Continuous and reflex secretion by the parotid gland in ruminants

Abstract

The parotid glands of adult ruminants secrete saliva rapidly and continuously. The Coats et al. (1956) found that although chemical, electrical or mechanical stimulation of the mouths of sheep sometimes increased the rate of parotid secretion, such stimuli were ineffective when applied to the rumen.The experiments described in this paper confirm and extend earlier work on the secretion of parotid saliva in sheep and define some of the reflex mechanisms which influence the rate of secretion. Observations were also made on the submaxillary glands of sheep and on the parotid glands of goats and calves. A preliminary account of some of these results has been given (Comline & Kay, 1955). METHODSPreparations. Nineteen experiments were undertaken on Welsh Mountain sheep 6-15 months of age. These were decerebrated in the manner described by Comline & Titchen (1951). After fasting for 12-48 hr. anaesthesia was induced with ethyl chloride and maintained with ether; the brain stem was transected in a plane passing through the anterior colliculi and the mammillary bodies, and anaesthesia was then discontinued.

Abomasal secretion in the sheep

“…Such would be the case if receptors were located elsewhere than the buccal cavity and in this respect it may be pertinent to note that sensory nerve endings have, in fact, been demonstrated in the reticulorumen epithelium (Hill, 1959b). Whether these are concerned in the reflex control of gastric secretion remains to be seen but it is of interest that vagal afferents concerned with salivary secretion have already been described in the reticulo-rumen (Kay, 1958). Harper, Kidd & Scratcherd (1959) have also shown that stimulation of the central end of the abdominal vagus in the cat causes secretion of acid and pepsin in the gastric juice.…”

The development of parotid salivary secretion in young goats

“…The ability to secrete is especially poorly developed during the first 5 weeks of life, when there is almost no continuous secretion and the response to stimulation is only about one third of that of an equal weight of adult parotid tissue. In young calves also the parotid glands secrete slowly if at all (Epaneshnikov, 1935;Kay, 1958b) and it is possible that they develop less rapidly than in the goat for Kay & Phillipson (1959) found that the maximum rate of secretion by reflexly stimulated parotid glands (ml./g. hr) is considerably less in calves from 4 to 8 months old than in adult sheep.…”

“…The onset of ruminal digestion introduces nervous and possibly humoral factors which may augment self-differentiation (Borghese, 1950) and inductive processes in determining the rate of growth and differentiation of the parotid gland. The chewing of solid food, rumination and the presence of digesta in the forestomach will cause reflex stimulation of the parotid gland from the sensory areas of the mouth, oesophagus and forestomach (Clark & Weiss, 1952;Kay 1958b; Ash & Kay, 1959) that will have been almost wholly lacking when only milk was consumed. The existence of a humoral factor influencing parotid secretion was claimed by Krinitsin (1940), who showed that the rate of secretion of the denervated parotid gland declines little in calves that are fed normally but almost ceased in calves that fasted for 5 days following bilateral vagotomy.…”

“…In the most extreme instance PAROTID SECRETION IN YOUNG GOATS encountered, in which oesophageal distension increased the flow from the innervated gland sixfold, the same stimulus still caused a threefold increase after the parotid nerve had been cut. In previous studies on sheep (Kay, 1958b) section of the parotid nerve had always wholly abolished reflex parotid secretion.…”

“…We know that in young calves the parotid glands secrete very little saliva (Krinitsin, 1940; Kay, 1958b) although in adult sheep these glands supply about half of the estimated total salivary secretion (Kay, 1960). More detailed information concerning the flow and composition of saliva in young ruminants was desirable, and a study of the development of parotid secretion in young goats was therefore undertaken.…”