Intracisternal urocortin inhibits vagally stimulated gastric motility in rats: role of CRF(2)

Abstract

1. Corticotropin-releasing factor (CRF) acts in the brain to inhibit thyrotropin-releasing hormone (TRH) analogue, RX-77368-induced vagal stimulation of gastric motility. We investigated CRF receptor-mediated actions of rat urocortin (rUcn) injected intracisternally (ic) on gastric motor function. 2. Urethane-anaesthetized rats with strain gauges on the gastric corpus were injected i.c. with rUcn and 20 min later, with i.c. RX-77368. CRF antagonists were injected i.c. 10 min before rUcn. 3. RX-77368 (1.5, 3, 10, 30 and 100 ng, i.c.) dose-dependently increased corpus contractions, expressed as total area under the curve (AUC, mV min(-1)) to 2.6+/-2.5, 6.1+/-5.9, 9.8+/-2.6, 69.7+/-21.7 and 74.9+/-28.7 respectively vs 0.2+/-0.1 after i.c. saline. Ucn (1, 3 or 10 microg) inhibited RX-77368 (30 ng)-induced increase in total AUC by 28, 62 and 93% respectively vs i.c. saline+RX-77368. 4. The CRF(1)/CRF(2) antagonist, astressin-B (60 microg, i.c.) completely blocked i.c. rUcn (3 microg, i.c.)-induced inhibition of gastric motility stimulated by RX-77368 (30 ng). 5. The selective CRF(2) antagonist, astressin(2)-B (30, 60 or 100 microg, i.c. ) dose-dependently prevented i.c. rUCn action while the CRF(1) antagonist, NBI-27914 did not. 6. In conscious rats, rUcn (0.6 or 1 microg, i.c.) inhibited gastric emptying of an ingested chow meal by 61 and 92% respectively. rUcn action was antagonized by astressin(2)-B. 7. These data show that i.c. rUcn acts through CRF(2) receptors to inhibit central vagal gastric contractile response and postoprandial emptying.

Figure 1

Dose-related stimulation of gastric contractions induced by intracisternal injection of the TRH analogue, RX-77368 in 18-h fasted urethane-anaesthetized rats. After a 30 min basal period, different groups of rats were injected i.c. with either saline or RX-77368 (1.5, 3, 10, 30 and 100 ng) and corpus contractions were recorded for 120 min. Each bar represents the mean±s.e.m. of total AUC of gastric contractions; the number of rats per group is indicated on top of bars; *P<0.05 compared with other doses (ANOVA).

Figure 2

(a) Time course of gastric contractile response to i.c. RX-77368 and dose-related inhibitory effect of i.c. urocortin in 18-h fasted urethane-anaesthetized rats. Each point represents the mean AUC min⁻¹ of corpus contractions; (b–f) Representative traces of the dose-related and temporal inhibitory effect of intracisternal urocortin on RX-77368-induced stimulation of gastric contractions. Note the marked increase in corpus contractility induced by i.c. injection of the TRH analogue (c) compared with that of saline (b) and the dose-related inhibition of contractile response (magnitude and duration) by urocortin at 1, 3 and 10 μg (d–f).

Figure 3

Dose-related inhibitory effect of intracisternal urocortin on RX-77368-induced stimulation of gastric contractions in 18-h fasted urethane-anaesthetized rats. After 30 min basal period, different groups of rats were injected i.c. with vehicle or rUcn (1, 3 or 10 μg) and 20 min later with RX-77368 (30 ng) or saline, and corpus contractions were recorded for 120 min. Bar graphs represent the mean±s.e.m. of total AUC (a), mean spike amplitude (b), and mean spike duration (c); the number of animals is indicated on top of the columns. *P<0.05 compared with vehicle+RX-77368; #P<0.05 vs vehicle+vehicle or urocortin+vehicle.

Figure 4

Intracisternal astressin B antagonized intracisternal urocortin-induced inhibition of RX-77368 induced stimulation of gastric contractions in 18-h fasted urethane-anaesthetized rats. Intracisternal injection of astressin B or vehicle was followed 10 min later by that of urocortin or vehicle and 20 min later by RX-77368. Gastric contractility was monitored for 40 min before and 120 min after RX-77368 injection. Each bar represents the mean±s.e.m. of total AUC of corpus contractions; the number of rats per group is indicated on top of each bar. *P<0.05 compared with vehicle+urocortin+RX-77368; #P<0.05 compared with vehicle+vehicle+RX-77368.

Figure 5

Intracisternal astressin₂-B dose-dependently antagonized intracisternal urocortin-induced inhibition of RX-77368 stimulated gastric contractions in 18 h-fasted urethane-anaesthetized rats. Intracisternal injection of astressin₂-B or vehicle was followed 10 min later by that of urocortin or vehicle and 20 min later RX-77368. Gastric contractility was monitored for 40 min before injections and up to 120 min after RX-77368. Each bar represents the mean±s.e.m. of total AUC of contractions; the number of rats per group is indicated on top of each bar (a). Time course of contractile response with each point representing the mean of AUC min⁻¹ (b). *P<0.05 compared with vehicle+urocortin+RX-77368; #P<0.05 compared with vehicle+vehicle+RX-77368.

Figure 6

Representative tracing of blockade of intracisternal urocortin-induced inhibition of gastric motor activity stimulated by RX-77368: blockade by the CRF₁/CRF₂ receptor antagonist, astressin B and the selective CRF₂ receptor antagonist, astressin₂-B but not by the selective CRF₁ receptor antagonist, NBI-27914 in 18-h fasted urethane-anaesthetized rats. Note the marked increase in corpus contractility induced by i.c. injection of the TRH analogue (a) and the inhibitory effect of i.c. rUcn (b) and the dose-related reversal by astressin B (c,d) and astressin₂-B (e) while NBI-27914 had no effect (f).

Figure 7

Dose-related inhibition of gastric emptying of a solid meal by intracisternal injection of urocortin in conscious fed rats (a) and blockade of urocortin effects by pretreatment with the selective CRF₂ receptor antagonist astressin₂-B (b). Fasted rats were given free access to Purina chow and water for 3 h, then food and water were removed; (a) saline or rUcn (0.3–1 μg) was injected i.c. in different groups of rats; (b) vehicle or astressin₂-B was injected i.c. followed by i.c. injection of saline or rUcn (1 μg) and gastric emptying monitored 5 h later. Each bar represents the mean±s.e.m.; the number of rats per group is indicated on top of each bar. *P<0.05 compared with vehicle (0.0) and rUen (0.3). #P<0.05 compared with other experimental groups.