The oxytocic substance of posterior pituitary extracts is normally present in equal amounts in both sexes (van Dyke, Adamsons & Engel, 1955). So far two physiological functions have been ascribed to oxytocin, namely, as one of the factors causing contraction of the uterus in parturition, and as the factor responsible for contraction of the mammary myo-epithelial cells in lactation. Several workers have tried to find some other function for this substance. Positive results were obtained by Dicker & Heller (1946) who reported that when Pitocin (oxytocin; Parke, Davis) was given subcutaneously to rats in doses of 3 m-u/100 g rat, glomerular filtration rate (G.F.R.) and renal plasma flOW (R.P.F.) were increased and Cl reabsorption diminished. Demunbrun, Keller, Levkoff & Purser (1954) observed that Pitocin and du Vigneaud's highly purified oxytocin when infused intravenously in large amounts, or given subcutaneously in doses of 2-7-5 i.u., raised renal clearances in dogs with diabetes insipidus, and they suggested that one of the normal functions of oxytocin was to maintain renal blood flow. Brunner, Kuschinsky & Peters (1956) gave doses of 1-50 m-u. oxytocic extract subcutaneously to rats and observed that following hydration with saline solutions, or when the animals were dehydrated, the extract acted as a diuretic and increased Na and K excretion in parallel with the increase in rate of urine flow.The experiments described below were made in another attempt to find out whether oxytocin has some other function than its acknowledged and intermittent ones and whether there is a physiological interdependence of vasopressin and oxytocin. The latter question arises since it has been observed that whatever stimulus is applied to the posterior pituitary-electric, suckling, osmotic etc.-the gland liberates simultaneously both the vasopressor and oxytocic factors, and that the oxytocic one is liberated in greater amounts than the vasopressor by about 4-20 times (Harris, 1955). It was therefore
We investigated the gastric acid secretory and motility responses to microinjection into the dorsal motor nucleus of the vagus (DMV) of RX 77368, a stable thyrotropin-releasing hormone (TRH) analogue, and bicuculline, a gamma-aminobutyric acid (GABAA) receptor antagonist in ketamine-chloralose-anesthetized cats. Gastric acid output was collected every 15 min through a gastric cannula after saline flush and titrated to pH 7.0. Antral contractions were continuously recorded by an extraluminal strain gauge force transducer. The chemicals were dissolved in saline and unilaterally microinjected in volumes of 200 nl. RX 77368 or bicuculline microinjected into the DMV induced significant dose-dependent (50-500 ng) increases in gastric acid secretion and significant dose-dependent (50-200 ng) increases in the force of antral contractions. In response to both chemicals the gastric acid output increased in the first 15 min and peaked in the second and third collections. RX 77368 (500 ng) had a second greater peak 90 min after microinjection. The motility responses were rapid in onset and lasted 60 min for RX 77368 and 30 min for bicuculline. The minimal effective dose for eliciting increased motility was consistently lower than inducing acid secretion. Electrical stimulation of the DMV with 100 microA, 50-Hz, and 0.2-ms pulse duration increased the force of antral contractions but had no effect on gastric acid secretion. Our results demonstrate that the DMV exerts important control over both gastric acid secretion and motility in cats. TRH exerts a stimulatory influence, while GABAA receptors mediate an inhibitory influence on this vagal control.
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