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Effects of hepatic vagotomy on suppression of water intake induced by hepatic portal infusion of water in water-deprived rats
68
Neuroscience Letters, 150 (1993) 68-70 © 1993 Elsevier Scientific Publishers Ireland Ltd. All rights reserved 0304-3940/93/$ 06.00
NSL 09268
Effects of hepatic vagotomy on suppression of water intake induced by hepatic portal infusion of water in water-deprived rats Motoi Kobashi and Akira Adachi Department of Physiology, Okayama University Dental School, Okayama, (Japan)
(Received 16 September 1992; Revised version received 30 October 1992; Accepted 30 October 1992) Key words: Hepatic;Portal; Osmoreceptor;Drinking; Water intake; Water deprivation; Hepatic vagotomy; Rat
We investigated the effects of hepatic vagotomy on the suppression of water intake induced by hepatic portal infusion of water by 24-h waterdeprived rats. In sham-operated rats, water intake of the portal infusion group was significantlyless than that of the jugular infusion group during and after the infusion of deionized water for 3.5 h at a rate of 52/~l/min. This result reconfirmed our previous findings. On the other hand, in hepatic-vagotomized rats, the suppression during the portal infusion of water was not observed, but the suppression after portal infusion was observed. It is concluded that the suppression, at least during the portal infusion of water, was mediated by hepatoportal osmo-receptive (or sodium-receptive)afferent signals contained in the hepatic branch of the vagus nerve.
Hepatoportal osmo-receptors (or sodium-receptors) participate in the body fluid homeostasis in regulating fluid ingestion. Portal infusion of hypertonic saline suppressed saline intake but not water intake in normal rats [8], in water-deprived rats [2] and in sodium-deficit rats [10, 11]. Thus, possible participation of these osmoreceptors in the control of fluid ingestion has been studied by salt preference tests. Recently, we reported that portal infusion of water suppressed water intake in water-deprived rats, although portal infusion of isotonic or hypertonic saline did not affect water intake [7]. It is speculated that the hepatoportal osmo-receptive afferent signals mediate this suppression. The hepatic branch of the vagus nerve contains afferent neurons that convey hepatoportal osmo-receptive signals to the central nervous system [1, 4-6]. It is known that the saline intake was regulated by the afferents contained in the hepatic branch of the vagus nerve [3, 10, 11]. In the present experiments, to know whether or not the afferents contained in the hepatic branch of the vagus nerve regulate the water intake, we investigated the effect of hepatic vagotomy on the suppression of water intake induced by the hepatic portal infusion of water in waterdeprived rats. Eight-week-old male Sprague-Dawley rats (Charles River) weighing 27(~335 g (mean + S.E., 292.8 + 2.8) Correspondence: M. Kobashi, Department of Physiology, Okayama University Dental School, Shikata-cho, Okayama, 700, Japan.
were used in all experiments, All rats (n -- 32) underwent catheterization surgery of the hepatic portal vein and the right jugular vein. Detailed procedure of the catheterization was already stated in our previous report [7]. H a l f of the rats (n = 16) underwent hepatic vagotomy. Another half (n = 16) received sham operation. In hepatic-vagotomized rats, two sutures were tied around the hepatic branch extending from ventral trunk of subdiaphragmatic vagus, 0.5 cm apart, and the nerve inbetween the sutures was sectioned. In sham-operated rats, the hepatic vagus was exposed for approximately the time required to perform hepatic vagotomy, but the vagus was not interfered with. Rats receiving surgery were housed in 25 x 25 x 40 cm Plexiglas cages, on a 12:12 light:dark cycle (light from 6.00 to 18.00 h), in a r o o m at 23-24°C. Rats were maintained in this cage on tap water except when deprived and normal chow until the end of the experiments. All rats were tested in a water-deprived state. Eight or nine days after surgery, rats were deprived of water from 18.00 h (at the beginning of the dark period). One hour before the start of the next dark period (17.00 h), food was removed. Infusion of deionized water was started at 17.30 h for 3.5 h at a rate of 52/A/min. At 18.00 h, tap water was supplied again. Water intake without food was measured for 24 h by a drop counter and recorded on a pen recorder for later analysis. Each rat received the portal or the jugular infusion of deionized water. Each rat was tested only once. Therefore, rats were divided
69
into 4 groups; sham-operated rats with portal infusion (n = 8), sham-operated rats with jugular infusion (n = 8), hepatic-vagotomized rats with portal infusion (n = 8), hepatic-vagotomized rats with jugular infusion (n = 8). F o o d intake from the start of the dark period until the start of infusion was measured daily for 3 days. Water intake was measured at all times after surgery. For the 3 days before the test, daily food and water intake were not significantly different among the 4 groups. After all experiments, the animals were sacrificed by over-doses of anesthesia. Water intake was expressed in ml by multiplying the number of drops by 0.067. The results of each 3-h intake in the dark period and 12-h intake in the light period are presented as bar graphs (Fig. 1). Cumulative intake is presented at 0.5, 1, 2, 3 h after presentation of tap water (Fig. 2). Data are presented as means + S.E. Results were analyzed using Student's t-tests. Fig. 1 shows the 3-h water intake in the dark period and the 12-h water intake in the light period. In shamoperated rats (left panel), the water intake of the portal infusion group was significantly less than that of the jugular infusion group from 0 to 3 h (t = 4.190, P < 0.001), from 3 to 6 h (t = 2.788, P < 0.05) and from 6 to 9 h (t --- 2.269, P < 0.05). N o significant differences were seen in the water intake from 9 to 12 h (t = 1.862, n.s.) and from 12 to 24 h (t = 0.297, n.s.). In hepatic-vagotomized rats (right panel), significant differences of the water intake between the portal infusion and the jugular infusion group from 3 to 6 h (t = 2.561, P < 0.05) were observed. No significant differences were seen in the water intake from 0 to 3 h (t = 0.186, n.s.), from 6 to 9 h
15"
Sham Operated
Hepatic Vagotomized
r-i Portal Infusion of water {N-8) • Jugular intusion of water (N=8)
[~ Portal Infueion of water (N-8) • Jugular infusion of water (N,,8) NS
E v
lO P
~i~ NS
~
NS F--7
NS
P
3-6
6-9
9-12
Ns
P
0
0-3
3-6
6*9
9-12
Time (hours)
12-24
0-3
12-24
Time (hours)
Fig. 1. Water intake of sham-operated (left) and hepatic-vagotomized (right) rats. Water intake shown for a successive 3-h period except for final column (12-h intake) in each graph.
8
¸
6
***
'_
Q> 4 //i i
I/ I/
//
Hepatic Vagotornlzed Groups --o--
2 I/i/
: -
I
0
0
eo.= Int=.k~ ON-8)
"-~D~ JugularInfusion(N-8)
; Time
G.,.,. Portal Inlusion(N-8) JugularInfusion(N=8) 2'
3'
(hours)
Fig. 2. Effect of hepatic vagotomy on cumulative water intake during the infusion of water. *P < 0.05, **P < 0.01, ***P < 0.001, when water intake during the portal infusion of sham-operated rats is compared with the water intake of the jugular infusion to sham-operated rats. # P < 0.05, # # P < 0.01, when water intake during the portal infusion of sham-operated rats is compared with the water intake of the portal infusion to hepatic-vagotomized rats.
(t = 1.717, n.s,), from 9 to 12 h (t = 0.749, n.s.) and from 12 to 24 h (t = 0.564, n.s). Detailed analysis of cumulative water intake during the infusion is shown in Fig. 2. Cumulative water intake during portal infusion of shamoperated group suppressed water intake significantly compared to those during jugular infusion of sham-operated group (t = 1.955, n.s., 0.5 h; t = 2.612, P < 0.05, 1 h; t = 2.986, P < 0.01, 2 h; t = 4.190, P < 0.001, 3 h) and those during portal infusion of hepatic-vagotomized group (t = 2.657, P < 0.05, 0.5 h; t = 3.016, P < 0.01, 1 h; t = 2.971, P < 0.05, 2 h; t = 2.461, P < 0.05, 3 h). Cumulative water intake during portal infusion of hepaticvagotomized groups was not changed in comparison with that during jugular infusion of hepatic-vagotomized groups ( t = 0.102, n.s., 0.5 h; t = 0 . 4 6 6 , n.s., 1 h; t = 0.106, n.s., 2 h; t = 0.186, n.s., 3 h). Results from the hepatic portal and the jugular infusion to sham-operated rats reconfirmed our previous observation [7]. The portal infusion of water suppressed water intake induced by the 24-h water deprivation dur-
70
ing and after the infusion. The suppressive effect during the portal infusion of water was completely abolished by the hepatic vagotomy. Therefore, it is concluded that the suppression, at least, during the portal infusion of water is mediated by the osmo-receptive afferents included in the hepatic branch of the vagus nerve. Smith and Jerome [9] reported that the hepatic vagotomy produced the over-ingestion of water after water deprivation. Our observation is similar to their results. Water intake was facilitated by the hepatic vagotomy. However, general facilitation of water intake by the hepatic vagotomy was not observed in our experiments, because significant differences were not observed between sham-operated and hepatic-vagotomized groups treated by the jugular infusion of water. Our results showed the disappearance of the suppression of water intake during the portal infusion of water by the hepatic vagotomy. In hepatic-vagotomized group, the suppression after the infusion remained. Hepatic vagal afferent is not involved in this relatively longer term suppression. In the present experiments, we are unable to delineate a possible neural mechanism of this suppression. In conclusion, the suppression during the portal infusion of water is mediated by the hepatoportal osmo-receptive afferent signals contained in the hepatic branch of the vagus nerve. Therefore, hepatic vagal afferent signals resulting from the hypotonicity of the hepatoportal region have an inhibitory effect on water intake. This work was supported by Grant-in-Aid for Encouragement of Young Scientists 01771510 from the Ministry
of Education, Science and Culture of Japan, and Grantin-Aid for General Scientific Research 02670831 from the Ministry of Education, Science and Culture of Japan. 1 Adachi, A., Niijima, A. and Jacobs, H.L., An hepatic osmoreceptor mechanism in the rat: electrophysiological and behavioral studies, Am. J. Physiol., 231 (1976) 1043-1049. 2 Blake, W.D. and Lin, K.K., Hepatic portal vein infusion of gJucose and sodium solutions on the control of saline drinking in the rat, J. Physiol., 274 (1978) 129 139. 3 Contreras, R.J. and Kosten, T., Changes in salt intake after abdominal vagotomy: evidence for hepatic sodium receptors, Physiol. Behav., 26 (1981) 575-582. 4 Haberich, F.J., Osmoreception in the portal circulation., Fed. Proc., 27 (1968) 1137 1141. 5 Kahrilas, P.J. and Rogers, R.C., Rat brainstem neurons responsive to changes in portal blood sodium concentration, Am. J. Physiol., 247 (1984) R792-R 799. 6 Kobashi, M. and Adachi, A., Convergence of hepatic osmoreceptive inputs on sodium-responsive units within the nucleus of the solitary tract of the rat, J. Neurophysiol., 54 (1985) 212 219. 7 Kobashi, M. and Adachi, A.. Effect of hepatic portal infusion of water on water intake by water-deprived rats, Physiol. Behav., 52 (1992) in press. 8 Lin, K.K. and Blake, W.D., Hepatic sodium receptor in control of saline drinking behavior, Commun. Behav. Biol.. 5 (1971) 359 363. 9 Smith, G.P. and Jerome, C., Effects of total and selective abdominal vagotomies on water intake in rats, J. Auton. Nerv. Syst., 9 (1983) 259-271. 10 Tordoff, M.G., Schulkin, J. and Friedman, M.I., Hepatic contribution to satiation of salt appetite in rats, Am. J. Physiol., 25 l (1986) Rl095 Rl102. 11 Tordoff, M.G., Schulkin, J. and Friedman, M.I.. Further evidence for hepatic control of salt intake in rats, Am. J. Physiol., 253 (1987) R444-R449.
Neuroscience Letters, 150 (1993) 68-70 © 1993 Elsevier Scientific Publishers Ireland Ltd. All rights reserved 0304-3940/93/$ 06.00
NSL 09268
Effects of hepatic vagotomy on suppression of water intake induced by hepatic portal infusion of water in water-deprived rats Motoi Kobashi and Akira Adachi Department of Physiology, Okayama University Dental School, Okayama, (Japan)
(Received 16 September 1992; Revised version received 30 October 1992; Accepted 30 October 1992) Key words: Hepatic;Portal; Osmoreceptor;Drinking; Water intake; Water deprivation; Hepatic vagotomy; Rat
We investigated the effects of hepatic vagotomy on the suppression of water intake induced by hepatic portal infusion of water by 24-h waterdeprived rats. In sham-operated rats, water intake of the portal infusion group was significantlyless than that of the jugular infusion group during and after the infusion of deionized water for 3.5 h at a rate of 52/~l/min. This result reconfirmed our previous findings. On the other hand, in hepatic-vagotomized rats, the suppression during the portal infusion of water was not observed, but the suppression after portal infusion was observed. It is concluded that the suppression, at least during the portal infusion of water, was mediated by hepatoportal osmo-receptive (or sodium-receptive)afferent signals contained in the hepatic branch of the vagus nerve.
Hepatoportal osmo-receptors (or sodium-receptors) participate in the body fluid homeostasis in regulating fluid ingestion. Portal infusion of hypertonic saline suppressed saline intake but not water intake in normal rats [8], in water-deprived rats [2] and in sodium-deficit rats [10, 11]. Thus, possible participation of these osmoreceptors in the control of fluid ingestion has been studied by salt preference tests. Recently, we reported that portal infusion of water suppressed water intake in water-deprived rats, although portal infusion of isotonic or hypertonic saline did not affect water intake [7]. It is speculated that the hepatoportal osmo-receptive afferent signals mediate this suppression. The hepatic branch of the vagus nerve contains afferent neurons that convey hepatoportal osmo-receptive signals to the central nervous system [1, 4-6]. It is known that the saline intake was regulated by the afferents contained in the hepatic branch of the vagus nerve [3, 10, 11]. In the present experiments, to know whether or not the afferents contained in the hepatic branch of the vagus nerve regulate the water intake, we investigated the effect of hepatic vagotomy on the suppression of water intake induced by the hepatic portal infusion of water in waterdeprived rats. Eight-week-old male Sprague-Dawley rats (Charles River) weighing 27(~335 g (mean + S.E., 292.8 + 2.8) Correspondence: M. Kobashi, Department of Physiology, Okayama University Dental School, Shikata-cho, Okayama, 700, Japan.
were used in all experiments, All rats (n -- 32) underwent catheterization surgery of the hepatic portal vein and the right jugular vein. Detailed procedure of the catheterization was already stated in our previous report [7]. H a l f of the rats (n = 16) underwent hepatic vagotomy. Another half (n = 16) received sham operation. In hepatic-vagotomized rats, two sutures were tied around the hepatic branch extending from ventral trunk of subdiaphragmatic vagus, 0.5 cm apart, and the nerve inbetween the sutures was sectioned. In sham-operated rats, the hepatic vagus was exposed for approximately the time required to perform hepatic vagotomy, but the vagus was not interfered with. Rats receiving surgery were housed in 25 x 25 x 40 cm Plexiglas cages, on a 12:12 light:dark cycle (light from 6.00 to 18.00 h), in a r o o m at 23-24°C. Rats were maintained in this cage on tap water except when deprived and normal chow until the end of the experiments. All rats were tested in a water-deprived state. Eight or nine days after surgery, rats were deprived of water from 18.00 h (at the beginning of the dark period). One hour before the start of the next dark period (17.00 h), food was removed. Infusion of deionized water was started at 17.30 h for 3.5 h at a rate of 52/A/min. At 18.00 h, tap water was supplied again. Water intake without food was measured for 24 h by a drop counter and recorded on a pen recorder for later analysis. Each rat received the portal or the jugular infusion of deionized water. Each rat was tested only once. Therefore, rats were divided
69
into 4 groups; sham-operated rats with portal infusion (n = 8), sham-operated rats with jugular infusion (n = 8), hepatic-vagotomized rats with portal infusion (n = 8), hepatic-vagotomized rats with jugular infusion (n = 8). F o o d intake from the start of the dark period until the start of infusion was measured daily for 3 days. Water intake was measured at all times after surgery. For the 3 days before the test, daily food and water intake were not significantly different among the 4 groups. After all experiments, the animals were sacrificed by over-doses of anesthesia. Water intake was expressed in ml by multiplying the number of drops by 0.067. The results of each 3-h intake in the dark period and 12-h intake in the light period are presented as bar graphs (Fig. 1). Cumulative intake is presented at 0.5, 1, 2, 3 h after presentation of tap water (Fig. 2). Data are presented as means + S.E. Results were analyzed using Student's t-tests. Fig. 1 shows the 3-h water intake in the dark period and the 12-h water intake in the light period. In shamoperated rats (left panel), the water intake of the portal infusion group was significantly less than that of the jugular infusion group from 0 to 3 h (t = 4.190, P < 0.001), from 3 to 6 h (t = 2.788, P < 0.05) and from 6 to 9 h (t --- 2.269, P < 0.05). N o significant differences were seen in the water intake from 9 to 12 h (t = 1.862, n.s.) and from 12 to 24 h (t = 0.297, n.s.). In hepatic-vagotomized rats (right panel), significant differences of the water intake between the portal infusion and the jugular infusion group from 3 to 6 h (t = 2.561, P < 0.05) were observed. No significant differences were seen in the water intake from 0 to 3 h (t = 0.186, n.s.), from 6 to 9 h
15"
Sham Operated
Hepatic Vagotomized
r-i Portal Infusion of water {N-8) • Jugular intusion of water (N=8)
[~ Portal Infueion of water (N-8) • Jugular infusion of water (N,,8) NS
E v
lO P
~i~ NS
~
NS F--7
NS
P
3-6
6-9
9-12
Ns
P
0
0-3
3-6
6*9
9-12
Time (hours)
12-24
0-3
12-24
Time (hours)
Fig. 1. Water intake of sham-operated (left) and hepatic-vagotomized (right) rats. Water intake shown for a successive 3-h period except for final column (12-h intake) in each graph.
8
¸
6
***
'_
Q> 4 //i i
I/ I/
//
Hepatic Vagotornlzed Groups --o--
2 I/i/
: -
I
0
0
eo.= Int=.k~ ON-8)
"-~D~ JugularInfusion(N-8)
; Time
G.,.,. Portal Inlusion(N-8) JugularInfusion(N=8) 2'
3'
(hours)
Fig. 2. Effect of hepatic vagotomy on cumulative water intake during the infusion of water. *P < 0.05, **P < 0.01, ***P < 0.001, when water intake during the portal infusion of sham-operated rats is compared with the water intake of the jugular infusion to sham-operated rats. # P < 0.05, # # P < 0.01, when water intake during the portal infusion of sham-operated rats is compared with the water intake of the portal infusion to hepatic-vagotomized rats.
(t = 1.717, n.s,), from 9 to 12 h (t = 0.749, n.s.) and from 12 to 24 h (t = 0.564, n.s). Detailed analysis of cumulative water intake during the infusion is shown in Fig. 2. Cumulative water intake during portal infusion of shamoperated group suppressed water intake significantly compared to those during jugular infusion of sham-operated group (t = 1.955, n.s., 0.5 h; t = 2.612, P < 0.05, 1 h; t = 2.986, P < 0.01, 2 h; t = 4.190, P < 0.001, 3 h) and those during portal infusion of hepatic-vagotomized group (t = 2.657, P < 0.05, 0.5 h; t = 3.016, P < 0.01, 1 h; t = 2.971, P < 0.05, 2 h; t = 2.461, P < 0.05, 3 h). Cumulative water intake during portal infusion of hepaticvagotomized groups was not changed in comparison with that during jugular infusion of hepatic-vagotomized groups ( t = 0.102, n.s., 0.5 h; t = 0 . 4 6 6 , n.s., 1 h; t = 0.106, n.s., 2 h; t = 0.186, n.s., 3 h). Results from the hepatic portal and the jugular infusion to sham-operated rats reconfirmed our previous observation [7]. The portal infusion of water suppressed water intake induced by the 24-h water deprivation dur-
70
ing and after the infusion. The suppressive effect during the portal infusion of water was completely abolished by the hepatic vagotomy. Therefore, it is concluded that the suppression, at least, during the portal infusion of water is mediated by the osmo-receptive afferents included in the hepatic branch of the vagus nerve. Smith and Jerome [9] reported that the hepatic vagotomy produced the over-ingestion of water after water deprivation. Our observation is similar to their results. Water intake was facilitated by the hepatic vagotomy. However, general facilitation of water intake by the hepatic vagotomy was not observed in our experiments, because significant differences were not observed between sham-operated and hepatic-vagotomized groups treated by the jugular infusion of water. Our results showed the disappearance of the suppression of water intake during the portal infusion of water by the hepatic vagotomy. In hepatic-vagotomized group, the suppression after the infusion remained. Hepatic vagal afferent is not involved in this relatively longer term suppression. In the present experiments, we are unable to delineate a possible neural mechanism of this suppression. In conclusion, the suppression during the portal infusion of water is mediated by the hepatoportal osmo-receptive afferent signals contained in the hepatic branch of the vagus nerve. Therefore, hepatic vagal afferent signals resulting from the hypotonicity of the hepatoportal region have an inhibitory effect on water intake. This work was supported by Grant-in-Aid for Encouragement of Young Scientists 01771510 from the Ministry
of Education, Science and Culture of Japan, and Grantin-Aid for General Scientific Research 02670831 from the Ministry of Education, Science and Culture of Japan. 1 Adachi, A., Niijima, A. and Jacobs, H.L., An hepatic osmoreceptor mechanism in the rat: electrophysiological and behavioral studies, Am. J. Physiol., 231 (1976) 1043-1049. 2 Blake, W.D. and Lin, K.K., Hepatic portal vein infusion of gJucose and sodium solutions on the control of saline drinking in the rat, J. Physiol., 274 (1978) 129 139. 3 Contreras, R.J. and Kosten, T., Changes in salt intake after abdominal vagotomy: evidence for hepatic sodium receptors, Physiol. Behav., 26 (1981) 575-582. 4 Haberich, F.J., Osmoreception in the portal circulation., Fed. Proc., 27 (1968) 1137 1141. 5 Kahrilas, P.J. and Rogers, R.C., Rat brainstem neurons responsive to changes in portal blood sodium concentration, Am. J. Physiol., 247 (1984) R792-R 799. 6 Kobashi, M. and Adachi, A., Convergence of hepatic osmoreceptive inputs on sodium-responsive units within the nucleus of the solitary tract of the rat, J. Neurophysiol., 54 (1985) 212 219. 7 Kobashi, M. and Adachi, A.. Effect of hepatic portal infusion of water on water intake by water-deprived rats, Physiol. Behav., 52 (1992) in press. 8 Lin, K.K. and Blake, W.D., Hepatic sodium receptor in control of saline drinking behavior, Commun. Behav. Biol.. 5 (1971) 359 363. 9 Smith, G.P. and Jerome, C., Effects of total and selective abdominal vagotomies on water intake in rats, J. Auton. Nerv. Syst., 9 (1983) 259-271. 10 Tordoff, M.G., Schulkin, J. and Friedman, M.I., Hepatic contribution to satiation of salt appetite in rats, Am. J. Physiol., 25 l (1986) Rl095 Rl102. 11 Tordoff, M.G., Schulkin, J. and Friedman, M.I.. Further evidence for hepatic control of salt intake in rats, Am. J. Physiol., 253 (1987) R444-R449.