- Email: [email protected]
Effect of cortisol on mammary tight junction (TJ) permeability in lactating dairy cows
ELSEVIER
Livestock Production
Science 50 (1997) 39-40
Effect of cortisol on mammary tight junction (TJ) permeability in lactating dairy cows K. Stelwagen a3*, G.A. Verkerk b, A.H. Phipps ‘, L.R. Matthews a ’ Agresearch, b Dairying
Hamilton,
Research Corporation,
New Zealand Hamilton,
New, Zeuland
Abstract Intact mammary epithelial TJ are important for milk synthesis. Recent in vitro studies indicate that glucocorticoids are important for maintenance of mammary TJ. In the present study, we examined the effects of cortisol on mammary TJ integrity in vivo. In two experiments, endogenous levels of cortisol in plasma were manipulated by challenging cows with (0.05 mg, 40 IU; i.v.) adrenocorticotropic hormone (ACTH,, _24)) or by inducing transport-related stress. In experiment 1, 20 cows were subjected to an ACTH challenge 4, 2, or 1 h before milking, or no challenge (control). In experiment 2, 2 h before milking, 15 cows were challenged with ACTH, transported for 2 h, or used as controls. Blood samples were collected at - 5, 60, and 120 min following the start of treatments. Decreased plasma lactose and increased milk K content were used as indicators of TJ permeability. Both ACTH and transport caused a 6-fold increase (P < 0.0 1) in plasma cortisol at 60 min. Time of ACTH challenge (exp. 1) did not affect plasma lactose, allowing the data to be pooled. ACTH decreased plasma lactose in experiment 1 (-5 vs 60 vs 120 min: 28.0” vs 26.9” vs 24.9b + 0.8 M, “%bP< 0.05) and experiment 2 (26.1” vs P < O.Ol), whereas K content in milk increased (exp. 1, control vs 4 vs 2 vs 1 h: 31.8” vs 32.1” 24.6” vs 23.6b f 0.8 M, aXb vs 32.0” vs 33.5b + 0.2 mmol/l, a,bP < 0.01; exp. 2, control vs ACTH: 41.1 vs 42.1 + 0.4 mmol/l, P < 0.01). These changes are consistent with decreased TJ permeability. Moreover, these changes occurred rapidly (I 1 h). Despite elevated cortisol levels with transport, no changes in plasma lactose were observed, but K in milk increased (control vs transport: 40.9 vs 42.1 + 0.4 mmol/l, P < 0.05). This variable response with stress may be due to increased secretion of epinephrine, overiding the beneficial effects of cortisol on TJ. In conclusion, our data, obtained in vivo, support the findings of recent in vitro studies that glucocorticoids play a role in maintaining the integrity of TJ in the epithelium of the mammary gland. Published by Elsevier Science B.V.
Discussion Chris Knight: It would be nice to look at the effects of depressed cortisol on tight junctions. Do you have any plans along those lines? Kerst Stelwagen: No, not at the moment.
* Correponding author. Tel.: + 64 7 838 5180; fax: +64 7 838 5628: e-mail: [email protected] 0301-6226/97/$17.00
Published
PII SO301 -6226(97)0007
l-7
by Elsevier Science B.V.
Giuseppe Bertoni: As I understand it, you have not measured potassium in plasma. We did some experiments a few years ago, and stress conditions particularly with catecholamines and oxytocin, reduce potassium in blood. Kerst Stelwagen: Yes, but our measurements were in milk. Giuseppe Bertoni: Yes I know, but to understand what happened and why there is an increase in milk, you may have to look at the blood as well because
40
K. Stelwagen et al. /Livestock
there maybe some leakage of potassium. It has to come from somewhere. Kerst Stelwagen: Potassium comes more than likely through the cell due to increased activity of the Na/K pump on the basal side, and indeed ultimately from the blood. But, the changes observed in milk are so small that corresponding changes in blood would almost certainly not be noticed. Christian Burvenich: I have a question and a comment. Maybe I missed it, but what happens to milk secretion in the animals? A comment: I think it is essential to demonstrate that there is an effect on the blood-milk barrier and at that time you need to measure sodium, potassium, chloride and lactose in milk. Then you have to look at the correlations, because if there is a correlation between the increase in sodium and chloride, and if you find a negative correlation between sodium and lactose, then you can be quite sure that it is an effect on the milk barrier. I am referring to the work of Linzell. I think this is a more safe way to see if it is really an effect on the blood-milk barrier. Could you comment please? Kerst Stelwagen: First the part on secretion: There was no significant effect there, but it was a very short-term study - only 2 hours. Perhaps the changes we saw were too small to see in terms of milk secretion. Also, I would like to point out that the changes we saw in lactose in blood and also the increase in potassium in milk were very small com-
Production Science SO (1997) 39-40
pared to the opposite, i.e., in the case of leaky tight junctions. You easily get a 1Cfold increase in lactose in blood. But here we are starting from a “tight” tight junction status, trying to get it even tighter. So the changes are bound to be a lot smaller. We did not look at sodium because we were not able to measure it at the time, and we had quite a bit of data on lactose and sodium, potassium and chlorine from previous experiments. Therefore, I felt fairly comfortable looking at potassium by itself in this case, especially when combined with lactose. Rupert Bruckmaier: One short comment: The difference between response to transportation and the ACTH challenge is interesting. In all recent work, there is a really strong response of cortisol, but stress-like transportation normally will not enhance catecholamine concentrations, And the question is, if these catecholamines antagonize the effect of cortisol on the tight junctions, why does this difference remain such that the effect on is still there, but there is no effect on lactose? Kerst Stelwagen: That is a good point First, catecholamines in relation to transport. There are some published data showing that transport increases catecholamines. Your second point is why there is an increase in potassium and not lactose? I really have no explanation for that other than perhaps potassium is an ion and a lot smaller than lactose. And if you see any effect you would see it a lot sooner with potassium and not with the bigger lactose.
Livestock Production
Science 50 (1997) 39-40
Effect of cortisol on mammary tight junction (TJ) permeability in lactating dairy cows K. Stelwagen a3*, G.A. Verkerk b, A.H. Phipps ‘, L.R. Matthews a ’ Agresearch, b Dairying
Hamilton,
Research Corporation,
New Zealand Hamilton,
New, Zeuland
Abstract Intact mammary epithelial TJ are important for milk synthesis. Recent in vitro studies indicate that glucocorticoids are important for maintenance of mammary TJ. In the present study, we examined the effects of cortisol on mammary TJ integrity in vivo. In two experiments, endogenous levels of cortisol in plasma were manipulated by challenging cows with (0.05 mg, 40 IU; i.v.) adrenocorticotropic hormone (ACTH,, _24)) or by inducing transport-related stress. In experiment 1, 20 cows were subjected to an ACTH challenge 4, 2, or 1 h before milking, or no challenge (control). In experiment 2, 2 h before milking, 15 cows were challenged with ACTH, transported for 2 h, or used as controls. Blood samples were collected at - 5, 60, and 120 min following the start of treatments. Decreased plasma lactose and increased milk K content were used as indicators of TJ permeability. Both ACTH and transport caused a 6-fold increase (P < 0.0 1) in plasma cortisol at 60 min. Time of ACTH challenge (exp. 1) did not affect plasma lactose, allowing the data to be pooled. ACTH decreased plasma lactose in experiment 1 (-5 vs 60 vs 120 min: 28.0” vs 26.9” vs 24.9b + 0.8 M, “%bP< 0.05) and experiment 2 (26.1” vs P < O.Ol), whereas K content in milk increased (exp. 1, control vs 4 vs 2 vs 1 h: 31.8” vs 32.1” 24.6” vs 23.6b f 0.8 M, aXb vs 32.0” vs 33.5b + 0.2 mmol/l, a,bP < 0.01; exp. 2, control vs ACTH: 41.1 vs 42.1 + 0.4 mmol/l, P < 0.01). These changes are consistent with decreased TJ permeability. Moreover, these changes occurred rapidly (I 1 h). Despite elevated cortisol levels with transport, no changes in plasma lactose were observed, but K in milk increased (control vs transport: 40.9 vs 42.1 + 0.4 mmol/l, P < 0.05). This variable response with stress may be due to increased secretion of epinephrine, overiding the beneficial effects of cortisol on TJ. In conclusion, our data, obtained in vivo, support the findings of recent in vitro studies that glucocorticoids play a role in maintaining the integrity of TJ in the epithelium of the mammary gland. Published by Elsevier Science B.V.
Discussion Chris Knight: It would be nice to look at the effects of depressed cortisol on tight junctions. Do you have any plans along those lines? Kerst Stelwagen: No, not at the moment.
* Correponding author. Tel.: + 64 7 838 5180; fax: +64 7 838 5628: e-mail: [email protected] 0301-6226/97/$17.00
Published
PII SO301 -6226(97)0007
l-7
by Elsevier Science B.V.
Giuseppe Bertoni: As I understand it, you have not measured potassium in plasma. We did some experiments a few years ago, and stress conditions particularly with catecholamines and oxytocin, reduce potassium in blood. Kerst Stelwagen: Yes, but our measurements were in milk. Giuseppe Bertoni: Yes I know, but to understand what happened and why there is an increase in milk, you may have to look at the blood as well because
40
K. Stelwagen et al. /Livestock
there maybe some leakage of potassium. It has to come from somewhere. Kerst Stelwagen: Potassium comes more than likely through the cell due to increased activity of the Na/K pump on the basal side, and indeed ultimately from the blood. But, the changes observed in milk are so small that corresponding changes in blood would almost certainly not be noticed. Christian Burvenich: I have a question and a comment. Maybe I missed it, but what happens to milk secretion in the animals? A comment: I think it is essential to demonstrate that there is an effect on the blood-milk barrier and at that time you need to measure sodium, potassium, chloride and lactose in milk. Then you have to look at the correlations, because if there is a correlation between the increase in sodium and chloride, and if you find a negative correlation between sodium and lactose, then you can be quite sure that it is an effect on the milk barrier. I am referring to the work of Linzell. I think this is a more safe way to see if it is really an effect on the blood-milk barrier. Could you comment please? Kerst Stelwagen: First the part on secretion: There was no significant effect there, but it was a very short-term study - only 2 hours. Perhaps the changes we saw were too small to see in terms of milk secretion. Also, I would like to point out that the changes we saw in lactose in blood and also the increase in potassium in milk were very small com-
Production Science SO (1997) 39-40
pared to the opposite, i.e., in the case of leaky tight junctions. You easily get a 1Cfold increase in lactose in blood. But here we are starting from a “tight” tight junction status, trying to get it even tighter. So the changes are bound to be a lot smaller. We did not look at sodium because we were not able to measure it at the time, and we had quite a bit of data on lactose and sodium, potassium and chlorine from previous experiments. Therefore, I felt fairly comfortable looking at potassium by itself in this case, especially when combined with lactose. Rupert Bruckmaier: One short comment: The difference between response to transportation and the ACTH challenge is interesting. In all recent work, there is a really strong response of cortisol, but stress-like transportation normally will not enhance catecholamine concentrations, And the question is, if these catecholamines antagonize the effect of cortisol on the tight junctions, why does this difference remain such that the effect on is still there, but there is no effect on lactose? Kerst Stelwagen: That is a good point First, catecholamines in relation to transport. There are some published data showing that transport increases catecholamines. Your second point is why there is an increase in potassium and not lactose? I really have no explanation for that other than perhaps potassium is an ion and a lot smaller than lactose. And if you see any effect you would see it a lot sooner with potassium and not with the bigger lactose.