Cold ambient temperature reverses abdominal surgery-induced delayed gastric emptying and decreased plasma ghrelin levels in rats

Abstract

We investigated whether acute cold-induced vagal activation through brainstem thyrotropin-releasing hormone (TRH) signaling influences abdominal surgery-induced delayed gastric emptying (GE) in fasted rats. Laparotomy and cecal palpation or sham (short anesthesia alone) was performed 10 min before or 30 min after cold exposure (4-6°C) lasting 90 min. Non-nutrient GE was assessed during 70-90 min of cold exposure. Control groups remained at room temperature (RT). The stable TRH analog, RX-77368 (50 ng/rat) was injected intracisternally immediately before surgery and GE monitored 30-50 min postsurgery in rats maintained at RT. Plasma acyl (AG) and total ghrelin levels were assessed using the new RAPID blood processing method and radioimmunoassays. Desacyl ghrelin (DAG) was derived from total minus AG. In rats maintained at RT, abdominal surgery decreased GE by 60% compared to sham. Cold before or after surgery or RX-77368 normalized the delayed GE. In non-fasted rats, cold exposure increased plasma AG and DAG levels at 2 h (2.4- and 2.7-times, respectively) and 4 h (2.2- and 2.0-times, respectively) compared to values in rats maintained at RT. In fasted rats, abdominal surgery decreased AG and DAG levels by 2.4- and 2.1-times, respectively, at 90 min. Cold for 90 min after surgery normalized AG and DAG levels to those observed in sham-treated animals kept at RT. These data indicate that endogenous (cold exposure) and exogenous (TRH analog) activation of medullary TRH vagal signaling prevent abdominal surgery-induced delayed GE. The restoration of circulating AG levels inhibited by abdominal surgery may contribute to alleviate postoperative gastric ileus.

Fig. 1

Cold ambient temperature reverses or prevents the abdominal surgery-induced delay of gastric emptying. (A) Overnight fasted rats were subjected to abdominal surgery (laparotomy and cecal palpation) or sham treatment (anesthesia alone) and thereafter kept in semi-restraint Bollman cages under normal (21–23 °C) or cold (4–6 °C) ambient temperature for 90 min. Animals received an orogastric gavage of 1.5 ml viscous solution 70 min after the start of the different ambient temperatures and gastric emptying was monitored 20 min later. (B) Rats were placed in semi-restraint Bollman cages and kept at normal (21–23 °C) or cold (4–6 °C) ambient temperature starting at 30 min before sham procedure or abdominal surgery. After undergoing sham procedure or abdominal surgery, animals were housed for another 60 min at normal or cold ambient temperature. At 20 min before the end of this period, rats received an orogastric gavage of a liquid non-nutrient solution and gastric emptying was assessed 20 min later. Each bar represents the mean ± sem of the number of rats indicated at the bottom of the column. * p < 0.05 and *** p < 0.001 vs. all other groups.

Fig. 2

Intracisternal injection of the TRH analogue RX-77368 prevents the abdominal surgery-induced delayed gastric emptying. Rats fasted overnight were injected intracisternally with either the TRH analogue, RX-77368 (50 ng/10 µl saline) or vehicle (10 µl saline) and afterwards subjected to abdominal surgery or sham treatment. Animals received an orogastric gavage of 1.5 ml viscous solution 30 min after the end of the surgery or sham and gastric emptying was monitored 20 min later. Each bar represents the mean ± sem of the number of rats indicated at the bottom of the column. * p < 0.05 vs. all other groups.

Fig. 3

Cold ambient temperature increases acyl and desacyl ghrelin levels and decreases rectal temperature. Chronically intravenously cannulated, ad libitum fed rats were divided into two groups and kept in semi-restraint Bollman cages at either normal (21–23 °C) or cold (4–6 °C) ambient temperature for 4 h. Blood was withdrawn before and at 2 and 4h after start of the experiment. Acyl ghrelin (A) and total ghrelin levels were assessed by radioimmunoassay. Desacyl ghrelin (B) levels were obtained by calculating the difference of total ghrelin minus acyl ghrelin. Rectal temperature was assessed at the same time before and at 2 and 4h (C). Each bar or line represents the mean ± sem of 5 rats/group. * p < 0.05, ** p < 0.01 and *** p < 0.001 vs. control at the respective time point. # p < 0.05 vs. same group at time point 0 h.

Fig. 4

Cold ambient temperature reverses the abdominal surgery-induced decrease of acyl and desacyl ghrelin levels. Overnight fasted rats equipped with a chronic intravenous catheter underwent abdominal surgery and were kept in semi-restraint Bollman cages at normal (21–23 °C) or cold (4–6 °C) ambient temperature for 90 min. A control group was sham treated (anesthesia alone) and kept at room temperature afterwards. Blood was withdrawn at 30 and 90 min post treatment. Acyl ghrelin (A) and total ghrelin levels were assessed by radioimmunoassay. Desacyl ghrelin (B) was obtained by calculating the difference of total ghrelin minus acyl ghrelin. Each bar represents the mean ± sem of 4–5 rats per group. * p < 0.05 and ** p < 0.01 vs. sham at the respective time point. ## p < 0.01 and ### p < 0.001 vs. abdominal surgery/cold at the respective time point.