Effect of Basal Gastric Acid Secretion on the Pharmacodynamics of Ranitidine

Twelve patients with inactive ulcer disease were administered placebo and ranitidine via bolus and continuous intravenous infusions, at doses ranging from 50 every 8 h, to 12.5 mg/h for 24 h. Gastric acid was collected for 20 min each h for 24 h, and ranitidine serum concentrations were measured ± every 2 h, during each of the six study periods. Cosinor analysis of gastric acid secretion during placebo treatment revealed a significant circadian rhythm in all subjects. Mesor acid output ranged from 1.7 to 11.6 mmol/h (mean 5.6 ± 2.8 mmol/h) and the amplitude ranged from 0.7 to 6.5 mmol/h (mean 2.8 ±1.6 mmol/h). Peak acid output (acrophase) occurred at 10 p.m. ± 3 h. A pharmacodynamic model, relating ranitidine serum concentration to hourly acid secretion, was derived, which incorporated the circadian change in basal acid output. Data for this fractional response model included basal acid secretion–as determined by time of day, measured acid secretion, and associated serum ranitidine concentration. The 50% inhibitory concentration (IC₅₀) for ranitidine ranged from 10-75 ng/ml, with a mean of 44 ng/ml. The variation in IC₅₀ and in basal acid secretion combined to produce a wide variation in the pharmacodynamic response to ranitidine. The model-predicted serum concentrations, required to maintain acid secretion at 0.1 mmol/h, ranged from 250 to 1550 ng/ml, at the time of peak evening acid secretion. Despite a constant degree of acid inhibition by ranitidine during the day, higher serum concentrations are required during times of peak acid output to maintain adequate suppression of hydrogen ion secretion.     

Intragastric pH and Pharmacokinetics of Intravenous Ranitidine During Sinusoidal and Constant-Rate Infusions

Six patients with healed duodenal ulcer completed two treatment periods with continuous i.v. infusion ranitidine. A 25-mg i.v. bolus was followed by a constant infusion at 6.25 mg/h or a sinusoidal infusion with infusion rates ranging from 3.125 to 9.375 mg/h. The sinusoidal infusion rate was designed to match the previously observed circadian changes in basal acid secretion. The peak infusion rate occurred at 19:30 h. A pharmacokinetic method was designed to predict the resultant plasma concentrations of ranitidine. Intragastric pH and plasma ranitidine concentration data were fit to a cosine function to evaluate circadian and ultradian rhythms. Plasma concentrations during the sinusoidal infusion exhibited a circadian rhythm according to model predictions. Cosinor analyses of the mean ranitidine plasma concentration data showed a mesor concentration of 237 ng/mL and amplitude of 76 ng/mL (coefficient of determination [CD] = 0.98). The acrophase in plasma concentration occurred at 2223 h, a delay of approximately 2.9 hours from the peak in the infusion rate. The constant-rate infusion resulted in a mean plasma concentration of 222 ± 32 ng/mL. The 24-h mean intragastric pH values for the sinusoidal and constant regimens were 5.4 and 5.1, respectively (p = 0.170). The intragastric pH during the constant-rate infusion exhibited a significant circadian rhythm (CD = 0.52). The minimum pH (bathy-phase) occurred at 2031 h. No circadian rhythm was present during the sinusoidal-rate infusion (CD = 0.08). At the approximate time of the peak basal acid secretion, between 21:00 hours and midnight, the mean pH for the sinusoidal infusion was 5.77 versus 4.5 for the constant-rate infusion (p = 0.112). Sinusoidal infusions or alternate methods of increased doses at the times of peak acid output may improve around-the-clock control of intragastric pH.     

Effect of pancreatic polypeptide-antiserum on bombesin-stimulated pancreatic exocrine secretion in dogs

Bombesin is a potent stimulus of both pancreatic protein secretion and plasma pancreatic polypeptide (PP) release in dogs. Physiological plasma levels of PP have been shown to inhibit pancreatic exocrine secretion in dogs. We examined the question whether the concomitant release of PP exerts a suppressive action on the pancreatic exocrine response to bombesin in dogs by measuring pancreatic exocrine secretion with and without in vivo immunoneutralization of PP with a high affinity PP-antiserum. Bombesin was infused in a dose of 150 ng/kg·hr, resulting in a rise of plasma PP from 24±5 to 224±25 pM (p<0.01). Before this bombesin infusion, 7 ml of normal rabbit serum had been administered to the dogs (n=8). At a later stage, the study was repeated after administration of 7 ml of PP-antiserum to the same animals. The bombesin induced increase in pancreatic exocrine secretion during administration of PP-antiserum (flow rate 24±10 ml/hr, protein output 1.35±0.43 g/hr, and bicarbonate output 3.25±1.42 mmol/hr) was not significantly different from that during control rabbit serum (flow rate 21±7 ml/hr, protein output 1.26±0.38 g/hr, and bicarbonate output 3.18±1.10 mmol/hr). It is therefore concluded that the pancreatic exocrine response to bombesin is not affected by the concomitant secretion of PP.     

Circadian variations in plasma concentrations of melatonin and prolactin during breeding and non-breeding seasons in yak (Poephagus grunniens L.)

Circadian variations of plasma melatonin and prolactin concentrations were determined during breeding as well as non-breeding seasons in yak. Blood samples (5 ml) were collected during different phases of estrous cycle, viz. early (0-6 days), mid (7-12 days) and late luteal (13-19 days) at 2 h interval for 24 h from eight yaks during one breeding month (November); the same yaks were bled at 2 h interval during one non-breeding month (February) for 24 h. Plasma melatonin concentrations rose sharply (P < 0.01) after sunset to record peak concentrations between midnight and 2 a.m. declining sharply thereafter in both breeding as well as non-breeding seasons. Basal melatonin concentrations were recorded between 0600 and 1600 h. Stage of luteal phase did not influence the diurnal hormone change (P < 0.01). In the breeding season, mean plasma prolactin concentrations displayed circadian variations with maximum value at 0400 h (41.22+ /- 1.5 ng/ml) and minimum at 1400 h (12.0 +/- 4.02 ng/ml). In the non-breeding season plasma prolactin concentrations showed circadian variation with maximum value at 0000 h (59.9 +/- 10.5 ng/ml) and minimum at 1200 h (32.13 +/- 3.2 ng/ml). A positive correlation in breeding (r = 0.75) and in non-breeding season (r = 0.65) between circadian changes in mean plasma prolactin and melatonin concentrations were seen. Circadian changes of mean plasma melatonin concentrations during breeding and non-breeding seasons were not different (P > 0.05). However, mean plasma prolactin concentrations were found to be higher (P < 0.01) in the non-breeding season. Three conclusions were drawn from the study: (i) melatonin and prolactin concentrations followed a circadian pattern of secretion (ii) melatonin and prolactin secretion may be closely interrelated and (iii) higher prolactin concentrations during the non-breeding season could be due to nutritional and environmental stress and hence might be contributing to lack of cyclicity.     

Effect of histamine and cimetidine on amino acid meal-stimulated gastrin release at a controlled intragastric pH in healthy human beings

Results of several experiments have suggested that histamine-2 receptors play an inhibitory role in regulating gastrin release. We evaluated this prospectively in healthy human beings by infusing intravenously either histamine (0.33 μg/kg/min) or cimetidine (3.33 mg/min) during a continuous 3-h intragastric infusion of a 3% mixed amino acid meal, a potent stimulus of gastrin release. In order to be certain that effects of histamine or cimetidine on gastrin release were independent of their known effects on gastric acid secretion, intragastric pH was maintained at 5.0 by in vivo intragastric titration with sodium bicarbonate or hydrochloric acid. Although histamine and cimetidine had significant effects on gastric acid secretion, neither significantly affected the rises in serum gastrin concentrations during intragastric amino acid infusion. For example, mean gastrin rises above basal concentrations were 39 ± 9 pg/ml on the control day, 39 ± 9 pg/ml on the histamine day and 44 ± 11 pg/ml on the cimetidine day (P > 0.05). Thus, blockade or stimulation of H₂-receptors at the doses tested had no effect on gastrin release in response to an amino acid meal in humans when intragastric pH was maintained at 5.0.     

Day-Night and Individual Differences in Response to Constant-Rate Ranitidine Infusion

Twelve ulcer patients with inactive disease received constant-rate infusions of ranitidine, in doses of 6.25 and 10.0 mg/hr, during separate 24-h spans. Gastric pH and serum ranitidine concentrations were monitored. Serum ranitidine concentrations did not vary significantly after attainment of steady-state. For the group, gastric acidity was controlled above pH 4 during the day; however, at night, when gastric acid secretion was greatest under placebo conditions, ranitidine less effectively controlled gastric pH. There was individual variation in response to ranitidine. Patients (8/12) evidencing control of gastric acidity (pH ± 4) for at least 16 h when infused with ranitidine (6.25 mg/h) were considered re-sponders. Those (4/12) not so well controlled were designated poor responders. With parenteral infusion of 6.25, as well as 10.0 mg/h ranitidine, responders evidenced a relatively high 24-h mean pH and only minor day-night variation in gastric acidity. In contrast, poor responders were characterized by a low 24-h mean pH and high-amplitude circadian variation in gastric acidity. Poor responders evidenced statistically significant (p < 0.05) lower gastric pH responses to parenteral infusions than did responders. A similar, significant difference between the two groups was observed when the percentage of time that gastric pH was maintained below 4 was considered. Differences between responders and poor responders to ranitidine infusion are unknown. Since Zollinger-Ellison syndrome patients were not included in the study, observed differences in drug response cannot be ascribed to hypersecretion of gastric acid.     

Culture of bovine granulosa cells in a chemically defined serum-free medium: the effect of insulin and fibronectin on the response to FSH

Granulosa cells from fully differentiated bovine follicles were cultured in serum-free medium for 4 days. At the end of culture, the number of viable cells was low (10-15% of cells plated on day one) and only progesterone secretion responded to FSH. Insulin increased the number of viable cells at the end of culture (ED50 # 70 ng/ml) and stimulated progesterone secretion (ED50 # 50 ng/ml); the secretion of oestradiol-17 beta over basal value was evident only for concentrations of 1000 and 10,000 ng/ml. FSH acted synergistically with insulin to modify steroid secretion. In the presence of 50 ng/ml of insulin, dose-response studies indicated that secretion of progesterone was maximal at 10 ng/ml of FSH and plateaud thereafter, while oestradiol output peaked at 2 ng/ml of FSH, decreasing at higher concentrations. When cells were seeded in wells precoated with fibronectin, a comparison with cells cultured on plastic showed an increase (30-40%) in the number of viable cells at the end of culture and in oestradiol secretion but a decrease in progesterone output. These results indicate that granulosa cells from large bovine follicles, cultured in a serum-free medium containing insulin, maintain their steroidogenic potency for at least 4 days. Moreover, they show that oestradiol and progesterone synthesis are differentially sensitive to FSH concentrations and that fibronectin increases oestradiol secretion in response to FSH.     

Quantification of retinoic acid by gas-liquid chromatography-mass spectrometry: total versus all-trans-retinoic acid in human plasma

An assay based on negative ion chemical ionization mass spectrometry has been developed to quantify retinoic acid in plasma or serum. The lower limit of detection is 75 pg (240 fmol); normal values of retinoic acid can be determined on as little as 40 microliters of human plasma. The plasma concentrations of total retinoic acid in 12 healthy male volunteers taking no medication or vitamin supplementation ranged from 2.8 to 6.6 ng/ml; the mean was 4.9 ng/ml. The assay can be manipulated to measure all-trans-retinoic acid alone; about 75% of retinoic acid in human plasma or rat serum is all-trans-retinoic acid. Both retinol and retinoic acid can be quantified on the same 0.1-ml sample; the concentration of retinoic acid in human plasma or rat serum is at least 150-fold less than that of retinol.     

Maternal serum progesterone concentration during pregnancy and lamb birth weight at parturition in Javanese Thin-Tail ewes with different litter sizes

Pregnant ewes, (N=38), with similar body weight and age (19, 13 and 6 carrying 1, 2 and 3 fetuses, respectively) were used to study the relationship between maternal serum progesterone concentration during pregnancy and lamb birth weight at parturition. Average maternal serum progesterone concentration in the ewes carrying 1, 2, and 3 fetuses was: 5.3±0.3, 6.2±0.7 and 6.6±0.5 ng/ml, during weeks 0 to 7 of gestation; 16.9±1.4, 25.3±1.5, and 26.8±2.5 ng/ml, during weeks 8 to 20; and 13.2±1.0, 18.7±1.0, and 19.8±1.7 ng/ml, during the entire gestation period respectively. Total lamb birth weight in ewes carrying 1, 2, and 3 fetuses was 1.9±0.1, 3.2±0.2, and 4.2±0.4 kg, respectively. In the respective litter sizes, ewes with higher mean serum progesterone concentration during the whole pregnancy gave birth to lambs with higher birth weight (r²=0.76, 0.42 and 0.46, for ewes carrying 1, 2 and 3 fetuses, respectively). The results of the study indicated that prenatal growth could probably be improved by increasing endogenous secretion of maternal progesterone during pregnancy.     

Effect of acute hyperglycemia on basal, secretin and secretin + cholecystokinin stimulated exocrine pancreatic secretion in humans

Pancreatico-biliary secretion is reduced during acute hyperglycemia. We investigated whether alterations in pancreatico-biliary flow or volume output are responsible for the observed reduction in duodenal output of pancreatic enzymes and bilirubin during hyperglycemia. Eight healthy subjects were studied on two occasions during normoglycemia and hyperglycemia (15 mmol/l). Pancreatico-biliary output was measured by aspiration using a recovery marker under basal conditions (60 min), during secretin infusion (0.1 CU/kg.h) for 60 min and during secretin + CCK (0.5 IDU/kg.h) infusion for 60 min. Secretin was infused to stimulate pancreatico-biliary flow and volume output. Secretin significantly (P<0.005-P<0.05) increased volume and bicarbonate output and CCK significantly (P<0.01) increased the output of bilirubin, pancreatic enzymes, bicarbonate and volume, both during normoglycemia and hyperglycemia. During hyperglycemia basal, secretin stimulated and secretin + CCK stimulated total pancreatico-biliary output were significantly (P<0.005-P<0.05) reduced compared to normoglycemia. The incremental outputs, however, were not significantly different between hyper- and normoglycemia. Pancreatic volume output was significantly (P<0.05) reduced during hyperglycemia compared to normoglycemia under basal conditions (31+/-16 m/h versus 132+/-33 m/h) during secretin infusion (130+/-17 ml/h versus 200+/-34 m/h) and during secretin + CCK infusion (370+/-39 ml/h versus 573+/-82 ml/h). Plasma PP levels were significantly (P<0.05) reduced during hyperglycemia. It is concluded that 1) hyperglycemia significantly reduces basal pancreatico-biliary output 2) the incremental pancreaticobiliary output in response to secretin or secretin + CCK infusion is not significantly affected during hyperglycemia, 3) a reduction in volume output contributes to the inhibitory effect of hyperglycemia on pancreatico-biliary secretion, 4) hyperglycemia reduces PP secretion suggesting vagal-cholinergic inhibition of pancreatico-biliary secretion and volume during hyperglycemia.     

Seasonal differences in plasma testosterone profiles in buffalo bulls

Testosterone was measured by radioimmunoassay in blood samples collected hourly over 10 h from two adult buffalo bulls in April, May, August and December. The basal concentrations were below 0.2 ng/ml while peak concentrations ranged from 0.35 to 1.65 ng/ml, with not more than one complete peak occurring during a 10 h period. Both bulls had similar testosterone profiles within each sampling period but differences were evident between periods, the mean concentration being highest in August and falling through December and April to the lowest levels in May. Testosterone concentrations in buffaloes are therefore lower than those in other domestic species, and appear to vary during different times of the year.     

Simple and robust high-performance liquid chromatographic method for the determination of ranitidine in microvolumes of human serum

A simple robust high-performance liquid chromatographic method is described for the determination of ranitidine in microvolumes of human serum. The drug of interest was isolated using liquid–liquid extraction with dichloromethane and back-extraction with 0.1% phosphoric acid and separation was obtained using a reversed-phase column under isocratic conditions, with ultraviolet detection at 313 nm. Intra-day and inter-day coefficients of variation ranged from 1 to 6% and 3 to 10%, respectively. Accuracy of the assay was less than 10% at all concentrations. The limit of detection and the limit of quantitation were 2 and 7 ng/ml, respectively. The linearity was assessed in the range 10–1000 ng/ml. It was shown that a group of common drugs co-administered with ranitidine did not interfere with its determination. The applicability of this method for the pharmacokinetic study of ranitidine following i.v. infusion in patients was demonstrated using only 100 μl of serum. The ruggedness of the assay was demonstrated over a three-year period.     

Measurement of meal-stimulated gastric acid secretion by in vivo gastric autotitration.

Measurement of meal- stimulated gastric acid secretion using manual intragastric titration is demanding in terms of personnel and specialized equipment. In the present study, we used a new method, in vivo gastric autotitration, to determine meal-stimulated gastric acid secretion. Gastric pH was measured every 4 s before, during, and after ingestion of a standard meal in 24 healthy subjects. Placebo, ranitidine (150 mg), ranitidine (75 mg), or famotidine (10 mg) was given 1 h after the beginning of the meal. Meal-stimulated gastric acid secretion was calculated from the amount of HCl required to titrate the homogenized standard meal to pH 2 in vitro (119 mmol) and the time required for the pH of the ingested meal to decrease to pH 2 in vivo. Values for pH were also converted to acid concentration (mM), and integrated acidity was calculated from the cumulative, time-weighted means of the acid concentrations for every fourth second of the postprandial recording period. Control meal-stimulated gastric acid secretion was 60 (40-71) mmol/h (median; interquartile range), and each histamine H(2)-receptor antagonist significantly decreased secretion by approximately 50%. Meal-stimulated acid secretion correlated directly with postprandial integrated gastric acidity (r = 0.72; P = 0.0001). Thus intragastric autotitration is a convenient, reproducible method for measuring gastric acid secretion after ingestion of a solid meal and offers several advantages over manual intragastric titration.     

Purification of ovine transferrin and study of the hormonal control of its secretion in enriched cultures of ovine Sertoli cells.

Ovine transferrin (o-transferrin) was purified from sheep serum by fractionated precipitation with ammonium sulphate, ion-exchange chromatography on DEAE trisacryl and finally by affinity chromatography on Affigel blue to remove albumin. Ovine transferrin was identified by its apparent molecular weight in sodium dodecyl sulphate polyacrylamide gel electrophoresis and by its N-terminal amino-acid sequence. The procedure presented in this report permits the preparation of highly purified o-transferrin with a good recovery (52% of initial total immunoactivity). An antiserum against o-transferrin was then raised in rabbits, using this highly purified preparation. A specific radioimmunoassay was set up using 125I-labelled o-transferrin. Its detection threshold (4 ng/ml) was low enough to measure o-transferrin in spent culture media of ovine Sertoli cells, which ranged between 15 and 600 ng/ml. Sheep seminiferous tubule cells, containing approximately 80% Sertoli cells, were cultured at a high density (1.5 x 10(6) cells/cm2) on a thin layer of reconstituted basement membrane. Kinetic studies showed that basal daily secretion of o-transferrin was reduced by half (-49%) between Day 1 and Day 2 of culture, and progressively decreased thereafter. Under FIRT (500 ng ovine follicle-stimulating hormone (FSH)/ml + 10 micrograms insulin/ml + 500 ng retinol/ml + 5 x 10(-7) mol/l testosterone) stimulation, the ratio of stimulated to basal secretions increased 11-fold between Day 1 (1.1) and Day 6 (12). When 10% fetal calf serum was added, mean o-transferrin secretion was a third of that in serum-free medium, suggesting that fetal calf serum contains factors that inhibit secretion of ovine Sertoli cell transferrin. In the presence of serum, the ratio of FIRT-stimulated to basal secretions doubled between Day 1 (1.0) and Day 4-6 (2.0). Between Days 2 and 4 of culture, insulin had a slight stimulatory effect on o-transferrin secretion (128% of control at 10 micrograms insulin/ml), as well as epidermal growth factor (124% of control at 50 ng/ml). Testosterone at up to 5 x 10(-7) mol/l had no effect; 500 ng retinol/ml doubled o-transferrin secretion (218% of control) as did 500 ng FSH/ml (220% of control). A combination of retinol and FSH increased the secretion 4-fold, indicating that maximal stimulation of o-transferrin secretion by ovine Sertoli cells requires the combined actions of mechanisms dependent and independent of cAMP.     

Urinary N tau-methylimidazole acetic acid excretion in respiratory disease

N tau-methylimidazole acetic acid (N tau-MIAA) is the principal urinary metabolite of histamine. The basal urinary excretion rate of N tau-MIAA was determined as 0.117 +/- 0.008 (SE) mg/h, with a renal clearance for N tau-MIAA of 273 +/- 27 ml/min implying active secretion. After subpharmacological infusion of histamine (50 ng.kg-1.min-1 over 2 h) in five volunteers that increased plasma histamine from 0.28 +/- 0.04 to 0.71 +/- 0.15 ng/ml, urinary excretion of N tau-MIAA over 8 h was increased by less than 17% compared with a control saline infusion. Urinary N tau-MIAA excretion in normal controls (273 +/- 14 micrograms/mmol creatinine) was similar to that observed in patients with severe acute asthma (253 +/- 22 micrograms/mmol), antigen-induced bronchoconstriction (269 +/- 21 micrograms/mmol), seasonal allergic rhinitis (304 +/- 31 micrograms/mmol), and clinically stable bronchiectasis (270 +/- 22 micrograms/mmol). In contrast, large increases in metabolite excretion (greater than 7,000 micrograms/mmol creatinine) were observed in a patient with systemic mastocytosis where very high plasma histamine levels were recorded (greater than 500 ng/ml) and marked systemic hemodynamic effects occurred. We conclude that urinary N tau-MIAA will only be increased in pathologies where sustained hyperhistaminemia occurs and that increased local histamine production in the lung or the upper airway does not cause a measurable change in the basal urinary excretion of this metabolite.     

Radioimmunoassay of 17-hydroxyprogesterone

A method is described for the determination of 17-hydroxyprogesterone in peripheral venous plasma (0.1–1.0 ml) from men and women using an antiserum to 17-hydroxyprogesterone-3-carboxymethyl oxime bovine serum albumin (BSA).

The coefficients of variation on replicate analyses ranged from 7–16%. The louest level of 17-hydroxy-progesterone uhich may be determined is 5 ng/100 ml plasma. The concentration (mean ± S.D.; ng/100 ml plasma) in a group of healthy men (aged 20–40 yrs) uas 123 ± 65. From women during days 1–10 of the menstrual cycle the value uas 40 ± 15, during days 18–32 of the cycle 134 ± 57 and during pregnancy (12th week to term) 622 ± 262. Progesterone was determined in the same samples using an antiserum to 11-hydroxyprogesterone-11-hemisuccinate-BSA.     

Involvement of hypothalamic somatostatin in glucagon-induced suppression of growth hormone secretion in conscious rats

The role of central glucagon in regulating GH secretion was studied in conscious male rats with chronic indwelling intra-atrial and intracerebro-ventricular (ICV) cannulae. Repeated blood sampling every 20 min from 1000 hr to 1700 hr showed two major GH bursts occurring at regular intervals (3.6±0.1 hr) around 1200 hr and 1540 hr. The ICV (lateral ventricle) injection of glucagon (10 μg/rat) at 1100 hr inhibited spontaneous GH secretion, and the mean (±SE) plasma GH levels from 1120 hr to 1700 hr were lower than those in controls injected ICV with the vehicle solution only (31.9±7.8 ng/ml vs. 157.1±13.4 ng/ml, p<0.01). The GH bursts did not appear until 5 hr after the injection. The intravenous (IV) injection of glucagon (10 μg/rat) did not change plasma GH levels or the occurrence of spontaneous GH bursts. The glucagon-induced suppression of GH release was attenuated when anti-somatostatin serum (ASS), but not normal rabbit serum (NRS), was given IV in a volume of 0.25 ml immediately before the ICV injection of glucagon (10 μg/rat) (mean GH levels at 1120–1700 hr: ASS+glucagon, 133.6±26.7 ng/ml vs. NRS+glucagon, 30.5±7.4 ng/ml, p<0.01). These findings suggest that central glucagon may play an inhibitory role in regulating GH secretion by stimulating SRIF release from the hypothalamus in the rat.     

Inhibition of gastric acid secretion in rat stomach by PACAP is mediated by secretin, somatostatin, and PGE(2)

Pituitary adenylate cyclase-activating polypeptide (PACAP), existing in two variants, PACAP-27 and PACAP-38, is found in the enteric nervous system and regulates function of the digestive system. However, the regulatory mechanism of PACAP on gastric acid secretion has not been well elucidated. We investigated the inhibitory action of PACAP-27 on acid secretion and its mechanism in isolated vascularly perfused rat stomach. PACAP-27 in four graded doses (5, 10, 20, and 50 microg/h) was vascularly infused to determine its effect on basal and pentagastrin (50 ng/h)-stimulated acid secretion. To study the inhibitory mechanism of PACAP-27 on acid secretion, a rabbit antisecretin serum, antisomatostatin serum, or indomethacin was administered. Concentrations of secretin, somatostatin, PGE(2), and histamine in portal venous effluent were measured by RIA. PACAP-27 dose-dependently inhibited both basal and pentagastrin-stimulated acid secretion. PACAP-27 at 10 microg/h significantly increased concentrations of secretin, somatostatin, and PGE(2) in basal or pentagastrin-stimulated state. The inhibitory effect of PACAP-27 on pentagastrin-stimulated acid secretion was reversed 33% by an antisecretin serum, 80.0% by an antisomatostatin serum, and 46.1% by indomethacin. The antisecretin serum partially reduced PACAP-27-induced local release of somatostatin and PGE(2). PACAP-27 at 10 microg/h elevated histamine level in portal venous effluent, which was further increased by antisomatostatin serum. However, antisomatostatin serum did not significantly increase acid secretion. It is concluded that PACAP-27 inhibits both basal and pentagastrin-stimulated gastric acid secretion. The effect of PACAP-27 is mediated by local release of secretin, somatostatin, and PGE(2) in isolated perfused rat stomach. The increase in somatostatin and PGE(2) levels in portal venous effluent is, in part, attributable to local action of the endogenous secretin.     

Prolactin reference range and pulsatility in male dogs

Little is known about serum prolactin (PRL) concentrations and secretion patterns in male dogs. Blood samples (n = 65) were collected from crossbred dogs and from Beagles and German Shepherd dogs to describe the PRL reference range, and from five male Beagles at 15-min intervals for 6 h (n = 24 samples/dog) to describe the ultradian rhythm of this hormone. Serum PRL was measured by a homologous endpoint enzyme immunometric assay. The reference range was established from nondetectable to 6.0 ng/mL. There was an effect of breed; serum PRL concentrations in Beagles were higher (P < 0.05) than in crossbreeds and German Shepherds. However, there was no significant correlation between PRL concentration and age of the dog. During the ultradian study, PRL was characterized by a fluctuating baseline with occasional distinct elevations, indicating a pulsatile secretion. The mean basal PRL concentration was 1.4 +/- 0.6 ng/mL and the mean AUC was 9.9 +/- 2.7 ng/mL/6h. Prolactin pulse frequency ranged from one to two peaks/6h, pulse duration between 15 and 75 min, and amplitude from 1.7 to 2.4 ng/mL. In conclusion, this reference range, pulsatility and breed differences should be taken into account when interpreting serum PRL concentrations, for clinical or research purposes.     

Circadian and pulsatile variations in plasma levels of inhibin, FSH, LH and testosterone in adult Murrah buffalo bulls

The present study investigated pulsatile and circadian variations in the circulatory levels of inhibin, gonadotrophins and testosterone. Six adult buffalo bulls (6 to 7 yr of age) were fitted with indwelling jugular vein catheters, and blood samples were collected at 2-h intervals for a period of 24 h and then at 15-min interval for 5 h. Plasma concentrations of inhibin, FSH, LH and testosterone were determined by specific radioimmunoassays. Plasma inhibin levels in Murrah buffalo bulls ranged between 0.201 to 0.429 ng/mL, with a mean of 0.278 +/- 0.023 ng/mL. No inhibin pulses could be detected during the 15-min sampling interval. Plasma FSH levels ranged between 0.95 to 3.61 ng/mL, the mean concentration of FSH over 24 h was 1.66 +/- 0.25 ng/mL. A single FSH pulse was detected in 2 of 6 bulls. The LH levels in peripheral circulation ranged between 0.92 to 9.91 ng/mL, with a mean concentration of 3.33 +/- 1.02 ng/mL. Pulsatility was detected in LH secretion with an average of 0.6 pulses/h. Plasma testosterone levels in 4 buffalo bulls ranged from 0.19 to 2.99 ng/mL, the mean level over 24 h were 1.34 +/- 0.52 ng/mL. Testosterone levels in peripheral circulation followed the LH secretory pattern, with an average of 0.32 pulses/h. The results indicate parallelism in inhibin, FSH and LH, and testosterone secretory pattern. Divergence in LH and FSH secretory patterns in adult buffalo bulls might be due to the presence of appreciable amounts of peripheral inhibin.