Intravenous injection of the a-adrenergic receptors agonist xylazine (0.3 mg/kg b. w.) produced hyperglycaemia with its peak (1 10 mg/100 ml) 30 min later in sheep. This hyperglycaemia was statistically significant for 3 hours. When xylazine was administered after pretreatment of the animals with either the a,-adrenergic receptors blocker prazosin (0.5 mg/kg i. v.) or the a2-blocker yohimbine (0.5 mg/kg i. v.) a hyperglycaemia was also produced but in the case of prazosin its peak did not exceed 95 mg/100 ml, and in the case of yohimbine it was only 70 mg/100 ml (control value 55 mg/ lOOml). When animals were pretreated with either yohimbine plus prazosin or the a,-and a,-blocker tolazoline (3 mg/kg i. v.) the hyperglycaemic effect of xylazine was inhibited. These results suggest that, in the regulation of blood glucose levels by the a-adrenergic receptors, the a, play the main role, while the a, are also involved.

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We wanted to determine if an acceleration of the normal emptying rate by motor stimulants interfers with control mechanisms limiting gastric emptying. Therefore, we studied the effects of 5-hydroxytryptophane (5-HTP) and cisapride on canine gastrointestinal motility and gastric emptying after ingestion of viscous acaloric and nutritive meals. Prolonged contractions and relaxations that change lumen size (isotonic component) and wall tension (isometric component) are defined as "basal contractions" and "basal relaxations", respectively. The nutrient meal emptied much slower than the acaloric meal due to several alterations of gastric, pyloric, and duodenal motility. Both drugs stimulated antral motility but failed to accelerate gastric emptying of the nutrient meal. The main causes for the failure were a basal relaxation of the proximal antrum and a basal contraction of the duodenum. In conclusion, basal contractions of the proximal antrum and duodenum play an important role in the process of gastric emptying, and under physiological conditions the control mechanisms of gastric emptying provide an optimal emptying rate that cannot be markedly accelerated by 5-HTP and cisapride.

Summary Forestomach motility during sedation induced by xylazine (0.3 mg/kg body weight i. m.) was studied in sheep by means of electromyography. The response of the reticulum to xylazine lasted 80 min; it started with a 45 min period of inactivity followed by a period of decreased activity. The ruminal response was manifested by a 70 min period of decreased activity which was characterized mainly by a decrease in frequency of the primary contractions, so that they became less frequent than the secondary ones. This explains the absence of development of bloat. The differences in response between reticulum and rumen are though to be linked to a difference in alpha2‐adrenergic receptors, in the CNS, which may exist between the motoneurones which innervate the reticulum and those which innervate the rumen. The omasal motor response to xylazine lasted 70 min and was opposite to that of the reticulo‐rumen. Since xylazine excites omasal motility through its action of the CNS, this supports the suggestion that although the motility of the omasum is considered to be mainly intrinsic, a possible CNS inhibitory control on its activity should not be disregarded. Zusammenfassung Über die Wirkungen von Xylazin auf die Vormagenmotilität beim Schaf Mittels Elektromyographie wurde die Vormagenmotilität bei Schafen nach Sedierung mit Xylazin (0,3 mg/Kg KGW, i. m.) überprüft. Die Reaktion des Netzmagens auf Xylazin dauerte 80 Minuten; sie begann mit einer Phase der Inaktivität (45 min) und war gefolgt von einer Phase herabgesetzter Motilität. Der Pansen reagierte während 70 min in Form einer herabgesetzten Aktivität, hauptsächlich gekennzeichnet durch eine Abnahme der Frequenz von primären Kontraktionen, die dadurch weniger häufiger als die sekundären waren. Dies erklärt das Ausbleiben von Blähungen. Die unterschiedlichen Reaktionen von Netzmagen und Pansen werden auf Unterschiede der α2‐adrenergischen Rezeptoren im ZNS zurückgeführt, die möglicherweise bestehen zwischen den Motoneuronen, die den Netzmagen bzw. den Pansen innervieren. Die Reaktion des Psalters auf Xylazin dauerte 70 min und war entgegengesetzt derjenigen von Netzmagen und Pansen. Da Xylazin über seine Wirkung auf das ZNS die Psaltermotilität anregt, wird darauf hingewiesen, daß ungeachtet der weitgehenden Intrinsic‐Motilität des Psalters eine mögliche inhibitorische Kontrolle des ZNS in Betracht zu ziehen ist.