The rat external urethral sphincter an in vitro model to evaluate the activity of drugs on the smooth and striated components of the urinary bladder outlet.

Electrical field stimulation (EFS, 2.5 Hz, 60 V, 1 ms, trains of 5 sec every 5 min) of the rat external urethral sphincter (EUS) produced contractile responses characterized by a "slow" tonic contraction on which was superimposed a series of phasic "twitch-like" contractions. Both responses were abolished by tetrodotoxin (0.6 microM), and their amplitude was significantly lower in samples taken from denervated (15 days before) sphincters. The tonic contraction showed duration, voltage, and frequency dependency, whereas the twitches were markedly duration dependent. No correlation was found between the amplitude of the tonic and that of the twitch-like contractions. Phentolamine (3 microM) reduced by 95% the amplitude of the tonic contraction produced by maximal parameters, whereas it did not affect the twitches. On the other hand, hexamethonium (10 microM) was ineffective on both components. Dantrolene (10 microM) inhibited the twitch response, whereas it did not influence the tonic component. Preincubation with d-tubocurarine (0.2 mM) or succinylcholine (2 mM) significantly inhibited the amplitude of twitches produced by EFS (0.1 Hz, 60 V) up to a duration of 50 microseconds. Stimulus width higher than 50 microseconds, resulted in twitches that were resistant to neuromuscular blocking agents but sensitive to dantrolene (10 microM). Our results indicate that the rat external urethral sphincter is a reliable and easy "in vitro" model for studying the activity of drugs capable of interfering with the nerve-mediated activity of the striated and smooth muscle portion of the urinary bladder outlet.

Aberrant craniopharyngeal structures within the neurohypophysis of rats.

Aberrant craniopharyngeal structures within the neurohypophysis were analyzed in 17 rats, originating from four different colonies of Sprague-Dawley- and Wistar-derived strains, which were used for toxicity studies in five different laboratories. Males were more frequently affected than females. The incidence of these findings, which occurred spontaneously and mainly in aged rats, was very low. Predominant features included tubular or acinar glandular structures, rarely embedded in a fibrous stroma, and, as a rule, not compressing adjacent tissue. In some cases, large cysts filled with colloid-like, amorphous material and cellular debris were present. The tubular structures consisted of a rather flat epithelium, while the cystic elements were lined by a cuboidal or columnar, rarely ciliated epithelium, containing goblet cells, or by a stratified squamous epithelium. These structures reacted positively for cytokeratin. Acinar structures mimicked salivary glands of the serous or mucinous type. In a few cases, small, round or fusiform cells were present. Distribution and predominance of the various epithelial structures depended on the strain and colony of rats. Considering the ontogenic development of the pituitary gland, the morphological aspect of these lesions, their immunoreactivity and former reports on similar findings, we concluded that these rats have aberrant craniopharyngeal structures within the pars nervosa of the hypophysis, originating from remnants of the oro-pharyngeal epithelium of the craniopharyngeal duct (RATHKE's pouch). These lesions, which occurred in different strains and colonies of laboratory rats, represent heterotopias or choristomas, consisting of non-neoplastic growth disturbances. Being of a distinctly non-proliferative nature, they should not be confused with craniopharyngiomas.

Long term toxicity and carcinogenicity of a new protein source in rats.

Sprague Dawley rats were fed with yeast (Candida Maltosa) obtained by fermentation of n-Paraffins F.U. grade (C12-C19). The yeast was incorporated in the diet at 7.2, 18.4 and 34.5% by weight. Each diet was isocaloric and isoproteic with the others and with the standard diet. The yeast supplied 20, 50, 80% of the proteins of the diet respectively. 65 rats per sex per group were selected at random from over 1000 rats and assigned to each of the 4 diets for the carcinogenicity study; 57 rats per sex group were selected at random from the same 1000 rats and assigned to each of the 4 diets for the long term study. In long term study the rats were sacrificed at 3, 6, 15 and 24 months. In the carcinogenicity study the animals were kept till less than 10% of the starting number was surviving; the experiment lasted 30 months. Animals dead spontaneously or killed at the end of the trial were autopsied and the main organs fixed for histological examination. Lesions and tumours were classified. Biochemical, haematological and autopsy variations at the times of sacrifice were observed in the long term study. The experiment showed no pathological differences between controls and animals treated with 20 and 50% proteins from yeast. The group fed with 80% single cell protein showed a significant increase of malignant lymphomas incidence.

Hyperresponsiveness to non-adrenergic, non-cholinergic vagal stimulation following multiple antigen challenge in guinea-pigs.

The role of airway inflammation, induced by weekly antigen challenge, in the airway hyperresponsiveness to vagal (whole and NANC components) nerve stimulation and to neurotransmitters (acetylcholine and selective agonists for tachykinin NK1 and NK2 receptors) has been studied in the guinea-pig. Primarily, the time course (3, 7 and 14 days following the last challenge) of the effects of repeated aerosol antigen challenge on airway inflammation and bronchoalveolar fluid cellular composition was investigated. At 7 days following the last antigen challenge a maximal (as compared to 3 and 14 days) inflammatory response, in terms of a diffuse mild to marked infiltration of eosinophils, neutrophils and lymphocytes, was evident throughout pulmonary tissues. Only at this time some evidence of eosinophilia and neutropenia was detectable in BAL fluids. In these animals there was a normal bronchial responsiveness to iv administration of acetylcholine, selective synthetic agonists for the tachykinin NK2 receptors and capsaicin. On the other hand a remarkable airways hyperresponsiveness to iv administration of selective agonists for tachykinin NK1 receptors, as well as electrical stimulation of the vagal nerves (in presence and in absence of atropine), was detected. As a whole, these data indicate that at the peak of the inflammatory airway response following multiple antigen challenge there is a selective hyperresponsiveness to stimulation of vagal (mainly the non-adrenergic, non-cholinergic component) nerves associated with an increase in tachykinins (NK-1)-mediated bronchospasm.