Effect of feed restriction on plasma dantrolene concentrations in horses.

REASONS FOR PERFORMING STUDY: Dantrolene sodium is used to prevent exertional rhabdomyolysis in predisposed horses. Food intake might negatively impact dantrolene bioavailability in horses; however, prolonged feed restriction might be detrimental to performance. OBJECTIVE: To determine a minimum duration of feed restriction that would optimise plasma dantrolene concentrations in horses after nasogastric administration. It was hypothesised that feed restriction for 4, 8 or 12 h before dantrolene administration would result in higher plasma dantrolene concentrations than achieved with no feed restriction before treatment. METHODS: Five healthy horses were randomly rotated through 4 feed restriction periods of 0, 4, 8 and 12 h duration prior to nasogastric administration of dantrolene sodium (6 mg/kg bwt). Plasma dantrolene concentration was measured by spectrofluorometry at 60, 90, 120, 150, 180 and 210 min after administration. Data were analysed via repeated measures ANOVA. RESULTS: Peak plasma dantrolene concentration was highest when horses had 0 and 4 h of feed restriction (0.65 ± 0.10 µg/ml at 120 min; 0.66 ± 0.17 at 180 min, respectively) and was lower when horses were restricted from feed for 8 h (0.45 ± 0.15 at 150 min) and 12 h (0.21 ± 0.09 at 180 min). Mean plasma dantrolene concentration did not differ between 0 and 4 h feed restriction at any sample time, but feed restriction for 8 h resulted in significantly lower plasma dantrolene concentration at 60 and 180 min after treatment than when horses were restricted 0 and 4 h, respectively. Plasma dantrolene concentration was significantly lower at all sample times when horses were restricted from feed 12 h compared to 0 or 4 h. CONCLUSIONS: Absorption of nasogastrically administered dantrolene is inhibited by feed restriction before administration. To achieve optimal plasma dantrolene concentrations, feed restriction before oral administration should not exceed 4 h.

Inhibition of gastric acid secretion in vivo and in vitro by a new calmodulin antagonist, CGS 9343B.

The new calmodulin antagonist, CGS-9343B, was found to inhibit both histamine plus 3-isobutyl-1-methylxanthine and carbachol-induced [14C]aminopyrine accumulation in dispersed, fundic mucosal cells of rats. The IC50 value for CGS-9343B inhibition of histamine plus 3-isobutyl-1-methylxanthine-induced [14C]aminopyrine accumulation was 306 nM. The drug was more potent than the H2-histamine receptor antagonist, cimetidine (1128 nM), less potent than the nonspecific calmodulin antagonists, trifluoperazine and fenoctimine (IC50 = 40 and 224 nM, respectively), and equipotent with the H+, K+-adenosine triphosphatase inhibitor, omeprazole (365 nM). CGS-9343B showed an IC50 of 369 nM for carbachol-induced [14C]aminopyrine accumulation in dispersed mucosal cells. CGS-9343B must be added to cells before or simultaneously with acid secretagogues in order to be effective. The drug did not reverse previously stimulated secretion. Unlike trifluoperazine and fenoctimine, CGS-9343B had anticamodulin activity for inhibition of calmodulin-activated (Type I) phosphodiesterase in the same range of potency as observed for the inhibition of aminopyrine accumulation. In anesthetized rats and dogs the i.v. infusion of CGS-9343B did not block histamine plus pentagastrin-stimulated acid secretion. However, i.a. administration of CGS-9343B to anesthetized rats produced a significant inhibition of acid secretion. In vivo the order of potency was omeprazole greater than cimetidine much greater than CGS-9343B. These data provide evidence for involvement of calmodulin in the acid secretory process and suggest that the pursuit of selective calmodulin antagonists such as CGS-9343B may prove useful for understanding the regulation of the hydrogen ion secretory process.

Correlation of cell-free brain cyclic nucleotide phosphodiesterase activities to cyclic AMP decay in intact brain slices.

Differential and gradient centrifugation of rat brain cerebral cortical homogenates show three cyclic nucleotide phosphodiesterase (CN PDE) activities localized to different subcellular fractions with varying relative specific activities and responsiveness to pharmacologic agents. Type I (calcium/calmodulin-activatable) CN PDE is found primarily in the cytosolic fraction, Type II (cGMP-activatable) CN PDE is predominately membrane associated, and Type IV (cGMP-insensitive) cAMP PDE is distributed equally between soluble and particulate fractions. Fractionation of cerebral cortical membranes shows that Type II and Type IV CN PDE activities reside in synaptosomes. Type II CN PDE is the predominate hydrolytic activity in synaptosomes whereas Type IV cAMP PDE contributes only a small percentage of the total cAMP hydrolysis and Type I CN PDE is not detected in this fraction. The contribution of CN PDE isozymes to the regulation of intracellular cAMP levels was studied using rat brain cortical slices. The rate of cAMP decay in the absence and presence of selective CN PDE inhibitors after adenosine or beta-adrenergic agonist stimulation was determined using an adenine prelabeling technique. These studies show that a rolipram-sensitive, high affinity cAMP PDE (Type IV) is principally responsible for cyclic AMP decay in intact cortical tissue following elevation of cyclic AMP levels by either adenosine or beta-adrenergic receptor agonists. However, this isozyme, which is sensitive to inhibition by rolipram, RO 20-1724 and SQ 65442 contributes only a small percentage of the total cAMP hydrolytic activity in cell-free preparations of cortex.

Effect of CGS-8216 on high-dose flurazepam convulsive threshold.

Flurazepam, a clinically proven and widely accepted sedative hypnotic, has been shown by a number of investigators to produce convulsions at toxic doses. In the present study, CGS-8216, a benzodiazepine receptor antagonist, reduced the dose of flurazepam required to produce convulsions. This suggests that the convulsant action of FLZ is exerted at a site other than the benzodiazepine receptor.

Convulsant component of a depressant benzodiazepine.

The convulsant influence of high doses of diazepam, in the presence of the benzodiazepine receptor antagonist Ro 15-1788, was studied in rats. Animals were implanted with permanent cortical screw electrodes for EEG recording. EEG spiking and accompanying clonic activity was observed in rats receiving greater than or equal to 200 mg/kg diazepam, followed 10 minutes later by Ro 15-1788 (20 mg/kg). Pentylenetetrazole and picrotoxin seizure thresholds, measured during constant rate iv infusion, were significantly lowered by pretreatment with diazepam (250 mg/kg) and Ro 15-1788 (20 mg/kg) administered 30 and 20 minutes, respectively, before seizure threshold measurement. It is proposed that this convulsive activity of diazepam is mediated through the picrotoxinin receptor.

Reduction of flurazepam convulsive threshold by Ro 15-1788.

The influence of the benzodiazepine (BZ) receptor antagonist Ro 15-1788 on the convulsant properties of flurazepam (FLZ) was studied in rats. Animals were prepared with chronic epidural electrodes for EEG recording and respiratory rates were recorded via a rubber bulb connected to a pressure transducer. FLZ convulsive thresholds were determined by continuous IV infusion in the presence and absence of Ro 15-1788 pretreatment. All animals receiving the FLZ infusion experienced convulsions preceded by dose-dependent reduction of respiratory rate. Pretreatment with Ro 15-1788 substantially reduced the FLZ convulsive threshold, suggesting a blockade of the depressant (anticonvulsant) aspect of the FLZ effect, thus, augmenting a convulsant effect at a separate receptor. An alternate hypothesis is that Ro 15-1788 may increase the affinity or intrinsic activity of the receptor responsible for the convulsant aspect of FLZ. Ro 15-1788 did not appear to alter the respiratory rate depressant effect of FLZ, although early onset of convulsions in the pretreated animals precluded measurement of respiration at the higher dose of FLZ allowable in animals that were not pretreated with the antagonist.

Increased susceptibility of audiogenic rats to barbital withdrawal convulsions.

Non-responsive progeny from Sprague-Dawley derived rats genetically susceptible to sound-induced (audiogenic) convulsions (AGS-negative) and non-responsive progeny from Sprague-Dawley derived rats not gentically susceptible to audiogenic convulsions (SD-negative) were subjected to a seven-day treatment regimen of sodium barbital. 125 mg/kg, every 12 hours. This represents a lower dose and shorter treatment period than that normally used in this laboratory to induce barbiturate dependence in rats. Animals were subjected to a 115 dB sound stimulus 38 hours following the last dose of sodium barbital. SD-negative rats did not become susceptible to sound-induced convulsions, but AGS-negative rats did experience convulsions when exposed to the sound stimulus during withdrawal. These results are consistent with the hypothesis that rats generally referred to as "audiogenic" may actually suffer from differences which result in an increase of susceptibility to seizures induced by any of several means.

Message cues, intelligibility, and comprehension: a follow-up investigation.

From an earlier study (Garrett and Saint-Pierre, J. Aud. Res., 1980, 20, 71-80) on the perception of sentences in noise (S/N = -5, -3, -1 db) showing that cues identifying the topic of messages can significantly increase comprehension, the effect of the cues was reasoned to be the result of improving either the peripheral processes of recognition associated with initial word reception or the more central processes of interpreting sense and meaning. Supplementary analyses are here performed on these data: number of words heard correctly, length of response, accuracy of repeated messages, and an overall Performance Index. The lesser significance in all these analyses for the cue condition than was found in the original analyses for comprehension only, coupled with the consistent and highly significant differences across S/N for the same statistics, was taken as indirect support for the view that the primary effect of the cues was operative at the level of central rather than of peripheral processes associated with initial reception.

Message comprehension as a function of intelligibility and advance knowledge of the topic.

The relationship was investigated between estimated intelligibility (EI) and message comprehension (ability to answer questions presented at various levels of intelligibility). In Exper. I, 10 young adults identified the S/N ratio they associated with 0, 25, 50, 75, and 100% intelligibility for easy story material in speech-shaped noise at a constant 75 db SPL; subsequently, at the S/N's thus determined, comprehension was measured with easy short-answer questions. There was a very strong relationship between EI and comprehension, suggesting that the two were more or less synonomous. In Exper. II, comprehension with easy short-answer questions was measured at EI's of 25, 50, and 75% when each question was preceded by relevant, irrelevant, or no cues to the general topic of the question. Relevant cues had a positive effect which was significant at the 25 and 75% EI levels. The suggestion from Exper. I on the identity of EI and comprehension was modified to show that EI levels are a psychoacoustic variable which can be used to identify a regular decrease in comprehension when the speech signal is progressively masked by speech-shaped noise, but that the actual level and rate of decrease in intelligibility is a function of other factors, including psycholinguistic features of the message itself.

The effect of sex, dietary energy, meat protein, ascorbic acid and iron on broiler skin collagen.

Two studies were conducted to determine if variation of sex, dietary energy, meat protein, ascorbic acid or iron had any effect on collagen metabolism in broilers. In the first experiment day-old broiler type chicks were fed diets which contained 3190 or 3410 kcal. M.E./kg. of diet, 0 or 15% meat and bone meal and 0 or 1 g./kg. ascorbic acid. In the second experiment the day-old broiler chicks were fed diets which had 3190 or 3410 kcal. M.E./kg. of diet and 60 or 260 p.p.m. of iron. At 56 days of age the broilers were weighed, a representative number of birds killed from each group and skin samples collected. The skin samples were analyzed for the degree of collagen cross-linking and the total and insoluble collagen contents. An alteration of energy, meat protein, ascorbic acid or iron in the diet had no effect on collagen formation in the skin of broilers reared in cool environmental temperatures. Female broilers had a significantly higher percentage of insoluble collagen in the skin tissue but the level of total collagen and insoluble collagen was higher in the male birds.

Effect of micelle formation on the absorption of neutral fat and fatty acids by the chicken.

Experiments were conducted to determine the absorption of various dietary fatty acids and glycerides singly and in mixtures. Chickens with or without cannulated bile ducts or ligated pancreatic ducts were used to evaluate the absorption of fatty acids or mixtures of fatty acids and the absorption patterns of several classes of lipids and their effect on the absorption of palmitic acid under in vivo conditions. In spite of wide melting point differences, isomers of various monoglycerides or 18-carbon unsaturated fatty acids exhibited identical absorption and solubility patterns. A homologous series of saturated monoglycerides showed a maximum absorption value for the monoglycerides with fatty acids of 12 and 14 carbons. Absorption decreased with increasing chain lengths of the fatty acid in the monoglyceride. Conversely, the absorption of palmitic acid when fed with the various monoglycerides progressively increased to a maximum in the mixture containing monomyristin and then decreased when fed with monopalmitin or monostearin.