CRF and GRF, respectively, and also showed an abnormal GH response to CRF. The serum GH showed a rapid increase to maximum levels (12.9 ng/ml) within 30 to 60 min followed by decrease. The possibility of secretion of abnormal GH could be excluded by the fact that on serum dilution, GH value gave a linear plot passing through zero. In addition, serum PRL, LH and FSH levels after CRF administration in case 1 and PRL after GRF in case 2 were also slightly increased but these responses were marginal. The mother of the patients, patients with congenital primary hypothyroidism, and normal healthy controls showed normal responses of pituitary hormones throughout the experiment. Data from the present study and a previous report show that abnormal GH response to the hypothalamic hormones (CRF, TRH and LHRH) may be observed in patients with congenital isolated TSH deficiency.     

Provocation of a paradoxical growth hormone response to corticotropin-releasing hormone by pretreatment with metoclopramide in patients with acromegaly and normal subjects

Two of 7 patients with acromegaly and one of 7 normal subjects exhibited a paradoxical rise in growth hormone (GH) to human corticotropin-releasing hormone (CRH) when pretreated with metoclopramide, although CRH alone did not induce an increase in GH. In one of these two patients with acromegaly, the GH increase to metoclopramide alone also reached the criteria of a paradoxical response. These two acromegalic patients showed a GH increase to metoclopramide pretreatment before and up to two months after surgery. In another acromegalic patient, whose GH level remained high 5 months after surgery, metoclopramide induced an increase in GH level, while in a patient who had an above-normal GH level 18 months after surgery, the resumption of physiological GH secretion after surgery was evidenced by a postoperative absence of a GH response to metoclopramide. It is suggested from these results that the GH response to metoclopramide and the metoclopramide-provoked GH response to CRH in patients with acromegaly result from the secretion of GH from nonadenomatous cells of the pituitary.     

GH3 cell secretion of growth hormone and prolactin increaseases spontaneously during perfifusion

Summary GH₃ cell secretory activity was studied in long-term perifusion to define previously reported spontaneous increases in growth hormone (GH) and prolactin production (PRL). Mechanically harvested cells (1×10⁷/column) were perifused at 4 ml/h for 72 h. A basal period of variable duration (8 to 12 h), during which hormone secretion was stable, was followed by steadily increasing secretion rates. Changes in cell number were not sufficient to acount for increased jormone secretion rates: a) there was no significant change in cell count after 72 h (0.97±0.03×10⁷;n=18); b) mean cell column DNA content increased 25.5% above the base value, whereas GH secretion rose 385% and PRL rose 178% (n=5). Observed differences in the duration of the basal secretion period, the basal secretory rate, and the magnitude of secretory rate increase were associated with several variables: a) variablility within a subline was a function of passage number: GH secretion decreased and PRL secretion increased with subculture number; b) cells with identical lot and freeze numbers, but received at different times, behaved differently; c) the presence of an antifungal agent (nystatin) altered hormone secretion reproducibly. Conclusions: a) rates of GH and PRL secretion rise spontaneously in perifusion without a proportional increase in GH₃ cell number; b) fluctuations in the rate of GH₃ cell secretion of GH and PRL are not entirely random but are determined by several definable variables. Supported by a grant to MES from the National Institutes of Health (AM33388) and in part by the Medical Research Service of the Veterans Administration.     

M1 muscarinic antagonists interact with sigma recognition sites.

The M1-selective muscarinic antagonists aprophen, caramiphen, carbetapentane, 2-DAEX, dicyclomine, hexahydrosiladifenidol, iodocaramiphen, nitrocaramiphen, oxybutynin and trihexyphenidyl potently inhibited binding to sigma sites in brain. Both basic ester and non-ester structural type compounds which exhibit affinity for the muscarinic receptor also demonstrated affinity for the sigma site, while the classical antimuscarinic agents atropine and QNB, and the tricyclic pirenzepine, were ineffective in binding to this site. We also observed a significant correlation between the Ki values for sigma compounds to inhibit [3H]pirenzepine binding and their IC50 values to inhibit carbachol-stimulated phosphoinositide turnover. These observations may aid in elucidating the relationship of sigma binding to inhibition of phosphoinositide turnover stimulated by cholinergic agonists.     

Pharmacological evidence for cardiac muscarinic receptor subtypes

The chronotropic and inotropic effects of muscarinic receptor agonists (Acetylcholine, Arecoline, Carbachol, Furtrethonium) and antagonists (Atropine, N-methyl and N-butyl scopolammonium, pirenzepine) on isolated guinea-pig atria were studied. All had a greater affinity constants for muscarinic receptors as assessed in terms of inotropic effects than in terms of chronotropic effects. This difference, well correlated with the pharmacological effect, suggests the occurrence of cardiac muscarinic receptor subtypes, one mediating heart rate and the other contractile force. The ratio of chronotropic to inotropic potencies for each agent shows that the physiological mediator. Acetylcholine, differentiates best between the two subtypes, while atropine is the least discriminatory.